Tropical Cyclone Research and Review最新文献

This study used the dynamic synthetic analysis method to analyze the causes of attenuated heavy rainfall from a westward moving typhoon after landfall over Fujian by focusing on the genetic diagrgnosis of the strongest 12 h rainstorms based on typhoon data obtained from the Shanghai Typhoon Institute, precipitation data from Fujian Province, and NCEP reanalysis data from the United States. The results showed that: (1) the environmental field of the westward moving typhoon benefits the long-term maintenance of convergence in coastal areas, which provides synoptic scale forcing for rainstorm intensification along the southeastern coast; (2) the southwest jet in the boundary layer transports warm water vapor from low latitudes into the eastern circulation of typhoon; the water vapor peak occurs 6 h before the strongest rainstorm and can be used as a reference index to predict heavy rainstorms; (3) the high altitude strong divergence center is located at 100–150 hPa, and the strong convergence center is located near 925–950 hPa in the boundary layer, which is higher (lower) than the 200 hPa divergence layer (850 hPa convergence layer) commonly used in professional work; (4) warm and wet advection in the boundary layer transports unstable energy and weak cold air southward, strengthens the baroclinic pressure, increases the latent heat flux on the sea surface, and plays a significant role in triggering and developing mesoscale convective clouds along the southeast coast.

This paper deals with the comparison of cyclone forecasts from the two versions of the operational global ensemble prediction system (EPS) at the National Centre for Medium Range Weather Forecasting (NEPS). The previous version had a horizontal resolution of 33 km with 44 ensemble members (NEPS) whereas the updated version of this EPS has a resolution of 12 km with 11 members (NEPS-UP). The ensemble mean forecasts from both the models are compared using the direct position (DPE), along (ATE) and cross track (CTE) errors. For the verification of strike probability, Brier Score (BS), Brier Skill Score (BSS), Reliability Diagram, Relative Operating Characteristic (ROC) Curve and Root Mean Square Error (RMSE) in mean Vs Spread in members are used. For verification of intensity, RMSE in maximum wind speed from the ensemble mean forecasts are compared.

Comparison of ensemble mean tracks from both models showed lower errors in NEPS-UP for all forecast lead times. The decrease in the DPE, ATE and CTE in NEPS-UP was around 38%, 48% and 15% respectively. NEPS-UP showed lower BS and higher BSS values indicating a better match between observed frequencies and forecast probabilities as well as higher prediction skills. The reliability diagram showed higher accuracy for NEPS-UP as compared to NEPS. The ROC curves showed that for forecasts with higher probabilities the hit rate was high in NEPS-UP. There was a greater consensus between the RMSE and Spread for NEPS-UP at all lead times. It was also seen that the RMSE in mean showed a 41% decrease from NEPS to NEPS-UP. On comparing maximum wind, it was found that for all lead times the RMSE in maximum wind speed for NEPS-UP was lower than NEPS.

This review article summarizes recent (2014–2019) advances in our understanding of tropical cyclogenesis, stemming from activities at the ninth International Workshop on Tropical Cyclones. Tropical cyclogenesis involves the interaction of dynamic and thermodynamic processes at multiple spatio-temporal scales. Studies have furthered our understanding of how tropical cyclogenesis may be affected by external processes, such as intraseasonal oscillations, monsoon circulations, the intertropical convergence zone, and midlatitude troughs and cutoff lows. Additionally, studies have furthered our understanding of how tropical cyclogenesis may be affected by internal processes, such as the organization of deep convection; the evolution of the “pouch” structure; the role of friction; the development of the moist, warm core; the importance of surface fluxes; and the role of the mid-level vortex. A relatively recent class of idealized, numerical simulations of tropical cyclogenesis in radiative-convective equilibrium have highlighted the potential importance of radiative feedbacks on tropical cyclogenesis. We also offer some recommendations to the community on future directions for tropical cyclogenesis research.

