Astronomy

How significantly does the intensity of a meteor shower diminish after the peak?

How significantly does the intensity of a meteor shower diminish after the peak?


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Every August 12 I take the family to the desert to enjoy the Perseid meteor shower. This year there will be an especially bright moon rising before 1:00, which is when the shower really peaks. Last year especially was a disappointment as the moon did not set until 2 or 3 in the morning, and there was little to see until it did, so I don't want to disappoint the family two years in a row.

If I wait a day or two (depending on scheduling conflicts), so that the moon might rise later and be a bit less full, how much would that be expected to reduce the intensity of the meteor shower? I've found this paper discussing meteor shower activity profiles, but nothing that I could apply to this year's Perseid shower. This question also seemed relevant, but it does not contain the detail need to determine if waiting a day or two would significantly reduce the visible activity.

Is meteor activity significantly reduced a day or two after the peak, for purposes of recreational observation by experienced observers?

I understand that nobody can predict (space) weather. But the Perseid shower typically persists for two weeks after the peak. Is that a linear drop off? Exponential? Does the shower typically loose 5% of its intensity in two days, or 50%, or 95%?


Comparison of two meteor trajectory solvers on the 2020 Perseid shower

Abstract: The Global Meteor Network trajectory solver obtains higher initial and geocentric velocities for identical Perseid meteors than the UFO solver of SonotaCo. Also, the average velocity for the GMN is slightly but statistically significant higher than for the UFO solver. The higher velocity explains a higher eccentricity for the orbits obtained by GMN. In spite of the lower velocity for the UFO solver, it has statistically significant higher beginning heights for these meteors while the ending heights are comparable. The length of the trajectories seems longer for the UFO solver than for the GMN while the durations are comparable. The differences between both solvers cannot be explained unless insight is provided in the computation method of the UFO solver.


Major Meteor Showers

The meteor showers discussed below recur each year in some cases they have been recognized for hundreds of years. The name of the shower in most cases indicates the constellation from which the meteors appear. Also discussed are sporadic rates. Sporadic meteors are those random meteors not associated with a particular shower they are the random detritus left over from the creation of the solar system or are old dispersed debris not recognizable today as shower meteors. Click on the shower names (when linked) for more detail on any given shower. For meteor observers, those located in the northern hemisphere have a distinct advantage as shower activity is stronger there than that seen by observers located south of the equator. The reason for this is that most of the major showers have meteors that strike the Earth in areas located far above the equator. As seen from the northern hemisphere these meteors would appear to rain down from high in the sky in all directions. From those situated in the southern hemisphere only a small percentage of this activity is visible. Any activity would appear to travel upwards from radiants located low in the sky.

There are a few meteor showers best seen from the southern hemisphere. These would include any radiant with a declination (celestial latitude) below -20 and those that reach maximum activity during the southern hemisphere’s winter months (July-August-September). These showers would include the Alpha Centaurids, Gamma Normids, Pi Puppids, Piscis Austrinids, Delta Aquarids, Alpha Capricornids, Dec Phoenicids, and the Puppid/Velids.

The year begins with the intense but brief Quadrantid maximum (January 3/4). Its brevity combined with typically poor winter weather hampers observation. January overall has good meteor rates restricted to the last third of the night. Rates to 20/hour can be obtained. A large number of radiants spread along the ecliptic from Cancer to Virgo. This activity diminishes somewhat in February with the same areas active.

Late-night rates are fair in the first half of March, but become poor rather suddenly after mid-March. The very poor rates, seldom reaching 10/hour, continue into early June. However, two major showers appear in this interval. The Lyrids past mid-April (max: April 22/23) raise meteor rates for several nights. The Eta Aquariids (max: May 7/8) enrich late nights of May’s first half, sometimes substantially.

February, March, and April evenings have another notable feature. An unusual number of sporadic fireballs come in this interval, possibly one every few nights.

June to mid-July has fair rates. The last half of July has rates increasing steadily as the Delta Aquariids (July 29/30) and Alpha Capricornids (July 27-28) have maxima at month’s end. Even the Perseids are beginning to show a little.

Overall, late July to mid-August is very rich in meteors. The Perseid maximum, just before mid-August (August 12/13), is fairly prolonged and quite rich.

High sporadic activity after midnight continues for the rest of the year, but especially in September and the first half of December. Sporadic rates over 20/hour are possible for this entire interval. September radiants are numerous in Aries and Taurus.

Mid-October to mid-December is a nearly continuous period of heavy meteor activity. The Orionids (max: October 21/22) during the second half of October have a prolonged, plateau maximum for several nights, usually rich. The Taurids (max: October 11 for S. Taurids, November 13/14 for N. Taurids), active for two months, are most numerous in November’s first half, and can be rather variable in strength. This period is the best for a couple of Taurid fireballs each night, if the shower is not too weak. The Leonids of mid-November (max: November 17-19) are quite unpredictable, with rich displays occuring roughly every 33 years. The last Leonid storm period occurred from 1998 through 2002. Studies have shown that no Leonid storms will occur in either 2033 or 2066. We will have to wait until 2099 for a return of the activity recently seen during the past few years.

Finally the Geminids of mid-December (max: December 13/14) climax the year with the strongest dependable and observable display. Geminid rates usually pass 60-70/hour at maximum. Concurrent activity from Leo and Canis Minor is also notable during the Geminids. Finally, the oft-overlooked Ursids complete the year’s activity, reaching maximum on December 22/23. Nearly half the year’s visual meteor activity is crammed into the two-month interval just described.


Viewing the eta Aquariid Meteor Shower in 2020

Many of our readers were born after the last appearance of Halley’s comet in 1986. They will have to wait until 2061 for it’s next appearance. For those of us who did see it 34 years ago, most of us will not be around for it’s return in 2061. We can all take solace in the fact that remnants from Halley’s comet are circling the solar system, often far from the comet, and encounter the Earth twice each year in the form of meteors from the eta Aquariids of May and the Orionids of October. So while we cannot view the comet itself, we can see bits of ice and dust it has left behind over the past few millennia.

The Orionids are the inbound particles of Halley’s comet while the eta Aquariids are the outbound particles. It should be noted that the particles we see as meteors separated from the comet many hundreds of years ago as the current orbit of the comet does not cross the orbit of the Earth.

