AB STRACTCon stel la tion Ob serv ing Sys tem for Me te o rol ogy Ion o sphere and Cli mate (COS MIC), con sist ing of six Low Earth Or bit (LEO) Global Po si tion Sys tem (GPS) re ceiv ers, on board the Formosat Sat el lite 3 (FORMOSAT-3) is pro vid ing dense ob ser va tions of den sity, refractivity, tem per a ture and wa ter va por pro files of the neu tral at mo sphere since mid dle of July 2006. Spe cial ra dio sonde (Väisälä) cam paign was con ducted at Gadanki (13.48°N, 79.18°E), a trop i cal site in In dia, dur ing July 2006 to March 2007 to val i date these me te o ro log i cal pa ram e ters. Co-lo cated Nd: YAG Ray leigh lidar was also op er ated dur ing the over pass of COS MIC and is uti lized to val i date the tem per a tures in the height range of 30 to 40 km. A to tal of 142 over passes oc curred dur ing the above men tioned pe riod within 300 km dis tance from Gadanki out of which 41 over passes oc curred within a time dif fer ence of ±4 hours of ra dio sonde launch. In ad di tion, 18 over passes oc curred within the time dif fer ence of ±4 hours of lidar op er a tion. A de tailed com par i son has been made with all these over passes for the refractivity, tem per a ture and wa ter va por ob tained from COS MIC. The wa ter va por com par i son has shown gen er ally a good agree ment with a mean dif fer ence of 5 -10% be low 6 -7 km. Al though there is a colder bias be tween COS MIC and ra dio sonde, a very good com par i son in tem per a ture is also found be tween 10 and 27 km with a mean dif fer ence of less than 1 K (RMS dif fer ence is only 0.64 K). There ex ists a large dif fer ence in tem per a ture of about 8 K be tween 30 and 40 km (be tween COS MIC and lidar). Pos si ble rea sons for these large dif fer ences are given. There was one event that oc curred just over Gadanki for which a de tailed com par i son has been made with spe cial em pha sis on wa ter va por re triev als. Sen si tiv ity test is also done on the frac tional dif fer ence in N for the event that occurred on 24 July 2006 between COSMIC (1D-var) and radiosonde and found that pressure plays a key role than temperature in determining the refractivity. Atmos. Ocean. Sci., 20, 59-70, doi: 10.3319/ TAO.2008.01.23.01(F3C) IN TRO DUC TIONRa dio occultation soundings of the sig nals from the Global Po si tion ing Sys tem Sat el lites (GPS) are be ing used to ob tain ver ti cal pro files of at mo spheric tem per a ture, pressure and wa ter va por for cli mate re search and weather predic tion (Kursinski et al. 1997). The GPS Ra dio occultation tech nique has emerged as a pow er ful tool for ex plor ing the earth's at mo sphere from ground to a height of around 40 km and also in the ion o sphere af ter the suc cess ful launch of GPS/MET which has pro vided a 'proof of con cept' of GPS Ra dio Occultation (RO) tech nique. Sev eral mis sions such as Oers ted and SAC-C (Hajj et al. 2004) fol lowed GPS/

We analyzed the structure and variability of observed winds and tides in the Antarctica mesosphere and lower thermosphere (MLT) during the 2002 major sudden stratospheric warming (SSW) and the 2010 minor SSWs. We noted the effect of SSW on the variability of MLT tides for the first time in the Southern Hemisphere, although it has been well recognized in the Northern Hemisphere. We utilized the winds measured by Rothera (68°S, 68°W) medium frequency radar and King Sejong Station (62.22°S, 58.78°W) meteor radar for estimating the tidal components (diurnal, semi‐diurnal, and ter‐diurnal) in the MLT region. The unusual behavior of diurnal tide (DT) and semidiurnal tide (SDT) was observed in 2002. Zonal SDT amplitudes were enhanced up to 27 m/s after 18 days from the associated SSW day. However, the meridional tidal amplitudes of both DT and SDT suddenly decreased during the peak SSW, and SDT amplitudes slightly increased to 18 m/s afterward. In the normal years, SDT amplitude stays below 15 m/s. During the 2010 SSW, SDT zonal amplitudes increased up to 40 m/s and 50 m/s at altitudes of 80 km and 90 km, respectively, ~30 days after the associated SSW. Similar but weaker effect is noticed in the meridional components. The ter‐diurnal tide does not show any significant variation during the SSW. The two SSWs offered a challenging issue to answer: why tidal amplitudes are enhanced with a delay after the SSW. The reasons for the delay are discussed in accordance with theoretical predictions.

