nasa-gesdisc/es-publications-researchareas huggingface dataset:
Spatial and temporal dynamics of the urban heat island effect in a small Brazilian city (2023)

This study examined the spatial and temporal patterns of the canopy layer urban heat islands (UHIUCL) in a small city in southeastern Brazil using the local climate zone (LCZ) system. We analysed the influence of weather conditions, LCZs characteristics, and local surface relief on the UHIUCL magnitudes. Mobile traverses were used to measure air temperatures during representative nights of wet and dry seasons. Daily maximum magnitudes were observed in compact classes (LCZs 3 and 7) under ideal weather conditions (dry, clear skies, and calm) and higher anthropogenic heat release (weekdays). Seasonal effects on LCZ thermal differences were negligible. The peripheral landscapes were warmer than the city centre in both seasons. Among the warmer areas in the city, magnitudes in compact LCZs 3 and 7 were consistently higher than in LCZ 6. In general, representative sites of the main 'built' LCZs in the study area exhibit similar inter‑zone temperature patterns to those reported for cities of different sizes from tropical and midlatitude regions. Thermal contrasts of ΔTLCZ 3 − D in the study area reveal significant evidence that small cities can have as strong heat islands as bigger cities. These findings highlight the importance of the LCZ system to identify the main controlling factors driving such thermal differences and the need to extend the application of this approach in other South American cities to yield systematic data of UHIUCL for urban planning given the coming challenges of climate change over the region.

Research areas: Heat
Decline in surface urban heat island intensity in India during heatwaves (2019)

Heatwaves cause human mortality around the world and are projected to rise in the future. Despite the influence of urban heat island (UHI) on heatwaves, the role of UHI on heatwave intensification in urban areas in India remains unrecognized. Here using in situ, satellite observations, and model simulations, we show that urban areas in India do not intensify heatwaves. The frequency of hot-days has significantly (p-value &lt;0.05) increased in urban areas during 1951-2016. The frequency of hot-nights has also increased in the majority of urban areas in India except those located in Indo-Gangetic Plain (IGP). We show that a decline in the frequency of hot-nights (-4.5 ± 1.6 hot-nights) in IGP during 1951-2016 is mainly due to intensive irrigation in the region. We confirm the influence of irrigation on land surface temperature (LST) over IGP using simulations from Community Land Model (CLM4). Our results show that Surface Urban Heat Island (SUHI) intensity in major urban areas in India declines during heatwaves both during the day (-0.3 ± 0.7 °C) and night (-0.3 ± 0.4 °C) from the reference SUHIs. Surrounding non-urban areas (44.5 ± 5.5 °C) are warmer than urban areas (43.7 ± 6.8 °C) during heatwaves due to the absence of vegetation. Our results have implications for policy related to health impacts during heatwaves.

Research areas: Heat, Habitat Conversion/Fragmentation
Trends and drivers of land surface temperature along the urban-rural gradients in the largest urban agglomeration of China (2020)

Urban heat magnitude and effects may represent harbingers of future climate change and the urban-rural gradients provide a unique natural laboratory for identifying both problems and solutions to climate change mitigation and adaptation. Here, we explored the trends and driving forces of land surface temperature (LST) along the urban-rural gradients of 26 cities in the largest urban agglomeration of China, the Yangtze River Delta Urban Agglomeration, using MODIS LST data combined with urban intensity, background climate, vegetation greenness, landscape structure, albedo, population and gross domestic product (GDP). We found that LST generally increased with increasing urban intensity along the urban-rural gradients while with large diurnal and seasonal variability. Large variability also existed between the maximum and minimum LST within the same urban intensity (e.g., 6.4 C), suggesting cities themselves provide ready-made solutions (minimum) to resolving heat island problems. However, the range of LST within the same intensity decreased with the urban intensity and narrowed drastically when the intensity reached certain thresholds (e.g., 5887% varying with season, time of day, and city), implying that the space for climate mitigation is very limited once the urbanization intensity exceeds critical thresholds. The roles of landscape structure (composition and configuration) for greenspace and urban land have become increasingly important in driving the variation of LST with increasing urban intensity from low (20%30%), middle (45%55%) to high (70%80%), clearly indicating that subtle urban landscape designing, such as less aggregated urban configuration and more irregular greenspace shape are effective strategies to mitigate climate change in highly urbanized areas and cities themselves already provide such vivid demonstrations for us to find and learn.

