Search

The influence of stratospheric gravity waves (SGWs) on the intensity of convection (CI) in the area of heavy precipitation around Typhoon Lekima (2019) is studied. Using theory and simulations, the energy and phase of the SGWs are shown to propagate upward and downward. The SGWs can propagate downward into the areas of convective instability in the upper troposphere in 35–85 min. Downward‐propagating SGWs can promote the release of convective instability energy, so the CI is enhanced. The relationship between SGWs and CI after 85 min is studied using a two‐layer model hypothesis for both a linear regression model and a Long Short‐Term Memory neural network model (nonlinear). The relationship is shown to be primarily linear (nonlinear) when the SGWs are weak (intensive). Therefore, the SGWs may be used as a proxy for the CI. Plain Language Summary: The source of convection is typically investigated in the troposphere, ignoring the role of the stratosphere. The energy of stratospheric gravity waves (SGWs) generated by convection propagates upward. Accompanying the upward energy propagation, SGWs can propagate downward into the troposphere; however, it remains unclear whether and how the SGWs influences convection in the troposphere. To answer this question, the relationship between the SGWs and convection during Typhoon Lekima 2019 has been studied. The vertical phase speed and intensity of the SGWs are large, which means that the SGWs can propagate downward into the troposphere. The SGWs can promote the release of the instability energy and enhance the intensity of convection (CI). A linear regression and a Long Short‐Term Memory neural network model are used to fit the CI with a lag of 85 min by the SGWs. The relative errors are only 9.3% and 5.8%, which indicates a strong linear relationship between the SGWs and convection in the troposphere. Nevertheless, the small error derived from the nonlinear model shows that the role of nonlinear interaction cannot be ignored, especially when the SGWs are strong. Therefore, the SGWs may be used as a proxy for CI prediction. Key Points: The stratospheric gravity waves (SGWs) with downward propagating phase can reach down into the troposphereDownward‐propagating gravity waves promote the release of convective instability energy in the upper troposphereThe intensity of SGWs can be used as a proxy for the intensity of the convection [ABSTRACT FROM AUTHOR]

The mechanism by which a mid‐latitude trough influenced the gravity waves (GWs) generated by Typhoon Lekima (2019) was studied by changing the initial fields in a series of model experiments. A peak in GW intensity (GWI) develops as typhoons weaken. The vertical speed shows the patterns of GWs generated by the typhoon and trough are the same during this peak GWI period. The typhoon generates the main part of the GWs and the trough enhances their intensity. The phase speed spectra show intense GWs occur when the GWs generated by the typhoon and trough propagate at the same phase speed. The GWI generated by the trough and typhoon were calculated separately in the control experiment, and their sum shows the peak GWI was caused mainly by in‐phase superposition. Finally, the model of the GWs superposition was proposed to quantitatively verify the existence of waves liner positive superposition. Plain Language Summary: Gravity waves (GWs) generated by typhoons are typically strongest as the typhoon intensifies. However, a sudden increase of GWs occurred when Typhoon Lekima (2019) weakened when there was a westerly trough to the north of the typhoon. The assumption of in‐phase superposition between the GWs generated by the typhoon and the trough has been proposed to explain this phenomenon. To verify this assumption, the typhoon and trough were removed from the control experiments so that the GWs were generated by each system alone. The results showed the GW patterns generated by typhoon or trough were the same, as were the speed and direction of GW propagation, which indicates superposition can cause a sudden increase of GW intensity (GWI). The typhoon is the main source of GW generation, but the trough can then intensify these GWs. The difference between the GWI from the control experiment and the sum of the GWI generated separately by the typhoon and the trough was small. Finally, we proposed the model of the GWs superposition to quantitatively verify the existence of waves liner positive superposition. This finding supports that in‐phase superposition played an important role in the GW development. Key Points: The peak intensity of gravity waves (GWs) during typhoon weakening is caused by in‐phase superposition of gravity wavesThe in‐phase superposition occurs when GWs generated by the typhoon and trough maintain the same pattern and phase speedThe typhoon generates the main part of the GWs, whereas the trough enhances the intensity [ABSTRACT FROM AUTHOR]

