nasa-gesdisc/es-publications-researchareas huggingface dataset:
Experimental Proof of Concept for the Hurricane Imaging Radiometer (HIRAD) Measurement of a Hurricane Ocean Surface Wind Speed Field (2022)

The objective of the Hurricane Imaging Radiometer (HIRAD) is to produce wide-swath images of hurricane wind and rain fields during a single pass from a high-altitude aircraft. This instrument could be a prototype for the next generation of airborne hurricane remote sensors that operate on NOAA/USAF surveillance flights over named storms and hurricanes. The improved two-dimensional surface wind field measurements provided by the HIRAD approach are crucial to improved forecasts and warnings. For almost a decade, HIRAD has been used in research flights over hurricanes; however, because of various hardware issues, the scientific potential of its measurements has not been fulfilled. This paper presents a reanalysis of HIRAD measurements over Hurricane Gonzalo on 17 October 2014 that demonstrate remarkable results. The basis for this novel approach is to use coincident surface wind speed (WS) and rain rate (RR) measurements from another source to calibrate the HIRAD brightness temperature measurements. As a result, the HIRAD retrievals of WS and RR are in excellent agreement with the accompanying airborne remote sensors and in situ surface wind speed measurements, which validates the HIRAD technique proof of concept.

Research areas: Severe Storms
Recent global decrease in the inner-core rain rate of tropical cyclones (2021)

Heavy rainfall is one of the major aspects of tropical cyclones (TC) and can cause substantial damages. Here, we show, based on satellite observational rainfall data and numerical model results, that between 1999 and 2018, the rain rate in the outer region of TCs has been increasing, but it has decreased significantly in the inner-core. Globally, the TC rain rate has increased by 8  4% during this period, which is mainly contributed by an increase in rain rate in the TC outer region due to increasing water vapor availability in the atmosphere with rising surface temperature. On the other hand, the rain rate in the inner-core of TCs has decreased by 24  3% during the same period. The decreasing trend in the inner-core rain rate likely results mainly from an increase in atmospheric stability.

Research areas: Severe Storms
A coupled model analyses on the interaction between oceanic eddies and tropical cyclones over the Bay of Bengal (2020)

The Bay of Bengal (BOB) region of Indian Ocean is affected by numerous tropical cyclones during pre- and post-monsoon seasons when various eddies are generated in the central and western bay. Here, numerical simulations of few tropical cyclones (Aila, Laila, Phailin, Hudhud and Madi) that occurred in different seasons are carried out using an ocean atmosphere coupled numerical model, consisting of Weather Research and Forecasting (WRF) and Regional Ocean Modeling Systems (ROMS), to analyse the influence of eddies on tropical cyclone intensifications over the bay. The model is able to track the tropical cyclones with less error, while the central pressure and wind speed are underestimated. Also, the coupling process steer the cyclones to the observed track compared to standalone WRF model. The variations in simulated sea surface temperature and salinity are in agreement with the satellite and in situ measurements. During the passage of Phailin and Hudhud over the eddies, the cyclones intensified almost twice of their initial central pressure and wind (before interacting with eddies), which the model captured very well. The eddy feedback factor, which estimate the influence of warm eddies on tropical cyclones, is about 152% for Phailin and 90% for Hudhud. In the case of the pre-monsoon cyclones, Aila and Laila, the eddy feedback factor is estimated up to 36% and 21%, respectively. Madi cyclone lost its intensification up to 80% because of its interaction with a cold eddy. These predictions are comparable with that of the observations during the cyclone passage. Also it is noted that the warm eddy regions resulted in the maximum transfer of latent heat resulting in strong intensifications of the cyclones. Our study reveals that the eddies play an important role in the intensification and dissipation of BOB cyclones and understanding their nature can help in estimating the track and intensity of cyclones.

