A Comparison of Spectral Bin Microphysics versus Bulk Parameterization in Forecasting Typhoon In-Fa (2021) before, during, and after Its Landfall

Abstract

Typhoon In-Fa hit continental China in July 2021 and caused an unprecedented rainfall amount, making it a typical case to examine the ability of numerical models in forecasting landfalling typhoons. The record-breaking storm was simulated using a 3-km-resolution weather research and forecast (WRF) model with spectral bin microphysics scheme (BIN) and two-moment seven-class bulk parameterization scheme (BULK). The simulations were then separated into three different typhoon landfall periods (i.e., pre-landfall, landfall, and post-landfall). It was found that typhoon intensity prediction is sensitive to microphysical schemes regardless of landfall periods, while typhoon track prediction tends to be more (less) sensitive to microphysical schemes after (before) typhoon landfall. Moreover, significant differences exist between BIN and BULK schemes in simulating the storm intensity, track, and rainfall distribution. BIN scheme simulates stronger (weaker) typhoon intensity than BULK scheme after (before) landfall, while BULK scheme simulates typhoon moving faster (slower) than BIN scheme before (after) landfall. BIN scheme produces much more extensive and homogeneous typhoon rainbands than BULK scheme, whereas BULK scheme produces stronger (weaker) rainfall in the typhoon inner (outer) rainbands. The possible reasons for such differences are discussed. At present, the ability of WRF and other mesoscale models to accurately simulate the typhoon precipitation hydrometeors is still limited. To evaluate the performances of BIN and BULK schemes of WRF model in simulating the condensed water in Typhoon In-Fa, the observed microwave brightness temperature and radar reflectivity from the core observatory of Global Precipitation Mission (GPM) satellite are directly used for validation with the help of a satellite simulator. It is suggested that BIN scheme has better performance in estimating the spatial structure, overall amplitude, and precise location of the condensed water in typhoons before landfall. During typhoon landfall, the performance of BIN scheme in simulating the structure and location of the condensate is close to that of BULK scheme, but the condensate intensity prediction by BIN scheme is still better; BULK scheme performs even better than BIN scheme in the prediction of condensate structure and location after typhoon landfall. Both schemes seem to have poorer performances in simulating the spatial structure of precipitation hydrometeors during typhoon landfall than before/after typhoon landfall. Moreover, BIN scheme simulates more (less) realistic warm (cold) rain processes than BULK scheme, especially after typhoon landfall. BULK scheme simulates more cloud water and larger convective updraft than BIN scheme, and this is also reported in many model studies comparing BIN and BULK schemes

Improving the WRF Forecast of Landfalling Tropical Cyclones Over the Asia‐Pacific Region by Constraining the Cloud Microphysics Model With GPM Observations

“…(2022) and Zhang et al. (2022). For instance, abnormally high concentration of small drops occurs near the melting layer due to unrealistic melting processes, causing largely lower radar reflectivity seen in WRF simulation as compared to GPM observation (Zhang et al., 2022).…”

“…Except for the traditional GPM satellite data assimilation (Okamoto et al., 2016), we attempt to use GPM observations as direct constraints on model physical process. As reported by plenty of literature that parameterization of detailed microphysics processes is instrumental to LTCs forecasts (Fovell & Su, 2007; Khain & Lynn, 2011; Tao et al., 2011; Wu, Zhang, Xie, et al., 2022; Zhang et al., 2022). By using GPM satellite data to evaluate the prediction of two LTCs Lekima (2019) and In‐Fa (2021) over the Asia‐Pacific region, it is found that the WRF Double‐Moment 7‐Class (WDM7) cloud microphysics scheme (Bae et al., 2018) shows distinct advantages in LTC forecasts as compared to other microphysical parameterization schemes (Wu, Zhang, Xie, et al., 2022; Zhang et al., 2022).…”

“…As reported by plenty of literature that parameterization of detailed microphysics processes is instrumental to LTCs forecasts (Fovell & Su, 2007; Khain & Lynn, 2011; Tao et al., 2011; Wu, Zhang, Xie, et al., 2022; Zhang et al., 2022). By using GPM satellite data to evaluate the prediction of two LTCs Lekima (2019) and In‐Fa (2021) over the Asia‐Pacific region, it is found that the WRF Double‐Moment 7‐Class (WDM7) cloud microphysics scheme (Bae et al., 2018) shows distinct advantages in LTC forecasts as compared to other microphysical parameterization schemes (Wu, Zhang, Xie, et al., 2022; Zhang et al., 2022). Moreover, WDM7 scheme even overwhelms spectral bin microphysics scheme under certain circumstances, such as in the forecast of typhoon landfall (Zhang et al., 2022).…”

“…By using GPM satellite data to evaluate the prediction of two LTCs Lekima (2019) and In‐Fa (2021) over the Asia‐Pacific region, it is found that the WRF Double‐Moment 7‐Class (WDM7) cloud microphysics scheme (Bae et al., 2018) shows distinct advantages in LTC forecasts as compared to other microphysical parameterization schemes (Wu, Zhang, Xie, et al., 2022; Zhang et al., 2022). Moreover, WDM7 scheme even overwhelms spectral bin microphysics scheme under certain circumstances, such as in the forecast of typhoon landfall (Zhang et al., 2022). Since 2019, WDM7 scheme has been officially employed in the Korean Integrated Model (KIM) system.…”

“…(2022). For instance, abnormally high concentration of small drops occurs near the melting layer due to unrealistic melting processes, causing largely lower radar reflectivity seen in WRF simulation as compared to GPM observation (Zhang et al., 2022). This study further proposes a way to alleviate such flaws by using GPM observations as direct constraints on the relevant microphysical processes in WDM7 scheme.…”