Abstract : The atmosphere s response to the total solar eclipse of 4 December 2002 is studied using a prototype high-altitude global numerical weather prediction model (NOGAPS-ALPHA). Local reductions in solar ultraviolet (UV) radiation during the eclipse are estimated using astronomical calculations of umbral and penumbral surface trajectories and observed solar limb darkening at ~ 200-300 nm. In NOGAPS-ALPHA these UV eclipse shadows yield stratospheric radiative cooling rate footprints peaking near 27 K day 1, a value 2 3 times larger than assumed in previous modeling. Difference fields between NOGAPS-ALPHA runs with and without this eclipse forcing reveal vertically deep middle atmospheric responses, with three-dimensional horizontal structures very similar to the large-scale bow-wave response first proposed by Chimonas (1970). Such structure appears clearly only at later times when total eclipses have abated and gravity waves generated in the stratosphere have had time to propagate vertically. Bow-wave amplitudes and direct thermal cooling responses are both small (]1 K for temperature and ]2 3 m s 1 for horizontal winds), contradicting some rocketsonde measurements that suggest much larger responses near 50 60 km altitude. We also find clear evidence of a bow-wave-like response in the model s surface pressure fields, with an amplitude 0.1 0.5 hPa, while surface air temperatures in NOGAPS-ALPHA show 4 K cooling over Africa during the eclipse. Both findings are consistent with surface atmospheric data acquired during previous eclipse passages.

Middle and lower atmospheric effects of the total solar eclipse of 4 December 2002 simulated with a high-altitude global model

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2020SW002643

Multilayered Sporadic E Response to the Annular Solar Eclipse on June 21, 2020

As part of the “GPS Attitude, Positioning, and Profiling experiment (GAP)” of the Canadian CASSIOPE science and technology mission, a set of four geodetic GPS receivers connected to independent antennas on the top-panel of the spacecraft can be operated concurrently to collect dual-frequency code and phase measurements on both the L1 and L2 frequencies. The qualification of the commercial off-the-shelf (COTS) GPS receivers is discussed, and flight results of precise orbit and attitude determination are presented. Pseudorange and carrier phase errors amount to roughly 65 cm and 8 mm for the ionosphere-free dual-frequency combination, which compares favorably with other missions using fully qualified space GPS receivers and is mainly limited by choice of simple patch antennas without choke rings. Precise orbit determination of CASSIOPE using GPS observations can achieve decimeter-level accuracy during continued operations but suffers from onboard and mission restrictions that limit the typical data availability to less than 50% of each day and induce regular long-duration gaps of 4–10 h. Based on overlap analyses, daily peak orbit determination errors can, however, be confined to 1 m 3D on 84% of all days, which fulfills the mission needs for science data processing of other instruments. The attitude of CASSIOPE can be determined with a representative precision of about 0.2° in the individual axes using three GAP receivers and antennas. Availability of dual-frequency measurements is particularly beneficial and enables single-epoch ambiguity fixing in about 97% of all epochs. Overall, the GAP experiment demonstrates the feasibility of using COTS-based global navigation satellite system receivers in space and the benefits they can bring for small-scale science missions.

/pdf/cassiope-orbit-and-attitude-determination-using-commercial-14hzueludl.pdf

CASSIOPE orbit and attitude determination using commercial off-the-shelf GPS receivers

Effects of the 21 June 2020 Solar Eclipse on Conjugate Hemispheres: A Modeling Study

Local and conjugate ionospheric total electron content variation during the 21 June 2020 solar eclipse

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2019GL083195

Topside Ionospheric Disturbances Detected Using Radio Occultation Measurements During the August 2017 Solar Eclipse

We present in situ ion composition and velocity measurements during the August 2017 solar eclipse from the Enhanced Polar Outflow Probe (e-POP), which crossed the path of totality at ~640-km altitude within 10 min of totality passing. These measurements reveal two distinct H ion populations, an ~40% decrease in topside plasma density, a similar drop in upward but not downward H ion flux, and a downward O ion velocity of ~100 m/s. These features are directly linked to changes in the H/O composition and in interhemispheric or field-aligned light ion flow and to a reduction in the negative spacecraft potential. These observed features were absent on the preceding, noneclipse days and corroborate the reduction in F region plasma density and topside total electron content observed by the Global Positioning System receivers on board. They are attributed to the temporary reduction of photoionization in the eclipsed F region. Plain Language Summary During a solar eclipse, the Earth’s ionosphere undergoes rapid and drastic changes in response to the sudden reduction in solar extreme ultraviolet flux along the eclipse path. The Enhanced Polar Outflow Probe crossed the eclipse path over the State of Idaho within 10 min following totality during the August 2017 Great American Solar Eclipse. Using the ion mass spectrometer and Global Positioning System receivers on board, the Enhanced Polar Outflow Probe observed several important changes in the eclipsed ionosphere, some for the first time, including a rapid ~40% decrease in electron density, an ~100% change in ion composition (H/O ratio), and a disruption of light (H) ion flow between the eclipsed and opposite hemispheres. These observations demonstrate that in addition to the ionospheric changes, the solar eclipse also induces significant changes to the upper atmosphere (thermosphere) and the plasmasphere.

/pdf/eclipse-induced-changes-to-topside-ion-composition-and-field-55gi5fyprg.pdf

Victoria Foss

Papers

Topside Ionospheric Disturbances Detected Using Radio Occultation Measurements During the August 2017 Solar Eclipse

Eclipse-Induced Changes to Topside Ion Composition and Field-Aligned Ion Flows in the August 2017 Solar Eclipse: e-POP Observations