The Structure of Tropical Cyclone from Advanced Microwave Sounding Unit

Strong sounding abilities of atmospheric temperature and moisture, cloud and precipitation are provided by the Advanced Microwave Sounding Unit (AMSU) on-board the new generation polar orbit meteorological satellite series—NOAA-KLM. Two parts are included in the AMSU: AMSU-A and AMSU-B. The frequency of 50—60 GHz O₂ absorption band is mainly covered by AMS-A channels, and is used to retrieve the temperature profile. The water vapor absorption line centered at 183.31 GHz is covered by AMSU-B and is mainly used to get moisture vertical distribution of atmosphere. The AMSU-A and AMSU-B data from NOAA series satellites are used to analyze the thermal and cloud structure of tropical cyclone and the relation between TC intensity and its central warming and the change of could and rain structure.The AMSU-A and AMSU-B data are limb adjusted based on Wark and mapped at the center of the tropical cyclone (TC) to prepare for analysis of TC thermal and cloud structure. Firstly, the warming anomaly of two TC cases occurring over the northwestern Pacific Ocean in 2003 is analyzed with AMSU-A channel 6—9 data from NOAA-16/17 satellites, it is found that the warming anomaly of the weak TC Kronvan at its most intensive stage is only about 2.5 K and occurs at lower layers, but Maime, the strongest TC of that year, had more than 5 K anomaly and the warming occurs at all levels from 350 hPa to 100 hPa. The statistic relation between the intensity of TCs and their strongest warming anomaly is analyzed with TC cases in 2001—2003, it shows that the anomaly increases as the TC intensity becomes stronger, with related coefficients of 0.778.Then the cloud structure of the TCs is analyzed based on AMSU-B data. The data from AMSU-B window channel at 150 GHz are used to show the total cloud and rain structure of TC and that from high level channels centered at 183.31 GHz are used to show its convection distribution. The results show that the strong convection occurs at the eyewall and the outside rainband has obvious characteristics in the microwave images at 183.31 ±1 GHz , the low level stratus cloud would be viewed in window schannel image. The time series data of Dujuan are used to analyze the change of cloud structure of TC and its relation to the intensity, it is found that the highest intensity of TC is got after the convection burst out.It is concluded that the observation from AMSU-A temperature channels, especially for those weighting functions at upper troposphere has good response to the TC warm core. The observation from high frequency channels of AMSU-B shows the structure of could and the distribution of deep convection. The warming anomaly and the deep convection structure of TC have a close relation to the TC intensity. Further research would be done for this target.