Using multi‐satellite observations, the cloud dynamic and microphysical characteristics were revealed during the rapid intensification (RI) of super‐typhoon Nanmadol (2022). As the storm intensifies, the eyewall contracts, the upper‐level divergence strengthens, and the cirrus cloud increases, leading to stronger upper‐level radial outflow and the vertical updraft. Meanwhile, it is found that there exists a dynamically attractive area in the outer rainbands, where particles grow effectively and form "a small amount of large particles" around 300 km from the eye. A theory of cloud dynamics‐microphysics interaction, called "tunnel theory," is further proposed to explain the generation, accumulation, and concentrated downflow of large particles in the outer rainbands during RI. Results suggest the unique feature of particle distribution in the outer rainbands could be a potential indicator for RI. Plain Language Summary: The rapid intensification (RI) of tropical cyclones (TCs) becomes more frequent in recent years, but the TC RI forecasts still remain challenging. Better understanding of the physical processes associated with RI of TCs would essentially improve its forecasting capability. The cloud dynamical and microphysical processes, especially their interactions that respond to RI are not well explored. In this study, the cloud macro and micro characteristics associated with RI of a super‐typhoon Nanmadol (2022) over the western Pacific are investigated using multiple satellites observations. The storm underwent RI during 15–16 September 2022, and it has wreaked havoc on Japan's most cities as it moved across the Japanese island afterward with a track length of about 1,120 km. It is found inside Nanmadol as well as other typhoons that a few large particles tend to occur in the outer rainbands during RI, due to the interaction of cloud dynamical and microphysical processes. Such unique feature of particle distribution in the outer rainbands could be a potential indicator for RI, and should also be paid attention to in model forecasting of typhoon precipitation. Key Points: First satellite‐based observational study on the interaction of cloud dynamics and microphysics during typhoon rapid intensification (RI)The eyewall contracts, the upper‐level divergence strengthens, and the convection column increases, providing kinetic energy for typhoon RIA "tunnel theory" is proposed for the generation, accumulation, and downflow of large particles in the outer rainbands during typhoon RI [ABSTRACT FROM AUTHOR]

