Tropopause inversion layer: Seasonal and latitudinal variations and representation in standard radiosonde data and global models

Abstract

Previous publications have given information on the seasonal and latitudinal variations of the tropopause inversion layer (TIL), as seen in high‐resolution radiosonde data sets, when soundings are averaged using the tropopause as a reference level. This paper presents a more quantitative analysis of the latitudinal and seasonal structure of the TIL than has been given previously. To do this, we define the region over which the static stability relaxes from its overshoot value at the tropopause to its local minimum in the stratosphere. This region is seen to increase monotonically in thickness from about 1 km at low latitudes to about 4 to 5 km at high latitudes. When the seasons are defined as winter (DJF), spring (MAM), summer (JJA), and fall (SON), the transition from tropical behavior occurs a little poleward of 20°N in both DJF and MAM and moves to a little poleward of 30°N in JJA and SON. Somewhat surprisingly, it is also shown that almost identical information about the TIL can be derived from standard radiosonde data for our period of analysis because of their reporting of the tropopause and other “significant levels,” but caution needs to be used in doing this since the number of reported significant levels has varied significantly over the long term and with some distinct discontinuities. Finally, we discuss what sort of information on the TIL can be obtained from global models given their relatively coarse vertical resolution.