Meteor showers on Earth are caused by streams of meteoroids hitting our atmosphere. These meteoroids are sand- and pebble-sized bits of rock that were once released from their parent comet. The above visualization shows the meteoroid streams of the Halley’s comet orbiting the Sun.

Eta Aquariids 2020 will peak on May 5/6

Since the eta Aquariids are the outbound particles of the Halley’s comet, we see them to the west of the sun from April 17-May 24 each year. This positioning only allows these meteors to be seen on the morning side of Earth. To make matters more restrictive, the source of these meteors, located in the constellation of Aquarius, does not clear the horizon until 2:00 to 3:00am local daylight saving time. Viewing circumstances for the eta Aquariids are best for those located in the southern tropics where the source of these meteors rises highest in a dark sky. This window of opportunity to view these meteors in a dark sky shrinks as one moves north until one reaches latitude 60°N. At that point the source rises at the same time as dawn breaks, therefore no activity can be seen. Most observers in the northern hemisphere have a two hour window prior to dawn to view these meteors.

In 2019, the new moon coincided with the shower’s maximum and hourly rates as high as 39 as seen from Australia. Unfortunately this year the moon will be full on May 7, compromising observations near maximum activity (May 5 & 6). Currently the moon is a waxing gibbous that sets during the early morning hours. The potential observer has the chance to view increasing eta Aquariid activity by viewing when the moon is low in the sky up until the first light of dawn begins to interfere. Activity from this shower will increase nightly and peak on May 5 and 6. After maximum, rates will slowly diminish until no activity appears at all around May 24. Also after maximum, the moon will remain in the sky all morning long further impeding observations.

To best view these meteors, look toward the eastern half of the sky during the last couple of hours prior to dawn. This will keep the moon at your back if it is still above the horizon. Find yourself a comfortable lounge chair and use it to center your view half-way up in the eastern sky. You will see eta Aquariid meteors shooting upward from the eastern horizon. These meteors are striking the Earth from a head-on position so they will be swift, often covering several tens of degrees in a split second. They may appear in any portion of the sky but will all trace back to their source in Aquarius. There will be other meteors visible too, some from minor showers and most from random activity. These meteors will most likely be slower than the eta Aquariids.

Hourly observations are accepted by the International Meteor Organization. Simply register (it’s free) or log in at www.imo.net and enter your data on their visual meteor observing form. We ask for sessions of at least an hour long due to the fact that meteor activity is notoriously clumpy. This means you may see no activity for 10-15 minutes and then a many meteors within a few minutes. If you limit you watch to less than an hour, you may witness one of those short lulls and be dissatisfied with your results.

This is your last chance to see amplified meteor activity until late July so if your skies are clear during the next few mornings, I encourage you to take advantage of the chance to see bits of Halley’


Contribution of meteor flux in the occurrence of sporadic-E (Es) layers over the Arabian Peninsula

A sporadic-E (Es) layer is generally associated with a thin-layered structure present in the lower ionosphere, mostly consisting of metallic ions. This metallic ion layer is formed when meteors burn in the upper atmosphere, resulting in the deposition of free metal atoms and ions. Many studies have attributed the presence of the Es layer to the metallic ion layer, specifically when the layer is observed during the nighttime. Using data from a network of meteor monitoring towers and a collocated digital ionosonde radar near the Arabian Peninsula, in this paper, we report our observations of Es layer occurrences together with the meteor count. The trend of monthly averages of Es layer intensity shows a maximum in late spring and early summer months and a minimum in winter months, whereas the meteor counts were highest in winter months and lowest in spring and early summer months. This shows that the presence of the Es layer and the meteor counts have no correlation in time, both diurnally and seasonally. This leads us to conclude that the presence of meteors is not the main cause of the presence of the Es layer over the Arabian Peninsula.

Meteors are the visible appearance of extraterrestrial dust, generally known as meteoroids. They appear in the sky when meteoroids ablate in the Earth's atmosphere. Meteors can be categorized as being either part of a shower or of the background meteor flux. There is a vast amount and variety of meteoroid material entering the atmosphere every day (Ceplecha et al., 1998), and its deposition is highly variable spatially as well as temporally. These variations are attributed to the inconsistency of the meteoroid material density surrounding the Earth, seasonal changes of the atmosphere and the Earth's movement around the Sun, the methods of observing them such as the geographical location of the observing site, and geometrical factors related to the observing instruments' capability and positions of sources. This extraterrestrial influx changes the metallic composition of the Earth's atmosphere and lower ionosphere. This happens when meteors burn in the dense atmosphere, resulting in the heating and deposition of free metal atoms and ions (Ceplecha et al., 1998). It is now a well-established fact that the permanent ionized metal layer in the lower ionosphere, at around 90–130 km altitude, is due to the ablation of meteors in that region (Plane et al., 2015). Meteor observations can be performed with the radio (Stober and Chau, 2015 Lima et al., 2015 Yi et al., 2016) as well as with visual means (Vitek and Nasyrova, 2018 Kozlowski et al., 2019 Fernini et al., 2020). Detection using visual cameras can only be performed during the night compared to radio-based observations that can be performed throughout the day and suitable for estimating total meteor activity. A combination of multiple types of observations may also be used (Brown et al., 2017).

Kopp (1997) showed that the thin-layered structured sporadic-E (Es) layer in the Earth's ionosphere, lying in the altitude range of 90–130 km, mostly consists of ionized metal atoms FeC, MgC, and NaC. At mid-latitudes, the so-called “wind-shear” theory is thought to be the mechanism responsible for this formation (Whitehead, 1989). Therefore, the intensity and occurrence of the Es layer are expected to be proportional to the amount of metal ion content in the lower ionosphere and its chemical processes as well as meteorological processes in the lower ionosphere (Feng et al., 2013 Yu et al., 2015). The nature of the Es layer observed globally has been a function of many factors, such as geographical latitude or observing instruments' sensitivity of the viewing system. For example, the Es layer can be observed at almost all times at some geographical locations around the globe (Shaikh et al., 2020a, b), thus making the term “sporadic” misleading. The behavior of the Es layer over the Arabian Peninsula has not been studied by many. Recently, Shaikh et al. (2020a, b) demonstrated the relationship between L-band scintillation and the occurrence of the Es layer over the Arabian Peninsula. The study also revealed a consistent presence of the Es layer during the nighttime hours, between sunset and sunrise.

