Influence of Tropical Storms in the Northern Indian Ocean on Dust Entrainment and Long-Range Transport

Major Tropical Cyclone (TC) events cause extensive damage in coastal regions of the western North Atlantic Basin. The short instrumental record leaves significant gaps in understanding long‐term trends in TC recurrence and intensity, creating uncertainty about future storm trends. Analysis of an ∼520‐year core record from Harvey Lake, located >80 km from the Atlantic coast in southwestern New Brunswick, Canada was carried out using: (a) end‐member mixing analysis (EMMA) of lake sediment grain size data to identify storm‐linked sedimentological processes; and (2) ITRAX X‐ray fluorescence (XRF) derived element/ratios (Fe, Ti, Ca/Sr, Zr/Rb, K/Rb, and Br + Cl/Al) associated with precipitation, weathering, catchment runoff, and air masses. Three derived end members were correlated to heavy rainfall events (EM01), spring freshet (EM02), and TCs (EM03). CONISS analysis of the EMMA and XRF core data resulted in recognition of four unique climatic zones distinguished by distinct distributions of TC and rainfall/weathering/runoff/and air masses. Numerous, major (EM01) rainfall events and (EM03) TC events characterized the basal core record during the early Little Ice Age (LIAa; Zone 1) phase, terminating at ∼1645. A near cessation of heavy rainfall and TC events differentiated the subsequent colder LIAb (∼1645–1825; Zone 2) and subsequent Little Ice Age Transition (∼1825–1895; Zone 3). A resurgence of major rainfall and TC events occurred during recovery from the LIA starting in ∼1895 (Zone 4). EMMA provides a robust tool for recognition of TC and major rainfall events, and greatly expands the potential for paleo‐storm activity research well inland from coastal regions.

On average, about two tropical storms or cyclones enter or form in the Mozambique Channel between the African mainland and Madagascar each year. Their impact can be devastating. The tropical cyclone Idai, which hit land in Mozambique in 2019, was one of the deadliest storms on record in the Southern Hemisphere. Previous studies have found that the tracks and strengths of tropical storms and cyclones are difficult to predict more than a few days ahead. An extension of this forecast horizon would be crucial for enabling authorities to take precautionary actions. Here, the ability of the European Centre for Medium‐range Weather Forecasts (ECMWF) state‐of‐the‐art ensemble prediction model to predict Idai and 38 other tropical systems is assessed. Local wind speed maxima and sea‐level pressure (SLP) minima were predicted by about 25% of the ensemble members at lead times of 1–3 days but only about 5% of the members at 7–9 days' lead times. However, several variables showed potential as precursors of tropical storms and cyclones, and some of these could be predicted at long lead times. In particular, SLP anomalies, which were significantly lower than normal multiple days before the peaks of the storms, were skilfully predicted by the ensemble mean at lead times of at least 3 weeks. Specific humidity at 500 hPa and divergence at 200 hPa were higher than normal several days before the peaks, and these potential precursors were also forecasted with skill up to about 2 weeks in advance. The inclusion of forecasts of these variables as predictors in hybrid statistical–dynamical forecasting systems could potentially extend the time horizon for prediction and early detection of possible tropical storms and cyclones in the region.

This study cross-validates the radar reflectivity Z, the rainfall drop size distribution parameter (median volume diameter, Do ) and the rainfall rate R estimated from the Tropical Rainfall Measuring Mission (TRMM) satellite Precipitation Radar (PR), a combined PR and TRMM Microwave Imager (TMI) algorithm (COM) and a C-band dual-polarised ground-radar (GR) for TRMM overpasses during the passage of tropical cyclone (TC) and non-TC events over Darwin, Australia. Two overpass events during the passage of TC Carlos and eleven non-TC overpass events are used in this study and the GR is taken as the reference. It is shown that the correspondence is dependent on the precipitation type whereby events with more (less) stratiform rainfall usually have a positive (negative) bias in the reflectivity and the rainfall rate whereas in the Do the bias is generally positive but small (large). The COM reflectivity estimates are similar to the PR but it has a smaller bias in the Do for most of the greater stratiform events. This suggests that combining the TMI with the PR adjusts the Do towards the "correct" direction if the GR is taken as the reference. Moreover, the association between the TRMM estimates and the GR for the two TC events, which are highly stratiform in nature, is similar to that observed for the highly stratiform non-TC events (there is no significant difference) but it differs largely from that observed for the majority of the highly convective non-TC events.

