Simulations of Cloud-Radiation Interaction with Imposed Large Scale Dynamics from the DYNAMO Northern Sounding Array

The recently accomplished CINDY/DYNAMO project observed three MJO events in the equatorial Indian Ocean from October to December 2011. Analysis of the moist static energy budget by Sobel et al. (2014) indicates 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 the same DYNAMO MJO events.

The simulations are driven by the large scale forcing dataset from the DYNAMO northern sounding array, and carried out in doubly-periodic domains using the WRF model. Simulated cloud properties and radiative fluxes are compared to the observed reflectivity from the SPolka radar and observed radiative fluxes from the CERES and VISST datasets. To accommodate the uncertainty in cloud microphysics, we have tested a number of single moment (SM) and double moment (DM) microphysical schemes in the WRF model.

We find that in general the SM schemes tend to underestimate radiative flux anomalies in the active phase of the MJOs, while DM performs better but can still overestimate radiative fluxes. All the microphysics schemes tested exhibit bias in the shape of the histograms in radiative fluxes and radar reflectivity. Analysis of CRM-simulated radar reflectivity indicates that this radiative flux uncertainty is closely related to how much stratiform clouds the CRM can simulate. SM underestimates stratiform clouds by a factor of 2, while DM simulates much more stratiform cloud but shows a peak in the histogram at 15-20 dBz that is absent in observations. The double-moment Morrison scheme appears to give the best results in TOA fluxes associated with the MJO convective anomalies despite the bias in the histograms of cloud and radiative fluxes.