Research areas: Severe Storms
Evaluating South African Weather Service information on Idai tropical cyclone and KwaZulu- Natal flood events (2021)

Severe weather events associated with strong winds and flooding can cause fatalities, injuries and damage to property. Detailed and accurate weather forecasts that are issued and communicated timeously, and actioned upon, can reduce the impact of these events. The responsibility to provide such forecasts usually lies with government departments or state-owned entities; in South Africa that responsibility lies with the South African Weather Service (SAWS). SAWS is also a regional specialised meteorological centre and therefore provides weather information to meteorological services within the Southern African Development Community (SADC). We evaluated SAWS weather information using near real-time observations and models on the nowcasting to short-range forecasting timescales during two extreme events. These are the Idai tropical cyclone in March 2019 which impacted Mozambique, Zimbabwe and Malawi resulting in over 1000 deaths, and the floods over the KwaZulu-Natal (KZN) province in April 2019 that caused over 70 deaths. Our results show that weather models gave an indication of these systems in advance, with warnings issued at least 2 days in advance in the case of Idai and 1 day in advance for the KZN floods. Nowcasting systems were also in place for detailed warnings to be provided as events progressed. Shortcomings in model simulations were shown, in particular on locating the KZN flood event properly and over/underestimation of the event. The impacts experienced during the two events indicate that more needs to be done to increase weather awareness, and build disaster risk management systems, including disaster preparedness and risk reduction.

Research areas: Severe Storms
Dynamics and predictability of the intensification of Hurricane Edouard (2014) (2017)

Abstract The dynamics and predictability of the intensification of Hurricane Edouard (2014) are explored through a 60-member convection-permitting ensemble initialized with an ensemble Kalman filter that assimilates dropsondes collected during NASAs Hurricane and Severe Storm Sentinel (HS3) investigation. The 126-h forecasts are initialized when Edouard was designated as a tropical depression and include Edouards nearrapid intensification (RI) from a tropical storm to a strong category-2 hurricane. Although the deterministic forecast was very successful and many members correctly forecasted Edouards intensification, there was significant spread in the timing of intensification among the members of the ensemble. Utilizing composite groups created according to the near-RI-onset times of the members, it is shown that, for increasing magnitudes of deep-layer shear, RI onset is increasingly delayed; intensification will not occur once a critical shear threshold is exceeded. Although the timing of intensification varies by as much as 48 h, a decrease in shear is observed across the intensifying composite groups ~612 h prior to RI. This decrease in shear is accompanied by a reduction in vortex tilt, as the precession and subsequent alignment process begins ~2448 h prior to RI. Sensitivity experiments reveal that some of the variation in RI timing can be attributed to differences in initial intensity, as the earliest-developing members have the strongest initial vortices regardless of their environment. Significant sensitivity and limited predictability exists for members with weaker initial vortices and/or that are embedded in less conducive environments, under which the randomness of moist convective processes and minute initial differences distant from the surface center can produce divergent forecasts.

Research areas: Severe Storms
The roles of climate change and climate variability in the 2017 Atlantic hurricane season (2018)

The 2017 Atlantic hurricane season was extremely active with six major hurricanes, the third most on record. The sea-surface temperatures (SSTs) over the eastern Main Development Region (EMDR), where many tropical cyclones (TCs) developed during active months of August/September, were ~0.96 C above the 19012017 average (warmest on record): about ~0.42 C from a long-term upward trend and the rest (~80%) attributed to the Atlantic Meridional Mode (AMM). The contribution to the SST from the North Atlantic Oscillation (NAO) over the EMDR was a weak warming, while that from El NinoSouthern Oscillation (ENSO) was negligible. Nevertheless, ENSO, the NAO, and the AMM all contributed to favorable wind shear conditions, while the AMM also produced enhanced atmospheric instability. Compared with the strong hurricane years of 2005/2010, the ocean heat content (OHC) during 2017 was larger across the tropics, with higher SST anomalies over the EMDR and Caribbean Sea. On the other hand, the dynamical/thermodynamical atmospheric conditions, while favorable for enhanced TC activity, were less prominent than in 2005/2010 across the tropics. The results suggest that unusually warm SST in the EMDR together with the long fetch of the resulting storms in the presence of record-breaking OHC may be key factors in driving the strong TC activity in 2017.

