Investigating the Spatio-Temporal Distribution of Gravity Wave Potential Energy over the Equatorial Region Using the ERA5 Reanalysis Data (original) (raw)
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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.
Springer Atmospheric Sciences, 2013
Gravity waves (GW) are important for the coupling between the different regions of the middle atmosphere. They are normally generated in the troposphere, are filtered by the wind field in the stratosphere and lower mesosphere and dissipate at least partly in upper mesosphere and lower thermosphere (MLT). The activity of gravity waves, their filtering by the mean circulation, and the variation of GW activity with solar activity have been studied using long-term wind measurements with Medium Frequency (MF) radars and meteor radars at high and middle northern latitudes. The GW activity is characterized by a semi-annual variation with a stronger maximum in winter and a weaker in summer consistent with the selective filtering of westward and eastward propagating GWs by the mean zonal wind. The latitudinal variation of GW activity shows the largest values in summer at mid-latitudes between 65 km and 85 km accompanied with an upward shift of the height of wind reversal towards the pole. Long-term observations of the MLT winds at mid latitudes indicate a stable increase of westward directed winds below about 85 km and an increase of eastward directed winds above 85 km especially during summer. The observed long-term trend of zonal wind at about 75 km goes along with an enhanced activity of GWs with periods of 3 to 6 hours at altitudes between 80 km and 88 km. In addition, the mesosphere responds to severe solar proton events (SPE) with increased eastward directed winds above about 85 km. The vertical coupling from the troposphere up to the lower thermosphere due to gravity waves and planetary waves is discussed for major sudden stratospheric warmings (SSW) for the winters 2006 and 2009.
The variability of zonal winds and the horizontal wind velocity variance of short period (20–120 min) gravity waves (GWs) in the equatorial mesopause region are studied using medium frequency (MF) radar observations from Pameungpeuk (7.4° S, 107.4° E) during 2004–2010. The zonal winds display a distinct semiannual oscillation (called mesospheric semiannual oscillation, MSAO), with westward winds during equinoxes and eastward winds during solstices. Furthermore, the westward winds during March equinox are larger during 2008 and 2009. The short period GW variance also shows a semiannual oscillation with enhanced activity during equinoxes. A good correlation is observed between the zonal winds and the short period GW variance from 2008–2010, with the winds being westward during the times of enhanced GW activity. Such a correlation, however, is less obvious during 2004–2006. The long period (10–20 h) GW variance, on the other hand, does not show such a correlation throughout the observation period.
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.
Effects of Latitude-Dependent Gravity Wave Source Variations on the Middle and Upper Atmosphere
Frontiers in Astronomy and Space Science, 2021
Atmospheric gravity waves (GWs) are generated in the lower atmosphere by various weather phenomena. They propagate upward, carry energy and momentum to higher altitudes, and appreciably influence the general circulation upon depositing them in the middle and upper atmosphere. We use a three-dimensional first-principle general circulation model (GCM) with implemented nonlinear whole atmosphere GW parameterization to study the global climatology of wave activity and produced effects at altitudes up to the upper thermosphere. The numerical experiments were guided by the GW momentum fluxes and temperature variances as measured in 2010 by the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument onboard NASA's TIMED (Thermosphere Ionosphere Mesosphere Energetics Dynamics) satellite. This includes the latitudinal dependence and magnitude of GW activity in the lower stratosphere for the boreal summer season. The modeling results were compared to the SABER temperature and total absolute momentum flux and Upper Atmosphere Research Satellite (UARS) data in the mesosphere and lower thermosphere. Simulations suggest that, in order to reproduce the observed circulation and wave activity in the middle atmosphere, GW fluxes that are smaller than observed fluxes have to be used at the source level in the lower atmosphere. This is because observations contain a broader spectrum of GWs, while parameterizations capture only a portion relevant to the middle and upper atmosphere dynamics. Accounting for the latitudinal variations of the source appreciably improves simulations.
Earth Science Research, 2012
We investigate the role of convective processes in triggering middle atmospheric gravity waves with the help of simultaneous measurements of middle atmospheric temperature variability from two tropical stations, Gadanki (13.5 o N, 79.2 o E) and Arecibo (18.3 o N, 66.7 o W). Our data reveal that some of the wave periods are similar at both locations indicating the source regions of waves to be similar at both the stations. However, the potential energies of short period gravity waves are found to be significantly higher over Gadanki compared to that at Arecibo. The most striking observation is that background wind conditions were similar and convective processes occurred very close to Gadanki compared to Arecibo. In the view absence of other wave sources during the period of observations, we suggest the strength as well as the distance of convective cells from the location of the observations is responsible for the observed differences in gravity wave spectrum and energies.
Geophysical Research Letters, 2006
A new methodology is applied to ERA40 reanalysis in order to quantify large-scale inertia-gravity wave activity in the equatorial lower stratosphere. Both eastward and westward propagating waves are identified in the data set and a good agreement is found with previously published in situ observations. Global estimates of vertical fluxes of zonal momentum associated with such waves are obtained. Typical amplitudes of order 10 À2 m 2. s À2 suggest that the forcing of the Quasi-Biennial Oscillation by large-scale inertia-gravity waves is tantamount to that by Kelvin waves. This method can be used to document the space-time variability of the wave-activity in order to improve the wave-drag parameterizations in climate models.
Journal of Geophysical Research, 2003
1] An all-sky charge-coupled device imager capable of measuring wave structure in the OH, O 2 , and O I (557.7 nm) airglow emissions was operated at Cachoeira Paulista, Brazil (23°S, 45°W), for 2 years in collaboration with Utah State University, Logan. The dominant quasi-monochromatic gravity wave components investigated over a 1yearperiod(September1998toOctober1999)havebeenextracted,andtheirseasonalvariationshavebeenmeasured.Atotalof283waveeventsweremeasured,exhibitinghorizontalwavelengthsfrom5to60km,observedperiodsfrom5to35min,andhorizontalphasespeedsofupto1 year period (September 1998 to October 1999) have been extracted, and their seasonal variations have been measured. A total of 283 wave events were measured, exhibiting horizontal wavelengths from 5 to 60 km, observed periods from 5 to 35 min, and horizontal phase speeds of up to 1yearperiod(September1998toOctober1999)havebeenextracted,andtheirseasonalvariationshavebeenmeasured.Atotalof283waveeventsweremeasured,exhibitinghorizontalwavelengthsfrom5to60km,observedperiodsfrom5to35min,andhorizontalphasespeedsofupto80 m s À1 . The large-scale ''band'' wave patterns (horizontal wavelength between 10 and 60 km) exhibited a clear seasonal dependence on the horizontal propagation direction, propagating toward the southeast during the summer months and toward the northwest during the winter. The direction of propagation was observed to change abruptly around the equinox period in mid March and at the end of September. Using a numerical simulation of gravity wave propagation in a seasonally variable climatological wind field, we have determined that the observed anisotropy in the wave propagation directions can be attributed to a strong filtering of the waves in the middle atmosphere by stratospheric winds.