Research areas: Heat, Habitat Conversion/Fragmentation
Global long-term mapping of surface temperature shows intensified intra-city urban heat island extremes (2021)

Surface temperatures are generally higher in cities than in rural surroundings. This phenomenon, known as Surface Urban Heat Island (SUHI), increases the risk of heat-related human illnesses and mortality. Past global studies analysed this phenomenon aggregated at city scale or over seasonal and annual time periods, while human impacts strongly depend on shorter term heat stress experienced locally. Here we develop a global long-term high-resolution dataset of daytime SUHI, offering an insight into the spacetime variability of the urbanrural temperature differences which is unprecedented at global scale. Our results show that across urban areas worldwide over the period 20032020, 3-day SUHI extremes are on average more than twice as high as the warm-season median SUHI, with local exceedances up to 10 K. Over this period, SUHI extremes have increased more rapidly than warm-season medians, and averaged worldwide are now 1.04 K or 31% higher compared to 2003. This can be linked with increasing urbanisation, more frequent heatwaves, and greening of the earth, processes that are all expected to continue in the coming decades. Within many cities there are hotspots where extreme SUHI intensity is 1015 K higher compared to relatively cooler city parts. Given the limited human adaptability to heat stress, our results advocate for mitigation strategies targeted at reducing SUHI extremes in the most vulnerable and exposed city neighbourhoods.

Research areas: Heat, Habitat Conversion/Fragmentation
Changes in the length of the season with favorable environmental conditions for tropical cyclones in the North Atlantic basin during the last 40 years (2022)

Abstract Analyses of two high-resolution reanalysis products show high values of hurricane potential intensity (PI) are becoming more frequent and covering a larger area of the Atlantic, which is consistent with the lengthening of the tropical cyclone season previously reported. These changes are especially pronounced during the early months of the storm season (May to July) in subtropical latitudes. The western subtropical Atlantic features increases in mean PI as well as the areal coverage and frequency of high PI throughout the storm season; the length of the season with high PI has grown since 1980. The number of days with low vertical wind shear increases in the tropical North Atlantic during the early and middle months of the storm season, but trends are mixed and generally insignificant elsewhere. A thermodynamic parameter measuring the ratio of mid-level entropy deficits to the strength of surface fluxes that work to eliminate them, is sensitive to the choice of the pressure level(s) used to calculate its value in the boundary layer, as well as to subtle differences in temperature and humidity values near the surface in different reanalysis datasets, leading to divergent results in metrics like the ventilation index that depend on its value. Projections from a high-resolution simulation of the remainder of the 21st century show the number of days with high PI is likely to continue increasing in the North Atlantic basin, with trends especially strong in the western subtropical Atlantic during the early and late months of the season.

Research areas: Severe Storms, Atmospheric/Ocean Indicators
A New Perspective on the Development of the Great Arctic Cyclone in August 2012 (2022)

