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Tropical Cyclone Research and Review  
  Tropical Cyclone Research and Review--2014, 3 (4)   Published: 2014-12-15
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Characteristics of tropical cyclone genesis forecasts and underdispersion in high-resolution ensemble forecasting with a stochastic kinetic energy backscatter scheme

Levi Thatcher, Zhaoxia Pu
Tropical Cyclone Research and Review. 2014, 3 (4): 203;  doi: 10.6057/2014TCRR04.01
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This study evaluates ensemble forecasts with a stochastic kinetic energy backscatter scheme (SKEBS) to predict tropical cyclone (TC) genesis and also to characterize the related ensemble underdispersion. Several sets of ensemble forecasts are generated using an advanced research version of the Weather Research and Forecasting model at 5 km horizontal resolution to predict the genesis of Hurricane Ernesto (2006) and Typhoon Nuri (2008).Ensemble forecasts with SKEBS are compared against a control ensemble forecast with the WRF model using downscaled initial conditions derived from the NCEP Global Ensemble Forecasting System.
It is found that ensemble forecasts with SKEBS are able to generate probabilistic forecasts for TC genesis and also capable of indicating the forecast uncertainties. Compared with the deterministic forecast that fails to predict the genesis of Typhoon Nuri, the ensemble forecast with SKEBS is able to produce the genesis forecast. However, the underdispersion of ensemble forecasts with SKEBS is also present in all cases in terms of the simulation period and over the whole model domain, TC environment, and inner core regions, although it is reduced near the TC inner core region. In addition, the initial perturbation–based ensemble forecasts shows slightly less underdispersion compared with the SKEBS ensembles.

Parameterization of Subgrid Deep Convective Cloud at Gray-Zone Resolutions: Preliminary Results

Wei Huang, Jian-Wen Bao, Baode Chen
Tropical Cyclone Research and Review. 2014, 3 (4): 218;  doi: 10.6057/2014TCRR04.02
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When the horizontal grid size of a numerical weather prediction (NWP) model is between a few hundred meters and ~10 km, referred to as the gray zone, updrafts in convective clouds cannot be fully resolved explicitly and the use of a subgrid convective cloud parameterization scheme is still necessary. Since some critical assumptions in the mass-flux formulation of conventional subgrid convective cloud parameterization become invalid for gray-zone resolutions, it is required for a generalized parameterization to be developed to properly describe subgrid convective clouds. To meet this requirement, a new subgrid convective cloud parameterization scheme that is based on the mass-flux formulation and suitable for gray-zone resolutions has been proposed and preliminarily tested in the Weather Research and Forecasting (WRF) model. This new scheme is automatically adaptive to variation in grid size (i.e., scale-aware), and accounts for microphysical processes consistently with grid-resolved clouds. Numerical experiment of an idealized tropical cyclone shows that this new scheme has a substantial impact on the tropical cyclone’s intensity and precipitation distribution due to the effect of subgrid clouds on the total diabatic heating.

Tropical Cyclone Forecast Verification by India Meteorological Department for North Indian Ocean: A review

M Mohapatra
Tropical Cyclone Research and Review. 2014, 3 (4): 229;  doi: 10.6057/2014TCRR04.03
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The tropical cyclone (TC) forecast verification procedure followed by India Meteorological Department (IMD) is reviewed herewith as compared to the standard prescribed by World Meteorological Organisation. The limitations in the present procedure and the future scope are presented and analysed.
The IMD has considerably increased its efforts in recent years in the areas of TC forecasting and verification. Many facilities have been developed to enable a detailed assessment of the global model’s performance in the forecasting of TCs as well as operational TC forecast performance. Further development of these facilities is being undertaken by IMD. There are grey areas in TC forecast verification of IMD in the field of calculation of forecast error in surface wind radii in geographical quadrants, which is yet to start. Also there is need for improvement in verification of storm surge, wave height, coastal inundation forecasts and heavy rainfall forecasts by calculating the skill parameters and also by improving the analysis data required for verification of forecasts. Similarly there is need for verification of strike probability as well as dynamical cone of uncertainty as given by ensemble prediction system.

A Review of the Storm Characteristics of Typhoon Kalmaegi (1415) and Related Forecasting Considerations in Hong Kong

Chun-wing Choy, Yee-ting Junella Tam, Dick-shum Lau and Wai-kin Wong
Tropical Cyclone Research and Review. 2014, 3 (4): 243;  doi: 10.6057/2014TCRR04.04
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Kalmaegi (1415) required the issuance of Gale or Storm Wind Signal No. 8 in Hong Kong in 2014, even though it passed by at a distance of 370 km from Hong Kong during its closest approach. Storm surges triggered by Kalmaegi caused backflow of sea water in some low lying areas in both Hong Kong and Macao. This paper reviews the use of observational data in monitoring the cyclone characteristics and studies the synoptic factors leading to its fast movement and extensive circulation. The combined analysis of multi-platform satellite wind retrieval, in-situ surface observations and aircraft reconnaissance data over the northern part of the South China Sea is found to be useful in depicting the cyclone structure. Synoptic analysis suggests that the relatively large size of Kalmaegi may be attributed to monsoon shear pattern during its formation stage and the subsequent strengthening of southwesterlies over the northern part of the South China Sea. A strong subtropical ridge north of Kalmaegi not only provides strong steering and thus its high translational speed, but also leads to extensive gale force wind distribution over its northern semi-circle. The performance of various numerical prediction models in forecasting the movement, intensity change and wind structure of Kalmaegi, as well as the storm surge triggered, is assessed and presented.

Tropical Cyclogenesis Detection in NWP at KMA

Woojeong Lee, KiRyong Kang, Jiyoung Kim, Kun-Young Byun
Tropical Cyclone Research and Review. 2014, 3 (4): 256;  doi: 10.6057/2014TCRR04.05
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In this study, a tropical cyclogenesis detection system, Tropical Cyclone Analysis & Forecast (TCAF), was evaluated with an operational numerical model of the Korea Meteorological Administration (KMA). The tracking performance was compared with the result with the ECMWF model input field (TCAF-ECMWF). In order to improve the performance, different tracking time at an interval of 6 hours were investigated. The lowest false alarm rate and the highest hit rat (correct detection) were achieved at 06 hour after the initial tracking time. The tracking performance was also tested on two typhoons in 2013, LEEPI (1304) and DANAS (1324). The results showed that the TCAF-ECMWF detected tropical depressions 72 hours before the formation of the typhoon DANAS, which is a 12-hour earlier detection compared with the current performance with the use of KMA’s numerical weather prediction (NWP) model data. So, it is expected that TC genesis detection could be improved by determining an optimal tracking time and by using more accurate NWP model data.

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