Tropical cyclones are devastating hazards and have been a major problem for the coastal population of Bangladesh. Among the advancements in atmospheric and oceanic prediction, accurate forecasting of storm surges is of specific interest due to their great potential to inflict loss of life and property. For decades, the numerical model based storm surge prediction systems have been an important tool to reduce the loss of human lives and property damage. In order to improve the accuracy in predicting storm surge and coastal inundation, recent model development efforts tended to include more modeling components, such as meteorology model and surface wave model in storm surge modeling. In this study, we used the outputs of an atmospheric model to force the ocean model for simulating storm surges in the Bay of Bengal with particular focus on the Bangladesh coast. The ability of the modeling system was investigated simulating water levels in the Bangladesh coast of two tropical cyclones Sidr (2007) and Aila (2009). The effectiveness of the model was verified through comparing the obtained computational outputs against tide gauge data. The cyclone tracks and intensities reproduced by the atmospheric model were reasonable, though the model had a tendency to overestimate the cyclone intensity during peaks and also close to coast. The water levels are reproduced fairly well by the ocean model, although errors still exist. The root mean square errors in water level at different gauges range from 0.277 to 0.419 m with coefficient of correlation (R²) between 0.64 and 0.97 in case of Sidr and 0.209–0.581 m with R² 0.62 to 0.98 for Aila. The overall coupled modeling system is found to be useful with reasonable accuracy and precision, though there are spaces for improvement. Higher-resolution modeling approaches are recommended to gain more skills.

This paper assesses published findings on projections of future tropical cyclone (TC) activity in the ESCAP/WMO Typhoon Committee Region under climate change scenarios. This assessment also estimates the projected changes of key TC metrics for a 2 °C anthropogenic global warming scenario for the western North Pacific (WNP) following the approach of a WMO Task Team, together with other reported findings for this region. For projections of TC genesis/frequency, most models suggest a reduction of TC frequency, but an increase in the proportion of very intense TCs over the WNP in the future. However, some individual studies project an increase in WNP TC frequency. Most studies agree on a projected increase of WNP TC intensity over the 21st century. All available projections for TC related precipitation in the WNP indicate an increase in TC related precipitation rate in a warmer climate. Anthropogenic warming may also lead to changes in TC prevailing tracks. A further increase in storm surge risk may result from increases in TC intensity. The most confident aspect of forced anthropogenic change in TC inundation risk derives from the highly confident expectation of further sea level rise, which we expect will exacerbate storm inundation risk in coastal regions, assuming all other factors equal.

The Publisher regrets that this article is an accidental duplication of an article that has already been published in TCRR, Volume 8, Issue 2, June 2019, Pages 95-102, http://dx.doi.org/10.1016/j.tcrr.2019.07.009. The duplicate article has therefore been withdrawn.

The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal

A vorticity budget diagnoses the growth or decay of a vortex from advective transport, or non-advective fluxes such as those due to friction or vortex tilting. However, when a budget calculation is performed with respect to a fixed coordinate, errors may result from time-dependence of the flow, leading to disagreement between the vorticity tendency and the observed vorticity field. An adaptive Lagrangian coordinate resolves this problem, provided that the resulting Lagrangian structure does not become too complicated.

In this study, a numerical simulation of Hurricane Nate (2011), the vorticity tendency is evaluated along distinguished material curves. There can be no net advective flux along a closed material curve, therefore, the total circulation tendency for a material region includes only the non-advective uxes acting along its boundary. A distinguished set of material curves (DMCs) associated with a distinguished hyperbolic trajectory (DHT) form a Lagrangian topology similar to that of a cat’s eye flow or “pouch” at each Eulerian snapshot. The time-dependence of velocities allows additional regions called lobes, which are formed by the intersections of DMCs, to exchange fluid across the vortex boundary by redefining the boundary.

Because the vortex boundary changes, we refer to this redefinition of material boundary as “topological rearrangement”. The method is useful for unsteady cat’s-eye flows and more complex interactions of multiple waves, vortices and background shear. All advective changes of the vortex circulation are identified by exchanges of the lobes, and all non-advective uxes act between the vortex and either the lobes or environmental flow. The Lagrangian topology and combination of advective and non-advective uxes relative to the topology is used to describe the evolution of the circulation of Nate during its time of formation.

