ATMS‐ and AMSU‐A‐derived hurricane warm core structures using a modified retrieval algorithm

Abstract

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).

Evaluation of Warm‐Core Structure in Reanalysis and Satellite Data Sets Using HS3 Dropsonde Observations: A Case Study of Hurricane Edouard (2014)

“…Temperature anomalies are traditionally computed with respect to a reference profile. Previous observational studies (e.g., Durden, ; Gao, Chen, et al, ; Komaromi & Doyle, ; Stern & Zhang, ; Tian & Zou, ; Wang et al, ; Zawislak et al, ; Zhu & Weng, ) used either the Dunion () moist tropical climatological sounding or the mean environmental sounding in an annulus. Several studies (e.g., Durden, ; Stern & Nolan, ; Stern & Zhang, ) showed that environmental soundings were generally warmer than the Dunion () sounding, especially at higher altitudes, which resulted in larger upper‐level anomalies and possibly greater maximum anomaly heights when using the Dunion () sounding.…”

“…However, these AMSU‐A or ATMS‐derived warm‐core structures (Kidder et al, ; Tian & Zou, ; Weng et al, ; Zhu & Weng, ) were not verified by in situ dropsonde observations. Several previous studies have claimed that upper‐tropospheric warm cores in reanalyses (Hatsushika et al, ; Onogi et al, ) and AMSU‐A (Kidder et al, ) were consistent with the dropsonde observations of Hurricane Hilda (1964; Hawkins & Rubsam, ).…”

“…Zhu and Weng () improved ATMS retrievals and indicated that when ATMS utilizes a finer spatial resolution, it can better resolve the eye of the storm in the lower troposphere than that via AMSU‐A. Tian and Zou () also improved the retrieval algorithm and showed that ATMS and AMSU‐A observations can more realistically capture TC warm‐core structure than the ECMWF Interim Reanalysis (ERA‐I, Deea et al, ).…”

Hurricane Warm‐Core Retrievals from AMSU‐A and Remapped ATMS Measurements with Rain Contamination Eliminated

“…The algorithm developed by Zhu et al () was applied to ATMS observations of Hurricane Sandy (2012) and a positive correlation between the maximum upper level warm anomaly and the maximum sustained winds was found (Zhu and Weng (). Due to scan biases found in the temperature retrievals obtained by the algorithm of Zhu et al () and Zhu and Weng (), Tian and Zou () proposed four modifications to the temperature retrieval algorithm: (i) replace the simple scan correction term with regression coefficients that are explicit functions of scan position; (ii) use only a subset of ATMS temperature‐sounding channels for retrieving the temperatures at certain pressure levels that are highly correlated (correlation coefficients greater than 0.5) to these channels; (iii) obtain regression coefficients using limb‐corrected ATMS and collocated Global Positioning System (GPS) radio occultation (RO) observations in the month prior to the lifetime of the hurricane as training data sets; and (iv) obtain two sets of regression coefficients, one for clear‐sky conditions and another for cloudy‐sky conditions. The refined algorithm was applied to both AMSU‐A and ATMS observations to demonstrate that the warm‐core structures for Hurricanes Michael (2012) and Sandy (2012) during their lifetimes were more realistic than those obtained by both the unmodified algorithm and the even more advanced one‐dimensional variational approach of the Microwave Integrated Retrieval System.…”

“…The refined algorithm was applied to both AMSU‐A and ATMS observations to demonstrate that the warm‐core structures for Hurricanes Michael (2012) and Sandy (2012) during their lifetimes were more realistic than those obtained by both the unmodified algorithm and the even more advanced one‐dimensional variational approach of the Microwave Integrated Retrieval System. Tian and Zou () applied the temperature retrieval algorithm in Tian and Zou () to microwave temperature sounders onboard four NOAA operational satellites to analyze the intensity variations in Hurricanes Harvey, Irma, and Maria (2017).…”