Modulation of tropopause temperature structure revealed by simultaneous radiosonde and CHAMP GPS measurements

Abstract

We have analyzed the behavior of Kelvin waves in the upper troposphere and lower stratosphere (UTLS), through an intensive radiosonde campaign conducted in November 2002 at Koto Tabang (0.2°S, 100.32°E), Indonesia. In addition, we employed simultaneous global CHAllenging Mini satellite Payload (CHAMP) Global Positioning System (GPS) radio occultation (RO) measurements, in which we fitted the temperature perturbations (T′F) along the longitude, assuming only zonal wave number 1 and 2 components. Height-time comparison of the Kelvin waves well above the tropopause (16.5 km) revealed good agreement between the two techniques, but disagreement is observed around and below the tropopause, probably due to the effects of higher zonal wave number (>2) components. We have derived longitude-time section of the deviation from the T′F (residual, T′R) with GPS RO measurements in order to confirm the existence of higher zonal wave number perturbations around the tropopause. By combining the T′F and T′R, we were able to reproduce well the major features of the radiosonde results even below the tropopause. Clear eastward motion of the convective centers, inferred from the outgoing long-wave radiation (OLR) distribution, was observed from the Indian Ocean, reaching Koto Tabang during 18-19 November, 2002. This coincided with the enhancement of Kelvin-wave-like perturbations around the tropopause, having the zonal wave number 4 in a limited longitude region around Koto Tabang. We also found modulation of the tropopause structure by both the global scale Kelvin waves, and those with higher wave number components. The cold-point tropopause (on average at 16.5 km) jumped to 19 km, which is the height with the minimum temperature phase of the global-scale Kelvin wave. Hence, caution is advised in relating the tropopause variations observed via the radiosonde measurements with large-scale Kelvin waves, as the Kelvin waves with higher zonal wave numbers (>2) could also be responsible for the modification of the tropopause structure. © 2006, Meteorological Society of Japan.