In this paper, we report the observations of the Es layer and the meteor counts simultaneously observed during nighttime over the Arabian Peninsula region for the first time. A well-established presence of the Es layer can be observed during all daytime and nighttime hours, with higher intensity around midday hours and lesser intensity at early morning and nighttime hours. A consistent meteor count is also present throughout the 1-year observation period (May 2019–April 2020) reported in this work. It has been observed that the presence of meteors is not the main cause of the presence of nighttime Es over the Arabian Peninsula since the Es layer intensity (average critical frequencies of the Es layers – foEs) shows no seasonal correlation with the number of meteors observed. The dependence of Es layer intensity (foEs) due to meteor count has been calculated using linear correlation coefficients. Negative values of correlation coefficient show an anti-correlation relationship between the two data sets.

The meteor counts for this study have been obtained in collaboration with the UAE (United Arab Emirates) Meteor Monitoring Network (UAEMMN) project (Fernini et al., 2020). The project aims to monitor and detect meteor occurrences in the region above the United Arab Emirates from sunset to sunrise. To achieve this, three monitoring towers have been constructed and installed in different parts of the country. For each tower, 16 cameras are distributed along with a ring-like structure with lenses of 6 and 8 mm, while the 17th camera utilizes a wide-angle lens and is located at the center of the structure (Fernini et al., 2020). Following a simulation using Systems Tool Kit software (STK: https://www.agi.com/products/50stk , last access: 16 September 2020) as shown in Fig. 1a, the towers' locations were selected as illustrated in Fig. 1b (made using ©Google Maps). In Fig. 1, the green color represents the area of the sky covered by the 8 mm lenses, while red represents the coverage of the 6 mm lenses. The yellow squares show what the wide-angle lens can see and cover. Thus, the STK simulation illustrates how much each tower covers the UAE sky, which adds up to 70 % coverage of the sky. Each of the three UAEMMN towers employs the use of the UFOCapture software developed by SonotaCo (SonotaCo, 2005) to detect meteor occurrences. The software can detect movements from the feed of the cameras on the towers. If a movement or action is detected, it writes the video of the action to the hard disk of the computer, from a few seconds before the action is recognized to a few seconds after the action is completed. During the night, the bright streaks produced by a meteor burning up in the atmosphere allow the software to detect movements from the sudden changes easily in pixel values.

Figure 1(a) Sky coverage simulation by all cameras using Systems Tool Kit (STK). (b) Location of the towers pinpointed on the UAE map using © Google Maps.

Two other software packages, UFOAnalyzer and UFOOrbit, also developed by SonotaCo (SonotaCo, 2007a, b), are used to calculate parameters that define the meteorite. UFOAnalyzer can calculate the direction and elevation of the meteorite occurrence. If the meteorite is detected by two or more sites, UFOOrbit can calculate the orbit and the radiant point of the meteorite. Figure 2 shows a radiant map obtained as a result of analyses by the software. The radiant map shows radiant points on a sinusoidal projection map of the observed meteors, which is defined as the point in the sky from which the path of the observed meteor begins. For a radiant point to be plotted on the map by the software, double detection of the meteor should occur, meaning that two cameras from at least two different towers need to observe the same meteor. Figure 2 shows the radiant points of meteors observed by the Sharjah and Al-Yahar towers during the period between May 2019 and April 2020. On the map, constellations such as Orionids and Taurids are denoted as J5_Orio, J5_nTa, and sTa, respectively. Hence, the radiant points that are close to a constellation imply that they belong to the respective meteor group. In this figure, there are meteors that belong to the Orionids meteor shower as well as Southern and Northern Taurids and several others, in addition to sporadic meteors that do not belong to any shower. By locating the radiant points on the map, the network ensures its accuracy in terms of linking a meteor to its respective shower. The radiant velocity is color coded as shown in the figure.

Table 1Location of the instruments used to generate data for this study.

The critical frequency of the Es layer (foEs) of the ionosphere is obtained from the ionosonde collocated with the Sharjah meteor monitoring tower. The ionosonde records one ionogram every 15 min, and it has been in operation since May 2019. All ionogram-derived parameters used in this study have been manually scaled. All the data used in this study are available from SWI Lab (2020). Since the data from the meteor towers are only available from nighttime observations and the data from the ionosonde are observed throughout the day and night, the daily Es intensity (average foEs value) has been used to compare with the daily meteor count to study the impact of the number of meteors present and their influence on the presence of Es (Haldoupis et al., 2007).

Figure 2A radiant map of meteor observations by the Sharjah and Al-Yahar stations during the period May 2019–April 2020.

Figure 3 shows the observation of the Es layer and meteor count. Figure 3a and b show that a constant presence of Es can be observed throughout the year and all hours of the day, with higher intensity (average foEs) around midday hours and lesser intensity at early morning and nighttime hours. An important point to note here is that this observation was performed during a time when the solar activity was low. The average F10.7 solar radio flux value during a 1-year observational period was recorded as 69.43 sfu. Only geomagnetically quiet days with an average daily Kp value of less than 3 were selected for the analysis. It is expected that the Es layer observations would be more substantial as solar cycle 25 gets stronger in the coming years. Figure 3c shows the hourly meteor count for the whole 1-year observational period. No observations were recorded during the daytime.

Figure 3Simultaneous monitoring of meteors and the Es layer over the Arabian Peninsula from May 2019 to April 2020. (a) Es occurrence frequency as a function of local time. (b) Hourly average of foEs recorded using ionosonde. (b) Hourly meteor count.

Figure 4 shows a comparison between the daily and monthly meteor counts with daily and monthly averages of foEs. Figure 4a shows all daily observations (24 h), and Fig. 4b provides observations for nighttime only. The trend of monthly averages of the Es layer intensity shows a maximum in late spring and early summer months and a minimum in winter months (except for a slight peak in January). At the other end, the monthly meteor count shows an opposite trend with a larger number of meteors observed during November–December 2019 and very low numbers in the spring and summer months. Both Fig. 4a and b show a very similar trend for foEs averages. The difference is in the intensity of the Es layer, which is greater when all observations are considered due to the inclusion of the daytime Es layer observations. The meteor count is the same in both cases since we have only observed meteors through visual cameras during the nighttime.

Figure 4Daily and monthly averages of foEs and meteor count over Sharjah. (a) Including all observations (24 h). (b) Nighttime observations only.

