This paper presents an analysis of the evolution of the inner-core thermodynamic structure of Hurricane Karl as observed by the newly upgraded High Altitude MMIC Sounding Radiometer (HAMSR) during the NASA Genesis and Rapid Intensification Processes (GRIP) field campaign. The GRIP experiment was conducted in August and September 2010 to study how tropical cyclones form and intensify. This ambitious campaign achieved several new benchmarks for the study of hurricanes, including the first flight over a mature hurricane with an unmanned aircraft and coordinated flying of six research aircraft in a hurricane at one time. Three NASA aircraft participated in the campaign, including the new NASA Global Hawk, which is an unmanned aircraft that can fly for over 30 hours at ~20 km altitude. The campaign also included the DC-8 and the WB-57. HAMSR flew on the Global Hawk with the High-Altitude Imaging Wind and Rain Airborne Radar (HIWRAP), which is a two frequency conical scanning radar.

HAMSR is a 25 channel cross-track scanning microwave sounder with channels near the 60 and 118 GHz oxygen lines and the 183 GHz water vapor line. We will present an analysis of temperature, water vapor and profiles derived from the HAMSR instrument, focusing on the unique long duration nature of the measurements and the new capability to resolve small scale water vapor features. In particular, the flight over Hurricane Karl yielded observations roughly every 30 minutes for 10 hours over the eye at 2-km resolution over a 60km swath. These data were gridded into a storm centric coordinate system allowing an analysis of the time evolution of moist thermodynamic structure of the inner core. These unprecedented measurements show that the warm anomaly in Karl propagated downward as the storm intensified, with the largest temporal change near the 500 mb level. A comparison of the warm anomaly change with the maximum sustained winds provided by the National Hurricane Center shows a strong correlation at all levels in the middle to upper troposphere, with a slope of 5-6 m/s/K. This demonstrates a capability for HAMSR to be used to monitor the real-time evolution of hurricane intensity. This technique is also used with AMSU data [Kidder et al., 2000; Brueske and Velden, 2003; Bessho et al., 2006], but additional uncertainties occur from eye wall precipitation contamination and dilution of the signal due to the large AMSU footprint relative to the diameter of most tropical cyclone eyes. A comparison of the AMSU warm core observations and AMSU estimated TC intensity with the high-resolution HAMSR observations will be presented.