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2020 |
The present paper reports coordinated ionospheric irregularity measurements at optical as well as GPS wavelengths. Optical measurements were obtained from Tiny Ionospheric Photometer (TIP) sensors installed onboard the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites. GPS radio signals were obtained from a dual frequency GPS receiver operational at Calcutta (22.58\textdegreeN, 88.38\textdegreeE geographic; geomagnetic dip: 32.96\textdegree; 13.00\textdegreeN, 161.63\textdegreeE geomagnetic) under the SCIntillation Network Decision Aid (SCINDA) program. Calcutta is located near the northern crest of Equatorial Ionization Anomaly (EIA) in the Indian longitude sector. The observations were conducted during the unusually low and prolonged solar minima period of 2008\textendash2010. During this period, four cases of post-sunset GPS scintillation were observed from Calcutta. Among those cases, simultaneous fluctuations in GPS Carrier-to-Noise ratios (C/No) and measured radiances from TIP over a common ionospheric volume were observed only on February 2, 2008 and September 25, 2008. Fluctuations observed in measured radiances (maximum 0.95 Rayleigh) from TIP due to ionospheric irregularities were found to correspond well with C/N0 fluctuations on the GPS links observed from Calcutta, such effects being noted even during late evening hours of 21:00\textendash22:00 LT from locations around 40\textdegree magnetic dip. These measurements indicate the existence of electron density irregularities of scale sizes varying over several decades from 135.6\ nm to 300\textendash400\ m well beyond the northern crest of the EIA in the Indian longitude sector during late evening hours even in the unusually low solar activity conditions. Paul, Ashik; Sur, Dibyendu; Haralambous, Haris; Published by: Advances in Space Research Published on: 03/2020 YEAR: 2020   DOI: 10.1016/j.asr.2019.11.035 GPS radio measurements; ionospheric irregularities; Northern crest of EIA; Optical measurements; solar minimum; TIP |
2014 |
Attribution of interminima changes in the global thermosphere and ionosphere We present a statistical attribution analysis of the changes in global annual average thermospheric mass density and ionospheric total electron content (TEC) between the cycle 22/23 solar minimum (which occurred at epoch 1996.4) and the prolonged cycle 23/24 minimum (2008.8). The mass density data are derived from orbital drag, and the TEC data are derived from ground-based GPS receivers. The interminima change in mass density was -36\% relative to the 1996.4 yearly average. Considering each multiplicative forcing independently, lower average geomagnetic activity during the cycle 23/24 minimum produced an interminima density change of at least -14\%, solar extreme ultraviolet (EUV) irradiance forcing produced a density change of -1\% to -13\%, and changes in thermospheric CO2concentration produced a density change of -5\%. There was essentially no interminima change in global TEC derived from ground-based GPS receivers or space-based altimeters, even though past behavior suggests that it should have changed -3\% (0.2 TEC units (1 TECU = 1016 el m-2)) in response to lower geomagnetic activity and -1\% to -9\% (0.1\textendash0.8 TECU) in response to lower EUV irradiance. There is large uncertainty in the interminima change of solar EUV irradiance; the mass density and TEC data suggest a plausible range of 0\% to -6\%. Emmert, J.; McDonald, S.; Drob, D.; Meier, R.; Lean, J.; Picone, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2014 YEAR: 2014   DOI: 10.1002/2013JA019484 ionosphere total electron content; solar minimum; thermosphere mass density |
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