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Christopher Lucas and Richard E. Orville

Abstract

A lightning detection network composed of three direction finders was installed in the western Pacific during TOGA COARE. The results are reported from one direction finder, at Kavieng, Papua New Guinea, for the months of January and February 1993, the latter half of the TOGA COARF 4-month period. Land and ocean sectors were defined. The land–ocean cloud-to-ground lightning ratio for 57 days of data is 8.7. The time between the two highest flash count days is 30–40 days, suggestive of the 30–60-day wave previously identified by Madden and Julian (1972). The highest lightning activity occurs around local midnight for both land and ocean sectors. The peak in activity of cloud-to-ground lightning over the ocean leads the peak in cold cloud area by 3–4 h. A small peak in lightning activity over the land sector occurs around 1500 LST, indicating the influence of the diurnal cycle of beating on convective activity around large tropical islands.

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Stefano Alessandrini, Luca Delle Monache, Christopher M. Rozoff, and William E. Lewis

Abstract

An analog ensemble (AnEn) technique is applied to the prediction of tropical cyclone (TC) intensity (i.e., maximum 1-min averaged 10-m wind speed). The AnEn is an inexpensive, naturally calibrated ensemble prediction of TC intensity derived from a training dataset of deterministic Hurricane Weather Research and Forecasting (HWRF; 2015 version) Model forecasts. In this implementation of the AnEn, a set of analog forecasts is generated by searching an HWRF archive for forecasts sharing key features with the current HWRF forecast. The forecast training period spans 2011–15. The similarity of a current forecast with past forecasts is estimated using predictors derived from the HWRF reforecasts that capture thermodynamic and kinematic properties of a TC’s environment and its inner core. Additionally, the value of adding a multimodel intensity consensus forecast as an AnEn predictor is examined. Once analogs are identified, the verifying intensity observations corresponding to each analog HWRF forecast are used to produce the AnEn intensity prediction. In this work, the AnEn is developed for both the eastern Pacific and Atlantic Ocean basins. The AnEn’s performance with respect to mean absolute error (MAE) is compared with the raw HWRF output, the official National Hurricane Center (NHC) forecast, and other top-performing NHC models. Also, probabilistic intensity forecasts are compared with a quantile mapping model based on the HWRF’s intensity forecast. In terms of MAE, the AnEn outperforms HWRF in the eastern Pacific at all lead times examined and up to 24-h lead time in the Atlantic. Also, unlike traditional dynamical ensembles, the AnEn produces an excellent spread–skill relationship.

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