Ionospheric and thermospheric response over Millstone Hill to the May 30, 1984, annular solar eclipse

Abstract

The National Center for Atmospheric Research (NCAR) thermospheric general circulation model (TGCM) is used to calculate the time‐dependent thermospheric response to the May 30, 1984, annular solar eclipse. The path of maximum obscurity begins at sunrise in the Pacific Ocean near 2°N and 135°W. It moves northeastward, passing across central Mexico, the eastern United States, and then the Atlantic before ending near 28°N and 4°E in Algeria. The area of the partial shadow is relatively large, and the total solar flux incident on the dayside of the earth is decreased by about 6% during the eclipse. The TGCM calculates the time‐dependent response of the winds, temperature, and the mass mixing ratios of the major constituents throughout the thermosphere. Perturbations follow the path of the annular eclipse, with maximum deviations occurring near 1700 UT at about 300 km for the temperature and at higher altitudes for the winds and composition. The perturbation winds converge from all directions toward the shadow at speeds reaching 75 m s−1 in the upper thermosphere. The maximum temperature anomaly (−55 K) and vertical wind anomaly (−7 m s−1) occur near the center of the shadow. At a constant altitude of 300 km, both the N2 density and the O density decrease by about 10% and 6%, respectively. The path of maximum obscuration passes within 3° of latitude of the incoherent scatter radar at Millstone Hill, Massachusetts (42.6°N, 71.5°W). The station experiences a maximum solar obscuration of 86% at 1700 UT (1200 LT). A time‐dependent one‐dimensional numerical model of the ionosphere that uses the TGCM‐calculated winds, temperature, and composition at Millstone Hill is used to calculate the electron and ion densities and temperatures and the densities of the odd‐nitrogen species NO, N(4S), and N(²D) during the eclipse. The calculated electron density decreases by about factors of 2 in the F region, 4 in the F1 region, and 3 in the E region compared to a similar control run without an eclipse. The F1 region emerges during the eclipse with an increase in the NO+/O+ ratio. The calculated electron temperature decreases by 460 K during the eclipse but then increases 200 K following the eclipse because of the intense solar heating in a region of reduced electron densities. The calculated ion temperature generally follows the changes in neutral temperature. The calculated thermospheric and ionospheric responses agree well with measurements made by the Millstone Hill incoherent scatter radar.

The ionospheric responses to the 11 August 1999 solar eclipse: observations and modeling

“…3, the modelled results suggest that there is a larger decrease in NmF1 than in NmE, which is in accord with the measured results. A similar result was reported by Roble et al (1986). Both measured and modelled results reveal that during the eclipse the response of electron density in the F1 layer is larger than that in the E layer.…”

“…There are some studies on the ionospheric response to solar eclipse on the basis of the numerical simulations in the past (e.g. Stubbe, 1970;Roble et al, 1986;Müller-Wodarg et al, 1998;Boitman et al, 1999;Liu et al, 1999;Korenkov et al, 2003a, b). However, for the variations of solar radiation during a solar eclipse, they only considered the occultation of the photosphere, i.e.…”

“…In the past, there have been some studies on the ionospheric response to solar eclipses on the basis of numerical simulations (e.g. Stubbe, 1970;Roble et al, 1986;Müller-Wodarg et al, 1998;Boitman et al, 1999;Liu et al, 1999;Korenkov et al, 2003aKorenkov et al, , 2003b. However, they only considered the occultation of the photosphere being shielded by the Moon for variations in solar radiation during a solar eclipse.…”

Ionospheric response to total solar eclipse of 22 July 2009 in different Indian regions

“…The sources of gravity waves were proposed to be the thermosphere where molecular oxygen heating begins (Chimonas, 1970), the stratosphere where ozone layer heating takes place (Fritts and Luo, 1993;Zerefos et al, 2000) and the troposphere where water vapor IR absorption and ground cooling occurs (Chimonas and Hines, 1971;Chimonas, 1973). Modeling studies supported the idea of eclipse-induced gravity wave generation in the thermosphere (Ridley et al, 1984;Roble et al, 1986;Muller-Wodarg et al, 1998), which is also supported by measurements (Liu et al, 1998;Altadill et al, 2001;Sauli et al, 2006). Zerefos et al (2007) reported waves with periods ranging from 30 to 40 min associated with thermal stratospheric ozone forcing.…”

Evidence of gravity waves into the atmosphere during the March 2006 total solar eclipse

“…Lastly, a source location has been identified in the thermosphere at 170 km altitude due to reduced heating by absorption of extreme ultraviolet solar radiation, based on the analysis of ionosonde measurements (Liu et al, 1998;Altadill et al, 2001;Sauli et al, 2006), while larger periods of about 1 h have also been reported (Altadill et al, 2001). Prior to those observations, the idea of an in-situ thermospheric wave source was highlighted by various modeling studies (Ridley et al, 1984;Roble et al, 1986;Müller-Wodarg et al, 1998).…”