End‐Member Mixing Analysis as a Tool for the Detection of Major Storms in Lake Sediment Records

Increasing evidence indicates that changes have occurred in heavy precipitation associated with tropical cyclone (TC) and local monsoon (non-TC) systems in the southeastern coastal region of China over recent decades. This leads to the following questions: what are the differences between TC and non-TC flooding, and how do TC and non-TC flooding events change over time? We applied an identification procedure for TC and non-TC floods by linking flooding to rainfall. This method identified TC and non-TC rainfall–flood events by the TC rainfall ratio (percentage of TC rainfall to total rainfall for rainfall–flood events). Our results indicated that 1) the TC rainfall–flood events presented a faster runoff generation process associated with larger flood peaks and rainfall intensities but smaller rainfall volumes, compared to that of non-TC rainfall–flood events, and 2) the magnitude of TC floods exhibited a decreasing trend, similar to the trend in the amount and frequency of TC extreme precipitation. However, the frequency of TC floods did not present obvious changes. In addition, non-TC floods decreased in magnitude and frequency while non-TC extreme precipitation showed an increase. Our results identified significantly different characteristics between TC and non-TC flood events, thus emphasizing the importance of considering different mechanisms of floods to explore the physical drivers of runoff response. Also, our results indicated that significant decreases occurred in the magnitude, but not the frequency, of floods induced by TC from the western North Pacific, which is the most active ocean basin for TC activity, and thus can provide useful information for future studies on the global pattern of TC-induced flooding.

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.

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.

Century-scale variability in late-summer rainfall events recorded over seven centuries in subannually laminated lacustrine sediments, White Pass, British Columbia

Landfalling tropical cyclones (TCs) often lead to widespread societal impacts due to their associated wind and flood hazards. Among these, pluvial and fluvial flooding depend primarily on the intensity and total rainfall released during TC events. As global warming increases atmospheric humidity according to the Clausius-Clapeyron relationship, TC rainfall is expected to intensify, exacerbating flood risks. However, additional climatic drivers may also contribute to long-term changes in TC-induced rainfall. To understand and disentangle these drivers, robust modeling efforts and reliable observational datasets are essential.In this study, we utilize a dataset from the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP), which includes rainfall estimates for historical TCs from 1950 to 2023. These estimates are derived using IBTrACS best-track data, two parametric wind models, and a physics-based Tropical Cyclone Rainfall (TCR) model. We validate the TCR model simulations by comparing them with TC rainfall estimates from ERA5 reanalysis data and the Integrated Multi-Satellite Retrievals for GPM (IMERG). This validation includes comparisons of lifetime accumulated rainfall for individual events and associated temporal trends across all events. Additionally, we use the TCR model to assess the role of climate change in driving long-term trends in TC rainfall. By generating counterfactual rainfall estimates, where the influence of increasing global mean temperature is removed through detrending of the temperature input data, we isolate a thermodynamic contribution of climate change to observed trends.We find that the TCR model produces higher maxima and more extreme rainfall events compared to ERA5, consistent with the tendency of reanalysis data to underestimate extremes. However, the relative intensity distribution of TC rainfall is captured in ERA5 and aligns with the patterns produced by the TCR model. The relative temporal trends between the datasets also align. Therefore, the TCR model might be a valuable tool for overcoming the underrepresentation of extreme TC rainfall in reanalysis data. Furthermore, our counterfactual estimates reveal that while the Clausius-Clapeyron relationship explains a significant portion of the observed increases in lifetime accumulated rainfall, residual trends persist, suggesting the influence of additional climatic drivers. This research highlights the importance of robust modeling frameworks, such as TCR, for understanding and attributing changes in TC rainfall, providing critical insights into the evolving hazards posed by tropical cyclones in a warming world.

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.

In this paper, a comparison study of three cumulus parameterization schemes (CPSs), Kain-Fritsch2 (KF2), Grell (GR) and Anthes-Kuo (AK), is carried out using the Pennsylvania State University-National Center for Atmospheric Research mesoscale model (i.e., MM5). The performances of three CPSs are examined in simulations of the long-term heavy Meiyu-frontal rainfall events over the middle to lower reaches of the Yangtze River Basin (YRB-ML) during the summer of 1998. The initial and lateral boundary atmosphere conditions are taken from the National Centers for Environmental Prediction/Department of Energy Reanalysis-2 (R-2) data. The experiment with KF2 scheme (EX_KF2) reproduces reasonably well the major rainfall events, especially the heavy rainfall over YRB-ML during the later stage, and the middle and lower troposphere circulation patterns. In contrast, the experiments with both GR and AK schemes (EX_GR and EX_AK) only simulate the heavy rainfall during the first Meiyu rainy phase with weak intensity, and almost miss the rainfall along YRB-ML during the second phase. The analyses show that the location of 500 hPa western Pacific subtropical high during the first rainy phase, the northward advance during the transition period and the retreat during the second rainy phase, observed from the R-2 data, are successfully captured by EX_KF2, compared to the poor performance of EX_GR and EX_AK. A reasonable proportion of the subgrid-scale rainfall and smaller biases of temperature and moisture from lower to middle troposphere in EX_KF2 decide its good rainfall simulations, in contrast with the absolutely high proportions and the cold and dry biases caused by the decreased vertically convective transportation and the weak southwesterly wind in EX_GR and EX_AK. Overall, the three CPSs show substantial intersimulation differences in rainfall as well as in three-dimensional atmospheric structures, and KF2 shows superior performances. The results suggest that the realistic subgrid-scale CPS is still highly required for the high-resolution regional climate models to simulate the heavy rainfall events.

