DYNAMO/CINDY Sounding Network – Performance and Preliminary Scientific Results

Two sounding arrays straddling the equator to the south of India were established during 2011-12 CINDY/DYNAMO. In addition, supplemental soundings were taken at operational sites along the equator from Africa to the western Pacific. The sounding network was designed to provide (1) environmental profiles of temperature, moisture, and wind during all phases of the MJO, and (2) corresponding estimates of large-scale divergence, vertical motion, and heating and moistening of the atmosphere by convection, with a particular focus on MJO initiation. The special sounding data were transmitted in real time to the GTS to be used in operational models at various centers around the world during the experiment.

Overall, the operation of the DYNAMO sounding network was a success, with over 95% of the planned soundings launched and placed on the GTS. The majority of the soundings ascended above 75 hPa, with many stations reaching above 50 hPa. Several sites occasionally experienced problems with balloon icing as a result of the abundant stratiform precipitation over the Indian Ocean, and a small number of ascents terminated near the 0 C level. Minor issues were experienced at several sites with surface relative humidity measurements used to calibrate the sondes prior to launch.

The two DYNAMO sounding arrays have provided an unprecedented view of the evolution of the October-November 2011 MJO over the Indian Ocean from its formative to mature to weakening phase. The moistening of the midtroposphere proceeding into the active phase was well observed, although the precise mechanisms for the moistening remain to be determined. Early indications are that the two sounding array quadrilaterals have provided reliable estimates of the divergence and vertical motion fields during the evolving convective cycle associated with the MJO. For the October-November MJO, gradual moistening of the midtroposphere in mid-October was accompanied by a descent of the upper-level easterlies and a change from eastward to westward propagation of cloud clusters over the Indian Ocean as tracked by their cold cloud-top signatures.

In addition, the 8/day releases during October and November will enable an evaluation of the characteristics of the diurnal cycle throughout all phases of the MJO, allowing an analysis of its coupling with the upper ocean and determination of its possible role in MJO evolution. A diurnal cycle of convection was observed at the various sites superimposed on a lower-frequency variation associated with 2-4 day equatorial disturbances. The variability on multiple time scales has been well sampled by the sounding network.