1.12 Limb Corrections to the Path Limits: Graze Zones
The northern and southern umbral limits provided in this publication were derived using the Moon’s center of mass and a mean lunar radius. They have not been corrected for the Moon’s center of figure or the effects of the lunar limb profile. In applications where precise limits are required, Watts’s limb data must be used to correct the nominal or mean path. Unfortunately, a single correction at each limit is not possible because the Moon’s libration in longitude and the contact points of the limits along the Moon’s limb each vary as a function of time and position along the umbral path. This makes it necessary to calculate a unique correction to the limits at each point along the path. Furthermore, the northern and southern limits of the umbral path are actually paralleled by a relatively narrow zone where the eclipse is neither penumbral nor umbral. An observer positioned here will witness a slender solar crescent that is fragmented into a series of bright beads and short segments whose morphology changes quickly with the rapidly varying geometry between the limbs of the Moon and the Sun. These beading phenomena are caused by the appearance of photospheric rays that alternately pass through deep lunar valleys and hide behind high mountain peaks, as the Moon’s irregular limb grazes the edge of the Sun’s disk. The geometry is directly analogous to the case of grazing oc- cultations of stars by the Moon. The graze zone is typically 5–10 km wide and its interior and exterior boundaries can be predicted using the lunar limb profile. The interior boundaries define the actual limits of the umbral eclipse (both total and annular) while the exterior boundaries set the outer limits of the grazing eclipse zone.
For years great interest has been taken in the effects of physical phenomena on ionosphere structure. A totalsolareclipse was visible in North America on August 21st, 2017. This event offered a great oppor- tunity for remote sensing the ionospheric behavior under the eclipse condition. In this study we investigated the effects of totalsolareclipse on variations of Total Electron Content (TEC), and conse- quently deviations on regional models of Vertical TEC (VTEC), as well as variations in ionospheric scintillation occurrence. Although variations of TEC due to totalsolareclipse are studied thoroughly by many authors, but the effect of solareclipse on ionospheric scintillation has never been considered before. Our study is based on measurements from a high-rate GPS network over North America on the day of eclipse, a day before and after its occurrence, on the other hand, GPS measurements from ground- based stations on similar days were used to model TEC on the day of event, and also one day before and after it. The results of this study demonstrate that solareclipse reduced scintillation occurrence at the totality region up to 28 percent and TEC values showed a decrease of maximum 7 TECU. Considering TEC models, our study showed apparent variations in the regional models, which conﬁrms previous studies on ionospheric responses to eclipse as well as theoretical assumptions.
km (peak of red line emission) as modeled by GITM for the eclipse and non-eclipse (control) conditions with actual geomagnetic conditions (top) and constant geomagnetic conditions (bottom) at Carbondale, IL. While the profiles are very similar, electron density and the O/N 2 ratios are ∼ 10% higher when the effects due the eclipse were included (for both actual and constant geomagnetic activity). All the temperatures (Tn: neutral temperature, Ti: ion temperature, Te: electron temperature) are slightly lower when the eclipse’s effect is included.
As already discussed in Sect. 3.1.1 one of the most dramatic meteorological impacts of a solareclipse is the change in sur- face temperature. A change in the radiative heating or cool- ing of the atmosphere is felt first in the Atmospheric Sur- face Layer (ASL) where turbulence processes dominate in the mass, energy and momentum transport. Not much effort has been devoted up to now to the study of turbulence and spectral characteristics of the ASL and by extension the Plan- etary Boundary Layer (PBL) during solar eclipses. How- ever, in the few studies investigating PBL changes during solar eclipses, important findings are reported. Antonia et al. (1979), Segal et al. (1996) and Eaton et al. (1997) showed that a solareclipse affects the sensible heat-flux and the ra- diation flux near the surface and that the surface layer tur- bulence approximately follows a continuum of equilibrium states in response to the stability changes brought about by the change in surface heat flux. During the solareclipse of 11 August 1999, Kolev et al. (2005) also demonstrated that the solareclipse affects the meteorological parameters of the atmosphere near the ground, the ozone concentration and the height of the mixing layer.
