Profile-based estimated inversion strength

Abstract

Abstract. To better measure the planetary boundary layer inversion strength (IS), a novel profile-based method of estimated inversion strength (EISp) is developed using the ERA5 daily reanalysis data. The EISp is designed to estimate the IS based on the thinnest possible reanalysis layer above the lifting condensation level encompassing the inversion layer. At a ground-based site in North America, the EISp correlates better with the radiosonde-detected IS (R=0.74) than the lower-tropospheric stability (LTS, R=0.53) and the estimated inversion strength (EIS, R=0.45). The daily variance in low cloud cover (LCC) explained by the EISp is twice that explained by the LTS and EIS. Higher correlations between the EISp and the radiosonde-detected IS are also found at other radiosonde stations of the subtropics and midlatitudes. Analysis of LCC observed by geostationary satellites and the Moderate Resolution Imaging Spectroradiometer shows that the EISp explains 78 % of the annual mean LCC spatial variance over global oceans and land, which is larger than that explained by the LTS and EIS (48 % and 13 %). Over tropical and subtropical low-cloud-prevailing eastern oceans, the LCC range is more resolved by the EISp (48 %) than by the LTS and EIS (37 % and 36 %). Furthermore, the EISp explains a larger fraction (32 %) in the daily LCC variance as compared to that explained by the LTS and EIS (14 % and 16 %). The seasonal LCC variance explained by the EISp is 89 %, which is larger than that explained by the LTS and EIS (80 % and 70 %). The LCC–EISp relationship is more uniform across various timescales than the LCC–LTS and LCC–EIS relationships. It is suggested that the EISp is a better cloud-controlling factor for LCC and is likely a useful external environmental constraint for process-level studies in which there is a need to control for large-scale meteorology in order to isolate the cloud responses to aerosols on short timescales.