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Cold point tropopause (CPT) plays a significant role to entry of water vapor into the lower stratosphere. Thus the variation in the tropopause plays an important role in the climate change by modifying the distribution in the stratospheric water vapor and hence the global radiation budget. The seasonal variability of the CPT is well known. During winter season, CPT is colder and higher but there are occasions when they observed to be warmer and lower.Similarly, during the summer season CPT is warmer and lower, however, we observed several cases when it becomes colder and higher. Not only this, there are several occasions when tropopause varies extremely. Thus, in this study, we have proposed a method to identify the extreme variability such as the coldest, warmest, highest and lowest tropopauses and examine the thermal their structure.Extreme variability of the cold point tropopause temperature (CPT-T) and height (CPT-H) are examined over a tropical station, Gadanki (13.45 N, 79.2 E)using high resolution radiosonde data during period 2006-2014. The extreme variabilities in the CPT-T and CPT-H are identified based on the 2 σ(standard deviation) departure from their monthly mean. In total 192 extreme cases such as the coldest (53) and warmest (41) CPT-T and the highest (61) and lowest (37) CPT-H are observed. The coldest (190±5 K, 17±2 km), warmest (190±5 K, 17±2 km), lowest (190±5 K, 17±2 km)and highest (190±5 K, 17±2 km) occurs without preference of season. Thermal structure of the coldest tropopause reveal that they often occur sharper with tropopause temperature and height are 189.3 K and 17 km, respectively. These cases are important for freeze drying mechanism.Whereas for all other cases such as the warmest, highest and lowest tropopause are broader in nature.Possible mechanisms responsible for such extreme variabilities such as equatorial wave propagation, deep convection and ozone transport are examined.

Abstract. Spatial and temporal variability in the convective boundary layer (CBL) height for the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) study period are examined using the data collected from high-resolution radiosondes during May-September 2009 over the Indian monsoon region. In total, 57 radiosonde launchings were carried out at ∼ 11:00-17:00 IST over six different stations covering a large geographical region, ranging from latitude ∼ 13 to 32 • N and longitude 73 to 92 • E. Of the total 57 launchings, 17 were made during cloudy conditions during which relative humidity (RH) was found to be greater than 83 % for an ∼ 1.0 km layer at various altitudes below 6 km. Within the layer the difference between saturated equivalent potential temperature and equivalent potential temperature is small, and it satisfies the condition that RH > 83 % for about 1 km is considered as the cloudy layer. There are eight cases when the cloud-topped boundary layer (CTBL) and 19 cases when fair-weather boundary layer (FWBL) is observed. The CBL heights are obtained using thermodynamic profiles, which vary from ∼ 0.4 to 2.5 km a.g.l. The formation of the cloud layers above the boundary layer generally lowers the CBL height and is responsible for its day-to-day variability. The development of the cloud beneath the boundary layer generally elevates the CBL, which is also responsible for the large day-to-day variability in the CBL. The FWBL identified using relative invariance of the thermodynamic profiles varies from ∼ 2.0 to 5.5 km, which is clearly marked by a local minimum in the refractivity gradient. During cloudy days, the CBL is found to be shallow and the surface temperature lower when compared to clear-sky days. The CBL and the lifting condensation level (LCL) heights are randomly related and are found to be at a lower height during cloudy days when compared to clear-sky days. Finally, the typical comparison between the CBL height obtained using thermodynamic profiles and backscattering profiles using Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) is examined.

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