2. Reports of current polar low research

2.6 A Three-Dimensional Temperature and Wind Analysis of a Polar Low Utilizing the Advanced Microwave Sounding Unit

Rich Moore, Department of Atmospheric Science, Colorado State University,  Foothills Campus, W. Laporte Ave., Fort Collins, Colorado  80523-1375

On 17 March 2000, a polar low formed over the Labrador Sea and, over the next 40 hours, intensified and moved to the east-northeast before encountering the west coast of Greenland and dissipating.  At maturity, the storm exhibited a clear eye approximately 85 km in diameter and two distinct spiral bands of convection (Figure 1).  During its brief lifespan, the Advanced Microwave Sounding Unit (AMSU) on board the NOAA-15 polar orbiting satellite captured the storm on three separate occasions.  An in-depth analysis of data from the AMSU was conducted to examine its utility in studying polar lows.

It is found that the storm center is diagnosed well by the limb-adjusted brightness temperature at 53.6 GHz (Figure 2).  The anomalously high temperatures observed in this field are indicative of an increase in the atmospheric temperature associated with the warm core of the polar low.  To better resolve the vertical structure of the temperature field, a retrieval technique is used that incorporates data from 12 frequencies in and near the oxygen absorption band centered at 60 GHz.  A nearly east-west cross section through the storm center (Figure 3) illustrates that the largest retrieved temperature anomaly of approximately 4 K is observed at the surface and is collocated with the eye of the system.

In addition, by choosing appropriate dynamical constraints, a 3D wind field is retrieved from the AMSU retrieved temperature data.  The derived wind field shows an intense, closed low-level circulation with a maximum wind speed of approximately 30 ms-1 (Figure 4).  The strongest winds are found at the surface.
The AMSU-derived fields compare well with radiosonde temperature and SSM/I and QuickSCAT surface wind data, lending credence to the retrieval techniques.  Given the general observational agreement, we believe that AMSU data can provide important and useful information in the study of polar lows.

Please see (http://phoenix.cira.colostate.edu/amsu/AMSU.htm) for additional information regarding this work.

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