Role of Tropical Convective Cells in the Observed Middle Atmospheric Gravity Wave Properties from Two Distant Low Latitude Stations (original) (raw)
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Annales Geophysicae, 2005
Atmospheric Gravity waves plays a significant role in controlling middle and upper atmospheric dynamics. Till date, frontal systems, convection, wind shear and topography have been thought to be the sources of gravity wave activity in the troposphere. All these studies pointed out that, it is very essential to understand generation, propagation and climatology of gravity waves. In this regard, several campaigns using Indian MST Radar have been carried out to explore the gravity wave activity in the troposphere and the lower stratosphere. The signatures of the gravity waves in the wind fields have been studied in the troposphere and lower stratosphere. The wave activity during pre monsoon, monsoon, post-monsoon and winter seasons have been studied. The large wind fluctuations are more prominent above 10 km during pre monsoon and monsoon seasons. The dominant wave periods and their height profiles of amplitudes are studied. The vertical wavelength and the propagation direction of gravity waves are determined using hodograph analysis and the same are presented.
Journal of Geophysical Research, 2007
1] Using a coordinated experimental observation under Middle Atmospheric Dynamics (MIDAS) program, an extensive study is carried out to quantify the role of gravity waves in driving the tropical Stratospheric Semiannual Oscillation (SSAO). Rayleigh lidar observations of middle atmospheric temperature over Gadanki (13.5°N, 79.2°E) and rocketsonde wind measurements over Trivandrum (8.5°N, 76.9°E) during the period November 2002 to June 2005 are used for the present study. Gravity waves with periods ranging from 2-4 hours and 0.5-1 hour are found to be dominant in the middle atmosphere throughout the observational period. The altitude profiles of momentum fluxes of gravity waves having these time periods are estimated and their seasonal variations are studied, which showed semiannual variation with maximum around equinoxes and minimum around solstitial months. The mean flow acceleration estimated from the divergence of momentum flux of gravity waves is compared with the mean flow acceleration observed using rocket measured zonal winds during three different cycles of SSAO. This comparison provided an opportunity to quantify the contribution of gravity waves toward generation of SSAO, which is found to be $30-50% of the observed acceleration during the evolution of the westerly phase of the SSAO. The present observations showed that the contribution of the gravity waves toward the westerly phase of SSAO varies significantly from cycle to cycle. The significance of the present results lies in quantifying the gravity wave-mean flow interaction during both easterly and westerly phases of SSAO for the first time over this tropical latitude.
Geophysical Research Letters, 2003
1] From OH airglow imaging observation carried out over one year in Indonesia, 74 events of gravity waves in the MLT (Mesosphere and Lower Thermosphere) region were extracted. Observed period, horizontal wavelength and observed horizontal phase speeds of gravity waves were typically 5 -13 min, 13-45 km and 37-75 m/s, respectively. Propagation directions were mostly southward except for the period between December and February, when eastward propagation was preferential. Spatial distributions of tropospheric clouds, estimated with GMS (Geostationary Meteorological Satellite) were consistent with the propagation direction of gravity waves, i.e., these clouds mainly existed in the opposite direction to the propagation direction of waves. This suggests that horizontal propagation characteristics of the short period gravity waves in the low latitude MLT region are mainly affected by the distribution of the wave sources in the troposphere, and the effect of the background mean wind in the middle atmosphere is smaller, as it is weaker ($20 m/s) in the equatorial region.
Characteristics of high-frequency gravity waves generated by tropical deep convection: Case studies
Journal of Geophysical Research, 2009
High frequency gravity waves generated by tropical deep convection play a major role in shaping the general circulation of the middle atmosphere. Special experiments were conducted to capture two convective events on 16 th May and 5 th June 2006 using VHF radar located at Gadanki (13.5° N, 79.2° E), a tropical Indian station. Control day observations were also made for necessary comparisons.
