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  • Analysis of long-term (2003–2015) spatial-temporal distribution of atmospheric methane in the troposphere over the Qinghai-Xizang Plateau based on AIRS data
    This paper has conducted a contrastive study on the AIRS retrieval results and the observational data of methane concentration at Mt. Waliguan atmospheric background station, and has analyzed the distribution characteristics of atmospheric methane concentration over the Qinghai-Xizang Plateau from 2003 to 2015. The results show that the AIRS retrieval data display the same monthly, annual, and seasonal variation trend, as well as segmental variation characteristics. The methane concentration features high in the north and low in the south along with the geographical line of Kunlun Mountains–Tanggula Mountains–Hengduan Mountains, and decreases significantly as the altitude rises, with the highest and the most sensitive variability in the south central region of the Qinghai-Xizang Plateau. From 2003 to 2015, the methane concentration in the Qinghai-Xizang Plateau continued to rise, with the fastest growth in autumn, the slowest in winter, and an annual growth rate of 5.2 nmol mol−1 a−1, while the growth rate from 2013 to 2015 was lower than the global average. The seasonal variation showed a unimodal curve, with the highest value in summer and the lowest value in spring, and with the altitude rising, the seasonal variation was more significant. more
  • A new thermal infrared channel configuration for accurate land surface temperature retrieval from satellite data
    Land surface temperature (LST) is an important parameter in many research fields. Many algorithms have been developed to retrieve LST from satellite thermal infrared (TIR) measurements; of these, the most widely used are the split window (SW) and temperature–emissivity separation (TES) methods. However, the performance of the SW and TES methods can be limited by the difficulty in obtaining sufficiently accurate prior knowledge—specifically, input land surface emissivity (LSE) for the SW method and atmospheric parameters for the TES method. In this study, a procedure was proposed for selecting specific channel pairs in the TIR spectral region to accurately retrieve ground brightness temperatures without prior atmospheric knowledge, using a method similar to the SW method. Subsequently, the TES method is applied to the retrieved ground brightness temperatures to separate the LST and LSE. In numerical simulations, the three ground brightness temperatures corresponding to 8.6 μm, 9.0 μm, and 10.4 μm are acquired with an accuracy of about 0.65 K by using five channels centered at 8.6 μm, 9.0 μm, 10.4 μm, 11.3 μm, and 12.5 μm, each with a width of 0.1 μm. When inputting the three retrieved ground brightness temperatures into TES method, LST could be recovered with an accuracy of 0.87 K. Sensitivity analysis shows that LST retrieval accuracy is less affected by channel width and atmospheric downwelling radiance than by the channel center locations and channel noise. Finally, the proposed method is preliminarily applied to actual satellite data from the Atmospheric InfraRed Sounder (AIRS) and the retrieved results are compared with the pixel-aggregated Moderate Resolution Imaging Spectroradiometer (MODIS) LST product. For the study area of Australia, discrepancies between our result and the MODIS LST product appear to be about 1.6 K during the day and 1.0 K at night, indicating that the new channel configuration can be used to retrieve accurate LST from satellite measurements. more
  • Dynamical Coupling Between Hurricane Matthew and the middle to Upper Atmosphere via Gravity Waves
    During 30 September to 9 October 2016, Hurricane Matthew traversed the Caribbean Sea to the east coast of the United States. During its period of greatest intensity, in the central Caribbean, Matthew excited a large number of concentric gravity waves (GWs or CGWs). In this paper, we report on hurricane‐generated CGWs observed in both the stratosphere and mesosphere from spaceborne satellites and in the ionosphere by ground Global Positioning System receivers. We found CGWs with horizontal wavelengths of ~200–300 km in the stratosphere (height of ~30–40 km) and in the airglow layer of the mesopause (height of ~85–90 km), and we found concentric traveling ionospheric disturbances (TIDs or CTIDs) with horizontal wavelengths of ~250–350 km in the ionosphere (height of ~100–400 km). The observed TIDs lasted for more than several hours on 1, 2, and 7 October 2016. We also briefly discuss the vertical and horizontal propagation of the Hurricane Matthew‐induced GWs and TIDs. This study shows that Hurricane Matthew induced significant dynamical coupling between the troposphere and the entire middle and upper atmosphere via GWs. It is the first comprehensive satellite analysis of gravity wave propagation generated by hurricane event from the troposphere through the stratosphere and mesosphere into the ionosphere. more
  • On the methods for recalibrating geostationary longwave channels using polar orbiting infrared sounders
    This study presents a common recalibration method that has been applied to geostationary imagers’ infrared (IR) and water vapour (WV) channel measurements, referred to as the multi-sensor infrared channel calibration (MSICC) method. The method relies on data of the Infrared Atmospheric Sounding Interferometer (IASI), Atmospheric Infrared Sounder (AIRS), and High-Resolution Infrared Radiation Sounder (HIRS/2) on polar orbiting satellites. The geostationary imagers considered here are VISSR/JAMI/IMAGER on JMA’s GMS/MTSAT series and MVIRI/SEVIRI on EUMETSAT’s METEOSAT series. IASI hyperspectral measurements are used to determine spectral band adjustment factors (SBAF) that account for spectral differences between the geostationary and polar orbiting satellite measurements. A new approach to handle the spectral gaps of AIRS measurements using IASI spectra is developed and demonstrated. Our method of recalibration can be directly applied to the lowest level of geostationary measurements available, i.e., digital counts, to obtain recalibrated radiances. These radiances are compared against GSICS-corrected radiances and are validated against SEVIRI radiances, both during overlapping periods. Significant reduction in biases have been observed for both IR and WV channels, 4% and 10%, respectively compared to the operational radiances. more