Global and Seasonal Variations of Stratospheric Gravity Wave Activity Deduced from the<i>CHAMP</i>/GPS Satellite

Ratnam, M. Venkat; Tetzlaff, G.; Jacobi, Christoph

doi:10.1175/1520-0469(2004)061<1610:gasvos>2.0.co;2

Cited by 96 publications

(105 citation statements)

References 30 publications

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“…The mean dif fer ence is found to be 12 K at 30 km which reduced to 5 K at 35 km and less (3 -4 K) above that height. This kind of large bias be tween CHAMP and Gadanki lidar is also re ported by Ratnam et al (2004). Sim i lar to that reported by Ratnam et al (2004), there al ways ex ists colder bias in the lidar mea sure ments.…”

Section: Com Par I Son Of Tem Per a Ture Be Tween Cos Mic And Ray Leisupporting

confidence: 61%

“…This kind of large bias be tween CHAMP and Gadanki lidar is also re ported by Ratnam et al (2004). Sim i lar to that reported by Ratnam et al (2004), there al ways ex ists colder bias in the lidar mea sure ments. A pos si ble rea son for the observed large dis crep ancy could be due to the pres ence of aero sol con cen tra tion up to 35 km which will con tam i nate the tem per a ture re trieval from lidar.…”

Section: Com Par I Son Of Tem Per a Ture Be Tween Cos Mic And Ray Leisupporting

confidence: 61%

“…Sim i lar bias is also re ported by Ratnam et al (2004) us ing ra dio sonde and CHAMP (over Tai wan). In ter est ingly the large dif fer ence ob served by Kuo et al (2005) us ing rou tine ra dio sonde ob ser va tions from India is not re flected in the pro files ob tained us ing the Väisälä GPS ra dio sondes over Gadanki.…”

Section: Com Par I Son Of Tem Per a Ture Be Tween Cos Mic And Ra Dio mentioning

confidence: 94%

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Validation of the COSMIC Radio Occultation Data over Gadanki (13.48°N, 79.2°E): A Tropical Region

Rao¹,

Ratnam²,

Mehta³

et al. 2009

Terr. Atmos. Ocean. Sci.

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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/

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Section: Com Par I Son Of Tem Per a Ture Be Tween Cos Mic And Ray Leisupporting

confidence: 61%

Section: Com Par I Son Of Tem Per a Ture Be Tween Cos Mic And Ray Leisupporting

confidence: 61%

Section: Com Par I Son Of Tem Per a Ture Be Tween Cos Mic And Ra Dio mentioning

confidence: 94%

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Validation of the COSMIC Radio Occultation Data over Gadanki (13.48°N, 79.2°E): A Tropical Region

Rao¹,

Ratnam²,

Mehta³

et al. 2009

Terr. Atmos. Ocean. Sci.

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“…But for this study GPS/MET satellite data are missing in the African tropical belt. Ratnam et al (2004) show a global coherence between the activities of GW with vertical wavelenths<10 km in the LS, derived from Challenging Minisatellite Payload (CHAMP) satellite observation and from Outgoing Longwave Radiation (OLR) data in tropical regions. In particular strong GW activities are mostly related to deep convection over the landmass of Africa.…”

Section: Introductionmentioning

confidence: 99%

Climatology of gravity wave activity during the West African Monsoon

Kafando

Chane-Ming²,

Petitdidier³

2008

Ann. Geophys.

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Abstract. Gravity wave activity is analysed in the lower stratosphere using 6 year radiosonde data (2001)(2002)(2003)(2004)(2005)(2006) above two meteorological stations in the West African tropical region such as Niamey (13.47 • N; 2.16 • E) and Ouagadougou (12.35 • N; 1.51 • W). Monthly total energy density of gravity waves is computed with temperature and horizontal wind perturbations to highlight the West African Monsoon period from June to September. Comparison with monthly total energy density calculated with temperature only supports that observed small-scale temperature and wind perturbations are mostly associated with gravity waves in the lower stratosphere especially for large values during the wet season. Above the two sites, monthly evolution of gravity wave total energy density reveals a maximum intensity of gravity wave activity in July during the West African Monsoon period. Indicators of convective activity such as mean Outgoing Longwave Radiation (OLR) and Tropical Rainfall Measuring Mission (TRMM) rain rates reveal to be adequate monsoon proxies to be compared to gravity wave energy intensity during the West African Monsoon.