Research areas: Severe Storms
Reduced Sea Ice Enhances Intensification of Winter Storms over the Arctic Ocean (2022)

Abstract The ideal environment for extratropical cyclone development includes strong vertical shear of horizontal wind and low static stability in the atmosphere. Arctic sea ice loss enhances the upward flux of energy to the lower atmosphere, reducing static stability. This suggests that Arctic sea ice loss may facilitate more intense storms over the Arctic Ocean. However, prior research into this possibility has yielded mixed results with uncertain cause and effect. This work has been limited either in scope (focusing on a few case studies) or resolution (focusing on seasonal averages). In this study, we extend this body of research by comparing the intensification rate and maximum intensity of individual cyclones to local sea ice anomalies. We find robust evidence that reduced sea ice in winter (DecemberMarch) strengthens Arctic cyclones by enhancing the surface turbulent heat fluxes and lessening static stability while also strengthening vertical shear of horizontal wind. We find weaker evidence for this connection in spring (AprilJune). In both seasons, lower sea ice concentration also enhances cyclone-associated precipitation. Although reduced sea ice also weakens static stability in September/October (when sea ice loss has been especially acute), this does not translate to stronger storms because of coincident weakening of wind shear. Sea ice anomalies also have little or no connection to cyclone-associated precipitation in these months. Therefore, future sea ice reductions (e.g., related to delayed autumn freeze-up) will likely enhance Arctic cyclone intensification in winter and spring, but this relationship is sensitive to simultaneous connections between sea ice and wind shear. Significance Statement Sea ice is a barrier between the ocean and atmosphere, limiting the exchange of energy between them. As the amount of sea ice in the Arctic Ocean declines, the ocean can transfer more heat to the atmosphere above in fall and winter. It is theorized that this extra energy may help intensify storms that pass through the Arctic. We examine individual storms over the Arctic Ocean and what sea ice conditions they experience as they develop. We find that storms intensify more when sea ice is lower than normal in the winter season only. This relationship may contribute to stronger Arctic winter storms in the future, including heavier precipitation and stronger winds (which can enhance wave heights and coastal erosion).

Research areas: Severe Storms
Recent decrease in inner-core rain rate of tropical cyclones over the western North Pacific (2022)

AbstractThe tendency in tropical cyclone (TC) rainfall is of great concern due to its remarkable contribution to global precipitation and extreme rainfall events. This study finds a decreasing trend in TC innercore rain rate over the western North Pacific (WNP) from 1998 to 2019. This basinwide trend is mainly induced by the decreasing TC innercore rain rates over the region west of 150E, while it is seldom linked to the changes in the distribution of TC occurrence. The maximum decreases in TC innercore rain rate are observed over the offshore areas along the coastlines of East Asia. Further analysis reveals that the change in atmospheric stability, referred to as a dominant environmental contributor to basinwide TC innercore rain rate decreases shown in previous studies, only has a primary impact over the northern South China Sea. By comparison, there is a positive correlation between the variations of the aerosol optical depth and TC innercore rain rate over the midlatitude regions extending from the East China Sea to Japan. Our result highlights the linkage of the recent decreasing trends in aerosol optical depth and TC innercore rain rate over the WNP.

Research areas: Severe Storms
The earlier end of the tropical cyclone season over the Western North Pacific by environmental cyclogenesis factors (2022)