The observations presented in Fig. 4 are inconsistent with Younger et al. (2009), who reported meteor flux data observed by radars installed at Esrange (68 ∘ N), Ascension Island (8 ∘ S), and Rothera (68 ∘ S). They showed that, for high latitudes, there is a clear annual cycle present where the maximum count rate is observed in summer, whereas for low-latitude Ascension Island, the maximum count rates were observed for both solstices (summer and winter). Similar observations were also reported by Singer et al. (2004) using a meteor radar situated at the ALOMAR observatory (69 ∘ N) and Haldoupis et al. (2007) from European latitudes.

There have been other studies that correlate meteor activity with the Es layer seen in ionograms, examples of which include Chandra et al. (2001), Haldoupis et al. (2007), and Ellyet and Goldsborough (1976). There are also numerous studies whose results are inconclusive. For example, Baggaley and Steel (1984) were unable to find any correlation between meteor activity and the Es layers' occurrence. Kotadia and Jani (1967) reported that they did not find any increase in the occurrence of the Es layers during a period of anomalously large increase in meteor incidence in 1963 but instead found that the Es layers were formed less frequently during that period, suggesting an inverse relationship between the formation of the Es layers or meteor incidents. The results presented in this paper also follow a similar pattern, with foEs decreasing significantly during the period between October 2019 and January 2020, even with the increased meteor count during that period (see Fig. 4). This may be because plasma density abnormalities may exist which may cause ionograms to record scatter echoes beyond the foEs. Cross-field plasma instabilities cause the abnormalities due to the various electrodynamic processes in the ionosphere. These instabilities are triggered by the enhancement of plasma density in a particular volume when an external force acts on that same volume. A small disturbance can then lead to the separation of charges, which produces a small electric field, which with the presence of the geomagnetic field increases the disturbance (Simon, 1963). Meteoric activity may provide metallic ions to the ionosphere, but they may not be displayed in ionograms if the conditions are unfavorable. The aforementioned instabilities have been shown to be capable of producing the diffuse type of Es layer (Tsuda et al., 1969). The formation of this diffuse layer may cause the ionogram to display scatter echoes that exceed the actual critical frequency of the sporadic-E layer formed as a result of metallic ions deposited by meteors. This may be why a good correlation between meteor activity and the Es layer is not seen (Chandra et al., 2001), which is also confirmed by the correlation plot in Fig. 5. It is shown in Fig. 5 that the annual variation of both observations, on average, does not correlate monthly, having linear correlation coefficients less than − 0.35 (negative 0.35) for both full-day and nighttime observations.

Figure 5Relationship between foEs monthly averages and monthly meteor count observed at Sharjah.

Figure 4 shows differences between the variations in foEs and meteor counts observed at both small and large timescales. The Es layer may be affected by differences in climatology and wind dynamics. For example, long-period zonal and meridional winds at the mesopause region, with periods between 2 and 18 d, may be considered to be planetary wave activity. Planetary waves have been observed to have strong variability between different seasons, with periods of 2 d in the summer, 5 d in spring, and even exceeding 10 d during the winter (Jacobi et al., 1998). Studies have proposed vortex flows associated with planetary waves to explain the seasonal dependence of sporadic-E layers (Shalimov et al., 1999). Vortex flows are already known to affect the development of E layers (Pancheva et al., 2003). The meteor count may also be influenced by some biases. A number of the recorded meteors may not be metallic in nature and would not deposit any metallic ions in the ionosphere, possibly explaining why a higher meteor count during winter months did not amount to a higher average foEs. Nevertheless, visual meteor counts may not include all meteors. The metallic ions deposited by a meteor in the ionosphere may not be proportional to the meteoric activity as well (Haldoupis et al., 2007). The exact relationship between metallic ion densities and meteoric activity is unknown, and the transportation of metallic ions by neutral winds is not accounted for. Due to these uncertainties, the incongruous relationship between foEs and visual meteors count is not unexpected however, they are not enough to explain the incongruity. Another possible scenario arises when neutral winds are considered, which could transport metallic ions to the local ionosphere under study irrespective of the number of observed meteors (Haldoupis et al., 2007). This may be an explanation of the inverse correlation between foEs and meteor counts observed during summer months.

Table 2Meteor showers observed by the UAEMMN network.

One can expect to see a meteor entering the Earth's atmosphere every 10 min or so, but there are predictable times during the year when the Earth's atmosphere is full of them, and these are referred to as meteor showers (Kronk, 2014). These showers occur monthly, with some meteor showers more pronounced than others, depending on their parents' progenitors (Collins, 2020). We can see about 30 meteor showers during the year. Since the meteors in each shower seem to come from a certain point in the sky, the shower is named after the constellation from which the meteors come. The Quadrantids, the Perseids, and the Geminids are the most prominent of all meteor showers. Table 2 shows the data obtained from the UAEMMN network about the meteor showers. The data are taken from the same 1-year study period used in this work. We can clearly observe that most meteor showers occurred from the period from August to December and resulted in a significant increase in the numbers of visual meteors observed in the UAE (see Fig. 4). However, it seems quite understandable here that not all those meteor showers contributed to the presence of the Es layer in the UAE since the Es layer observations were higher in summer than during the winter months.

The Es layer may not be observed if the meteoric activity period does not provide long-lived metallic ions in the background plasma density. However, under favorable conditions, the meteoric debris consisting mostly of metallic ions could be converged to form sharp layers of ionization leading to density gradients responsible for ionospheric irregularities and spreading of the echoes in the ionograms. Since the ionospheric background conditions considerably vary with latitudinal region, simultaneous observations from different geographical regions would be needed to confirm a certain meteoric activity and its linkage with the appearance of the Es layer. Therefore, a thorough analysis using the systematic analysis of past data taken simultaneously from different latitudinal regions yields a better picture of the role of meteoric activity in the E-region ionization.

In this paper, simultaneous observations of foEs and the meteoric influx (meteor count rates through visual cameras) show no diurnal or seasonal dependence over the Arabian Peninsula. We report the seasonal observations of the Es layer simultaneously taken with the visual count observations from a geographical region which has not been reported before. However, no attempt was made to link the simultaneous observation of the Es layer and meteor influx in detail.

