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RISS 인기검색어
- 검색키워드
- 저자 : Russell L. Elsberry (검색결과 23 건)
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Advances in Research and Forecasting of Tropical Cyclones from 1963-2013
Russell L. Elsberry 한국기상학회 2014 Asia-Pacific Journal of Atmospheric Sciences Vol.50 No.1
A review of progress over the past 50 years in observingand forecasting of tropical cyclones is presented. Tremendous progresshas been made in track forecasting in the past 20 years with theimprovement in numerical model guidance and the use of consensusforecasting, and this has contributed to a number of warning centersnow issuing five-day track forecasts that are as accurate as three-dayforecasts of a decade ago. Techniques are now available to specifythe track forecast uncertainty for assessing the risk of a tropicalcyclone. With the advent of five-day forecasts, a focus on improvedunderstanding of formation has led to two field experiments. Arecent advance has been in extended-range (5-30 days) forecasts oftropical cyclone events (formations and tracks) in the western NorthPacific from the ECMWF 32-day ensemble predictions. This advanceis a contribution to a goal of seamless forecasting from one day to aseason for tropical cyclones. Little progress has been made inintensity forecasting, although the Hurricane Forecast ImprovementProject in the United States and recent field experiments may offersome future advances. Some advances in forecasting tropical cycloneimpacts such as storm surge, surface waves, and precipitation havebeen achieved. Future opportunities for continued advances arepossible such that improved warnings can lead to reductions in lossesof lives and minimizing damages from tropical cyclones.
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Russell L. Elsberry,Hsiao-Chung Tsai 한국기상학회 2014 Asia-Pacific Journal of Atmospheric Sciences Vol.50 No.3
A situation-dependent intensity prediction (SDIP) technique is developed for western North Pacific tropical cyclones that is based on the average of the intensity changes from the 10 best historical track analogs to the Joint Typhoon Warning Center best-tracks. The selection of the 10 best track analogs is also conditioned on the current intensity, and it is demonstrated that for a subsample of current intensities less than or equal to 35 kt the intensity mean absolute errors (MAEs) and biases are smaller than for the greater than 35 kt intensity subsample. The SDIP is demonstrated to have advantages as an intensity skill measure at forecast intervals beyond 36 h compared to the current climatology and persistence technique that uses only variables available at the initial time. The SDIP has significantly smaller intensity MAEs beyond 36 h with an almost 20% reduction at 120 h, has significantly smaller intensity biases than the present skill metric beyond 12 h, and explains 36% of the intensity variability at 120 h compared to 20% explained variance for the current technique. The probability distributions of intensities at 72 h and 120 h predicted by the SDIP are also a better match of the distribution of the verifying observations. Intensity spread guidance each 12 h to 120 h is developed from the intensity spread among the 10 best historical track analogs. The intensity spread is calibrated to ensure that the SDIP forecasts will have a probability of detection (PoD) of at least 68.26%. While this calibrated intensity spread is specifically for the SDIP technique, it would provide a first-order spread guidance for the PoD for the official intensity forecast, which would be useful intensity uncertainty information for forecasters and decision-makers.
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Russell L. Elsberry,Mary S. Jordan,Frederic Vitart 한국기상학회 2011 Asia-Pacific Journal of Atmospheric Sciences Vol.47 No.4
The performance of the ECMWF 32-day ensemble predictions of western North Pacific tropical cyclone events (formation plus track) made once a week during the 2009 season is evaluated with the same procedures as for the 2008 season. Seventeen of the 23tropical cyclones during the 2009 season occurred during multiple storm scenarios that are more difficult to predict, and many of the deficient track predictions involved unusual and rapidly changing tracks that typically involve interactions with adjacent synoptic circulations that are not predictable on intraseasonal timescales (10-30 days). Such incorrect predictions of the duration and tracks of these multiple cyclones were found to degrade the performance in predicting subsequent tropical cyclone formations and tracks during the 32-day integration. Predominantly northward tracks throughout the life cycle tended to be less predictable on intraseasonal timescales. Given these caveats, the overall performance of the ECMWF ensemble for the 12 typhoons was more successful than during the 2008 season. However, the performance for three tropical storms during the 2009 season was less successful due to the difficult track forecast scenarios. A surprisingly good performance was found in predicting the formation location and early track segments of eight minimal tropical storms or tropical depressions. The less satisfactory aspect for many of the late season tropical depressions was that the ECMWF ensemble continued to predict member vortices for extended periods after the system had actually dissipated.
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Russell L. Elsberry 한국기상학회 2010 Asia-Pacific Journal of Atmospheric Sciences Vol.46 No.2
Tropical cyclone track forecasts have been improved, and forecast intervals have been extended to five days, owing to improved global and regional numerical model guidance. Critical time requirements that must be met for operational use of the deterministic model track forecasts are summarized for the U.S. and other selected non-U.S. tropical cyclone warning centers. One of the most accurate deterministic model forecasts from the European Center for Medium-range Weather Forecasts arrives too late to be used with other models at the + 6 h warning time, and thus is at least 12 h old before it can be operationally used. The time-critical nature of the tropical cyclone warning system is a major obstacle to operational use of single-model, or proposed multi-model, ensemble prediction system (EPS) mean and spread information, which is 12 h (or 18 h) delayed. This EPS mean and spread must also be superior to the mean and spread of the consensus of deterministic models that are available six hours earlier. These requirements must be met before the EPS tropical cyclone tracks will be operationally useful in specifying the uncertainty in the official track forecasts, which is the next challenge in tropical cyclone track warnings.
