A Case Study of Shallow Cumulus Clouds in DYNAMO

During the Dynamics of Madden Julian Oscillation (DYNAMO) field experiment, ocean and atmospheric measurements were carried out over the Topical Indian Ocean (TIO; 8E-EQ and 72E-81E) from NOAA's WP-3D Orion aircraft (WP-3D). On 19 November 2011, WP-3D conducted five vertically stacked legs with 4-5 measurement levels in the middle of the DYNAMO array over the tropical southern Indian Ocean. High frequency (25 Hz) measurements of temperature, humidity as well as wind components along with the measurements of radiometric sea surface skin temperature and liquid water content were performed during a total of ~6 hour flight period. C-band radar mounted on the lower fuselage provided the precipitation reflectivity measurements. Average vertical levels of the stacked legs were at 60 m, 120 m, 350 m, 475 m and 650 m. The lowest three levels were well inside the boundary layer while the upper two levels were at the cloud base and within the cloud, respectively. Boundary layer profiling by the aircraft was also performed between the successive vertical stacks. The WP-3D penetrated through at least one trade wind cumulus in each vertically stacked leg. A few of the observed trade wind cumuli were precipitating during the measurements. The case to be presented is the only flight when shallow precipitating cumulus clouds were sampled intensively before the active phase of the November MJO event. Precipitating cumuli observed in two legs were found to produce cold pools. Cooling of up to 1.5°C was observed in surface air temperature and sea surface skin temperature during the cold pool events. Increased wind speed and change in wind direction was also noticed in the cold pools in comparison with the surroundings. Increased temperatures and decreased equivalent potential temperature were also observed in the cloud level data. We will discuss the mean vertical structure and the horizontal variability of this cumulus-topped boundary layer. Fluxes of momentum, sensible heat and latent heat calculated using the eddy correlation method will be presented to illustrate the energy and water vapor transport in this type of boundary layer in the DYNAMO domain.