To meet the challenges in satellite data assimilation involving cloud and precipitation processes, an all-sky radiance assimilation scheme (referred to as the 'scheme') that includes hydrometeor analysis is constructed based on the Proper Orthogonal Decomposition (POD)-3DEnVar method. Three key elements of the scheme are: (1) four hydrometeor mixing ratios for cloud-water, cloud-ice, rain, and snow in the control variables of the POD-3DEnVar method; (2) an extension of the Community Radiative Transfer Model interface to include hydrometeor profiles; and (3) multiple physical process model forecasts that use multiple microphysical and cumulus parameterization schemes as ensemble samples to estimate the flow-dependent background error covariance of the control variables, including those for hydrometeors. To evaluate the performance of the scheme, single-observation experiments and observation system simulation experiments (OSSEs) were designed for a binary typhoon case. Results for the single observation experiments show that the scheme can accurately assimilate satellite radiance near typhoon centers and produce reasonable increments for the hydrometeor variables. The background error covariances of the hydrometeor variables have reasonable flow-dependent characteristics. Results for the OSSEs have root-mean-square errors for all control variables of the assimilation analysis field with respect to the 'true' field that are lower than those obtained without assimilation. This indicates that the scheme effectively reduces error for all control variables, including those for hydrometeors. Forecasting experiments reveal that these improvements in the assimilation of control variables result in improved forecasts. However, improvements in the hydrometeor variables are of shorter duration than are those of the other control variables. The impact of improvements in the assimilation on typhoon track and intensity are obvious in the forecasting field. • An all-sky radiance assimilation scheme is constructed based on the POD-3DEnVar method. • The OSSEs indicate that the scheme reduces error for all control variables, including those for hydrometeors. • The impact of improvements in the assimilation on typhoon track and intensity are obvious in the forecasting field. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Locally-originated typhoons in the South China Sea (SCS) are characterized by long duration, complex track, and high probability of landfall, which tend to cause severe wind, rainstorm, and flood disasters in coastal regions. Therefore, it is of great significance to conduct research on typhoon precipitation microphysics in the SCS. Using GPM satellite observations, the precipitation microphysics of typhoons in the SCS are analyzed by combining case and statistical studies. The precipitation of Typhoon Ewiniar (2018) in the SCS is found to be highly asymmetric. In the eyewall, the updraft is strong, the coalescence process of particles is distinct, and the precipitation is mainly concentrated in large raindrops. In the outer rainbands, the "bright-band" of melting layer is distinct, the melting of ice particles and the evaporation of raindrops are distinct, and there exist a few large raindrops in the precipitation. Overall, the heavy precipitation of typhoons in the SCS is composed of higher concentration of smaller raindrops than that in the western Pacific (WP), leading to a more "oceanic deep convective" feature of typhoons in the SCS. While the heavy precipitation of typhoons in the SCS is both larger in drop size and number concentration than that in the North Indian Ocean (NIO), leading to more abundant rainwater of typhoons in the SCS. For the relatively weak precipitation (R < 10 mm h−1), the liquid water path (LWP) of typhoons in the SCS is higher than that of the NIO, while the ice water path (IWP) of the locally-originated typhoons in the SCS is lower than that of the WP. For the heavy precipitation (R ≥ 10 mm h−1), the LWP and IWP of typhoons in the SCS are significantly higher than those in the WP and NIO. [ABSTRACT FROM AUTHOR]

In July 2021, Typhoon In-Fa attacked eastern China and broke many records for extreme precipitation over the last century. Such an unrivaled impact results from In-Fa's slow moving speed and long residence time due to atmospheric circulations. With the supports of 66 networked surface disdrometers over eastern China and collaborative observations from the advanced GPM satellite, we are able to reveal the unique precipitation microphysical properties of the record-breaking Typhoon In-Fa (2021). After separating the typhoon precipitation into convective and stratiform types and comparing the drop size distribution (DSD) properties of Typhoon In-Fa with other typhoons from different climate regimes, it is found that typhoon precipitation shows significant internal differences as well as regional differences in terms of DSD-related parameters, such as mass-weighted mean diameter (Dm), normalized intercept parameter (Nw), radar reflectivity (Z), rain rate (R), and intercept, shape, and slope parameters (N0, µ, Λ). Comparing different rain types inside Typhoon In-Fa, convective rain (Nw ranging from 3.80 to 3.96 mm−1 m−3) shows higher raindrop concentration than stratiform rain (Nw ranging from 3.40 to 3.50 mm−1 m−3) due to more graupels melting into liquid water while falling. Large raindrops occupy most of the region below the melting layer in convective rain due to a dominant coalescence process of small raindrops (featured by larger ZKu, Dm, and smaller N0, µ, Λ), while small raindrops account for a considerable proportion in stratiform rain, reflecting a significant collisional breakup process of large raindrops (featured by smaller ZKu, Dm, and larger N0, µ, Λ). Compared with other typhoons in Hainan and Taiwan, the convective precipitation of Typhoon In-Fa shows a larger (smaller) raindrop concentration than that of Taiwan (Hainan), while smaller raindrop diameter than both Hainan and Taiwan. Moreover, the typhoon convective precipitation measured in In-Fa is more maritime-like than precipitation in Taiwan. Based on a great number of surface disdrometer observational data, the GPM precipitation products were further validated for both rain types, and a series of native quantitative precipitation estimation relations, such as Z–R and R–Dm relations were derived to improve the typhoon rainfall retrieval for both ground-based radar and spaceborne radar. [ABSTRACT FROM AUTHOR]

