Vertical and longitudinal electron density structures of equatorial E- and F-regions

From global soundings of ionospheric electron density made with FORMOSAT 3/COSMIC satellites for September 2006–August 2009, day-night variations in vertical and longitudinal structures of the electron densities in equatorial E- and F-regions for different seasons are investigated for the first time. The results reveal that the wavenumber-3 and wavenumber-4 patterns dominated the nighttime (22:00–04:00 LT) F-region longitudinal structures in solstice and in equinox seasons, respectively. In daytime (08:00–18:00 LT) F-region, the wavenumber-4 patterns governed the longitudinal structures in the September equinox and December solstice, and wavenumber-3 in March equinox and June solstice respectively. A comparison of the daytime and nighttime longitudinal electron density structures indicates that they are approximately 180° out of phase with each other. It is believed that this out of phase relation is very likely the result of the opposite phase relation between daytime and nighttime nonmigrating diurnal tidal winds that modulate background E-region dynamo electric field at different places, leading to the day-night change in the locations of the equatorial plasma fountains that are responsible for the formation of the F-region longitudinal structures. Further, a good consistency between the locations of the density structures in the same seasons of the different years for both daytime and nighttime epochs has been noticed indicating that the source mechanism for these structures could be the same

A study of temperature profiles and trends as revealed by COSMIC RO technique and balloon –borne radiosonde instrument

This research presents atmospheric temperature profiles and trends retrieved using COSMIC RO technique and balloon-borne radiosonde instrument in 2007 and a few cases during 2017. By effectively using ‘wet’ temperature product available at COSMIC Data Analysis and Archive Center (CDAAC) website, an analysis has been made to present temperature profiles and trends at various regions including, Indian, Taiwan and Japan. A one-to-one correspondence is, clearly, seen between temperature profiles retrieved with COSMIC RO and radiosonde instrument. But, few and dominant differences in temperature profiles are found below at an altitude of ~5 km and above around tropopause (~16-17 km). The dominant differences found at below ~5km could be due to the inhomogeneous distribution of humidity present, generally, at the tropical regions, whereas above the tropopause altitudes, differences might be due to the ionospheric residual correction as reported by other researchers. Further, temperature monthly trends at various regions show distinct characteristics including, a sharp temperature inversion up to tropopause altitude. In addition, it is also observed maximum temperatures (peaks) during the northern summer seasons (May, June, July, and August) and minimum temperatures (troughs) during the northern winter seasons (November, December, January, and February) near to the surface of the Earth. Interestingly, although it is generally observed that the tropopause altitude is located at ~ 16-17 km at various regions, a keen observation reveals that distinct seasonal and latitudinal variations can be witnessed. With this case study, it may be concluded that the COSMIC RO technique is able to provide very accurate measurement, which reiterates its importance as a powerful tool to explore the Earth’s atmosphere on the local and global scale

Anomalous wind circulation over Taipei, Taiwan during the northern winter seasons of 2004 and 2005- A case study

This research reports, for the first time, an anomalous wind circulation over Taipei (Latitude 25.030N, Longitude 121.510E), Taiwan during the northern hemisphere winter season (December, January, and February) of years 2004 and 2005. The anomalous wind circulation of meridional winds, which showed southward directions during the winter seasons of 2004 and 2005 instead of northward winds, is noticed from one kilometer altitude range (lower troposphere) and that trend continued till around 20 km altitude range (lower stratosphere). To ascertain whether such a disturbed nature of wind pattern existed over nearby locations to Taipei, we have analyzed radiosonde-measured meridional and zonal winds over four nearby stations station to Taipei including, Roig, Xiamen, Minami and Fuzhou. Surprisingly, no anomalous wind behavior is seen except over Taipei during the northern winter seasons of 2004 and 2005. On the other hand, the European Centre for Medium-Range Weather Forecasts (ECMWF) model-predicted winds do not show any anomalous wind patterns over Taipei and other nearby stations, possibly due to the large averaging of internal variabilities of reanalysis databases. The plausible physical mechanisms of these disturbed meridional wind patterns are not understood at this juncture, but it is believed that local winds and atmospheric pollutants might have created an amicable environment as to provide such a disturbed meridional wind pattern over Taipei, Taiwan in the winter season of 2004 and 2005