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“…Although spanning only a small portion of the gravity wave spectrum, satellite observations could provide some information on a global scale, especially on the seasonal and latitudinal variations of gravity waves with large vertical and horizontal scales (Fetzer and Gille 1994;Wu and Waters 1996;Eckerman and Preusse 1999;Tsuda et al 2000;Ratnam et al 2004). A few studies have also been successful in linking gravity waves with sources like topography (Hocke and Tsuda 2001) and convection (Tsuda et al 2000;Ratnam et al 2004). …”

Section: Introductionmentioning

confidence: 99%

Gravity Wave Characteristics over the Equator Observed During the CPEA Campaign using Simultaneous Data from Multiple Stations

Ratnam

Tsuda

Shibagaki

et al. 2006

Journal of the Meteorological Society of Japan

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The vertical and temporal variations of inertia-gravity waves are studied by means of an intensive radiosonde campaign conducted from 10 April to 9 May, 2004 at five sites, including the Equatorial Atmosphere Radar (EAR) site at Koto Tabang (0.2 S, 100.32 E) in west Sumatra, Indonesia. The four other balloon sounding sites are located about 75-400 km away from EAR. Dominant gravity waves with periods of 2-3 days and vertical wavelengths of approximately 3-5 km showing clear downward phase propagation were detected, particularly in the upper troposphere and lower stratosphere (UTLS) region. The gravity wave energy is found to become the largest at an altitude of approximately 20 km, although the enhancement was not continuous, but intermittent. The wave activity was similar at all five sites, having only a slight phase shift, which suggests that the horizontal scale of the wave is larger than the distance between the sites. We have applied a correlative analysis to delineate the horizontal propagation characteristics of gravity waves, and estimated the horizontal wavelength ðl h Þ to be approximately 1,700 km propagating toward 30 south from the east from 26-30 April, 2004, which is further verified by hodograph analysis for individual profiles. From 10-14 April, 2004 and 5-9 May, 2004, l h and the direction of the propagation were found to be 2,700 km and 3,250 km, and 26 and 3 north from the east, respectively. The spatial and temporal variations in the convection, which is thought to be a major Corresponding author: Dr. M. Venkat Ratnam, Research Institute for Sustainable Humanosphere (RISH), Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan. E-mail: vratnam@rish.kyoto-u.ac.jp ( 2006 Meteorological Society of Japan source in the generation of gravity waves, is also studied using satellite data of outgoing long-wave radiation (OLR). We noticed clear eastward advection of large super cloud clusters (SCCs) from the Indian Ocean to the maritime continent, with occasional movement towards the observational sites. The source of the gravity waves is strongly related to this slowly eastward-advecting tropospheric convection, implying that the wave activity observed in the UTLS region was generated by far distant sources located west of the EAR. In addition, we present a case study in which large wave activity did not correspond to the particular cloud convection.

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Global and Seasonal Variations of Stratospheric Gravity Wave Activity Deduced from theCHAMP/GPS Satellite

Cited by 96 publications

References 30 publications

Validation of the COSMIC Radio Occultation Data over Gadanki (13.48°N, 79.2°E): A Tropical Region

Validation of the COSMIC Radio Occultation Data over Gadanki (13.48°N, 79.2°E): A Tropical Region

Climatology of gravity wave activity during the West African Monsoon

Gravity Wave Characteristics over the Equator Observed During the CPEA Campaign using Simultaneous Data from Multiple Stations

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