The evolutionary process of "The Great Arctic Cyclone (AC) of August 2012" (hereafter named as AC2) was investigated by using the Arctic System Reanalysis version 2 data, from a new perspective of two cyclones' merging. The evolution of AC2 was affected by the merging process with a pre-existing AC (hereafter named as AC1) at lower-levels, and the impact of the two tropopause polar vortices (TPVs). The AC2's development showed a slowdown at the early stage of merging (before 00 UTC 5), and a rapid intensification at the later stage (after 00 UTC 5). The diagnostic results based on Zwack-Okossi equation showed that, at the early stage of merging when two TPVs had not merged, despite AC2's intensification was favored by vorticity advection provided by the upper-level jet stream, the warm advection supporting AC2's development, which was prevented by TPV2. AC2 weakened due to the joint influences of cold advection induced by the cold core beneath the TPV2 and AC1's cyclonic circulation at lower-levels. At the later stage of merging, AC2 rapidly intensified due to the joint influences of warm advection produced by the warm air advected from warm core above the merged TPV by the upper-level jet stream, and the warm advection induced by enhanced lower-level baroclinicity near the warm front. Diabatic heating near the upper- and lower-level fronts also played an important role in promoting AC2's development through its whole time.

Research areas: Severe Storms
CYGNSS observations and analysis of low-latitude extratropical cyclones (2021)

Abstract Latent and sensible heat fluxes over the oceans are believed to play an important role in the genesis and evolution of marine-based extratropical cyclones (ETCs) and affect rapid cyclogenesis. Observations of ocean surface heat fluxes are limited from existing in situ and remote sensing platforms, which may not offer sufficient spatial and temporal resolution. In addition, substantial precipitation frequently veils the ocean surface around ETCs, limiting the capacity of spaceborne instruments to observe the surface processes within maturing ETCs. Although designed as a tropics-focused mission, the Cyclone Global Navigation Satellite System (CYGNSS) can observe ocean surface wind speed and heat fluxes within a notable quantity of low-latitude extratropical fronts and cyclones. These observations can assist in understanding how surface processes may play a role in cyclogenesis and evolution. This paper illustrates CYGNSSs capability to observe extratropical cyclones manifesting in various ocean basins throughout the globe and shows that the observations provide a robust sample of ETCs winds and surface fluxes, as compared with a reanalysis dataset.

Research areas: Severe Storms, Atmospheric/Ocean Indicators
Contributions of Atmospheric Transport and Rain-Vapor Exchange to (2018)

Coastal mangroves are increasingly recognized as valuable natural resources and important sites of water and carbon exchange. In this study, we examine atmospheric water cycling in the boundary layer above a coastal mangrove forest in southern China. We collected site observations of isotopic ratios in water vapor and precipitation along with core meteorological variables during July 2017. Our evaluation of these data highlights the influences of large-scale atmospheric transport and rainvapor exchange in the boundary layer water budget. Rainvapor exchange takes different forms for different types of rainfall events. The evolution of isotopic ratios in water vapor suggests that substantial rain recycling occurs during the passage of large-scale organized convective systems, but that this process is much weaker during rainfall associated with less organized events of local origin. We further examine the influences of large-scale transport during the observation period using a Lagrangian trajectory-based moisture source analysis. More than half (63%) of the boundary layer moisture during the study period traced back to the South China Sea, consistent with prevailing southerly to southwesterly flow. Other important moisture sources included mainland Southeast Asia and the Indian Ocean, local land areas (e.g., Hainan Island and the Leizhou Peninsula), and the Pacific Ocean. Together, these five regions contributed more than 90% of the water vapor. The most pronounced changes in isotopic content due to large-scale transport during the study period were related to the passage of Tropical Storm Talas. The outer rain bands of this tropical cyclone passed over the measurement site on 1517 July, causing a sharp reduction in the heavy isotopic content of boundary layer water vapor and a substantial increase in deuterium excess. These changes are consistent with extensive isotopic distillation and rainvapor exchange in downdrafts associated with the intense convective systems produced by this storm.

