The Advanced Technology Microwave Sounder (ATMS) is a cross‐track microwave radiometer. Its temperature sounding channels 5–15 can provide measurements of thermal radiation emitted from different layers of the atmosphere. In this study, a traditional Advanced Microwave Sounding Unit‐A (AMSU‐A) temperature retrieval algorithm is modified to remove the scan biases in the temperature retrieval and to include only those ATMS sounding channels that are correlated with the atmospheric temperatures on the pressure level of the retrieval. The warm core structures derived for Hurricane Sandy when it moved from tropics to middle latitudes are examined. It is shown that scan biases that are present in the traditional retrieval are adequately removed using the modified algorithm. In addition, temperature retrievals in the upper troposphere (~250 hPa) obtained by using the modified algorithm have more homogeneous warm core structures and those from the traditional retrieval are affected by small‐scale features from the low troposphere such as precipitation. Based on ATMS observations, Hurricane Sandy's warm core was confined to the upper troposphere during its intensifying stage and when it was located in the tropics but extended to the entire troposphere when it moved into subtropics and middle latitudes and stopped its further intensification. The modified algorithm was also applied to AMSU‐A observation data to retrieve the warm core structures of Hurricane Michael. The retrieved warm core features are more realistic when compared with those from the operational Microwave Integrated Retrieval System (MIRS).

A recently refined hurricane warm-core retrieval algorithm was applied to data from multiple polar-orbiting satellites that carry the Advanced Technology Microwave Sounder (ATMS) and the Advanced Microwave Sounding Unit-A (AMSU-A) to examine the diurnal variability of the warm cores of Hurricanes Irma and Maria. These hurricanes occurred during the 2017 hyperactive Atlantic hurricane season. Compared with data gathered by dropsondes within 100–1700 km of Hurricanes Irma and Harvey, the means and standard deviations of the differences between ATMS-derived and dropsonde-measured temperature profiles were less than 0.7 and 1 K, respectively, in the vertical layer between ~180 and 750 hPa. The temporal evolutions of the ATMS-derived and AMSU-A-derived maximum warm-core temperature anomalies followed more closely that of the minimum mean sea level pressure and slightly less closely that of the maximum sustained wind. The radii of the ATMS-derived warm cores at 4 and 6 K compared favorably with the 34- and 50-kt-wind radii, respectively, of Hurricane Irma (1 kt = 0.51 m s−1). The vertical extent of the warm core toward lower levels increased with increasing intensity when Hurricane Irma experienced a strong intensification because of an enhanced latent heat release associated with diabatic processes. The tropical cyclone (TC) inner cores at upper-tropospheric levels (~250 hPa) were characterized by a single-peaked diurnal cycle with a maximum around midnight. This warm-core cycle may be an important element of TC dynamics and may have relevance to TC structural and intensity changes.

Due to a shorter effective integration time for each field of view of the Advanced Microwave Temperature Sounder (ATMS) onboard the Suomi National Polar-orbiting Partnership (S-NPP) satellite than that for the Advanced Microwave Sounding Unit-A (AMSU-A) onboard previous National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites NOAA-15 to NOAA-19, ATMS temperature-sounding channels have higher observational resolutions and larger noise equivalent differential temperatures than the corresponding AMSU-A channels. The high resolution of the ATMS allows hurricane rainband features that are not resolvable by AMSU-A to be captured. But the larger noise equivalent differential temperature of ATMS weakens this capability through the significant impact of observational noise on warm-core retrievals. In this study, a remapping algorithm is applied to obtain AMSU-A-like ATMS fields of view to suppress this noise. A modified warm-core retrieval algorithm, which consists of two sets of training coefficients for clear-sky and cloudy conditions, is applied to limb-corrected ATMS and AMSU-A measurements using collocated Global Positioning System radio occultation observations in the previous month of the targeted hurricanes as training data sets. ATMS channels 5, 6, and 7 (AMSU-A channels 4, 5, and 6) are excluded when training the coefficients for cloudy conditions to avoid cloud/rain contamination. As a result, the abnormal cold core in the low and middle troposphere and the banded warm structures in phase with rainbands are both successfully removed. The warm-core evolution of Hurricane Matthew (2016) during its entire life span is temporally consistent on intensity as obtained from NOAA-15, NOAA-18, and MetOp-B AMSU-A observations and S-NPP ATMS observations. ZOU AND TIAN 10,815