Comparison of Convective Regimes Observed in TRMM LBA

Note: results on this page represent work in progress and caution should be excercised in their interpretation

This page shows a comparison between one MCS sampled during low level westerly flow (990225) and an MCS sampled during low level easterly flow (990126). Radar analyses are based on dual Doppler synthesis of 15 volumes for 990126 and 19 volumes for 990225. Both sets of dual Doppler syntheses were performed at 10 minute intervals for a continuous period. Each dual Doppler volume was then partitioned into convective and non-convective components (click here for a description of the partitioning procedure). Profile plots were constructed by calculating a mean for each category in each volume and then compositing all the results. Probability density functions were constructed using all the partitioned data for each MCS.


Results

Other Results - Reflectivity and Mass Flux

 

Summary

1. Reflectivity: In the convective region, both the 990126 and 990225 profiles show fairly deep convection (> 16 km). The steeper gradient of the westerly event (990225) compared to the easterly case (990126) is evident in the mixed phase region, which is reminiscent of the differenences observed in Darwin MCSs (MCSs from the monsoon and break regimes both produce deep convection but have different dBZ vertical structure). The differences in vertical structure are also apparent in time-height cross sections which show the 30 dBZ contour unchanging over time in 990225 (~ 5km) compared to 990126 (8 km early on, decreasing to 5-6 km several hours later). The divergence in the profiles above 5 km in both convection and non-convection categories suggests that stronger convection results in more robust stratiform, which is consistent with previous results looking at the presence/absence of lightning in Darwin MCS stratiform regions.

2. Vertical Air motion: In the convective region, the profiles have similar shape through the lower to mid troposphere; however, note that the 990126 profile is ~50% larger up through 4-5 km, which is consistent with the differences in reflectivity in the mixed phase region (higher vertical motions lofting more liquid precip above the freezing level), again similar to Darwin MCS vertical structure. It is likely that these differences would also be reflected in the thermodynamic bouyance profiles. Close inspection shows that the 990126 profile peaks at a slightly higher elevation, around 9-10 km, while the 990225 case peaks down around 8 km. The 990126 also shows a second peak in the upper troposphere that isn't observed in 990225. This is somewhat different compared to Darwin, where the monsoon (i.e., westerly) systems seemed to have this characteristic spike in vertical air motion at high levels compared to the continental break systems. The 990126 "non-convective" profile looks like typical stratiform compared to 990225.

3. Vertical Mass flux: The distribution of mass flux appears to be regime dependent. For a given reflectivity bin, the mode of the easterly mass flux distribution is higher compared to the westerly - this is especially true for the highest reflectivity bins. Moreover, the tail of the easterly mass flux extends to larger values comapred to the westerly distribution. As height increases, the mode of the mass flux distribution shifts to larger values (more true for the east case).



 

 

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