Previous studies have demonstrated the capability of the European Centre for Medium-Range Weather Forecasts (ECMWF) 51-member, 32-day ensemble to forecast tropical cyclone (TC) events (formation and tracks) in the western North Pacific on the extended range (5–30 days). In this study, the performance of the ECMWF ensemble in extended-range forecasting of Atlantic TCs during May–December 2012 is evaluated using similar approaches. The conclusion from this evaluation is that Atlantic TC events have lower forecastability using the ECMWF ensemble than in the western North Pacific. Hurricanes Kirk and Leslie and Tropical Storms (TSs) Joyce and Oscar were successfully forecast in weeks 1–4 and, thus, are labeled as highly forecastable. Somewhat forecastable storms that are only forecast in three of the four weeks include Hurricanes Ernesto, Isaac, Nadine, and Sandy plus TS Florence. The limited forecastable storms that were successful in only the first two weeks include Hurricanes Gordon and Rafael plus TS Debby. The surprising result was that two hurricanes (Chris and Michael) and three TSs (Helene, Patty, and Tony) were not even forecast in week 1 before the starting time in the National Hurricane Center working best track (WBT) for these storms. As was the case in the western North Pacific, a substantial number of false alarm storms (no matches with any WBT) are predicted, with about 35% occurring in the first week. Except for the African wave–type false alarms, three other false alarm types may be easily recognized. A larger sample will be required to statistically verify the reliability of the probabilistic forecasts for the African wave–type ensemble storms.

The ionosphere plays a critical role in the electromagnetic waves in communication systems such as the global positioning system (GPS). However, it is suspected that the strong convection during the tropical cyclone (TC) events can be a trigger to anomalous electron density variation in the ionosphere. This study analyzed the variation of three ionosphere-related parameters based on the GPS data including scintillation index S4, cycle slips, and total electron content (TEC) rate (TECR) during the tropical cyclone event (the 2013 TC Usagi) in the Hong Kong region. The results showed that the ionosphere-related parameters had a consistent significant increase on the second day after the Usagi made landfall near Hong Kong. Consequently, the positioning performance of GPS precise point positioning (PPP) and relative positioning modes was degraded. The degradation was ~ 138%, ~ 181%, and ~ 460% in the east (root mean square (RMS) 0.050 m), north (RMS 0.045 m), and up (RMS 0.185 m), respectively, compared with the RMS of 0.021 m in the east, 0.016 m in the north, and 0.033 m in the up on the normal day. Regarding the relative positioning, the positioning errors in the east (RMS 0.134 m) and north (RMS 0.118 m) directions were ~ 7.1 and ~ 7.9 times, respectively, as large as the RMS of 0.019 m in the east and 0.015 m in the north on the normal day. The positioning errors in the up (RMS 0.513 m) direction were ~ 12.2 times larger than the RMS of 0.042 m on the normal day.