Ninety five tropical cyclonic events (tropical storms, depressions and cyclones) between 2001 and 2010 were studied to determine their impact on dust outbreaks and long-range transport over the northern Indian Ocean and south Asia. In addition to the winter and summer Shamal Winds, tropical cyclones are an important mechanism of dust entrainment and transport of dust in this region. Elevated dust levels were observed in the northern Arabian Sea during most tropical cyclone events. During the study period, fifteen tropical cyclones migrated close to the dust source areas leading to major dust storms. Anti-clockwise winds associated with these storms were observed to entrain dust and transport it mostly towards the west or south-westerly direction. Tropical cyclones and storms, located further away from dust source areas, significantly alter the dispersal pathways of dust plumes raised by other mechanisms. The Northern Bay of Bengal cyclone events are shown to aid advection of dust plumes from southwest Asia and Thar Desert over highly populated regions of the Indian Subcontinent. Tropical cyclones also play an important role in dispersal of fine-mode aerosols over South Asia and formation of complex aerosol-dust mixtures.

The contribution of Southwestern Indian Ocean (SWIO) Tropical cyclones (TCs) to the December to March (DJFM) rainfall season over Tanzania was analyzed. Seasonal, monthly and daily rainfall data were obtained from Tanzania Meteorological Authority (TMA), while data for sea surface temperatures (SSTs), relative and specific humidity, zonal and meridional winds were acquired from NOAA (NCEP – NCAR). Tropical Rainfall Measuring Mission (TRMM) daily average gridded rainfall estimates were used. The observed and gridded rainfall data for each TC day were extracted and computed to monthly and seasonal totals for all TCs and non TCs days. Correlation between DJFM TCs and DJF/DJFM rainfall were determined. Inter annual variability between TCs and DJF rainfall was analyzed. Wind patterns at 850 - 200 mb, relative humidity (850-700mb), vertically integrated horizontal wind and moisture divergence (1000-500 mb) for two TC events (Izilda and Fobane) were analyzed. The results revealed that, TCs contribution to the DJFM rainfall was very significant. The influence of TCs to monthly total rainfall showed a general increasing trend from north to south along the coast of Tanzania, with a southwest to northeast alignment. On the other hand correlation between DJFM TCs with DJF rainfall was relatively weak at some stations while few stations including Dodoma and Tabora were showing relatively higher correlations of about 0.39 (p ≤ 0.05) suggesting that these stations are highly vulnerable to the TCs impacts. Moreover, results had shown that the distribution of TCs rainfall prone areas run from southern parts (Mtwara) through central parts (Dodoma) to northeastern highlands (Kilimanjaro). Analyses revealed that 700 mb wind vectors, integrated moisture fluxes and their convergence from Congo air mass, northwesterly and northeastern Indian Ocean air masses were the main contributors of rainfall over Tanzania during TCs events. Conclusively, the study showed that TCs has significant contribution to the DJF and DJFM rainfall in Tanzania, thus more studies for understanding the dynamic of TCs in relation to rainfall is required for improving the weather forecasts in Tanzania.

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.

