Continuous monitoring of the atmospheric boundary layer (ABL) height from micro pulse lidar over a tropical coastal station, Kattankulathur (12.82° N, 80.04° E)

The continuous monitoring of the atmospheric boundary layer (ABL) height and its diurnal variation over the coastal station is generally a challenging task due to the frequent occurrence of the thermal internal boundary layer (TIBL), neutral boundary layer, and boundary layer with a strong residual layer (RL). The wavelet covariance transform (WCT) method provides robust estimates of the ABL height; however, it fails for the cases with strong RL and TIBL. Therefore, an improved fuzzy logic algorithm has been developed incorporating the sea breeze membership function besides the six membership functions used in previous studies. Fuzzy logic classifies the signals according to the membership functions based on the quality score of the individual extracted features, making it a robust method for identifying the different types of ABL. In this study, 78 days of micropulse lidar (MPL) observations over Kattankulathur (12.82° N, 80.04°E) during 2018 are utilized to identify the diurnal variation of the ABL using a fuzzy logic algorithm. Out of 78 cases, we have observed 12 convective or unstable ABL cases, 10 neutral ABL, 24 convective cases with strong RL, and 32 convective cases dominated by TIBL. For the unstable ABL, both fuzzy logic and WCT detect a similar diurnal pattern. For the neutral ABL, the stable boundary layer (SBL) does not evolve, and hence again, both fuzzy logic and WCT detect a similar ABL pattern. However, for the strong RL and TIBL cases, the ABL height obtained using the WCT method overestimates the fuzzy logic algorithm. The ABL height for various diurnal patterns obtained using fuzzy logic algorithm compares well with radiosonde observations at 05:30 IST and 17:30 IST. The daytime mean ABL height obtained using fuzzy logic compares well with the Indian monsoon data assimilation and analysis (IMDAA) re-analysis product (generated for the Indian monsoon region); however, IMDAA underestimates the night-time mean ABL height.