Swell-driven sediment resuspension in the Yangtze Estuary during tropical cyclone events

An experimental Warn-on-Forecast System (WoFS) ensemble data assimilation (DA) and prediction system at 1-km grid spacing is developed and tested using two landfalling tropical cyclone (TC) events, one springtime severe thunderstorm event, and one summertime flash flood event. To evaluate the impact of DA at 1-km grid spacing, two experiments are conducted. One experiment, namely, the WoFS-1km, generates 3-h ensemble forecasts from the 1-km WoFS analyses while another experiment, namely, the Downscaled-1km, generates 3-h ensemble forecasts from downscaled 3-km analyses. With 1-km DA, the two landfalling TC events and the summertime event show some improvement in predicting high reflectivity, while the springtime event performs worse. Meanwhile, WoFS-1km is slightly better at predicting heavier precipitation (>20 mm h−1) with lower bias. However, heavy precipitation spatial placement error is only mitigated in one TC event and the summertime event with 1-km DA but is neutral or worse in the other two events. Object-based verification for rotation objects indicates that WoFS-1km performs better in one of the TC events, but worse in the springtime event with lower probability of detection and higher false alarm ratio due to fewer strong rotation objects being generated. The forecast skill of WoFS-1km for the springtime event is degraded mainly because the convective cores do not sufficiently develop as the forecast advances. The conditional benefits from 1-km DA in this study highlights the need for evaluation of a larger sample of convective storm cases and further development of the system.

The impacts of Persian Gulf water and ocean-atmosphere interactions on tropical cyclone intensification in the Arabian Sea

The present study provides a climatology of multiple tropical cyclone (TC) events (MTCEs) and the potential environmental factors responsible for triggering MTCEs in the North Atlantic (NATL), eastern North Pacific (EPAC), and western North Pacific (WPAC). While single TC events (STCEs) occur more frequently than MTCEs in each basin, a substantial fraction (34%–57%) of all TCs within each basin occur during MTCEs. Comparison of the total monthly number of MTCEs and STCEs reveals significant correlations (0.79 ≤ R ≤ 0.90), while nonsignificant correlations exist between the annual number of MTCEs and STCEs. New TCs that form during MTCEs occur in the eastern main development region east of the STCE formation location in the NATL and EPAC, while new TC formation locations are spread evenly throughout the WPAC during both MTCEs and STCEs. The spatiotemporal separation between TCs during MTCEs is consistent among basins with median zonal distances between TCs of ~(1640–2010) km and median temporal separation between TC formation of 3.00–3.25 days. Composites of EPAC MTCEs suggest the existence of significantly stronger large-scale intraseasonal anomalies compared to STCEs, which may favor EPAC MTCE occurrence. Eastward zonal group velocities and the agreement of the zonal wavelength of TC-induced Rossby waves with the observed zonal distance between TCs suggests that Rossby wave radiation may contribute to a substantial fraction of MTCEs in all basins. These results suggest remarkable similarity in MTCE characteristics among basins, while potentially indicating that the large-scale environment is preconditioned for EPAC MTCE occurrence.

The development of megacities and irreversible trends in global warming have brought us new hazards through compound extreme weather events in the urban society. Extreme hot days are occasionally observed with subsidence and stagnant air conditions driven by far-distance approaching tropical cyclones. Instead of the cross-boundary poor air quality during the stagnant days, urban heat can also be potentially advected with a long-range air-mass transport under the tropical cyclone and extreme heat compound (TC-heat) events. Our previous study had suggested the peripheral circulation of distant TC located at 500-1250 km from Hong Kong may drive the downwind heating footprint from inland China to coastal cities. By integrating the gridded data from newly developed Japanese Reanalysis for Three Quarters of a Century (JRA-3Q) and ERA5-Land reanalysis dataset, this study aims to further explore the decadal variation in TC activities over the East-Asia domain (China, Japan, and Korea) under climate change, also to explore the patterns of 95th percentile extremes in TC peripheral subsidence warming from 1990s, 2000s to 2010s, and the amplification of extreme TC-Heat risks with Wet-bulb globe temperature (WBGT) thermal indices in urbanized areas. Probabilistic TC-Heat risk maps were generated to indicate the potential “hotspots” for different cities when TC are located at different assessment grids. The risk maps can provide heat adaptation and resilience recommendations on the heat threat vulnerable groups in different countries and cities to safeguard their citizens from experiencing extreme heat mortality in our future cities.