The appropriate design of infrastructure in tropical cyclone (TC) prone regions requires an understanding of the hazard risk profile underpinned by an accurate, homogenous long-term TC dataset. The existing Australian region TC archive, or ‘best track’ (BT), suffers from inhomogeneities and an incomplete long-term record of key TC parameters. This study assesses mostly satellite-based objective techniques for 1981–2016, the period of a geostationary satellite imagery dataset corrected for navigation and calibration issues. The satellite-based estimates of Australian-region TCs suffer from a general degradation in the 1981–1988 period owing to lower quality and availability of satellite imagery.

The quality of the objective techniques for both intensity and structure is compared to the reference BT 2003–2016 estimates. For intensity the Advanced Dvorak Technique algorithm corresponds well with the BT 2003–2016, when the algorithm can use passive microwave data (PMW) as an input. For the period prior to 2003 when PMW data is unavailable, the intensity algorithm has a low bias. Systematic corrections were made to the non-PMW objective estimates to produce an extended (1989–2016) homogeneous dataset of maximum wind that has sufficient accuracy to be considered for use where a larger homogeneous sample size is valued over a shorter more accurate period of record. An associated record of central pressure using the Courtney-Knaff-Zehr wind pressure relationship was created.

For size estimates, three techniques were investigated: the Deviation Angle Variance and the ‘Knaff’ techniques (IR-based), while the ‘Lok’ technique used model information (ECMWF reanalysis dataset and TC vortex specification from ACCESS-TC). However, results lacked sufficient skill to enable extension of the reliable period of record. The availability of scatterometer data makes the BT 2003–2016 dataset the most reliable and accurate. Recommendations regarding the best data source for each parameter for different periods of the record are summarised.

This paper demonstrates a modification method for real-time improvement of wind field forecasts for a typical cyclone VARDAH, which formed over the Bay of Bengal (BoB) in 2016. The proposed method to improve the wind field forecasts associated with tropical cyclone consists of two components. The first one is the relocation method, which relocates the wind field forecasts obtained from the Global Forecast System(GFS) data of National Centres for Environmental Prediction(NCEP). The relocation of the model forecasts wind field is made on forecast locations generated by Multi Model Ensemble (MME) track forecast of India Meteorological Department(IMD). The second one is the modification of wind speed, which directly modifies the NCEP GFS wind speed forecasts based on intensity forecasts by Statistical Cyclone Intensity Prediction(SCIP) model of IMD. Applying these two methods, the displacement of wind field and underestimation/overestimation of wind speed in the model forecast field can be improved. Both modification methods show considerable improvements in the displacement and speed of wind field forecasts. The displacement error of wind field is found to have improved by about 51% at 48 h and about 80% at 72 h forecast. Overestimation of maximum wind speed in the forecast field is found to be improved by about 88% at 48 h and about 38% at 72 h forecast. The spatial distributions of corrected wind speed forecasts are also found to be more analogous than direct model forecasts with the corresponding analysis wind at all forecast hours. Two proposed modification methods could provide improved wind field forecast associated with tropical cyclones in real-time.

Tropical cyclone (TC) track predictions of the 10-km resolution WRF (provisionally named "AAMC-WRF") of the Hong Kong Observatory (HKO), spanning (20⁰S - 60⁰N, 45⁰E − 160⁰E) is studied for a 1-year period from April 2018 to Mar 2019. Real-time predictions, up to 4 times a day and T+48 h ahead, are verified against operational analysis positions of HKO for storms over the South China Sea (SCS) and Western North Pacific (WNP); and of the New Delhi Regional Specialised Meteorological Centre (RSMC) for storms over the North Indian Ocean basin (NIO; including the Bay of Bengal). Out of 21 named TCs over SCS and WNP, mean positional errors of the AAMC-WRF are 33 km (T+0), 63 km (T+24), and 107 km (T+48) based on 209, 178 and 142 forecasts. The AAMC-WRF outperformed Meso-NHM, also run in real-time at HKO, with mean error reduction up to 34 km or 24%. Mean positional errors for 13 NIO storms are 38 km (T+0), 69 km (T+24) and 107 km (T+48) based on 183, 131 and 85 forecasts. This is the first study in which TC predictions of a regional model are simultaneously examined over the SCS, WNP and NIO basins through real-time experiments.