Abstract. The present study examines the role of tropical cyclones in the enhancement of tropospheric ozone. The most significant and new observation is the increase in the upper tropospheric (10–16 km) ozone by 20–50 ppbv, which has extended down to the middle (6–10 km) and lower troposphere (< 6 km). The descending rate of enhanced ozone layer is found to be 0.87–1 km day−1. Numerical simulation of potential vorticity, vertical velocity and potential temperature indicate the intrusion of ozone from the upper troposphere to the surface. Space borne observations of relative humidity indicate the presence of sporadic dry air in the upper and middle troposphere over the cyclonic region. These observations constitute quantitatively an experimental evidence of enhanced tropospheric ozone during cyclonic storms.

Abstract. Long-term VHF radar (53 MHz with 3 • beamwidth) observations at Gadanki (13.5 • N, 79.2 • E), India, during the period from September 1995 to August 1999 are used to study monthly, seasonal and annual medians of vertical eddy diffusivity, K in the troposphere, lower stratosphere and mesosphere. First, the spectral width contribution due to non-turbulent effects has been removed for further analysis and the monthly, seasonal medians of K are calculated. The monthly median of K in the troposphere shows maximum and minimum in June-July and November-December, respectively. In general, large values of K are seen up to 10 km and then decrease with height. Larger values of K are observed during monsoon and post-monsoon than in winter and summer. In general, the maximum and minimum values of the annual median of K (in logarithmic values) in the troposphere are found to be 0.25 and −1.3 m 2 s −1 respectively. In the mesosphere, the monthly median of K shows maximum and minimum during June-July and November-December, respectively, similar to the lower atmosphere. The value of K in the mesosphere becomes larger and it increases with height up to 75 km and again decreases above that height.The maximum values are seen during the summer, followed by equinoxes and a minimum during the winter. In general, the maximum and minimum values of K (in logarithmic values) are found to be 0.7 and 0.3 m 2 s −1 , respectively, in the mesosphere. A comparison of Doppler spectral parameters in different beam directions shows anisotropy in both signalto-noise ratio (SNR) and spectral widths in the mesosphere, whereas it shows isotropy in SNR and anisotropy in the spectral widths in troposphere and lower stratosphere.

1] In this paper, we present for the first time planetary-scale wave signatures in the low-latitude E region field-aligned irregularities (FAI) observed during June 2004 to May 2005 using the Gadanki mesosphere-stratosphere-troposphere radar. We have observed a clear signature of 5-8 day variability in echo occurrence, in SNR, and also in Doppler velocity observed above 100 km. Concurrent temperature observations made using the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on board the Thermosphere-Ionosphere-Mesosphere Energetic and Dynamics (TIMED) satellite have also clearly shown the presence of 5-8 day variability similar to that of FAI. The temperature variations have been characterized with zonal wave numbers of 3 and 4 and vertical wavelength of 15-20 km. These waves are found to have increasing amplitude with increasing height and phase progressing downward, suggesting that they were of lower atmospheric origin. It is emphasized that the planetary-scale characteristics of neutral atmosphere in the FAI observations are important in understanding the vertical coupling of the low-latitude ionosphere-atmosphere system. These observations and the pertinent issues are discussed in the light of current understanding of the planetary-scale role on the FAI variability. Citation: Phanikumar, D. V., A. K. Patra, M. V. Ratnam, and S. Sripathi (2009), Planetary-scale variability in the low-latitude E region field-aligned irregularities: First results from Gadanki observations,