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

In a Mediterranean climate the weak point of the staple normally occurs at the break of season in autumn, but it is not clear whether the staple simply breaks at the minimum fibre diameter or whether there is a specific weakness at this time. Three hypotheses were tested to determine if specific environmental effects on staple strength could be detected under field conditions. First, environmental stresses associated with rainfall and low temperature, resulting in a sudden disruption of warm summer–autumn conditions and lack of feed, may cause follicle shutdown. Second, the sudden decline in feed available following the rain event and the response of sheep to chase the green pick rather than eat the available dry feed may reduce the flow of nutrients to wool. Third, the slow adaptation by rumen microorganisms to changes in the diet from dry to green pasture may result in a further reduction of nutrients available to the wool follicle. We compared a group of sheep managed to minimise nutrient intake fluctuations at the break of season with a group grazing under normal farm practice and tested the hypothesis that a specific lowering of staple strength is associated with the break of season. On 2 April (3 days after the first rains of the season), 120, 18-month-old Merino wethers were allocated to 2 groups, paddock and yard. The paddock group comprised sheep following normal farm practice. The yard group was confined to yards and fed to maintain liveweight, to determine whether the break in the staple was associated with the rainfall event or with the subsequent changes in feed intake. These animals were left off feed for 4 days beginning 24 April. Within each group, 2 separate treatments were imposed. The paddock group was split, and half were moved into covered pens inside a shearing shed on 15 May, a few days before a second major rainfall event, to examine directly stresses associated with rainfall. The sheep from the yard group were kept as a single mob until 3 June, when they were split into 2 groups, sudden and gradual, in relation to their release onto green pasture, to examine the effect of adaptation time to green feed on the flow of nutrients to wool and staple strength. The sudden group was released onto green pasture, while the gradual group was given access to the pasture for increasing periods over the next week. The point of break was delayed by moving sheep into yards after the initial rainfall, suggesting that the rain event per se was not the direct cause of the break in the staple in this experiment. Furthermore, protecting the paddock sheep against the second major rainfall event by shedding half of them did not affect staple strength. The point of break in the staple in the yard group occurred after an accidental 4-day feed deprivation period. This indicates that even short periods of liveweight loss from feed deprivation due to poor or inattentive management when sheep are in low nutritional condition at this time of the year may precipitate the point of break. The rate of release onto green feed after yarding did not significantly affect staple strength and we conclude this was not an important factor. We conclude that neither stress associated with rainfall nor adaptation of ruminal microorganisms to the change in feed weakened the wool.

Meteorologists within the Forecast Branch (FB) of the National Meteorological Center (NMC) produce operational quantitative precipitation forecasts (QPFs). These manual forecasts are prepared utilizing various forecasting techniques, which are based on the subjective analysis and interpretation of the observed data and numerical model output. The manual QPFs from NMC generally have proven very successful in improving model QPF. This paper discusses several of the forecasting techniques employed by the FB, emphasizing the importance of subjective interpretation of the model guidance. The use of these methods in preparing a manual QPF for a heavy convective rainfall and flash-flood event that occurred over the southern Plains on 27–28 May 1987 is then examined. Results indicate that the manual QPF was quite successful in improving the models’ QPF and generally related well to the observed rainfall of up to 8 inches in this case. Thus, the importance of utilizing subjective techniques in preparing p...

In this study, analysis of the long term climatology, variability and trends in the daily rainfall events of ≥5 mm [or daily rainfall (DR) events] during the southwest monsoon season (June–September) over four regions of India; south central India (SCI), north central India (NCI), northeast India (NEI) and west coast (WC) have been presented. For this purpose, a new high spatial resolution (0.25° × 0.25°) daily gridded rainfall data set covering 110 years (1901–2010) over the Indian main land has been used. The association of monsoon low pressure systems (LPSs) with the DR events of various intensities has also been examined. Major portion of the rainfall over these regions during the season was received in the form of medium rainfall (≥5–100 mm) or moderate rainfall (MR) events. The mean seasonal cycle of the daily frequency of heavy rainfall (HR) (≥100–150 mm) or HR events and very heavy rainfall (VHR) (≥150 mm) or VHR events over each of the four regions showed peak at different parts of the season. The peak in the mean daily HR and VHR events occurred during middle of July to middle of August over SCI, during late part of June to early part of July over NCI, during middle of June to early July over NEI, and during late June to middle July over WC. Significant long term trends in the frequency and intensity of the DR events were observed in all the four geographical regions. Whereas the intensity of the DR events over all the four regions showed significant positive trends during the second half and the total period, the signs and magnitude of the long term trends in the frequency of the various categories of DR events during the total period and its two halves differed from the region to the region. The trend analysis revealed increased disaster potential for instant flooding over SCI and NCI during the recent years due to significant increasing trends in the frequency (areal coverage) and intensity of the HR and VHR events during the recent half of the data period. However, there is increased disaster potential over NEI and WC due to the increasing trends in the intensity of the rainfall events. There is strong association between the LPS days and the DR events in both the spatial and temporal scales. In all the four regions, the contributions to the total MR events by the LPS days were nearly equal. On the other hand, there was relatively large regional difference in the number of combined HR and VHR events associated with LPS days particularly that associated with monsoon depression (LPS stronger than monsoon depression) days. The possible reasons for the same have also been discussed. The increasing trend in the monsoon low (low pressure) days post 1970s is the primary reason for the observed significant increasing trends in the HR and VHR events over SCI and NCI and decreasing trend in HR events over NEI during the recent half (1956–2010). This is in spite of the decreasing trend in the MD days.

The weakening effect of urbanization on tropical cyclone surface winds : An observational study for Shanghai