Existing validation of mean wind speed estimates via reflectometry from global navigation systems of satellites (GNSS-R)—has been largely limited in spatial coverage to equatorial buoys or tropical cyclone events near continental United States. Two alternative validation techniques are presented for the Cyclone GNSS (CYGNSS) mission using surface-based observations along coasts and coral reefs instead of buoys, and triple collocation analysis (TCA) instead of a 1:1 gridded comparison for tropical cyclone (TC) events. For the surface-based analysis, Fully Developed Seas (FDS) v3.2 and NOAA v1.2 were compared to anemometer data provided by the Australian Bureau of Meteorology across the Australia and Pacific regions. Overall, the products performed similarly to previous studies with NOAA having higher correlations and lower errors than FDS, though FDS performed better than NOAA over the Australian dataset for high wind speed events. TCA was used to validate NOAA v1.2 and Merged v3.2 datasets with other satellite remotely sensed products from the Soil Moisture Active Passive (SMAP) mission and Synthetic Aperture Radar (SAR). Both additive and multiplicative error models for TCA were applied. The performance overall was similar between the two products, with NOAA producing higher errors. NOAA performed better than Merged for mean winds above 17 m/s as the large temporal averaging reduced sensitivity to high winds. For SMAP winds above 17 m/s, NOAA’s average bias (−2.1 m/s) was significantly smaller than the average bias in Merged (−4.4 m/s). Future ideas for rapid intensification detection and constellation design are discussed.

طوفان‌های حاره از پدیده‌های مهم پیرامون خط استوا هستند که در نیمه گرم سال در نیمکره شمالی یا جنوبی ایجاد می‌شوند. این چرخندها با گذر از اقیانوس و تکیه‌بر منبع عظیم انرژی گرمایی نهان تبخیر، قدرت قابل‌توجهی می‌یابند و در مدت کوتاهی به یکی از مخرب‌ترین مخاطرات طبیعی تبدیل می‌شوند. هدف این مطالعه، مقایسه و تحلیل ساختاری چرخندهای دریای عرب و عمان به‌منظور بررسی نقش پارامترهای جوی، اقیانوسی در تعیین مسیر حرکت آن‌هاست. بدین منظور با استفاده از آمار موجود در مرکز مشترک اخطار طوفان، اطلاعات مربوط به چرخندها تهیه شد. همچنین با استفاده از داده‌های باز تحلیل پایگاهECMWF متغیرهای فشار سطح دریا، ارتفاع ژئوپتانسیل سطح 850 هکتوپاسکال، دمای سطح 1000هکتوپاسکال و دمای سطح دریا در محدودۀ -5 تا 40 درجه عرض شمالی و 40 تا 80 درجه طول شرقی برای مدت‌زمان حیات چرخند استخراج گردید. تولید و تحلیل نقشه‌ها نیز در محیط GRADS و ArcGis با استفاده از تغییرات آزیموت، روابط همبستگی و قوانین کشش و رانش انجام شد. نتایج نشان داد که در لحظه تشکیل، جهت حرکت همه چرخندها به‌غیراز گونو شمال غرب بوده و همبستگی قوی منفی بین دما و فشار سطح دریا در زمان شروع وجود داشته است. اما به‌جز چرخند گونو در سایر چرخند‌ها زمان تغییر مسیر بازمان رسیدن آن به اوج، یکی نیست. تحلیل نقشه‌های فشار سطح دریا نیز نشان داد که مسیر حرکت چرخندهای موردمطالعه از قوانین کشش و رانش پیروی کرده و حاکمیت پرفشارها در فصل سرد باعث شده چرخندهای نیلوفر و چاپالا نسبت به سایر، به سمت عرض-های بالا گسترش پیدا نکنند.