Range rate variation studies of the low-altitude quasi-periodic radar echoes during SEEK-2 campaign

50-56The first experimental evidence on range rate reversal of lowaltitude quasi-periodic (LQP) echoes from nighttime midlatitude sporadic E region with systematic characteristics in their occurrences for the echoes observed during SEEK- 2 (Sporadic-E Experiment over Kyushu) campaign with 24.515 MHz frequency agile radar located at Tanegashima in southern Japan (30.75ºN, 130.03ºE, geomagnetic latitude 20.97ºN, dip angle 43.2ºN) is presented. Four reversal cases of LQP echoes are found during the observation period. The reversal times of these echoes from positive QP to negative QP are found between 2000 and 2400 hrs LT and negative QP to positive QP around 0200 hrs LT. Besides, Doppler velocities associated with these echoes show preferential directions meaning that they are consistent with the sign of range rate of QP echoes in most cases. As the backscatter echoes studied are confined to the collision dominated lower E region and semi-diurnal tide is most pronounced at latitude higher than 30º, large-period neutral winds such as tidal and planetary waves in addition to atmospheric gravity waves play a role in the generation and control of these backscatter echoes

F-2 region response to geomagnetic disturbances across Indian latitudes: O(S-1) dayglow emission

The morphology of ionospheric storms has been investigated across equatorial and low latitudes of Indian region. The deviation in F-2 region characteristic parameters (f(o)F(2) and hF) along with modeled green line dayglow emission intensities is examined at equatorial station Thiruvananthapuram (8.5 degrees N, 76.8 degrees E, 0.63 degrees S geomagnetic latitude) and low-latitude station Delhi (28.6 degrees N, 77.2 degrees E,19.2 degrees N geomagnetic latitude) during five geomagnetic storm events. Both positive and negative phases have been noticed in this study. The positive storm phase over equatorial station is found to be more frequent, while the drop in ionization in most of the cases was observed at low-latitude station. It is concluded that the reaction as seen at different ionospheric stations may be quite different during the same storm depending on both the geographic and geomagnetic coordinates of the station, storm intensity, and the storm onset time. Modulation in the F-2 layer critical frequency at low and equatorial stations during geomagnetic disturbance of 20-23 November 2003 was caused by the storm-induced changes in O/N-2. It is also found that International Reference Ionosphere 2012 model predicts the F-2 layer characteristic (f(o)F(2) and hF) parameters at both the low and equatorial stations during disturbed days quite reasonably. A simulative approach in GLOW model developed by Solomon is further used to estimate the changes in the volume emission rate of green line dayglow emission under quiet and strong geomagnetic conditions. It is found that the O(S-1) dayglow thermospheric emission peak responds to varying geomagnetic conditions

E-region irregularity observed by the Tanegashima Frequency Agile Radar during SEEK-2 campaign

42-49The present paper reports the nighttime field-aligned plasma irregularity (FAI) at 6.1 m in E-region during SEEK-2 (Sporadic E Experiment over Kyushu) campaign during July-August 2002 using Tanegashima (30.75ºN, 131.03ºE, geomagnetic 20.97ºN, dip 43.2ºN) Frequency Agile Radar (FAR) operated at 24.515 MHz. According to the characteristics of radar echo, the echoes are classified into four types: negative quasi-periodic (NQP) echo; positive quasi-periodic (PQP) echo; continuous echo; and undefined echo. A study shows that FAI appear generally at 80-110 km altitudes during 1800-0400 hrs LT, and FAI occur most frequently at 2200 hrs LT. Further, among the four different echo types, the occurrence probability of NQP is greater than other types