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Forcing mechanisms governing diurnal, seasonal, and interannual variability in the boundary layer depths: Five years of continuous lidar observations over a suburban site near Paris
Author(s) -
Pal Sandip,
Haeffelin Martial
Publication year - 2015
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2015jd023268
Subject(s) - daytime , atmospheric sciences , environmental science , planetary boundary layer , seasonality , climatology , forcing (mathematics) , lidar , boundary layer , aerosol , atmosphere (unit) , flux (metallurgy) , convective boundary layer , turbulence , meteorology , geography , physics , geology , statistics , remote sensing , mathematics , thermodynamics , materials science , metallurgy
The atmospheric boundary layer (ABL) depth, z i , is a fundamental variable of ABL and a climatologically important quantity. The exchange of energy between the Earth's surface and the atmosphere is governed by turbulent mixing processes in the daytime ABL, and thus, z i is important for scaling turbulence and diffusion in both meteorological and air quality models. A long‐term data set of z i was derived at the Site Instrumental de Recherche par Télédétection Atmosphérique (SIRTA) observatory near Paris, using measurements obtained from a ground‐based vertically pointing aerosol lidar and an autonomous algorithm STRAT+. Using multiparameter observational data sets covering a 5 year period (October 2008 to September 2013), this study aims to explore two interconnected ABL research topics: brief climatology involving multiscale temporal z i variability (diurnal, seasonal, annual, and interannual) and the relationship between z i and near‐surface thermodynamic parameters to determine meteorological processes governing z i variability. Both the z i and the growth rate over SIRTA showed large seasonal variability with higher mean values in spring (1633 m and 225 m h −1 ) and summer (1947 m and 247 m h −1 ) than in autumn (1439 m and 196 m h −1 ) and winter (1033 m and 149 m h −1 ). Seasonal variability of daytime maximum z i is found to be strongly and linearly correlated with downwelling solar radiation at the surface ( r = 0.92), while the dependence between daytime maximum z i and sensible heat flux (SHF) at seasonal scales is not fully linear, in particular, for summer months. Interannual variability is studied using deseasonalized monthly‐mean anomalies of each variable. Conditional sampling and linear regression analyses between the anomalies of deseasonalized SHF and daytime maximum z i , show (1) stronger correlation between the two parameters for the soil conditions compared to the wet soil conditions, (2) that z i anomalies were more dependent on SHF anomalies for negative than for positive boundary layer wind speed anomalies, and (3) in the summer season, z i anomalies varied more consistently with SHF anomalies for conditions with negative cloud cover anomalies than in conditions with positive cloud cover anomalies.