The third and fourth NASA Convection and Moisture Experiments (CAMEX-3 and CAMEX-4) during the Atlantic hurricane seasons of 1998 and 2001, respectively, have yielded comprehensive multi-aircraft datasets using, both remote and in-situ instrumentation. Among these are high-frequency in-situ measurements of vertical wind, horizontal wind, temperature, and water vapor, made from NASA's DC-8 aircraft in the upper portions of the hurricane (typically above 10 km). Wind and temperature measurements were made at 20 hz by the NASA/Ames Meteorological Measurement System, while water vapor was measured at 1 hz by the NASA/JPL Laser Hygrometer. Fluxes of heat, momentum, and moisture at these levels are important, since modeling studies have shown that ice processes, which are dominant at temperatures below -40C (where the DC-8 flies) are important for hurricane intensification. Also, there are indications from satellite studies that latent heat release at DC-8 levels is significant, perhaps a third of those in the mid-troposphere. Preliminary results show that typical updrafts in the eyewall region are comparable to or higher than previous observations of tropical convection, with several instances of updraft magnitudes of 15 meters per second (the maximum observed was 21 meters per second). They also show significant supersaturations (10-20% or more) in the updrafts, which would enhance the latent heat release at the upper levels of the hurricane. This paper will examine the magnitude and distribution of small and mesoscale vertical fluxes of mass, momentum, moisture, and heat. The goal is to examine the role of these fluxes in the overall budgets of the respective quantities in the upper portions of the hurricane.

Pfister, Leonhard↗

NASA NTRS2000

How do Polar Stratospheric Clouds Form?

SOLVE measurements have been compared with results from a microphysical model to understand the composition and formation of the polar stratospheric clouds (PSCs) observed during SOLVE. Evidence that the majority of the particles remain liquid throughout the winter will be presented. However, a small fraction of the particles do freeze, and the presence of these frozen particles can not be explained by current theories, in which the only freezing mechanism is homogeneous freezing to ice below the ice frost point. Alternative formation mechanisms, in particular homogeneous freezing above the ice frost point and heterogeneous freezing, have been explored using the microphysical model. Both nitric acid trihydrate (NAT) and nitric acid dihydrate (NAD) have been considered as possible compositions for the solid-phase nitric acid aerosols. Comparisons between the model results and the SOLVE measurements will be used to constrain the possible formation mechanisms. Other effects of these frozen particles will also be discussed, in particular denitrification.

Drdla, Katja↗