Lukianova R.,Arctic and Antarctic Research Institute |
Kozlovsky A.,Sodankyla Geophysical Observatory Sodankyla Finland |
Shalimov S.,Russian Academy of Sciences |
Ulich T.,Sodankyla Geophysical Observatory Sodankyla Finland |
Lester M.,University of Leicester
Journal of Geophysical Research A: Space Physics | Year: 2015
The upper mesospheric neutral winds and temperatures have been derived from continuous meteor radar (MR) measurements over Sodankyla, Finland, in 2008-2014. Under conditions of low solar activity pronounced sudden mesospheric coolings linked to the major stratospheric warming (SSW) in 2009 and a medium SSW in 2010 are observed while there is no observed thermal signature of the major SSW in 2013 occurred during the solar maximum. Mesosphere-ionosphere anomalies observed simultaneously by the MR, the Aura satellite, and the rapid-run ionosonde during a period of major SSW include the following features. The mesospheric temperature minimum occurs 1day ahead of the stratospheric maximum, and the mesospheric cooling is almost of the same value as the stratospheric warming (~50K), the former decay faster than the latter. In the course of SSW, a strong mesospheric wind shear of ~70m/s/km occurs. The wind turns clockwise (anticlockwise) from north-eastward (south-eastward) to south-westward (north-westward) above (below) 90km. As the mesospheric temperature reaches its minimum, the gravity waves (GW) in the ionosphere with periods of 10-60min decay abruptly while the GWs with longer periods are not affected. The effect is explained by selective filtering and/or increased turbulence near the mesopause. © 2015. American Geophysical Union. All Rights Reserved.
Nigussie M.,Bahir Dar University |
Radicella S.M.,Abdus Salam International Center For Theoretical Physics |
Damtie B.,Bahir Dar University |
Yizengaw E.,Chestnut Hill College |
And 2 more authors.
Radio Science | Year: 2016
This paper investigates a technique to estimate near-real-time electron density structure of the ionosphere. Ground-based GPS receiver total electron content (TEC) at low and high latitudes has been used to assist the NeQuick 2 model. First, we compute model input (effective ionization level) when the modeled slant TEC (sTEC) best fits the measured sTEC by single GPS receiver (reference station). Then we run the model at different locations nearby the reference station and produce the spatial distribution of the density profiles of the ionosphere in the East African region. We investigate the performance of the model, before and after data ingestion in estimating the topside ionosphere density profiles. This is carried out by extracting in situ density from the model at the corresponding location of C/NOFS (Communication/Navigation Outage Forecast System) satellite orbit and comparing the modeled ion density with the in situ ion density observed by Planar Langmuir Probe onboard C/NOFS. It is shown that the performance of the model after data ingestion reproduces the topside ionosphere better up to about 824km away from the reference station than that before adaptation. Similarly, for high-latitude region, NeQuick 2 adapted to sTEC obtained from high-latitude (Tromsø in Norway) GPS receiver and the model used to reproduce parameters measured by European Incoherent Scatter Scientific Association (EISCAT) VHF radar. It is shown that the model after adaptation shows considerable improvement in estimating EISCAT measurements of electron density profile, F2 peak density, and height. ©2016. American Geophysical Union. All Rights Reserved.