Research areas: Severe Storms, Ecosystems
Comparing Tropical Cyclone and King Tide Impacts on a South Carolina Coastal Dune System (2021)

Harris, M.E. and Ellis, J.T., 2021. Comparing tropical cyclone and king tide impacts on a South Carolina coastal dune system. Journal of Coastal Research, 37(5), 923932. Coconut Creek (Florida), ISSN 0749-0208.Coastal populations face an ever-growing threat as natural hazards increase in frequency and magnitude. In South Carolina, king tides (abnormally high tides) responsible for coastal flooding have increased by 126% between 2014 and 2019. King tides present an evolving threat as sea levels rise, yet the implications for coastal dune response have not been investigated. This study compares the geomorphic impacts from king tides to two tropical cyclones on a South Carolina barrier island during four time periods (TPs): Hurricanes Florence (TP1) and Michael (TP2) and two subsequent periods (TP3 and TP4) with king tides but devoid of tropical cyclone activity. Florence resulted in the greatest average change to the dunes, with normalized volumes (nv) equivalent to 11.6 m3/d. During Michael, the average change rate was nv = 1.5 m3/d. Dune changes during TP3 and TP4 averaged nv = 1.7 m3/d and nv = 2.3 m3/d, respectively. The reduction rate during nonstorm conditions is indicative of the erosive potential of king tides. The erosive potential should be further investigated in conjunction with king tide magnitude and frequency. Smaller, more pervasive coastal hazards, such as king tides, should be more strongly considered, in addition to larger singular events, such as tropical cyclones, when investigating the geomorphic change of coastal dune systems.

Research areas: Severe Storms
On the Relationship between CYGNSS Surface Heat Fluxes and the Life Cycle of Low-Latitude Ocean Extratropical Cyclones (2021)

Abstract Surface latent and sensible heat fluxes are important for extratropical cyclone evolution and intensification. Because extratropical cyclone genesis often occurs at low latitudes, Cyclone Global Navigation Satellite System (CYGNSS) surface latent and sensible heat flux retrievals are composited to provide a mean picture of their spatial distribution in low-latitude oceanic extratropical cyclones. CYGNSS heat fluxes are not affected by heavy precipitation and offer observations of storms with frequent revisit times. Consistent with prior results obtained for cyclones in the Gulf Stream region, the fluxes are strongest in the wake of the cold fronts and are weakest to negative in the warm sector in advance of the cold fronts. As cyclone strength increases or mean precipitable water decreases, the maximum in surface heat fluxes increases while the minimum decreases. This affects the changes in fluxes during cyclone intensification: the post-cold-frontal surface heat flux maximum increases as a result of the increase in near-surface winds. During cyclone dissipation, the fluxes in this sector decrease because of the decrease in winds and in temperature and humidity contrast. The warm-sector minimum decreases throughout the entire cyclone lifetime and is mostly driven by seaair temperature and humidity contrast changes. However, during cyclone dissipation, the surface heat fluxes increase along the cold front in a narrow band to the east, independent from changes in the cyclone characteristics. This result suggests that, during cyclone dissipation, energy transfers from the ocean to the atmosphere are linked to frontal processes in addition to synoptic-scale processes.

Research areas: Severe Storms
Satellite Observations of the Sea Surface Salinity Response to Tropical (2021)

Decade-long satellite sea surface slinity (SSS) observations show that rain dilution prevails in wakes of tropical depressions (∼-0.1 pss) and tropical storms (∼-0.05 pss) on the left (right) side of Northern (Southern) Hemisphere storms. For stronger storms, the rain-induced dilution is dominated by the saltier water entrainment, leading to surface median salinification of 0.3 pss for the most intense storms, peaking on the right-hand side at around twice the maximum wind radius. The magnitude of the salty wake increases for stronger slowly moving storms. The vertical salinity gradient in the upper ocean is a key factor explaining the geographic distribution of the SSS response. A striking example is the systematic mixing of fresh near-surface river plume waters with saltier subsurface waters. It is also found that barrier layers lead to saltier and warmer storm wakes compared to wakes produced over barrier layer free areas.