Accurate precipitation climatology is presented for tropical depression (TD), tropical storm (TS), and tropical cyclone (TC) over oceans using the recently-released, consistent and high quality precipitation datasets from all passive microwave sensors covering 1998-2012 along with the Automated Rotational Center Hurricane Eye Retrieval (ARCHER)-based TC center positions. Impacts with respect to the direction of both TC movement and the 200-850 hPa wind shear on the spatial distributions of TC precipitation are analyzed. The TC eyewall contraction process during its intensification is noted by a decrease in the radius of maximum rainrate with an increase in TC intensity. For global TCs, the maximum rainrate with respect to the direction of TC movement is located in the down-motion quadrants for TD, TS, and Cat 1-3 TCs, and in a concentric pattern for Cat 4-5 TCs. A consistent maximum TC precipitation with respect to the direction of the 200-850 hPa wind shear is shown in the down shear left quadrant (DSLQ). With respect to direction of TC movement, spatial patterns of TC precipitation vary with basins and show different features for weak and strong storms. The maximum rainrate is always located in DSLQ for all TC categories and basins, except the Southern Hemisphere basin where it is in the down shear right quadrant (DSRQ). This study not only confirms previously published results on TC precipitation distributions relative to vertical wind shear direction, but also provides a detailed distribution for each TC category and TS, while TD storms display an enhanced rainfall rate ahead of the down shear quadrants.

Quantifying the contribution of tropical cyclones to lightning activity over the Northwest Pacific

The review of the global state of the climate for 2012, issued by the World Meteorological Organiza� tion, has emphasized the record number of tropical and extratropical cyclones in the Russian Far East. In 2012, six tropical cyclones were reported in this region, while the previous record (since 1970) was five cyclones, in 1981 and 2011 (http://library.wmo. int/pmb_ged/wmo_1108_en.pdf). Intensive atmo� spheric eddies, which are tropical cyclones, and espe� cially the most powerful of them (typhoons, or hurri� canes), are associated with severe weather and climatic anomalies and with the social–economic conse� quences as well [1–5]. Many tropical cyclones trans� form into extratropical [6–8]. The question is in to degree this is manifested in changes of cyclonic activ� ity in the extratropical atmosphere with respect to glo� bal climate changes [9–11]. The recent data indicate the frequent occurrence of intensive cyclones, including those transformed from tropical ones into the North Atlantic and northwestern Pacific oceans in extratropical latitudes. Under the tendency towards global warming, we can expect an increase in the number of intensive cyclones in the warmer and more humid troposphere. In the present work, we estimate the tendencies of changes in pro� cesses of the transformation of tropical cyclones into extratropical ones for various oceanic basins in the Northern and Southern hemispheres, based on the data of 1970–2012 [12]. During this analysis, we also used specified and supplemented data from [13]. Table 1 presents the average annual numbers of tropical cyclones Ntc, those transformed into extratro� pical ones Netc, and the ratio Netc/Ntc, based on the data of 1970–2012, for various oceanic basins. In the Northern Hemisphere these are the NWPO (north� western Pacific Ocean), NEPO (northeastern Pacific Ocean), NAO (northern Atlantic Ocean), and NIO (northern Indian Ocean); in the Southern hemisphere these are the SIO (southern Indian Ocean), SPO (southern Pacific Ocean), and SAO (southern Atlantic Ocean). The table also contains the average values for hemispheres and the world. The average mean square interannual deviations from average values are given in brackets. The highest frequency of tropical cyclone transfor� mation into extratropical ones is typical for the NWPO region: more than ten per year on average, with the maximal value of 17 (in 2004) and a minimum of 2 (in 1973). In comparison to the NWPO region, the average frequency of the respective events in the NAO, SIO, and SPO regions is less by more than twice (5, lesser than 5, and lesser than 5, respectively). In particular years, the number of tropical cyclones that transform into extratropical ones can reach in the NAO region 8–10, up to the record value of 12 in 2012, when almost 2/3 of 19 tropical cyclones in the Atlantic Ocean transformed into extratropical ones.