Several of the best track datasets reveal the earlier end of the tropical cyclone (TC) season over the main WNP (the east of the Philippine Islands) from 1980 to 2019, especially by the date of the upper decile of the storm days (constructed by adding one to each date if any TC exists). The enhanced vertical wind shear (VWS) during the late season (October and November) is consistent with this earlier end of the TC season. In October, the enhanced VWS is the result of the increased zonal and meridional shears, which are affected by the earlier circulation transition of the East Asian summer monsoon recessed and winter monsoon onset during late October. During November, the zonal wind shear dominates the enhanced VWS, which vertically is the opposite trend of air temperature below and above the tropopause and the meridionally opposite trend of air temperature in the north and south of 30N. The opposite air temperature trends induce the thermal wind balance, which causes enhanced westerlies in the mid-latitudes and strong zonal shear. Three pathways increase VWS in the late season over the WNP, leading to the earlier end of the TC season. The strong impact of VWS limits TC formation, although the ambient warming underlying the surface (supports a broader and stronger potential intensity). The effect of the thermodynamical parameter, depending on relative humidity at the low and middle troposphere, is uncertain because of the inconsistent and weak trends in October between ERA5 and MERRA-2, but they both become unfavorable to TC genesis during November. The practically important meaning of the VWS for the TC season provides a possibility for future projections of the TC season.

Research areas: Severe Storms
Large-scale state and evolution of the atmosphere and ocean during PISTON 2018 (2021)

Abstract The Propagation of Intraseasonal Tropical Oscillations (PISTON) experiment conducted a field campaign in AugustOctober 2018. The R/V Thomas G. Thompson made two cruises in the western North Pacific region north of Palau and east of the Philippines. Using select field observations and global observational and reanalysis datasets, this study describes the large-scale state and evolution of the atmosphere and ocean during these cruises. Intraseasonal variability was weak during the field program, except for a period of suppressed convection in October. Tropical cyclone activity, on the other hand, was strong. Variability at the ship location was characterized by periods of low-level easterly atmospheric flow with embedded westward propagating synoptic-scale atmospheric disturbances, punctuated by periods of strong low-level westerly winds that were both connected to the Asian monsoon westerlies and associated with tropical cyclones. In the most dramatic case, westerlies persisted for days during and after tropical cyclone Jebi had passed to the north of the ship. In these periods, the sea surface temperature was reduced by a couple of degrees by both wind mixing and net surface heat fluxes that were strongly (~200 W m2) out of the ocean, due to both large latent heat flux and cloud shading associated with widespread deep convection. Underway conductivitytemperature transects showed dramatic cooling and deepening of the ocean mixed layer and erosion of the barrier layer after the passage of Typhoon Mangkhut due to entrainment of cooler water from below. Strong zonal currents observed over at least the upper 400 m were likely related to the generation and propagation of near-inertial currents.

Research areas: Severe Storms
Natural and anthropogenic contributions to the hurricane drought of the 1970s–1980s (2022)

Atlantic hurricane activity experienced a pronounced lull during the 1970s and 1980s. The current explanation that anthropogenic aerosol radiative forcing cooled the sea surface locally fails to capture the magnitude of this large decrease in activity. To explain this hurricane drought, we propose that the radiative effects of sulfate aerosols from Europe and North-America decreased precipitation in the Sahara-Sahel region, leading to an enhancement of dust regional emissions and transport over the Atlantic. This dust in turn enhanced the local decrease of sea-surface temperature and of hurricane activity. Here, we show that dust emissions from the Sahara peaked in phase with regional sulfate aerosol optical thickness and Sahel drought conditions, and that dust optical depth variations alone can explain nearly half of the sea-surface temperature depression in the 1970s and 1980s.

Research areas: Severe Storms
Super typhoons Hato (1713) and Mangkhut (1822), partII: challenges in (2020)

This is the second paper of a two-part series about Super Typhoons Hato (1713) and Mangkhut (1822), which hit Hong Kong successively in 2017 and 2018, respectively, and necessitated the issuance of the highest tropical cyclone warning signal. While their maximum intensity and wind structure are analysed in Part I, this paper covers the challenges in forecasting and early warning of the storms. The actual and predicted tropical cyclone track, intensity and storm surge in Hong Kong and their associated storm surge risk are reviewed. Experience in early warning and disaster risk reduction is also shared in this paper.

