The role of particle recycling on precipitation development in convective clouds in the United Arab Emirates

The characteristics of summer convective storms forming over the Al Hajir Mountains, commonly known as the Oman Mountains, along and east of the border between the United Arab Emirates and Oman are examined using a variety of data sources. General characteristics were deduced from soundings and radar data, while detailed microphysical observations from penetrating aircraft were examined for several cases. The convective storms resemble those of air mass storms in other sub-tropical regions. The majority are relatively short-lived although long-lived multi-cellular systems exist that produce a large fraction of the total precipitation from summer storms.

First-echo studies indicate that precipitation develops differently between isolated storms (particularly the initial storms of the day) and later, more multi-cellular storms. Some of the differences can be explained by the altitude and strength of the ubiquitous mid-level subsidence inversion in that region. A weakening of the inversion, coupled with other factors such as low-level moisture or circulations creating convergence zones, leads to cycling of convective clouds and storms. The radar data show that earlier convection likely pre-conditions the local area with mid-level moisture and ice particles. Subsequent cells and storms then develop significant precipitation as they grow above 6 km (around -5° C).

Airborne microphysical measurements from multiple cloud penetrations on several days were used to elucidate the development of precipitation consistent with the radar data. In particular, the analysis concentrated on detecting and describing drizzle formation and its recirculation or dispersion throughout the turret and into neighboring turrets. The role of drizzle and larger drops in the graupel formation and riming process is viewed as integral to the precipitation development in these storms. While conceptually straightforward, the microphysical details of the individual cases were not always clear. Further syntheses of the data is continuing with the goal to demonstrate and generalize the relative importance that recycling of particles into the same and adjacent turrets has on precipitation development for these clouds.