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- 주제어 : intensity forecast uncertainty (검색결과 2 건)
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Improved Tropical Cyclone Intensity and Intensity Spread Prediction in Bifurcation Situations
Hsiao-Chung Tsai,Russell L. Elsberry 한국기상학회 2014 Asia-Pacific Journal of Atmospheric Sciences Vol.50 No.5
Bifurcation or bi-modal tropical cyclone intensity forecastsmay arise due to uncertainty in the timing of formation, timing andmagnitude of rapid intensification periods, or track forecast uncertaintyleading to landfall or non-landfall or leading to interactionwith warm- or cold-ocean eddies. An objective technique isdeveloped and tested to detect these intensity bifurcation situations inour weighted-analog intensity (WANI) forecasts that are based on the10 best historical analogs to the Joint Typhoon Warning Center(JTWC) official track forecasts. About 19% of the overall sample of1136 WANI forecasts in the western North Pacific during the 2010-2012 seasons met the criteria for a substantial intensity bifurcationsituation. Using a hierarchical clustering technique, two clusters ofthe 10 best analogs are defined and separate WANI forecasts andintensity spreads are calculated for the two clusters. If an alwaysperfect selection of the correct cluster WANI forecast of eachbifurcation situation is made, a substantial improvement in theintensity mean absolute errors is achieved relative to the originalWANI forecasts based on all 10 of the best analogs. These perfectclusterselection WANI forecasts have smaller bias errors and aremore highly correlated with the verifying intensities at all forecastintervals through 120 h. Without further bias correction and calibration,the cluster WANI intensity spreads are under-determined asthe Probability of Detections are smaller than the desired 68%. Fourexamples of WANI cluster predictions of intensity bifurcationsituations are provided to illustrate how a correct choice of the intensityforecast and the intensity spread can be the basis for improvedwarnings of the threat from western North Pacific tropical cyclones.
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Hsiao-Chung Tsai,Russell L. Elsberry 한국기상학회 2014 Asia-Pacific Journal of Atmospheric Sciences Vol.50 No.4
A version of our situation-dependent intensity prediction (SDIP) is proposed for operational application after three modifications: (i) Ten historical track analogs are matched with Joint Typhoon Warning Center (JTWC) official track forecasts rather than besttracks; (ii) Giving two times as much weight to the 72 h - 120 h portion of the track as to the 0-72 h portion to give higher rankings for analog tracks with similar landfall or recurvature positions and timing; and (iii) Weighting both the intensity prediction technique and a new intensity spread guidance product according to new rankings of the track analogs rather than assuming all track analogs are equally likely. These special matchings and weightings of the track analogs in this weighted-analog intensity (WANI) add skill in the 72-120 h forecast intervals in regions where landfalls occur. Viability as an operational technique is demonstrated as the WANI has only 1 kt larger mean absolute errors than the JTWC intensity errors from 12 h through 72 h, and the WANI is 5 kt (20%) better at 120 h. The WANI rank-weighted intensity spreads each 12 h among the 10 best historical track analogs are processed to reduce any intensity bias and calibrated to reduce (increase) the over-determined (under-determined) intensity spreads at early (later) forecast intervals. Thus, the situation-dependent intensity spread guidance is generated that will include about 68% of the verifying intensities at all forecast intervals. Four examples of the WANI intensity predictions and intensity spread guidance are presented to illustrate how the forecaster might use this information in potential landfall and intensity bifurcation situations.
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