The totalsolareclipse event, 21 August 2017, occurred with a path of totality over the central USA, providing a good opportunity to investigate its effects on the photo- chemical and electrodynamic processes of the ionosphere. Using the ionospheric total electron content (TEC) ob- tained from a dense network of Global Navigation Satellite Systems (GNSS) receivers over North America, iono- spheric TEC structures, such as the large TEC depletion (Coster et al. 2017; Cherniak and Zakharenkova 2018), large-scale traveling ionospheric disturbances (TIDs) (Coster et al. 2017), eclipse-induced ionospheric bow waves and gravity wave-like structures of electron density (Zhang et al. 2017; Nayak and Yiğit 2018; Sun et al. 2018), and large-scale TEC enhancement after eclipse (Cherniak and Zakharenkova 2018) have been reported for the 2017 Augusteclipse. In this paper, a three-dimensional global assimilative system is used to investigate ionospheric vari- ation and its mechanisms during the 2017 Augustsolareclipse. We primarily focus on two ionospheric responses to the 2017 Augustsolareclipse: (1) the change in the ionospheric electric field system and (2) the resulting per- turbations of the conjugate EIAs.
Each profile of horizontal wind and vertical ascent speed collected within 24 hours of eclipse totality were filtered to isolate a pre-eclipse wave signal. Figure 4 displays the filtered wind profiles of u and v from each site 24 hours
prior to eclipse totality. A spike in winds from the west with phase opposition between the wind components u and v around 2 km provides a qualitative indication of high intrinsic frequency. Consistent phase opposition between u and v is found every 6 hours in the filtered center wind profiles C1– C4 within 5 to 7 km. Above the ferrel westerly cell and into the stratosphere, larger amplitude peaks of u and v are seen to be roughly half cycle out of phase at 18 km, shifting to one quarter out of phase with increasing altitude and eventually in phase around 20 km. These signatures correspond to the peaks seen in the raw profiles and indicate decreasing intrinsic frequency with altitude.
Figure 2a presents the NmF2 and hmF2 variations dur- ing the eclipse event and the control day over the Idaho National Lab, with an obscuration magnitude of 100 % around the daytime period. The effect of the disruption of solar radiation was evident as the NmF2 started decreas- ing at the first contact of the eclipse compared to an in- cessant increase on the control day in Fig. 2ai. The start time or first contact (08:43:31 LT), the maximum magni- tude period (10:01:53 LT) and the end time or the last con- tact (11:25:46 LT) of the eclipse are marked with the vertical lines S, M and E respectively. The decrement in NmF2 during the eclipse phase was due to reduction in the ionization. This reduction caused changes in the photochemical and trans- port process of the atmosphere during the daytime, thus ex- hibiting nighttime characteristics. It should be noted that the maximum decrease in NmF2 did not coincide with the maxi- mum magnitude of the eclipse obscuration, but rather with a time lag of few minutes, i.e. at 10:30 LT. This lag period fell within the relaxation period over the Idaho ionosphere, with NmF2 and hmF2 simultaneously attaining their peak magni- tudes of 1.67 e m −3 and ∼ 239 km. Hence, the ionosphere re- turned to its pre-eclipse state. Contrary to the decrease in the NmF2 amplitude at the recovery phase of the eclipse, hmF2 increases, attains 239 km peak around 10:30 LT and then de- creases, depicting the eclipse-caused morphology.
It is also clear from these observations that the complex mag- netic and density structures within the cavities are quite distinct from the magnetic structures defining the rest of the overlying arch-like structures forming the base of streamers, as well as the boundaries of streamers. The twisted and what seem observa- tionally to be helical structures within the cavities provide the most direct evidence for the emergence of helicity with promi- nences that is not limited to the prominences themselves but extends to their immediate surroundings. On the other hand, the global evolution model results of Yeates et al. ( 2007 , 2008 ) show that helicity associated with emerging active regions is likely to be the source of a significant (96%) fraction of the helicity in filaments, a process that may occur over a timescale of a few years. The 2008 observations were taken at the minimum of solar cycle 23 when no active regions were present for almost a year. Hence, they cannot conclusively provide supporting ev- idence for the helicity in prominences to be solely due to active regions.
