Extreme variability of the tropical tropopause over the Indian monsoon region

Abstract

The extreme variability of the tropical tropopause may serve as an important factor in understanding the critical conditions of dynamical and radiative coupling between the troposphere and stratosphere. The extreme variability of the cold point tropopause (CPT) temperature (TCPT) and height (HCPT) are examined over a tropical station, Gadanki (13.45° N, 79.2° E), using high-resolution radiosonde data during 2006–2014. We identified the extremely cold, warm, high, and low tropopauses. The extremely cold (warm) tropopause is defined as the TCPT lesser (greater) than the lower (upper) limit of the two standard deviations of its climatological monthly mean. While the extremely high (low) tropopause is defined as the HCPT greater (lesser) than the upper (lower) limit of the two standard deviations of its climatological monthly mean. In total, 161 cases comprising extremely cold (52), warm (30), high (57), and low (22) are observed. The extremely cold (187.2 ± 1.60 K, 17.3 ± 0.52 km), warm (194.2 ± 1.78 K, 16.9 ± 0.89 km), high (191.7 ± 1.78 K, 18.2 ± 0.55 km), and low (191.8 ± 2.11 K, 16.2 ± 0.38 km) tropopauses occur without preference of season. However, these extreme tropopause cases occur independently and show distinct thermal structures. The thermal structures of the extremely cold tropopause cases are often sharper, whereas the extremely warm, high, and low tropopause cases are broader. Water vapor and ozone concentrations are found to be high for the extremely warm tropopause and low for the extremely cold tropopause. Under the shallow convection, extreme temperature profiles, in general, show prominent warming between 8 and 14 km while anomalous cooling (warming) just below (above) the CPT. Plausible mechanisms responsible for extreme tropopause variabilities such as deep convection, equatorial wave propagation, transports of water vapor and ozone, and potential vorticity intrusions are examined.