Vertical fluctuation energy in United States high vertical resolution radiosonde data as an indicator of convective gravity wave sources

Abstract

Convectively generated internal gravity waves at extratropical latitudes are difficult to identify by climatological analysis of the temperature and horizontal wind fields from radiosonde profiles using traditional analysis methods. Here, we show that, by analyzing ascent rate profiles (we define a new variable, “vertical fluctuation energy (VE)”), we can identify convection sources in climatological analyses. Analysis of a 9‐year time series (1998–2006) of United States high vertical resolution radiosonde data shows that VE maximizes in summer in midlatitudes within the troposphere (2–8.9 km), and peaks at local afternoon–early evening during the summer over most of the contiguous United States. Furthermore, the apparent dominant vertical wavelength based on Fourier analysis of the low‐pass filtered ascent rate fluctuations also increase and decrease with VE, both on diurnal and seasonal timescales. VE in the lower stratosphere, however, does not show this same relationship to convection, but analysis of the vertical wavelength does show some of the features seen in tropospheric VE. Unlike midlatitude stations, VE within both the troposphere and the lower stratosphere over tropical western Pacific island stations is highly correlated with convective precipitation and inversely correlated with outgoing longwave radiation. We interpret this difference by using the 4‐D Gravity Wave Regional or Global Ray Tracer ray‐tracing model with a source spectrum representative of a convection source.