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Day 3: Grand Teton National Park This morning you rise early and drive to the best vantage point around the Jackson area to observe this incredible natural phenomenon. It is August 21st 2017 and millions of people around the United States will enjoy nature’s grandest show, a totaleclipse of the sun. This is a rare opportunity to view this celestial wonder. The totaleclipse will be visible from our location in Jackson. Our private vehicle will be on hand to deliver you to the centre line of the eclipse track if possible. Climate projections for the area are very positive, but if there is a possibility of local cloud, the coach can be diverted to another location. The eclipse is a certainty but weather is a factor and despite advertising a suggested itinerary for the day prior to the eclipse, it is important this be used as a guideline only in order to pick a site with a greater chance of visibility. With the rest of the day free for hiking, there may be time to head out on the Hermitage Point Trail near Colter Bay. The trail follows a loop and is a relatively easy ten mile hike. Take the trail past Heron Pond, Swan Lake and discover unbeatable views of Jackson Lake, with the stunning Teton Range as the back drop. This is a fantastic day hike off ering yet more fabulous views. Black Bear are a common sight but it’s also Grizzly country, so be alert! See glorious views of the Snake River winding its way through Jackson Hole as you climb ever higher. Please note, it’s not possible for the leader to accompany your walks in Grand Teton due to national park regulations however, you’ll be given all the information and maps needed to enjoy your walk.
Even though previous studies have shown the clear and sometimes significant effects of solareclipse on the geomagnetic field observed on ground level, the measurements and results have more or less be conflicting making it somehow confusing. Momani et al  in their study of the 2003 totalsolareclipse over Antarctica showed a pronounced decrease in the north-south (X) component of the magnetic field with no significant effect in the east-west (Y) and vertical (Z) components. They suggested that the decrease in the X component was consistent with the depletion in the ionospheric total electron content. Ladynin et al  observed a decrease in the X component and an increase in the Inclination I during the 1 August2008totalsolareclipse. They also reported that data analysis on the eclipse of August 11, 1999 in Europe failed to unambiguously reveal eclipse effects. On their part, Ozcan and Aydogdu reported no effect on the X component of the geomagnetic field during the 11 August 1999 totalsolareclipse over Turkey, but a significant decrease in the Y component of the geomagnetic field. They also suggested that a reduction in the ionospheric electron density during the eclipse may have caused a modification of the geomagnetic field at ground level. Malin et al.  reported a significant increase in the D (Y) component of the geomagnetic field during the 11 August 1999 totalsolareclipse at Elazing and Kandilli in Turkey. While Nevanlinna and Hakkinen  observed a decrease in the X, Y, and Z components of the geomagnetic field during the July 22 1990 solareclipse in Finland.
In recent works (e.g., (Druzhinin et al., 2010; De, S.S. et al., 2009, 2011; De, K.S. et al., 2011)) devoted to the solar eclipses of August 1, 2008, and June 22, 2009, it was also noted that VLF/LF propa- gation is affected by the passage of the Moon’s shadow during a solareclipse, and the signal phase is the most sensitive characteristic. In these works studies were performed for different signals (Al’fa Russian trans- mitters (~12–15 kHz), an NWC Australian transmit- ter (19.8 kHz), Russian 25-kHz transmitters, and a Japan 40-kHz time service transmitter) registered in Yakutsk and India. It was found that the amplitude changed by 3–5% and the phase varied by 30°–45° when signals crossed the Moon’s shadow region. The calculations indicated that the ionospheric height increased by 3–4 km during the eclipse. Guha et al. (2010) observed the amplitude and phase characteris- tics during the solareclipse of July 22, 2009, on the 2200 km path. The occultation was maximal during the morning terminator, i.e., during the transition from the nighttime to daytime ionosphere. The eclipse resulted in a change in the signal’s usual form during the terminator, and the amplitude decreased by 3.2 dB in this case.