Our 1-year observations clearly show that the Es layer intensity is not dependent on the presence of meteor flux since the meteor count trend, which peaks in winter and declines in summer, is found to be uncorrelated with the trend observed for Es layer intensity (see Figs. 4 and 5). This may have happened because plasma density abnormalities may exist which may cause ionograms to record scatter echoes beyond the foEs. The abnormalities are caused by plasma instabilities due to the various electrodynamic processes in the ionosphere. Meteoric activity may provide metallic ions to the ionosphere, but they may not be displayed in ionograms if the conditions are unfavorable. This may have been the reason why a good correlation between meteor activity and the Es layer intensity cannot be seen by our two collocated instruments. Such results have rarely been reported in the literature and do not comply with frequently reported studies which established a strong seasonal correlation between daily meteor counts with daily averages of the Es layer occurrences, as mentioned in the references above. It is also important to note that this study, unlike many of the previous studies, used visual observations for observing meteors. Since the data are manually checked and verified from the recorded visual data, unlike for radio-based radar observations where the rate of false observations is very high, the study is likely to provide a real picture since there is very little chance of having false data. Nevertheless, the authors believe that a more detailed study is required to fully investigate and properly identify the Es layer seasonal dependence on the meteor influx in the region around the Arabian Peninsula.

All data used in this work are available from the dataverse of SWI Lab and acquired and managed by the Sharjah Academy for Astronomy, Space Sciences and Technology ( https://dataverse.harvard.edu/dataset.xhtml?persistentId=doi:10.7910/DVN/U2UNWE , last access: 2 November 2020, SWI Lab, 2020).

MMS, as principal investigator, performed conceptualization, investigation, data curation, and written the original draft. GG contributed with investigation, software coding, data curation and with review and editing of the manuscript. AA participated in software coding and with review and editing of the manuscript. ME Sharif helped perform data simulation and with review and editing of the manuscript. IF reviewed and edited the manuscript.

The authors declare that they have no conflict of interest.

The authors are grateful to the two anonymous reviewers for their valuable comments which helped improve the quality of the paper.

This paper was edited by Ana G. Elias and reviewed by two anonymous referees.

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Pancheva, D., Haldoupis, C., Meek, C. E., Manson, A. H., and Mitchell, N. J.: Evidence of a role for modulated atmospheric tides in the dependence of sporadic E on planetary waves, J. Geophys. Res., 108, 1176, https://doi.org/10.1029/2002JA009788, 2003.

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Answers and Replies

meteor shower IS an astronomical term NOT media
there are radiant showers, sporadic showers and meteor storms
well is a reasonable shower compared to the much lower counts of purely random meteors where there may only be 2 or 3 an hour.
Some of these showers eg the Persieds, Leonids etc can produce anything up to 500 meteors / hr (8 / minute) in some years. What you also need to remember is that these figures are the visual figures. Photographic counts can be several times higher

The Leonids are known for high counts. The Leonids in 1868 reached an intensity of 1000 per hour in dark skies.
I like the Leonid shower, they are known for producing long trails. One I viewed in the 1990's from Dunedin, New Zealand its was only producing

25 meteors / hour, the meteors were coming in slow and ohhh the trails they were almost right across the sky, and long lasting ( many seconds) quite stunning!.

I don't know what you know about meteor shows ? if lots, then others may learn
the counts vary greatly for any shower year by year. The showers are produced when the Earth passes through the dust trail left in the wake of a comet. Every show there is has an identified comet assoc. with it eg the Leonids is with comet Tempel-Tuttle.
Because the Earth's orbit around the sun isn't on a flat plane (plain?), it doesn't always pass through the same part of the comet's trail. Some years it may pass through the core giving huge meteor counts . meteor storms as they are known by. Other years it may just graze through the edge of the dust trail and we get a low meteor count


Facts

The main radiant of the Perseids is located in the direction of the star Eta Persei, with other major radiants situated near Chi and Gamma Persei, and minor ones near Alpha and Beta Persei.

Direction of the Perseids in the night sky. Image: NASA

In Greek mythology, the Perseid meteor shower is associated with Perseus constellation. It is said to commemorate the time when Zeus, Perseus’ father, visited Danae, Perseus’ mother, in a shower of gold.

The Perseid meteor shower was first documented in Chinese annals, mentioning that “more than 100 meteors flew thither in the morning” in the year 36 AD. The meteor shower is mentioned in a number of records in China, Japan, and Korea between the 8th and 11th centuries, but there aren’t very many references to it between the 12th and 19th centuries.

Perseid meteor and the Pleiades star cluster. Image: Kim MyoungSung

The Belgian astronomer and mathematician Adolphe Quetelet is generally credited for recognizing the Perseids’ annual appearance. In 1835, he reported that there was a meteor shower occurring in August, appearing to come from Perseus constellation.

The comet Swift-Tuttle was discovered independently by two American astronomers, Lewis Swift and Horace Tuttle, in 1862. The comet is quite large, with a nucleus 26 kilometres or 16 miles across, which is more than twice the size of the object believed to have caused the demise of the dinosaurs. The comet’s size and the size of the meteoroids it leaves behind are the reason why we see so many fireballs during the peak.

Every year in mid-August the Perseid meteor shower has its peak. Meteors, colloquially known as “shooting stars”, are caused by pieces of cosmic debris entering Earth’s atmosphere at high velocity, leaving a trail of glowing gases. Most of the particles that cause meteors are smaller than a grain of sand and usually disintegrate in the atmosphere, only rarely reaching the Earth’s surface as a meteorite. The Perseid shower takes place as the Earth moves through the stream of debris left behind by Comet Swift-Tuttle. In 2010 the peak was predicted to take place between 12–13 August 2010. Despite the Perseids being best visible in the northern hemisphere, due to the path of Comet Swift-Tuttle’s orbit, the shower was also spotted from the exceptionally dark skies over ESO’s Paranal Observatory in Chile. In order not to miss any meteors in the display, ESO Photo Ambassador Stéphane Guisard set up 3 cameras to take continuous time-lapse pictures on the platform of the Very Large Telescope during the nights of 12–13 and 13–14 August 2010. This handpicked photograph, from the night of 13–14 August, was one of Guisard’s 8000 individual exposures and shows one of the brightest meteors captured. The scene is lit by the reddened light of the setting Moon outside the left of the frame. Image: ESO/S. Guisard

In 1865, the Italian astronomer and science historian Giovanni Schiaparelli was the one to make the connection between Swift-Tuttle and the Perseids, realizing that the comet was responsible for the meteor shower. This was the first time that a meteor shower was positively identified with a comet.

