Characteristics of gravity waves observed with intensive radiosonde campaign during November–December 2005 over western Sumatera

M Venkat Ratnam,Simon P Alexander,T Tsuda,T Kozu

doi:10.1186/bf03352948

Abstract

Abstract Characteristics of gravity waves are studied using radiosonde campaign conducted during November–December 2005 at Koto Tabang (KT, 0.2°S, 100.32°E). Intensive sounding with hourly launches was also conducted on seven days to study the characteristics of short period (2–6 hours) waves along with EAR data. Gravity waves with period (τ) of 3 hours and vertical wavelength (λ z ) of 10 km seemed to be generated due to localized convection around KT, which is inferred from X-band Doppler radar. The energy of the gravity wave with period of 2–3 days and vertical wavelength of 3–5 km is largest between 15 and 20 km and 25 and 30 km. We also report the comparison of the wave activity and its interaction with background wind between the three campaigns (CPEA-I, CPEA-II and Nov. 2002). Most of the time waves are propagating towards east and the source of gravity waves is strongly related to the slowly eastward-advecting tropospheric convection, implying that the wave activity was generated at far distant sources located west of KT. A key finding of this study is neither short period nor long-period gravity waves are generated during stationary type of convection. The change in the propagation direction of the short period waves within the event is observed which is not expected.

Highlights

The tropical atmosphere contains a number of spatial and temporal scales of motion
We collected Equatorial Atmosphere Radar (EAR) radar (Fukao et al, 2003) data located at KT (0.2◦S, 100.32◦E) which is available on continuous basis during these IOPs in order to delineate the characteristics of short period gravity waves and compare with hourly radiosonde observations
Summary and Conclusion As in Coupling Process in Equatorial Atmosphere (CPEA)-I campaign, intensive balloon soundings conducted over Koto Tabang during the CPEA-II campaign has been used to delineate the characteristics of various gravity waves

Summary

Introduction

The tropical atmosphere contains a number of spatial and temporal scales of motion. Modulation of these disturbances in the lower atmosphere will contribute significant variability in the upper atmospheric structure by transporting and depositing momentum and energy (Houghton, 1978; Lindzen, 1981; Holton, 1983; Warner and McIntyre, 1996; Fritts and Alexander, 2003 and references therein). As a part of this program, intensive radiosonde sounding were conducted for every 3 hours during CPEA-I campaign (Apr.–May 2004) This data has been utilized to explore the characteristics of long-period gravity waves and associated source mechanisms (Ratnam et al, 2006a). In the present study we combine both very high temporal resolution EAR measurements and hourly radiosonde soundings to study the characteristics of short period gravity waves (2–6 hours). We collected EAR radar (Fukao et al, 2003) data located at KT (0.2◦S, 100.32◦E) which is available on continuous basis during these IOPs in order to delineate the characteristics of short period gravity waves and compare with hourly radiosonde observations. The nine closest data points to the EAR site were averaged to produce a smoothed reflectivity value

Background

Vertical and horizontal group velocities

Findings

Gravity Wave Interaction with Background Wind