IV. Analysis and Results
To carry out the data analysis, five second measurements of GM counts during the ascent were accumulated into one minute sums. Only the ascent information was used due to the relatively uniform vertical velocities during the ascents. The one minute accumulations reduce the noise in the data and simplify the fitting process. In Figs. 2 – 5 the error bars in altitude show the range of altitudes over which the five second counts were accumulated into one minute sums. The error bars in counts per minute indicate the uncertainty in the counts assuming Poisson statistics. Poisson statistics are generally used in such counting measurements. The RP maximum was then determined by fitting a third order polynomial to the counts per minute versus altitude data above 10,000 m. Below 10,000 m the data have a different altitude dependence since few particles are being created and many particles are decaying. Third order polynomials were chosen by visually comparing second order polynomial and third order polynomial fits to the data. The third order polynomials, shown in the figures, provided a visually and statistically better fit. The uncertainties in the RP maxima were determined from the fitted altitudes of the maximum count rate plus and minus the standard error of the fit data. The fitting procedure and further examples of the fits have been presented by Taylor et al. . Table 1 and Table 2 provide the values for the RP maxima and their uncertainties for the omnidirectional and vertical coincident counts on the days before the eclipse and the day of the eclipse. The eclipse achieved totality at 13:01 CDT and continued in totality for two minutes along the balloons' trajectories.
It is possible that this is the first time ozonesondes have been flown during a totalsolareclipse. One ozonesonde mission has been reported during a non-totaleclipse. That research was just outside the main path of the 15 January 2010 annular eclipse (at a location where the eclipse reached a maximum of 79.4%). They detected no significant change in ozone during the eclipse, but a flight shortly after the eclipse did detect an increase in ozone that they attribute to the eclipse. Ozone was studied with a ground based spectrometer during the 1 August2008solareclipse which reached 98% at the location of the measurements. That group found no detectable changes beyond the expected normal fluctuations. Our results are consistent with both of these studies. Future work should plan to fly an ozonesonde shortly after the eclipse to determine if the post eclipse surge is actually associated with the eclipse.
Stacking or accumulating camera frames is a well-known technique in astrophysics (see Berry and Burnell, 2005). The track-and-stack technique is an effective method to obtain long exposures from many short ones of faint deep-sky ob- jects while tracking. Accumulation will reduce noise and in- crease the dynamical range. An inexpensive web camera sen- sor is capable of capturing a large number of faint and noisy exposures that can be stacked into sharp and clear images of deep-sky objects. Free software such as RegiStax (2008)
Eclipses have long been a source of wonder and fascination, but they also have a unique place in the scientific discovery process. On 21 August 2017, a celestial spectacle delighted millions of people across the United States, as a totalsolareclipse swept across the country. It provided an opportunity to test our understanding of the physics of the solar corona 1–3 , the region of the Sun’s atmosphere where the gas is heated to over a million degrees by processes that are still not fully understood 4–6 . During totality a solareclipse reveals the faint corona that is normally hidden from view, exposing intricate structures that are shaped by the magnetic field, including streamers, polar plumes, rays, and prominences. The coronal magnetic field is the source of the energy that is released during the solar flares 7 and coronal mass ejections that can damage Earth-orbiting satellites and cause power outages. It dominates the structure and dynamics of the corona, but is difficult to observe above the photosphere and chromosphere. It is of intense scientific interest to understand how the magnetic field emerges from beneath the Sun’s surface, how it evolves, when it is about to erupt, and how such ejections travel through interplanetary space. These eruptions have the potential to trigger a geomagnetic storm when they interact with the Earth’s magnetic field.
