Upper‐tropospheric inversion and easterly jet in the tropics

Abstract

[1] Shipboard radiosonde measurements revealed a persistent temperature inversion layer with a thickness of $200 m at 12-13 km in a nonconvective region over the tropical eastern Pacific, along 2°N, in September 1999. Simultaneous relative humidity measurements indicated that the thin inversion layer was located at the top of a very wet layer with a thickness of 3-4 km, which was found to originate from the intertropical convergence zone (ITCZ) to the north. Radiative transfer calculations suggested that this upper tropospheric inversion (UTI) was produced and maintained by strong longwave cooling in this wet layer. A strong easterly jet stream was also observed at 12-13 km, centered around 4°-5°N. This easterly jet was in the thermal wind balance, with meridional temperature gradients produced by the cloud and radiative processes in the ITCZ and the wet outflow. Furthermore, the jet, in turn, acted to spread inversions further downstream through the transport of radiatively active water vapor. This feedback mechanism may explain the omnipresence of temperature inversions and layering structures in trace gases in the tropical troposphere. Examination of high-resolution radiosonde data at other sites in the tropical Pacific indicates that similar UTIs often appear around 12-15 km. The UTI around 12-15 km may thus be characterized as one of the ''climatological'' inversions in the tropical troposphere, forming the lower boundary of the so-called tropical tropopause layer, where the tropospheric air is processed photochemically and microphysically before entering the stratosphere.

Correlation between equatorial Kelvin waves and the occurrence of extremely thin ice clouds at the tropical tropopause

“…Therefore, we interpret the observed waves that cause large-scale cirrus cloud formation as equatorial Kelvin waves, that were likely to have been caused by remote convective systems. The shorter periodicity observed in the lower stratosphere, sometimes down to 4 days, resembles that in the case reported by Holton et al (2001) in the western Pacific.…”

“…This compilation illustrates downward propagating warm and cold anomalies with a periodicity of 4 to 7 days (3-4 wave cycles in 19 days) that occur in the TTL and the lower stratosphere, across the cold point tropopause (dashed red line). The waves extend approximately down to the level of the upper tropospheric inversion (UTI) which is a weak inversion layer that is regularly found in tropical temperature profiles approximately 1-2 km below the temperature minimum and marks the lower boundary of the TTL (Immler and Schrems, 2002;Fujiwara et al, 2003).…”

Intensive radiosonde observations of lower tropospheric inversion layers over Yichang, China

“…The upper-tropospheric inversion, with a thickness of 200 m around 12-15 km, produced and maintained by strong longwave cooling in the wet layer, seems to be a common feature of the tropical upper troposphere. This may have important implications for air transport across the tropical tropopause, a key process to the global stratospheric composition and climate (Holton et al, 1995;Fujiwara et al, 2003).…”

Statistics of lower tropospheric inversions over the continental United States

“…This inversion layer, therefore, acts as a lid or barrier in regard to near-surface and atmosphere constituent exchange. The upper-tropospheric inversion (UTI), firstly reported by Fujiwara et al (2003), which is produced and maintained by strong longwave cooling in the wet layer, seems to be a common feature of the tropical upper troposphere. The height where LTI exists, usually ranged from 3 to 4 km, is between the height of boundary inversion layer and UTI.…”

“…Radiosonde soundings have been extensively applied to study the tropospheric inversions (Fujiwara et al, 2003;Birner et al, 2006;Nodzu et al, 2006;Zhang et al, 2009). Radiosonde observations made by meteorology stations have been conducted routinely for decades in many stations around the world.…”