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Russell L. Elsberry,Mary S. Jordan,Frederic Vitart 한국기상학회 2010 Asia-Pacific Journal of Atmospheric Sciences Vol.46 No.2
The objective of this study is to provide evidence of predictability on intraseasonal time scales (10-30 days) for western North Pacific tropical cyclone formation and subsequent tracks using the 51-member ECMWF 32-day forecasts made once a week from 5 June through 25 December 2008. Ensemble storms are defined by grouping ensemble member vortices whose positions are within a specified separation distance that is equal to 180 n mi at the initial forecast time t and increases linearly to 420 n mi at Day 14 and then is constant. The 12-h track segments are calculated with a Weighted- Mean Vector Motion technique in which the weighting factor is inversely proportional to the distance from the endpoint of the previous 12-h motion vector. Seventy-six percent of the ensemble storms had five or fewer member vortices. On average, the ensemble storms begin 2.5 days before the first entry of the Joint Typhoon Warning Center (JTWC) best-track file, tend to translate too slowly in the deep tropics, and persist for longer periods over land. A strict objective matching technique with the JTWC storms is combined with a second subjective procedure that is then applied to identify nearby ensemble storms that would indicate a greater likelihood of a tropical cyclone developing in that region with that track orientation. The ensemble storms identified in the ECMWF 32-day forecasts provided guidance on intraseasonal timescales of the formations and tracks of the three strongest typhoons and two other typhoons, but not for two early season typhoons and the late season Dolphin. Four strong tropical storms were predicted consistently over Week-1 through Week-4, as was one weak tropical storm. Two other weak tropical storms, three tropical cyclones that developed from precursor baroclinic systems, and three other tropical depressions were not predicted on intraseasonal timescales. At least for the strongest tropical cyclones during the peak season, the ECMWF 32-day ensemble provides guidance of formation and tracks on 10-30 day timescales.
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ADVANCES IN UNDERSTANDING OF TROPICAL CYCLONE WIND STRUCTURE CHANGES
Russell L. Elsberry,Robert A. Stenger 한국기상학회 2007 한국기상학회 학술대회 논문집 Vol.2007 No.-
The focus in this paper is on the outer wind structure and structure changes in tropical cyclones. Deviations from traditional wind profiles with radius will occur when secondary eyewalls form, and a recent high-resolution numerical simulation by Terwey and Montgomery (2007) suggests large increases in the radius of 50 kt (R??) and 35 kt (R₃?) winds as a result of a secondary eyewall. Creation of the conditions for an annular hurricane would also imply a large increase in R?? and R₃?. A unique set of H*Wind analyses of the surface wind in the Atlantic during the 2003-2005 seasons is examined to evaluate outer wind structure (R₃₄ and R??) changes. Whereas a small set of H*Wind analyses during the formation stage has the expected increases in R₃₄ values, a considerable percentage of R₃₄ decreases occur during the intensification stages when only increases would be expected. Similarly, a considerable percentage of R₃₄ increases are observed during the decay phase when decreases would be expected, although a forecaster rule-of-thumb is that the tropical cyclone circulation expands during the decay stage. The conclusion is that further study is required to understand the outer wind structure changes during the life cycle of the tropical cyclone. individual storm evolutions using the H*Wind analyses are presently being studied.
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Russell L. Elsberry,William M. Clune,Grant Elliott,Patrick A. Harr 한국기상학회 2009 Asia-Pacific Journal of Atmospheric Sciences Vol.45 No.3
One of the objectives of the combined Tropical Cyclone Structure (TCS08) and THORPEX Pacific Asian Regional Campaign (T-PARC) field experiment during August and September 2008 was to improve understanding and prediction of western North Pacific tropical cyclone formation. One approach during TCS08 was to subjectively monitor the performance of the four global models as to whether any of the more than 50 deep convective regions labeled as TCSxxx were predicted to become a tropical depression. When a 850-mb vorticity maximum associated with the convective region could be followed in all four models, a consensus of the track forecasts to 72 h provided surprisingly good guidance for the pre-tropical cyclone seedlings and tropical depressions. An experienced analyst was able to recognize signatures in each of the models that indicate tropical cyclone formation was likely or unlikely. When all four global model forecasts were in agreement that formation was likely, high confidence could be given to the predicted scenario. This four-model consensus approach to predict tropical depression formation was most effective for the four pre-tropical cyclone seedlings that would later become typhoons, and did predict with less advance warning two seedlings that later became tropical storms. However, the global models did not consistently predict the four pre-tropical cyclone seedlings that only attained tropical depression status. The four-model consensus had a relatively small number of false alarms. Even though a three-model consensus had somewhat more false alarms, in most of the low latitude cases the lack of time continuity and a systematic decrease in consensus time to formation will make these cases relatively easy to recognize as false alarms.
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