Research areas: Severe Storms, Atmospheric/Ocean Indicators
Strengthened tropical cyclones and higher flood risk under compound effect of climate change and urbanization across China's Greater Bay Area (2022)

Climate change and urbanization will further exacerbate tropical cyclones (TCs) causing severer flooding especially in coastal urbanized areas. In this study, the compound effects of climate change and urbanization on organized TC and its flood risk across the Guangdong-Hong Kong-Macau Greater Bay Area (GBA) were explored and future projections of 10 models in different Shared Socioeconomic Pathways (SSPs) and Representative Concentration Pathways (RCPs) in Coupled Model Intercomparison Project 6 (CMIP6). The typical TC named Ewiniar that caused tremendous rainfall and flooding over GBA is taken as a case. We found that future TC will be exacerbated with rainfall band shifting inland and covering larger areas compared to the current scenario due to climate change and urbanization, and rainfall amount in the central rainfall band increases by 24% and 28% under SSP2-RCP4.5 and SSP5-RCP8.5, respectively. Due to the land-atmosphere interactions, future actual direct runoff increased by 7.91%15.53% during the TC Ewiniar under SSP2-RCP4.5 and SSP5-RCP8.5, leading to further expansion of the area marked with the highest flood risk (24% and 39%, respectively). Our study highlights the adverse compound effect of climate change and urbanization on TC and flood risk, helping to develop TC-related disaster prevention and mitigation policies.

Research areas: Severe Storms, Habitat Conversion/Fragmentation, Floods
Physical and biological response of the Arabian Sea to tropical cyclone Phyan and its implications (2011)

The response to the tropical cyclone Phyan, which developed in the eastern Arabian Sea during 911 November 2009, was rapid cooling of sea surface temperature (SST), enhancement of chlorophyll a and two-fold increase in net primary productivity (NPP). Cooling of SST was immediate in response to the strong wind-mixing, and the subsequent upward Ekman pumping sustained the cooling even after the dissipation of Phyan. The biological response mediated by the upward Ekman pumping driven vertical transport of subsurface nutrient showed a time lag of 34 days. The CO2 flux to the atmosphere associated with Phyan was 0.123 Tg C, which accounted for 85% of the total out-gassing from the eastern Arabian Sea during November. Thus, an increased occurrence of cyclones in a warming environment will lead to an enhanced biomass production and also increase in CO2 out-gassing.

Research areas: Severe Storms
The impacts of horizontal grid spacing and cumulus parameterization on subseasonal prediction in a global convection-permitting model (2020)

Abstract
            
              A novel Bayesian Monte Carlo integration (BMCI) technique was developed to retrieve geophysical variables from satellite microwave radiometer data in the presence of tropical cyclones. The BMCI technique includes three steps: generating a stochastic database, simulating satellite brightness temperatures using a radiative transfer model, and retrieving geophysical variables such as profiles of temperature, relative humidity, and cloud liquid and ice water content from real observations. The technique also provides uncertainty estimates for each retrieval and can output the error covariance matrix of selected parameters. The measurements from the Advanced Technology Microwave Sounder (ATMS) on board
              Suomi National Polar-Orbiting Partnership
              (
              Suomi NPP
              ) and the Global Precipitation Measurement (GPM) Microwave Imager (GMI) were used as input. A new technique was developed to correct the ATMS and GMI observations for the beam-filling effect, which is due to small-scale variability of precipitation and clouds when compared with the instrument footprint and also the nonlinear relation between the brightness temperature and precipitation. In addition, the assimilation of the BMCI retrievals into the NASA GEOS model is discussed for Hurricane Maria. The results show that assimilating the BMCI retrievals can influence the dynamical features of the cyclone, including a stronger warm core, a symmetric eye, and vertically aligned wind columns. Two possible factors that may limit the impact of the BMCI retrievals include 1) the resolution of the model (about 25 km), which was too coarse to show the potential of the BMCI data in improving the representation of tropical storms in the model forecast, and 2) the data assimilation system not being able to consider vertically correlated observation errors.

Research areas: Severe Storms