uncovering weather signals in microwave temperature sounder data hidden by the limb effect
It’s been 40 years since microwave temperature sounders started to observe the Earth. Observations from microwave temperature sounders are critical for various areas of basic and applied science, including climatological studies, numerical weather forecasting, and extreme-weather monitoring. However, the cross-track scanning approach of temperature sounders can conceal weather signals in raw observations, which is problematic.
Professor Xiaolei Zou and Dr. Xiaoxu Tian from the Earth System Science Interdisciplinary Center at the University of Maryland, with Dr. Shengpeng Yang from Nanjing University of Information Science and Technology, propose a limb correction algorithm for observations from MWTS-2. Their findings are published in Advances in Atmospheric Sciences.
The limb correction method helps to uncover the underlying weather signals behind the scan-dependent features in observations. After limb correction, the observed brightness temperatures can be directly applied in analyzing large-scale weather patterns at a global range, as well as monitoring smaller-scale weather events such as typhoons or even convection systems.
Taking Super Typhoon Neoguri in 2014 as an example, the authors compare the brightness temperatures covering the storm before and after limb correction, as shown in Fig. 1. In the brightness temperature before limb correction, the typhoon structures can be vaguely seen, only with the more dominant scan-dependent features due to the varying scan angles within each scan line. In comparison, the storm structure as well as the temperature distribution of the ambient environment looks a lot clearer in the limb-corrected results (Fig. 1b). After comparing the MWTS-2 observations against geophysical variables including atmospheric temperature and liquid water path, the authors found the correlations between the observations and atmospheric temperature reached as high as 0.982, while the correlations with liquid water path increased by 30% to 55%.
The authors argue that there is considerable potential for more weather applications by using the limb-corrected brightness temperatures, like studying climatological trends and direct assimilation into numerical weather prediction models. In the meantime, the proposed algorithm is readily applicable to microwave temperature sounders carried by the future FengYun satellite series.