Abstract
Abstract. The diurnal variation of atmospheric boundary layer (ABL) height is studied using high-resolution radiosonde observations available at 3 h intervals for 3 days continuously from 34 intensive campaigns conducted during the period December 2010–March 2014 over a tropical station Gadanki (13.5° N, 79.2° E; 375 m), in the Indian monsoon region. The heights of the ABL during the different stages of its diurnal evolution, namely, the convective boundary layer (CBL), the stable boundary layer (SBL), and the residual layer (RL) are obtained to study the diurnal variabilities. A clear diurnal variation is observed in 9 campaigns out of the 34 campaigns. In 7 campaigns the SBL did not form in the entire day and in the remaining 18 campaigns the SBL formed intermittently. The SBL forms for 33–55 % of the time during nighttime and 9 and 25 % during the evening and morning hours, respectively. The mean SBL height is within 0.3 km above the surface which increases slightly just after midnight (02:00 IST) and remains almost constant until the morning. The mean CBL height is within 3.0 km above the surface, which generally increases from morning to evening. The mean RL height is within 2 km above the surface which generally decreases slowly as the night progresses. The diurnal variation of the ABL height over the Indian region is stronger during the pre-monsoon and weaker during winter season. The CBL is higher during the summer monsoon and lower during the winter season while the RL is higher during the winter season and lower during the summer season. During all the seasons, the ABL height peaks during the afternoon (∼ 14:00 IST) and remains elevated until evening (∼ 17:00 IST). The ABL suddenly collapses at 20:00 IST and increases slightly in the night. Interestingly, it is found that the low level clouds have an effect on the ABL height variability, but the deep convective clouds do not. The lifting condensation level (LCL) is generally found to occur below the ABL for the majority of the database and they are randomly related.
Highlights
The atmospheric boundary layer (ABL) is the lowest layer of the troposphere in which the flow field is directly influenced by the interaction of the Earth’s surface at a response timescale of about an hour or less (Stull, 1988; Garratt, 1994)
The diurnal variability is a dominant feature of the ABL, which plays an important role in the exchanges of heat, momentum, moisture, and chemical constituents between the surface and free atmosphere
Altitude profiles of temperature variables and moisture variables obtained from the radiosonde observations are used to estimate the ABL height based on different methods
Summary
The atmospheric boundary layer (ABL) is the lowest layer of the troposphere in which the flow field is directly influenced by the interaction of the Earth’s surface at a response timescale of about an hour or less (Stull, 1988; Garratt, 1994). The importance of the ABL stems from the fact that it is the gateway for the pollutants and anthropogenic emissions, moisture, heat, and momentum fluxes to the free atmosphere. Rapid transport in the ABL takes place in order to achieve the radiative balance between the surface and the free atmosphere. The ABL is the largest sink for atmospheric kinetic energy. The ABL height is a key parameter, providing a length scale for the vertical extent and concentration of atmospheric pollutants, convective activity, and cloud and fog formation (Deardorff, 1972; Holtslag and Nieuwstadt, 1986; Seibert et al, 2000; Konor et al, 2009). The diurnal variability is a dominant feature of the ABL, which plays an important role in the exchanges of heat, momentum, moisture, and chemical constituents between the surface and free atmosphere
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