resulting from reflected and outgoing terrestrial infrared radiation. During a totaleclipse under conditions of little cloud cover, such measurements would tend to overestimate the air temperature prior to and after totality, and underestimate the air temperature during totality, suggesting a larger temperature fall than would be recorded under standard meteorological conditions. The errors involved can be substantial and may amount to several degrees Celsius, even at low air temperatures. During the eclipse of 21 August 2017, nine automatic weather stations (AWSs) from the high- resolution US Climate Reference Network (USCRN – Diamond et al, 2013) lay directly under the path of totality, providing very high-quality and high-frequency surface measurements, including global solar radiation and aspirated air temperature records (NOAA, 2017). These sites are identified in Figure 1 . This article briefly summarises the reduction in air temperature and the response lag from time of totality to the time of minimum temperature at each of these CRN locations based upon information in NOAA (2017). A more detailed account follows of the observations from Moose, Wyoming, the AWS site located just a few kilometres from the author’s eclipse viewing point north- west of Jackson, Wyoming.
1999 was about 100 km south of Ahmedabad, with a max- imum obscuration of 99.4% at 1801 h (IST). A number of radio experiments were conducted from Ahmedabad (23 ◦ N, 73 ◦ E) where the Physical Research Laboratory (PRL) oper- ates a digital KEL ionosonde. Rapid radio soundings (ev- ery 2 min) were made on the eclipse day and control days (10 and 12 August 1999). A riometer operating at 30 MHz was set up by the Indian Institute of Geomagnetism (IIG) at the Thaltej campus of PRL, located 5 km west of the main campus; this riometer was functional during the pe- riod 7–13 August 1999. Field strength measurements were made along the three oblique incidence paths of Colombo- Ahmedabad (11905 kHz), Bombay-Ahmedabad (558 kHz) and Rajkot-Ahmedabad (810 kHz) by the Physics Depart- ment, Gujarat University, Ahmedabad during the eclipse day and on control days. In this paper, we report on the ionospheric effects of the totalsolareclipse of 11 August 1999 observed from Ahmedabad that were determined by a series of different experiments.
Therefore we selected only three sub-ionospheric paths, namely NPM-CHA, NML-CHA, and NAU-BIR (see Figure 2). The location of transmitter-receiver pairs enabled us to monitor the region from Hawaii, through North America, and on to Puerto Rico.
The results of the analysis are shown in Figures 3–5. In comparison to our previous study (Solovieva et al., 2016) none of the signals received during the eclipse revealed any noticeable changes in the ampli- tude. Figure 3 shows the amplitude and phase variations on 21 August 2017 (in red color) and the monthly averaged values (in black color). Small decrease (about 1 dB) of the NPM signal amplitude can be seen in Figure 3. Note, the decrease in the amplitude is within the standard deviation of the signal for quiet days. For the two other paths the amplitudes of signals are rather noisy, and it is impossible to identify any effects. Next we describe the results of the analysis on the three different paths, NPM-CHA, NML-CHA, and NAU-BIR, separately.
Figure 6: Time slice just before burst for flight 14D, the sun appears to be towards the left hand side of the page. Figures 7 and 8 show data from flights 15D and 1E. These flights used the same wake boom arm flown on a non- eclipse day and during the eclipse. The launch times for these two flights were no more than 5 ½ minutes apart and the burst times are within 3 minutes of each other. The 15D flight achieved an additional ~1600 meters in altitude. In comparing the data, we argue that the diurnal temperature effect (given the small differences at the start and end of the flight) and sensor-to-sensor offset effects (same calibration and sensors) are minimal. Flight 15D exhibits the thermal box effect on the left hand side of the boom, but note the improvement over flight 14D. We attribute this in part to better rigging that provided the prescribed 40cm distance separation between the payload box and wake boom. Also note the expected daytime wake temperature profile with lower temperatures as one moves outward horizontally along the wake boom arm. Flight 1E, an eclipse flight, is notable in the absence of the box effect. As the Moon shadowed the Sun, radiation effects from the box to the wake arm were altered. The collection of profiles from 1E all contained this trait and was an exciting discovery we made as we processed the data.