The Role of Radiation in Heating the Clear-Air Convective Boundary Layer: Revisiting CASES-97
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The Role of Radiation in Heating the Clear-Air Convective Boundary Layer: Revisiting CASES-97 Margaret A. LeMone1 · Wayne M. Angevine2 · Jimy Dudhia1 Received: 6 May 2020 / Accepted: 7 October 2020 © Springer Nature B.V. 2020
Abstract Using data for 3 days in the Cooperative Atmosphere-Surface Exchange Study 1997 field experiment that are analyzed in LeMone et al. (Boundary-Layer Meteorol 104:1–52, 2002, hereafter L2002), it is shown that direct radiative heating can have a significant role in warming the nearly cloudless fair-weather convective boundary layer (CBL). Radiative heating becomes especially important in the presence of aerosols in the CBL, with a moist layer above the CBL also contributing. Not only does inclusion of radiative heating help “close” their potential-temperature budgets, but it affects entrainment estimates. Combined, radiative heating rates are of the order of 0.2 K h−1 , based on calculations using the Rapid-Radiative Transfer Model for general circulation models (RRTMG) code in a single-column version of the Advanced Research Weather Research and Forecasting model and estimates of aerosol heating published in L2002. Our current estimates of clear-air direct radiative heating differ from the estimates in L2002 because the surface skin temperature was not included in the earlier calculations. Upwelling and downwelling longwave radiation computed using the RRTMG code agrees with aircraft measurements within 10–15 W m−2 . Keywords Convective boundary layer · Entrainment · Radiative heating · Radiation measurements · Surface-temperature measurements
1 Introduction Spurred by learning of previous efforts to understand the effects of direct heating by radiation on the evolution of the fair-weather boundary layer while writing LeMone et al. (2019), we decided to revisit the convective boundary layer (CBL) budgets in an earlier study by LeMone et al. (2002, hereafter L2002) of potential temperature [θ¯ ] and mixing ratio [q], ¯ where the overbars imply a horizontal average and the brackets a vertical average. (Note that here
Margaret A. LeMone and Jimy Dudhia: NCAR is sponsored by the National Science Foundation.
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Margaret A. LeMone [email protected]
1
Mesoscale and Microscale Meteorology Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
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CIRES, University of Colorado, and NOAA Chemical Sciences Laboratory, Boulder, CO, USA
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we use the shorter term “radiation” in place of the more precise “radiative flux density” or “irradiances”) L2002 estimated radiative heating and argued for its role in balancing the [θ¯ ] budget, using data from the 1997 Cooperative Atmosphere-Surface Exchange Study (CASES-97) field experiment in south-east Kansas, USA. However, the clear-air radiative heating estimates in L2002 were based on soundings only, and hence neglected the important effect of surface skin temperature. Our objectives are to obtain more accurate estimates of total boundary-layer radiative heating, to apply these to the [θ¯ ] budget, and to comb
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