Journal of Geophysical Research, 2008
Five years of tropospheric data below 12 km from the Equatorial Atmosphere Radar (EAR) are examined for seasonal and interannual gravity wave activity. Results are compared with data from the Tropical Rainfall Measuring Mission (TRMM) satellite. A semiannual cycle of vertical wind variances inside and above convection is found. Maxima occur at the equinoxes and minima at the solstices. This semiannual cycle is also observed in the TRMM storm height and surface rainfall. Half of the vertical wind variance above convection is due to waves with periods of less than 2 h, with the rest coming from waves with periods of less than 24 h. On average, 78% of the total horizontal wind variance above convection is due to waves with periods of less than 24 h. The TRMM rainfall at 2 km altitude is greater than the EAR surface rainfall, suggesting that the EAR site is not representative of regional rainfall conditions. Momentum fluxes are calculated and shown to be dominated by multiday processes, although standard deviations are greater than the mean values.
Theoretical and Applied Climatology, 2014
The present manuscript deals with the spatial distribution of gravity wave activity over the tropics using ten years (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010) of CHAllenging Mini Payloads (CHAMP) and Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Global Positioning System (GPS) Radio Occultation (RO) data and ground-based radiosonde measurements over an equatorial station Singapore (1.36°N, 103.98°E) and four tropical stations, Guam (13.48°N, 144.80°E), Palau (7.33°N, 134.48°E) in the northern hemisphere, Darwin (12.41°S, 130.88°E) and Pago-Pago (14.33°S, 170.71°W) in the southern hemisphere from January 2001-December 2010. It also aims to quantify the difference in wave activity in the two phases of QBO, climatologically. Space-time spectra have been constructed over a latitude band of ±10°and decomposing the CHAMP/COSMIC temperature perturbations into symmetric and antisymmetric modes about the equator. Clear signature of equatorial waves with higher wavelength and a constant background of gravity waves (GW) with inertial frequency are prominent in the spectra. Strong GW and mean flow interaction can be seen in the lower stratosphere potential energy density (E P ) and momentum flux with enhanced wave activity during the westerly (eastward wind) phase of quasi-biennial oscillation (QBO) (WQBO) over the equatorial and tropical stations like Singapore and Palau/Darwin, respectively. From the latitudinal distribution of energy density, the occurrence of two-peak structure in energy density can be seen in the middle and lower latitudes with an enhancement during the WQBO phase. The E P associated with GWs are calculated at lower stratospheric (19-26 km) heights and are compared with outgoing longwave radiation (OLR) to correlate the wave events with tropical deep convection during the easterly, i.e. westward wind (EQBO) and WQBO phases of QBO. Clear coherence of convection due to Asian summer monsoon with localized enhancement of wave activity over Western Pacific, South America and African region during the WQBO phase is observed at the lower stratospheric heights. Significant enhancement is observed during Northern Hemisphere winter months and minimum during summer. The longitudinally elongated portion of E P over the equator is partially affected by Kelvin wave (KW) like disturbances with short vertical scales and also by inertia GW.
Journal of the Atmospheric Sciences, 2007
Latitudinal variations of the convective source and vertical propagation condition of inertio-gravity waves (IGWs) in the tropical region (30°S–30°N) are examined using high-resolution Global Cloud Imagery (GCI) and 6-hourly NCEP–NCAR reanalysis data, respectively, for 1 yr (March 1985–February 1986). The convective source is estimated by calculating the deep convective heating (DCH) rate using the brightness temperature of the GCI data. The latitudinal variation of DCH is found to be significant throughout the year. The ratio of the maximum to minimum values of DCH in the annual mean is 3.2 and it is much larger in the June–August (JJA) and December–February (DJF) means. Spectral analyses show that DCH has a dominant period of 1 day, a zonal wavelength of about 1600 km, and a Gaussian-type phase-speed spectrum with a peak at the zero phase speed. The vertical propagation condition of IGWs is determined, in the zonal wavenumber and frequency domain, by two factors: (i) latitude, whi...