Swift-Tuttle has an eccentric orbit, one that takes it inside the Earth’s orbit at its closest approach to the Sun and way outside Pluto’s orbit when at its most distant from the Sun. The comet orbits the Sun with a period of roughly 133 years. Whenever it passes through the inner solar system, Swift-Tuttle is warmed by the Sun, which causes it to leave fresh debris along its orbit. Swift-Tuttle last reached its closest point to the Sun, known as the perihelion, in December 1992. It will reach it again in July 2126.

Perseid meteor shower
Parent body: Swift-Tuttle
Radiant: Perseus constellation
Radiant – coordinates: 03h 04m (right ascension), +58° (declination)
First record of the discovery: 36 AD
Dates: July 23 – August 20
Peak: August 13
Zenithal hourly rate: 80


NASA Prepares For "Last Chance" Meteor Shower

The early morning hours of Nov. 19 may be your last chance to see the spectacular Leonid meteor shower in its full glory, according to astronomers.

"Even with the full Moon, this year's Leonids will probably be better than any other for the next hundred years," said Dr. Don Yeomans, an astronomer at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "If you're ever going to see them, this might be the year to try." NASA is taking advantage of the event for several research efforts around the world.

The shower is predicted to have two peaks, each a couple of hours long, during which the most meteors can be seen. The shower's second peak, most prominent in North American skies, is expected at around 2:30 a.m. (Pacific time) Nov. 19, and promises the rare spectacle of a few meteors every minute or even more. "Observers in good locations away from city lights might see a few hundred per hour. You'll only get to see the bright ones because the moonlight will wash out the ones that aren't as bright," said Yeomans. Last year, observers did not have to contend with the Moon and saw meteors at a pace of several hundred per hour.

An earlier peak is expected over Europe and Africa the night of Nov. 18, and observers in North America might see a few grazers -- meteors skimming the top of the atmosphere -- from this first peak starting around 8:30 p.m. (Pacific time) Nov. 18.

The Leonids are grains of dust from comet Tempel-Tuttle colliding into Earth's atmosphere. Most Leonid particles are tiny and will vaporize very high in the atmosphere due to their extreme speed (about 71 kilometers or 44 miles per second), so they present no threat to people on the ground or even in airplanes. As it progresses in its 33-year orbit, the comet releases dust particles every time it comes near the Sun. Earth intersects the comet's debris trail every year in mid-November, but the intensity of each year's Leonid meteor shower depends on whether Earth ploughs through a particularly concentrated stream of dust within the broader debris trail.

The dust that Tempel-Tuttle shed in 1866 makes up the stream predicted to give Americans a good show this year. Last year, people in Asia saw the plentiful collisions within that stream. A dust stream from 1767 provided last year's peak hour of viewing in North America and will provide this year's peak hour of viewing in Europe. After 2002, Earth won't hit either of those streams again for decades to come, and is not predicted to encounter a dense Leonid stream until 2098 or 2131.

The golden rule for watching the Leonids -- or any meteor shower -- is to be comfortable. Be sure to wrap up warmly -- a sleeping bag placed atop a lawn chair facing east is a good way to enjoy the show. Put your chair in a clear, dark place with a view of as much of the sky as possible. Don't stare at any one place. Keep your eyes moving across the sky. Most Leonids will appear as fleeting streaks of light, but watch for the bigger ones that produce fireballs and trails. Some trails will remain visible for several minutes or more.

The Leonids get their name from the constellation where they appear to originate the meteors will be radiating from the Sickle pattern in the constellation Leo the Lion, which will be rising out of the east-northeast sky. Don't look directly at the constellation, but at the area above and around it. And, though you don't need them to see the Leonids, a pair of binoculars could come in handy.

Researchers think meteors might have showered the Earth with the molecules necessary for life's origin. A two-aircraft campaign, led by astronomer Dr. Peter Jenniskens of the SETI Institute and NASA's Ames Research Center, Moffett Field, Calif., will investigate this possibility. "We are looking for clues about the diversity of comets and their impact on the chemistry of life's origin on Earth," Jenniskens said.

"We are eager to get another chance to find clues to two puzzling questions: What material from space rains down on Earth, and what happens to the (meteor's) organic matter when it interacts with the atmosphere?" said Dr. Michael Meyer, senior scientist for astrobiology at NASA Headquarters, Washington, D.C.

On Nov. 15, a team of 42 astrobiologists from seven countries will depart from southern California's Edwards Air Force Base on a mission to Spain to observe this year's two Leonid storm peaks. The DC-8 Airborne Laboratory, operated by NASA's Dryden Flight Research Center, Edwards, Calif., will carry high-speed cameras a radio receiver to listen to upper atmosphere molecules and a team of meteor observers, who will keep track of the meteor activity for satellite operators concerned about impact hazards.

"This final deployment of the Leonid Multi-instrument Airborne Campaign program promises an important and unique database for the development of instruments targeted at in situ sampling of cometary materials and for the future definition of comet missions," said Dr. John Hillman, lead scientist for planetary astronomy at NASA Headquarters. "It is hoped that these scientific data will provide new insights for the comparative studies of comets."

Although the meteors are harmless to people, there is a slight chance that a satellite could be damaged if it was hit by a Leonid meteoroid. The meteoroids are too small to simply blow up a satellite. However, the Leonids are moving so fast they vaporize on impact, forming a cloud of electrified gas called plasma. Since plasma can carry an electric current, there is a risk that a Leonid-generated plasma cloud could cause a short circuit in a satellite, damaging sensitive electronic components.

NASA's Goddard Space Flight Center, Greenbelt, Md., is responsible for controlling a large number of satellites for NASA and other organizations and is taking precautions to mitigate the risk posed by the Leonids. These include pointing instrument apertures away from the direction of the Leonid stream, closing the doors on instruments where possible, turning down high voltages on systems to decrease the risk of a short circuit, and positioning satellites to minimize the cross-section exposed to the Leonids.

Minimizing the threat meteoroids pose to satellites is the second major area of NASA's Leonid research. From five key points on the globe and from the International Space Station, NASA researchers will use special cameras to scan the skies and report activity around the clock during the Leonid shower. Led by Dr. Rob Suggs of the engineering directorate at NASA's Marshall Space Flight Center in Huntsville, Ala., the research is part of a long-term goal to protect spacecraft from potentially damaging meteoroids.