Research areas: Severe Storms
Dependence of tropical cyclone damage on maximum wind speed and socioeconomic factors (2020)

Abstract
            Tropical cyclones (TCs) have devastating impacts and are responsible for significant damage. Consequently, for TC-induced direct economic loss (DEL) attribution all factors associated with risk (i.e. hazard, exposure and vulnerability) must be examined. This research quantifies the relationship between TC-induced DELs and maximum wind speed, asset value and Gross Domestic Product (GDP) per capita using a regression model with TC records from 2000 to 2015 for Chinas mainland area. The coefficient of the maximum wind speed term indicates that a doubling of the maximum wind speed increases DELs by 225% [97%, 435%] when the other two variables are held constant. The coefficient of the asset value term indicates that a doubling of asset value exposed to TCs increases DELs by 79% [58%, 103%]; thus, if hazard and vulnerability are assumed to be constant in the future, then a dramatic escalation in TC-induced DELs will occur given the increase in asset value, suggesting that TC-prone areas with rapid urbanization and wealth accumulation will inevitably be subject to higher risk. Reducing the asset value exposure via land-use planning, for example, is important for decreasing TC risk. The coefficient of GDP per capita term indicates that a doubling in GDP per capita could decrease DELs by 54% [39%, 66%]. Because accumulated assets constantly increase peoples demand for improved security, stakeholders must invest in risk identification, early warning systems, emergency management and other effective prevention measures with increasing income to reduce vulnerability. This research aims to quantitatively connect TC risk (expected DELs, specifically) to physical and socioeconomic drivers and emphasizes how human dimensions could contribute to TC risk. Moreover, the model can be used to estimate TC risk under climate change and future socioeconomic development in the context of China.

Research areas: Severe Storms
Polar Jet Associated Circulation Triggered a Saharan Cyclone and Derived (2018)

In this study, we identify a new mechanism by which dust aerosols travel over long distances across the eastern side of the North Atlantic Ocean toward the Arctic. The meandering polar jet was at the origin of both dust emission through cyclogenesis over Northwest Africa and poleward transport of the uplifted dust toward the Arctic, through cut-off circulation. The dust emission was associated with an intense Saharan cyclone that formed over Northwest Africa in early April 2011. The formation of the cyclone was caused by the intrusion into subtropics, of a high-latitude-upper-level trough, linked to the meandering polar jet. The trough initiated cyclogenesis over Northwest Africa after orographic blocking by the Anti-Atlas Mountains. The still meandering polar jet led to the formation of a cut-off low further south with which the Saharan dust-cyclone merged 2 days later and moved northward with the main stream. Beside satellite observations, a simulation at high resolution was performed using the prognostic-dust permitting model MesoNH. The total dust load carried during this event to areas located north of 40 N was estimated by the model to be 38 Tg and dust deposition was estimated to be 1.3 Tg. The Saharan dust reaching Greenland was accompanied by warm and moist air masses that caused a rise in surface temperature of about 10C for more than 3 consecutive days over the southeastern Greenland. Ice melt over this area of Greenland was detected in the brightness temperature observations.

Research areas: Severe Storms
Influence of vertical wind shear on the ocean response to tropical cyclones based on satellite observations (2021)

We here investigate the effects of tropical cyclone (TC)-induced rainfall asymmetries driven by vertical wind shear on ocean salinity and temperature response to TCs using satellite and in situ observations. On average, TCs tend to initially freshen the ocean surface due to heavy rainfall and subsequently salinity from upwelling and vertical mixing, with strongest surface salinification on the right-hand side of the Northern Hemisphere TCs. The direction of shear has been found to control the location of maximum TC rainfall, resulting in more freshwater accumulation on the right-hand side of the right-sheared storms. The accumulated freshwater strengthens salinity stratification and inhibits right-side biased vertical mixing, reducing subsequent surface salinification by 0.15-0.3 psu and slightly suppressing the surface cooling by about 0.15°C, relative to left-sheared storms. Thus, the directionality of shear can impact ocean-TC coupling.

Research areas: Severe Storms