Extreme precipitation concerning typhoons brings great losses to coastal cities every year. How to accurately describe the natural cloud and precipitation processes in model remains a major challenge in typhoon forecasts. Observations found rain and hail can both exist under severe typhoon convections. But current operational forecasting models fail to take hail into consideration in super-typhoon prediction. This study assesses the performances of five typical bulk microphysical schemes (BMSs) of the Weather Research and Forecasting (WRF) model in the forecast of Super-typhoon Lekima (2019) near landfall. Unlike other microphysical schemes, all the selected BMSs in this study incorporate seven hydrometeor species including hail, which can represent the hydrometeor distribution within natural super-storm more realistically as supported by field observational facts. Through statistical-physical evaluation processes and using radar-satellite joint observations, the goal is to identify the best scheme to accurately forecast Super-typhoon Lekima and to find the future avenue to possible microphysical scheme improvement. It is found that the WRF double-moment 7-class (WDM7) scheme exhibits the smallest root mean square error (RMSE) of approximately 1.5 for both composite reflectivity and brightness temperature signatures, and predicts the closest macro-physical hydrometeors structure, amplitude and location to observations. Moreover, the azimuthal mean brightness temperature distributions suggest large forecasting errors over typhoon inner rainband, with WDM7 scheme performing best. The vertical reflectivity profiles further suggest that WDM7 scheme could well characterize the updraft, water content, and cold-cloud processes, but needs further improvement in the representation of warm-cloud processes. The performances of BMSs are found to be closely related to the moments used to describe the evolution of the drop size distribution. Among all the schemes, the double-moment schemes generally perform better in simulating warm-cloud processes, while the single-moment schemes show better performance in simulating cold-cloud processes. As a partially double-moment and partially single-moment scheme, WDM7 scheme exhibits unique advantages over the others. The optimum choice of moments is an important step toward the future improvement of BMS. • First assessment on the seven-class bulk microphysical schemes in typhoon forecast. • The structure of typhoon condensate is more difficult to predict than its intensity or location. • The inner rainband prediction is worst, eyewall comes second, and outer rainband is best. • The double (single)-moment schemes can better simulate warm (cold)-cloud processes. [ABSTRACT FROM AUTHOR]

Radar and satellite joint observation data can provide a more efficient way to study landfalling typhoon precipitation, but rarely does this combination of circumstances occur. In this study, we attempt to reveal the precipitation characteristics of typhoon Lekima (2019) at landfall by using joint observations from GPM satellite and S-band Doppler radar. The results suggest that the precipitation microphysical mechanisms are different among typhoon eyewall (EW), inner rainband (IR), and outer rainband (OR) during landfall. Beneath melting layer, collision-coalescence process dominates the precipitation in EW region, with large‐/mid- size raindrops (~1.6 mm) as the main components of precipitation. Collision-coalescence, breakup, and evaporation processes are in near balance within the precipitation of IR region, leading to prevailing mid‐/small- size raindrops (~1.3 mm) of this region. Melting and evaporation processes are the main precipitation microphysical mechanism in OR region and a small amount of large-size drops (~1.7 mm) constitute the majority of precipitation. Moreover, the large values of radar spectrum width exhibit an appreciable correlation with satellite detected effective reflectivity (Z e) center, mass-weighted mean diameter (D m) center, and storm top height (STH) peak, jointly indicating the strong convection activity inside landfalling typhoon Lekima, which further enlightens us to make better use of joint observation data from Doppler weather radar and GPM satellite to analyze the microphysics and dynamics associated with heavy rainfall during typhoon landfall in operational applications. • Radar and satellite joint observations on super typhoon Lekima at landfall. • Collision-coalescence process dominates the precipitation beneath melting layer in Eyewall. • Collision-coalescence, breakup, and evaporation processes are nearly balanced in Inner rainbands. • Melting and evaporation are the main precipitation microphysical processes in Outer rainbands. • Applying joint observations to investigate typhoon microphysics and associated dynamics. [ABSTRACT FROM AUTHOR]