Quasi-periodic oscillations of aerosol backscatter profiles and surface meteorological parameters during winter nights over a tropical station

M G Manoj,P C S Devara

doi:10.5194/angeo-29-455-2011

Abstract

Abstract. Atmospheric gravity waves, which are a manifestation of the fluctuations in buoyancy of the air parcels, are well known for their direct influence on concentration of atmospheric trace gases and aerosols, and also on oscillations of meteorological variables such as temperature, wind speed, visibility and so on. The present paper reports quasi-periodic oscillations in the lidar backscatter signal strength due to aerosol fluctuations in the nocturnal boundary layer, studied with a high space-time resolution polarimetric micro pulse lidar and concurrent meteorological parameters over a tropical station in India. The results of the spectral analysis of the data, archived on some typical clear-sky conditions during winter months of 2008 and 2009, exhibit a prominent periodicity of 20–40 min in lidar-observed aerosol variability and show close association with those observed in the near-surface temperature and wind at 5% statistical significance. Moreover, the lidar aerosol backscatter signal strength variations at different altitudes, which have been generated from the height-time series of the one-minute interval profiles at 2.4 m vertical resolution, indicate vertical propagation of these waves, exchanging energy between lower and higher height levels. Such oscillations are favoured by the stable atmospheric background condition and peculiar topography of the experimental site. Accurate representation of these buoyancy waves is essential in predicting the sporadic fluctuations of weather in the tropics.

Highlights

Atmospheric gravity waves are essential parts of the dynamics of the atmosphere on all meteorological scales (Nappo, 2002), and their presence in a stably stratified environment could be an important feature of many mountainous/hilly regions (e.g., Ross and Vosper, 2003)
We examine the characteristic oscillations of tropospheric aerosol backscatter signal from a polarized lidar and that of surface weather parameters from an automated weather station
Overnight experimental data of aerosol backscatter signal strength from an autonomous micro pulse lidar and concurrent surface meteorological parameters were subjected to spectral analysis to explore the dominant mode of variability inherent in them, on 14 clear-sky nights in the backdrop of a stable atmosphere

Summary

Introduction

Atmospheric gravity waves are essential parts of the dynamics of the atmosphere on all meteorological scales (Nappo, 2002), and their presence in a stably stratified environment could be an important feature of many mountainous/hilly regions (e.g., Ross and Vosper, 2003) They are manifested as oscillations of air parcels by the lifting force of buoyancy and the restoring force of gravity; and disturbances to this type of balanced state result in the excitation of atmospheric gravity waves with a variety of spatial and temporal scales (Fritts and Alexander, 2003; Geller et al, 2006).

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Results

Conclusion