Ceilometer-Based Analysis of Shanghai’s Boundary Layer Height (under Rain- and Fog-Free Conditions)

AbstractTo investigate the boundary layer dynamics of the coastal megacity Shanghai, China, backscatter data measured by a Vaisala CL51 ceilometer are analyzed with a modified ideal curve fitting algorithm. The boundary layer height zi retrieved by this method and from radiosondes compare reasonably overall. Analyses of mobile and stationary ceilometer data provide spatial and temporal characteristics of Shanghai’s boundary layer height. The consistency between when the ceilometer is moving and stationary highlights the potential of mobile observations of transects across cities. An analysis of 16 months of zi measured at the Fengxian site in Shanghai reveals that the diurnal variation of zi in the four seasons follows the expected pattern; for all seasons zi starts to increase at sunrise, reflecting the influence of solar radiation. However, the boundary layer height is generally higher in autumn and winter than in summer and spring (mean hourly averaged zi for days with low cloud fraction at 1100–1200 l...