Using "night-vision" image-intensifier video systems and sky-watchers outfitted with Palm computer software developed to record visual counts, NASA engineers and astronomers will record their observations for later analysis. Another tool at Marshall's disposal is "forward-scatter radar" -- an early warning system built by Suggs, Dr. Jeff Anderson, also of Marshall's engineering directorate, and Dr. Bill Cooke, an astronomer at Marshall.

"Our system is pretty simple," said Suggs. "We use an antenna and a computer-controlled shortwave receiver to listen for 67 megahertz signals from distant TV stations." The transmitters are over the horizon and normally out of range. When a meteor streaks overhead, the system records a brief ping -- the echo of a TV signal bouncing off the meteor's trail. Like the image-intensified cameras, this system is capable of detecting meteors too dim to see with the unaided eye.

The research data from the Leonids shower will be analyzed to help NASA engineers refine their forecasts for spacecraft by better determining where, when and how the meteors will strike, NASA can improve protective measures to prevent or minimize damage to spacecraft.


Where, When, and How to Watch

Generally plan to start your meteor watch after midnight. That's when the night side of Earth faces in the direction in which it's moving around the Sun. The forward-facing side of Earth (after midnight) sweeps up more meteors than the trailing (before midnight) side.

To observe meteors, all you really need to do is find a dark observing site with a wide-open view of the sky. Bring a reclining lawn chair, bundle up warmly, and lie back and watch the stars.

Noting your sky's limiting magnitude is essential if you want to make a meaningful meteor count. Check the visibility of stars in and around the Little Dipper (if you live at a northerly latitude) and find the visual magnitude of the faintest one you can see with the naked eye. Click on the chart for a larger image.

Sky & Telescope illustration

Pick one of the areas highlighted here (click on the chart to see more zones) and count how many stars you can see in it, including the corner stars. Then find what limiting magnitude (LM) this number corresponds to in the following table.

Sky & Telescope illustration

North American Meteor Network (NAMN) provide an easy way to do this. They supply charts of various constellations with faint stars labeled. Compare one of these charts with what you see in the sky to find your limiting magnitude. Or just use the chart above of the Little Dipper.

Another approach is to use the chart on the right. Find one of the highlighted areas and count how many stars you can see in it, including the corners. Take a little time and use peripheral vision, but don't push very hard you want to characterize the ordinary state of your vision during the meteor watch. The table below then tells you the limiting magnitude (LM) that your star count corresponds to.

The limiting magnitude is an essential measure of your light pollution, sky clarity, and night vision. A meteor count is meaningless without it. Taking the average of several limiting-magnitude determinations will reduce random errors. Check again at least once an hour to track subtle changes in sky conditions, always noting the time. Even a small change has a big effect on the number of meteors you see.

Stars per Area of Preceding Chart
Area 3 Area 4 Area 8 Area 9
Beta ( b ),Theta ( q ),23 Alpha ( a ),Beta ( b ),Epsilon ( e ) Alpha ( a ),Beta ( b ),Zeta ( z ) Alpha ( a ),Gamma ( g ),Delta ( d ),Beta ( b )
UMa Gem Tau Leo
Num. LM Num. LM Num. LM Num. LM
5 4.5 5 4.3 4 4.7 7 4.4
6 4.6 6 5.0 5 4.8 8 5.0
7 4.8 7 5.1 7 5.1 11 5.6
8 5.2 8 5.3 8 5.3 13 5.7
9 5.4 9 5.6 9 5.5 15 6.0
11 5.7 10 5.7 10 5.9 18 6.1
13 5.8 11 5.9 11 6.0 20 6.3
14 6.0 12 6.1 12 6.1 21 6.4
15 6.1 13 6.2 15 6.2 24 6.6
16 6.2 14 6.3 16 6.3 25 6.7
17 6.3 15 6.4 17 6.4 29 6.9
18 6.4 16 6.5 20 6.5 32 7.0
19 6.5 18 6.6 21 6.6 34 7.1
20 6.6 20 6.7 23 6.7 38 7.2
23 6.7 22 6.9 26 6.8 40 7.3
25 6.8 23 7.0 28 6.9 44 7.4
27 6.9 25 7.2 29 7.0 45 7.5
29 7.0 26 7.3 31 7.4
33 7.1 30 7.5 32 7.5
37 7.2
44 7.3
49 7.4
54 7.5

Most observers like to take a break about once an hour to get up, move around, and open the coffee thermos. Note the beginning and end times of every break. If you're writing, also record how much time you spend looking down at your clipboard if this is more than a few percent of the total. Count how many seconds the job takes per meteor you may be surprised at how much time it adds up to.

Even if you observe without a break, separate your records with a time annotation at least once an hour. A watch that beeps on the hour will help remind you. If rates suddenly begin to rise or fall, note the time more often. Also note down the part of the sky where you spend most of the time looking.

For simple meteor counting, that's about it. If you want to do a little more, however, the IMO strongly encourages you to estimate the magnitude of each meteor you see. Large numbers of magnitudes are required for finding a shower's "population index," or r, the ratio of bright meteors to faint ones. This, in turn, is required for calculating the zenithal hourly rates for everyone who watched under a less-than-perfect dark sky. Some comparison magnitudes can be found below.

Make your magnitude estimates by imagining these stars zipping across the sky, not by trying to sum up the total light along a meteor's path. For example, when estimating magnitudes for the Leonids, a typical notation might be "L, 2.5."

It's important not to combine your counts with anyone else's! If you watch with friends, each person should conduct his or her session strictly separately and submit a separate report. In fact, you should really be positioned far enough apart so that you can't tell when someone else makes a note. The problem is not the bright meteor that draws a yell out of everybody, but the faint, questionable one that you would dismiss as an eye twitch if you didn't hear someone start muttering into a tape recorder. Including it will make your count artificially high for your limiting magnitude. It helps to watch different parts of the sky.

Nor should you confer about the sky's limiting magnitude. Your own determination needs to go with your count. If one observer finds 5.4 and another 6.0, each person is right — for the purpose of reducing his or her count.

