Convective Boundary Layer Clouds as Observed with Ground-Based Lidar at a Mid-Latitude Plain Site

Yifan Zhan,Fan Yi,Fuchao Liu,Changming Yu,Yunpeng Zhang,Jun Zhou

doi:10.3390/rs13071281

Yifan Zhan, Fan Yi + Show 4 more

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https://doi.org/10.3390/rs13071281

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Abstract

A total of 3047 individual shallow cumuli were identified from 9 years of polarization lidar measurements (2011–2019) at Wuhan, China (30.5°N, 114.4°E). These fair-weather shallow cumuli occurred at the top edge of the convective boundary layer between April and October with the maximum occurrence in July over the 30°N plain site. They persisted mostly (>92%) for a short period of ~1–10 min and had a geometrical thickness of ~50–600 m (a mean of 209 ± 138 m). The majority (>94%) of the cloud bases of these cumuli were found to appear ~50–560 m (a mean of 308 ± 254 m) above the lifting condensation level (LCL). In this height range from the LCL to the cloud base, the lidar volume depolarization ratio (δδV) slightly decreased with increasing height, showing gradually increasing condensation in this sub-cloud region due to penetrative thermals. Most of the observed shallow cumuli (79%) formed under the conditions of high near-surface air temperature (>30 °C) and water vapor mixing ratio (>15 g kg−1).

Highlights

A total of 3047 individual shallow cumuli were identified from 9 years of polarization lidar measurements (2011–2019) at Wuhan, China (30.5◦ N, 114.4◦ E)
Two typical convective boundary layer (CBL) cumulus occurrences in fair-weather summer over a megacity at a mid-latitude site was exhibited by polarization lidar, simultaneous surface weather station, and cloud camera measurements
The cumulus was most likely to form at the top of the CBL when the CBL height jumps over the lifting condensation level (LCL)

Summary

Introduction

A total of 3047 individual shallow cumuli were identified from 9 years of polarization lidar measurements (2011–2019) at Wuhan, China (30.5◦ N, 114.4◦ E) These fair-weather shallow cumuli occurred at the top edge of the convective boundary layer between April and October with the maximum occurrence in July over the 30◦ N plain site. Shallow cumuli have coverage of only ~5% over land and ~12% over ocean [16,17], they can significantly influence the solar radiation to the earth’s surface [18], modify the structure of the CBL by affecting turbulent mixing [19], and play a significant role in the initiation of ice or precipitation [20,21]. Various measurements with ground-based lidar/radar and airborne and spaceborne sensors have revealed the cloud morphology and statistical properties of shallow cumuli

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