J. Adv. Model. Earth Sys., submitted 3/2015.
Shuguang Wang
Department of Applied Physics and Applied Mathematics,
Columbia University, New York, NY.
Ann Fridlind
NASA Goddard Institute for Space Studies, New York, NY
Adam H. Sobel
Department of Applied Physics and Applied Mathematics and Lamont-Doherty Earth Observatory,
Columbia University, New York, NY.
Zhe Feng and Jennifer M. Comstock
Pacific Northwest National Laboratory, Richland, Washington.
Patrick Minnis
NASA Langley Research Center, Hampton, VA.
Michele L. Nordeen
Science Systems and Applications, Inc., Hampton, VA.
Abstract
The recently completed CINDY/DYNAMO field campaign observed two Madden-Julian oscillation (MJO) events in the equatorial Indian Ocean from October to December 2011. Prior work has indicated that the moist static energy anomalies in these events grew and were sustained to a significant extent by radiative feedbacks. We present here a study of radiative fluxes and clouds in a set of cloud-resolving simulations of these MJO events. The simulations are driven by the large scale forcing dataset derived from the DYNAMO northern sounding array observations, and carried out in a doubly-periodic domain using the Weather Research and Forecasting (WRF) model. Simulated cloud properties and radiative fluxes are compared to those derived from the S-Polka radar and satellite observations. To accommodate the uncertainty in simulated cloud microphysics, a number of single moment (1M) and double moment (2M) microphysical schemes in the WRF model are tested.
The 1M schemes tend to underestimate radiative flux anomalies in the active phases of the MJO events, while the 2M schemes perform better, but can overestimate radiative flux anomalies. All the tested microphysics schemes exhibit biases in the shapes of the histograms of radiative fluxes and radar reflectivity. Histograms of radiative fluxes and brightness temperature indicate that radiative biases are not evenly distributed; the most significant bias occurs in rainy areas with OLR less than 150 W/m2 in the 2M schemes. Analysis of simulated radar reflectivities indicates that this radiative flux uncertainty is closely related to the simulated stratiform cloud coverage. Single moment schemes underestimate stratiform cloudiness by a factor of two, whereas 2M schemes simulate much more stratiform cloud.