Comparisons for Meteor Magnitudes
Mag. Object Mag. Object Mag. Object
-13 Full Moon 0.5 Procyon 2 Gamma ( g ) Gem
-10 Quarter Moon 1 Aldebaran 2 Gamma ( g ) Leo
-4.5 Venus (avg.) 1 Pollux 2.5 Delta ( d ) Leo
-2.5 Jupiter (avg.) 1 Spica 2.5 Gamma ( g ) UMa
-1.5 Sirius 1.5 Regulus 3 Gamma ( g ) UMi
0 Capella 2 Polaris 3 Epsilon ( e ) Gem
0 Arcturus 2 Beta ( b ) UMi 3.5 Epsilon ( e ) Tau
0 Vega 2 Alpha ( a ) UMa 3.5 Beta ( b ) Boo

Reporting Your Meteor Counts

The Leonid shower normally continues at a rather low level for about a week. This profile shows the shower's average activity from 1988 through 1993 rates didn't pick up until 1994. Adapted from the IMO's journal, WGN, this graph is the fruit of 1,102 effective hours of meteor watching by 182 observers. During this time they recorded 2,697 Leonids. The more hours of observation, the shorter the error bars (blue) will be. Click on the chart for a larger view.

Sky & Telescope illustration

Universal Time. If you have any question about this, include your civil (clock) time and date, along with the time zone you are in, for clarification.

Also include your latitude and longitude to 1° or better (use a GPS receiver or find them on a map), the direction you were looking toward, and anything else relevant. The IMO urges observers to monitor the meteor showers for several nights before and after the predicted peak to help provide full coverage of the weeklong shower.

Reports can be sent to the IMO through its North American coordinator: Robert D. Lunsford, 1828 Cobblecreek St., Chula Vista, CA 91913-3917.

Observers outside North America can send reports directly to the IMO's Visual Commission. E-mail or write to Rainer Arlt, Friedenstr. 5, D-14109 Berlin, Germany

At Sky & Telescope we're always glad to see a copy of your report by e-mail or surface mail to Sky & Telescope, One Alewife Center, Suite 300B, Cambridge, MA 02140 USA, but please send your original to one of the addresses above.


Meteor Activity Outlook for February 2-8, 2013

February offers the meteor observer in the northern hemisphere a couple of weak showers plus falling sporadic rates. This may not seem too exiting but you never know when surprises are in store. An errant earthgrazer from the Centaurid complex may shoot northward. Better yet, a bright fireball may light up the sky. February is the start of the fireball season, when an abundance of fireballs seem to occur. This lasts well into April and seems to occur mostly during the early evening hours.

Observers in the southern hemisphere are treated to the Alpha Centaurid peak on the 8th plus the entire Centaurid complex of radiants is active all month long. Sporadic rates also peak this month south of the equator this month adding to the celestial show.

During this period the moon reaches its last quarter phase on Sunday February 3rd. At this time the moon is located ninety degrees west of the sun. The half illuminated moon will rise near midnight local standard time and will remain in the sky the remainder of the night. While producing much less light than a full moon, the last quarter moon will still hamper meteor observations during the morning hours. If your skies are transparent meteor observers can simply face the opposite direction of the moon and still carry on successful observations. As the week progresses the moon will less of a problem as the phase wanes and it rises later in the morning with each passing night. The estimated total hourly meteor rates for evening observers this week is near three no matter your location. For morning observers the estimated total hourly rates should be near seven from the mid-northern hemisphere and ten from the mid-southern hemisphere. The actual rates will also depend on factors such as personal light and motion perception, local weather conditions, alertness and experience in watching meteor activity. Morning rates are reduced due to moonlight.

The radiant (the area of the sky where meteors appear to shoot from) positions and rates listed below are exact for Saturday night/Sunday morning February 2/3. These positions do not change greatly day to day so the listed coordinates may be used during this entire period. Most star atlases (available at science stores and planetariums) will provide maps with grid lines of the celestial coordinates so that you may find out exactly where these positions are located in the sky. A planisphere or computer planetarium program is also useful in showing the sky at any time of night on any date of the year. Activity from each radiant is best seen when it is positioned highest in the sky, either due north or south along the meridian, depending on your latitude. It must be remembered that meteor activity is rarely seen at the radiant position. Rather they shoot outwards from the radiant so it is best to center your field of view so that the radiant lies at the edge and not the center. Viewing there will allow you to easily trace the path of each meteor back to the radiant (if it is a shower member) or in another direction if it is a sporadic. Meteor activity is not seen from radiants that are located below the horizon. The positions below are listed in a west to east manner in order of right ascension (celestial longitude). The positions listed first are located further west therefore are accessible earlier in the night while those listed further down the list rise later in the night.

The following showers are expected to be active this week:

The large Anthelion (ANT) radiant is currently centered at 09:48 (147) +11. This position lies in western Leo, four degrees west of the first magnitude star Regulus (Alpha Leonis). These meteors may be seen all night long but the radiant is best placed near 0100 LST when it lies on the meridian and is highest in the sky. Rates at this time should be near two per hour as seen from the northern hemisphere and one per hour from south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of slow velocity.

The Alpha Centaurids (ACE) are now active from a radiant located at 13:36 (204) -58. This position lies in southeastern Centaurus, five degrees northwest of the first magnitude star Hadar (Beta Centauri). These meteors cannot be seen north of the northern tropical regions. They are best seen from mid-southern latitudes where the radiant lies high in the sky near 0500 local summer time. As seen from the southern hemisphere rates will be rising this week and will peak on February 8th, when they should be near five per hour during the morning hours. At 56km/sec. the Alpha Centaurids would produce mostly swift meteors.

IMO Shower #22 is a weak unnamed shower active from January 29 through February 9. Peak activity occurs on February 8th from a radiant located at 13:42 (206) +09. This position is located in extreme southwestern Bootes, ten degrees southwest of the zero magnitude star Arcturus (Alpha Bootis). These meteors are best seen near 0400 LST, when the radiant lies highest above the horizon in a dark sky. Rates would mostly likely be less than one shower member per hour, no matter your location. At 65 km/sec. IMO Shower #22 would produce mostly swift meteors. It is possible that these meteors are a continuation of the Coma Berenicids which were active In December and January.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately five sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near two per hour. As seen from the mid-southern hemisphere (45S), morning rates would be near seven per hour as seen from rural observing sites and two per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Morning rates are reduced this week due to moonlight.

The table below presents a condensed version of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning .