Diurnal variability of the atmospheric boundary layer height over a tropical station in the Indian monsoon region

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.

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Diurnal variability of the Atmospheric Boundary Layer height over a tropical station in the Indian Monsoon Region

10.5194/acp-2016-542 ◽

2016 ◽

Cited By ~ 1

Author(s):

Sanjay Kumar Mehta ◽

Madineni Venkat Ratnam ◽

Sukumarapillai V. Sunilkumar ◽

Daggumati Narayana Rao ◽

Boddapati V. Krishna Murthy

Keyword(s):

Boundary Layer ◽

Atmospheric Boundary Layer ◽

Diurnal Variation ◽

Indian Monsoon ◽

Winter Season ◽

Monsoon Region ◽

Diurnal Variability ◽

The Mean ◽

Indian Monsoon Region ◽

Tropical Station

Abstract. The diurnal variation of atmospheric boundary layer (ABL) height is studied using high resolutions radiosonde observations available every 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), 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 variability. A clear diurnal variability in 9 campaigns is observed while in 7 campaigns the SBL does not form for the entire day and in the remaining 18 campaigns the SBL form intermittently. The SBL forms 33 %–55 % 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 (0200 IST) and remain almost steady till 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. 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 winter season and lower during summer season. During all the seasons, the ABL height peaks during the afternoon (~ 1400 IST) and remains elevated till evening (~ 1700 IST). The ABL suddenly collapses at 2000 IST due to cooling after the sunset and increases slightly over night. Interestingly, it is found that the low level clouds have an effect on the ABL height variability, but not the deep convective clouds.

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Supplementary material to "Diurnal variability of the Atmospheric Boundary Layer height over a tropical station in the Indian Monsoon Region"

10.5194/acp-2016-542-supplement ◽

2016 ◽

Author(s):

Sanjay Kumar Mehta ◽

Madineni Venkat Ratnam ◽

Sukumarapillai V. Sunilkumar ◽

Daggumati Narayana Rao ◽

Boddapati V. Krishna Murthy

Keyword(s):

Boundary Layer ◽

Indian Monsoon ◽

Monsoon Region ◽

Diurnal Variability ◽

Layer Height ◽

Boundary Layer Height ◽

Supplementary Material ◽

Indian Monsoon Region ◽

Tropical Station ◽

Atmospheric Boundary Layer Height

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Thermodynamic structure of the convective boundary layer (CBL) over the Indian monsoon region during CAIPEEX campaigns

Annales Geophysicae ◽

10.5194/angeo-35-1361-2017 ◽

2017 ◽

Vol 35 (6) ◽

pp. 1361-1379 ◽

Cited By ~ 1

Author(s):

Sanjay Kumar Mehta ◽

Devendra Ojha ◽

Shyam Mehta ◽

Devarajan Anand ◽

Daggumati Narayana Rao ◽

...

Keyword(s):

Boundary Layer ◽

Convective Boundary Layer ◽

Indian Monsoon ◽

Potential Temperature ◽

Equivalent Potential Temperature ◽

Monsoon Region ◽

Convective Boundary ◽

Clear Sky ◽

Equivalent Potential ◽

Indian Monsoon Region

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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