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  • Impact of Assimilating Himawari-8-Derived Layered Precipitable Water With Varying Cumulus and Microphysics Parameterization Schemes on the Simulation of Typhoon Hato
    Understanding moisture information ahead of tropical cyclone (TC) convection is very important for predicting TC track, intensity, and precipitation. The advanced Himawari imager onboard the Japanese Himawari-8/-9 satellite can provide high spatial and temporal resolution moisture information. Three-layered precipitable water (LPW) with its three water vapor absorption infrared bands can be assimilated to generate better understanding and prediction of TC evolution. The impacts of LPW assimilation in the Weather Research and Forecasting model with nine combinations of physical parameterization schemes, including three cumulus parameterization (CP) and three microphysics parameterization (MP) schemes on TC prediction, have been comprehensively analyzed using Typhoon Hato as a case study. The results indicate that LPW assimilation reduces the average track error and speed up TC movement by better adjustment of the atmospheric circulation fields via changing the vertical structure of moisture and thermal profile. The track forecasts retain sensitivity to CP schemes after LPW assimilation. Also, LPW assimilation improves TC intensity prediction because the latent heat release process is accurately adjusted. It has been revealed that LPW assimilation can weaken the intensity sensitivity to MP schemes more than to CP schemes. Skill scores were used to evaluate precipitation forecasts after Hato's landfall. The results indicate that heavy precipitation forecasts are more sensitive to the choice of MP schemes. After LPW assimilation, the equitable threat scores among different results become similar and all forecast skills are increased. In addition, group statistic results with different initial time show the same conclusions. more
  • Trajectory-Enhanced AIRS Observations of Environmental Factors Driving Severe Convective Storms
    We investigate environmental factors of severe convective weather using temperature and moisture retrievals from the Atmospheric Infrared Sounder (AIRS) that lie along parcel trajectories traced from tornado, large hail, and severe wind producing events in the central United States. We create AIRS proximity soundings representative of the storm environment by calculating back trajectories from storm times and locations at levels throughout the troposphere, using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model forced with the 32-km North American Regional Reanalysis (NARR) and 12-km North American Mesoscale Forecast System (NAM12). The proximity soundings are calculated for severe weather events including tornadoes, hail >= 2 in. diameter, and wind gusts >65 mph (29 m s(-1)) specified in the NCEI Storm Events database. Box-and-whisker diagrams exhibit more realistic values of enhanced convective available potential energy (CAPE) and suppressed convective inhibition (CIN) relative to conventional "nearest neighbor" (NN) soundings; however, differences in lifting condensation level (LCL), level of free convection (LFC), and significant tornado parameter (STP) from the HYSPLIT-adjusted back traced soundings are more similar to NN soundings. This methodology should be extended to larger swaths of soundings, and to other operational infrared sounders, to characterize the large-scale environment in severe convective events. more
  • Satellite-retrieved vertical profiles of methane over the Indian region: impact of synoptic-scale meteorology
    The altitude distribution of methane (CH4) is the least addressed topic in the greenhouse gas assessment over the Indian region. In the absence of the in-situ measurements, the satellite-based retrievals of the vertical distribution of CH4 using Atmospheric Infrared Sounder (AIRS) measurements during the period 2003-2015 were made use in this study for the first time to understand the 3D distribution (latitude-longitude-altitude) of CH4 over Indian region. Significant regional and seasonal variations are observed in the vertical distribution of CH4, even though it is a long-lived greenhouse gas and known to be well-mixed. Over most of the regions, the highest mixing ratio is observed during post-monsoon months and minimum in the pre-monsoon/monsoon season. The presence of a 'high altitude peak' in CH4 (around 1880 ppbv) around 300 hPa-250 hPa was noted in post-monsoon which is caused by the monsoon-associated convective updrafts and the anti-cyclonic system. The vertical profiles show seasonal variations which are region as well as altitude-dependent. Over the oceanic region, the highest seasonal amplitude of CH4 mixing ratio was observed over North-Arabian Sea due to the proximity of the source rich land regions. During the winter and pre-monsoon months, the latitudinal differences are absent throughout the troposphere. A consistent increasing trend in CH4, ranging from 1 ppbv year(-1) to 6 ppbv year(-1) is seen at all the tropospheric altitudes, with faster growth rates at higher altitudes, maximizing at 300 hPa-150 hPa. An approximate estimate of direct forcing due to CH4 lies in the range 0.80 W m(-2)-0.83 W m(-2). The paper also presents a comparison of the in-situ measured upper tropospheric CH4 mixing ratio from CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) flight data and AIRS retrievals. more
  • Characterization and evaluation of AIRS-based estimates of the deuterium content of water vapor
    Single-pixel tropospheric retrievals of HDO and H2O concentrations are retrieved from Atmospheric Infrared Sounder (AIRS) radiances using the optimal estimation algorithm developed for the Aura Tropospheric Emission Spectrometer (TES) project. We evaluate the error characteristics and vertical sensitivity of AIRS measurements corresponding to 5 d of TES data (or five global surveys) during the Northern Hemisphere summers between 2006 and 2010 (similar to 600 co-located comparisons per day). We find that the retrieval characteristics of the AIRS deuterium content measurements have similar vertical resolution in the middle troposphere as TES but with slightly less sensitivity in the lowermost troposphere, with a typical degrees of freedom (DOFS) in the tropics of 1.5. The calculated measurement uncertainty is similar to 30 parts per thousand (parts per thousand relative to the deuterium composition of ocean water) for a tropospheric average between 750 and 350 hPa, the altitude region where AIRS is most sensitive, compared to similar to 15 parts per thousand for the TES data. Comparison with the TES data also indicates that the uncertainty of a single target AIRS HDO/H2O measurement is similar to 30 parts per thousand. Comparison of AIRS and TES data between 30 degrees S and 50 degrees N indicates that the AIRS data are biased low by similar to -2.6 parts per thousand with a latitudinal variation of similar to 7.8 parts per thousand. This latitudinal variation is consistent with the accuracy of TES data compared to in situ measurements, suggesting that both AIRS and TES have similar accuracy. more