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

Abstract

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.

Gravity wave characteristics observed over a tropical station using high‐resolution GPS radiosonde soundings

“…The horizontal propagation direction of the GW is aligned toward the major axis of the wind vector hodograph. However, the exact direction of propagation is obtained from the corresponding temperature gradients [ Venkat Ratnam et al , 2006]. In the present study, temperature information has been used instead of vertical wind, unlike in the study of Venkat Ratnam et al [2008].…”

Characteristics of high‐frequency gravity waves generated by tropical deep convection: Case studies

“…There is good coincidence between satellite TBB measurements and large vertical velocities observed with MST radar in the first case (16 May) but not in the second case (5 June). One may thus conclude that TBB measurement cannot always be used as an exact proxy for convection [ Venkat Ratnam et al , 2006; Takayabu , 2006]. However, since large vertical velocities are noticed in the radar measurements at 2000 LT, deep convection must have taken place around Gadanki at that time.…”