Investigation of the atmospheric boundary layer characteristics over a high altitude station in North East India using measurements and reanalysis datasets

Atmospheric boundary layer (ABL) has been characterized over a high altitude station, Umiam in the North Eastern Region (NER) of India using observations and reanalysis products. In this study, we have used in situ data from Dr. Pisharoty GPS radiosonde launched using meteorological balloons during the years 2009 to 2013 and 2019 to 2020 during the afternoon time. For continuous measurement of ABL we have used the data obtained using ceilometer lidar from December 2019 to November 2023. For long term study of ABL height (ABLH) we have used three reanalysis datasets, viz. ERA5, IMDAA and MERRA2. Seasonal variation of ABLH from the radiosonde, ceilometer and reanalysis datasets showed highest during pre-monsoon followed by winter, post monsoon and minimum during monsoon. On both cloudy and clear-sky days, diurnal variability of ABLH was studied using ceilometer data where more than 55% of the total number of observations in each season, were found to be under cloudy conditions. Rapid growth of the ABL was seen from the morning hours during winter (~ 40 m h^− 1), pre-monsoon (~ 210 m h^− 1), monsoon (~ 291 m h^− 1) and post monsoon (~ 100 m h^− 1) season under clear-sky conditions as compared to the cloudy days. Hence lesser ABLH during cloudy conditions was prominent throughout the day during all the seasons. Maximum seasonal mean of 1102 (± 370) m was obtained from radiosonde observations during the pre-monsoon season. Comparison between ABLH retrieved from radiosonde and ceilometer were in good agreement with a correlation coefficient of 0.91. A comparison study of ABLH obtained from the reanalysis products with the ceilometer data showed better results from ERA5 and IMDAA rather than MERRA2. However, both IMDAA and MERRA2 were unable to capture the decaying of the ABL from the noon time peak during all the seasons. Distinct variability was observed in the absolute values of the ABLH obtained from both the observation and reanalysis datasets mainly due to the difference caused by the estimation methods used in the ABLH calculation.