High Resolution Analysis of the Structure of a Convective System in Developing Typhoon Nuri

We perform a high resolution analysis (~0.5 km horizontal grid spacing) using data acquired during TCS-08 of a convective system embedded in the tropical depression preceding typhoon Nuri. Radar and dropsonde data are combined to obtain a three dimensional wind field using the 3d-var technique developed by Raymond and López. This procedure retrieves the wind field by solving a minimization problem where the resultant field has to satisfy the reduced set of observations, mass continuity, and a smoothing condition.

Here we are able to isolate a line of strong convection consisting of intense vortices concentrated in small regions with a strong local circulation, and with downdrafts located along its sides. We find strong reflectivities (> 40 dbz) with maximum updrafts around 6 km which is indicative of a vigorous convective system in an early evolutionary stage. The feature develops in a high vorticity environment and within it we find vorticity in excess of 100 times the Coriolis parameter.

Of particular importance is the ability of this analysis to distinguish between the convective updraft and downdraft contributions to the vertical mass flux. The convective downdrafts peak at low levels and quickly drop off with height. Furthermore they only contribute in a minor way to the total vertical mass flux profile denoting the dominance of the convective updrafts for this particular convective system.

Thus far we have only studied this system but we plan to extend the analysis for comparative purposes to include cases where deep convective towers develop in low vorticity environments.