nasa-gesdisc/es-publications-researchareas huggingface dataset:
Spatial distribution of the iron supply to phytoplankton in the Southern Ocean: a model study (2009)

Abstract. An upgraded version of the biogeochemical model SWAMCO is coupled to the ocean-sea-ice model NEMO-LIM to explore processes governing the spatial distribution of the iron supply to phytoplankton in the Southern Ocean. The 3-D NEMO-LIM-SWAMCO model is implemented in the ocean domain south of latitude 30 S and runs are performed over September 1989December 2000. Model scenarios include potential iron sources (atmospheric deposition, iceberg calving/melting and continental sediments) as well as iron storage within sea ice, all formulated based on a literature review. When all these processes are included, the simulated iron profiles and phytoplankton bloom distributions show satisfactory agreement with observations. Analyses of simulations and sensitivity tests point to the key role played by continental sediments as a primary source for iron. Iceberg calving and melting contribute by up to 25% of Chl-a simulated in areas influenced by icebergs while atmospheric deposition has little effect at high latitudes. Activating sea ice-ocean iron exchanges redistribute iron geographically. Stored in the ice during winter formation, iron is then transported due to ice motion and is released and made available to phytoplankton during summer melt, in the vicinity of the marginal ice zones. Transient iron storage and transport associated with sea ice dynamics stimulate summer phytoplankton blooming (up to 3 mg Chl-a m-3 in the Weddell Sea and off East Antarctica but not in the Ross, Bellingshausen and Amundsen Seas. This contrasted feature results from the simulated variable content of iron in sea ice and release of melting ice showing higher ice-ocean iron fluxes in the continental shelves of the Weddell and Ross Seas than in the Eastern Weddell Sea and the Bellingshausen-Amundsen Seas. This study confirms that iron sources and transport in the Southern Ocean likely provide important mechanisms in the geographical development of phytoplankton blooms and associated ecosystems.

Research areas: Ecosystems
Rift Valley fever in a zone potentially occupied by Aedes vexans in Senegal: dynamics and risk mapping (2009)

This paper presents an analysis of the interaction between the various variables associated with Rift Valley fever (RVF) such as the mosquito vector, available hosts and rainfall distribution. To that end, the varying zones potentially occupied by mosquitoes (ZPOM), rainfall events and pond dynamics, and the associated exposure of hosts to the RVF virus by Aedes vexans, were analyzed in the Barkedji area of the Ferlo, Senegal, during the 2003 rainy season. Ponds were identified by remote sensing using a high-resolution SPOT-5 satellite image. Additional data on ponds and rainfall events from the Tropical Rainfall Measuring Mission were combined with in-situ entomological and limnimetric measurements, and the localization of vulnerable ruminant hosts (data derived from QuickBird satellite). Since Ae. vexans productive events are dependent on the timing of rainfall for their embryogenesis (six days without rain are necessary to trigger hatching), the dynamic spatio-temporal distribution of Ae. vexans density was based on the total rainfall amount and pond dynamics. Detailed ZPOM mapping was obtained on a daily basis and combined with aggressiveness temporal profiles. Risks zones, i.e. zones where hazards and vulnerability are combined, are expressed by the percentages of parks where animals are potentially exposed to mosquito bites. This new approach, simply relying upon rainfall distribution evaluated from space, is meant to contribute to the implementation of a new, operational early warning system for RVF based on environmental risks linked to climatic and environmental conditions.

Research areas: Public Health, Ecosystems
Remote sensing of mineral dust over land with MSG infrared channels: A new Bitemporal Mineral Dust Index (2009)

A new Bitemporal Mineral Dust Index (BMDI) is derived from Meteosat Second Generation (MSG) infrared observations over land at two different time slots per day. This daily dust index is evaluated with AErosol RObotic NETwork (AERONET) surface observations, MODerate resolution Imaging Spectro-radiometer (MODIS) Deep Blue Aerosol Optical Depth (AOD) and Ozone Monitoring Instrument (OMI) Aerosol Index, showing a good capability of the BMDI for dust detection and dust load estimation over land and also over deserts. BMDI dust detection is shown to be limited in scenes with high atmospheric humidity as e.g. coastal regions. In particular the insensitivity of BMDI to biomass burning aerosol is shown, leading to the possibility of remote sensing of mineral dust also in regions with large contributions of biomass burning aerosol to the total column aerosol concentrations. Time series of mineral dust as inferred from BMDI for the year 2006 are presented for four regions over the Sahara. These time series show strong (and different) annual cycles of dust load for all four regions. Especially the strong episodic character of atmospheric dust in the main source regions can be inferred from BMDI observations.

Research areas: Validation
Quantitative observation of cyanobacteria and diatoms from space using PhytoDOAS on SCIAMACHY data (2009)

Abstract. In this study the technique of Differential Optical Absorption Spectroscopy (DOAS) has been adapted for the retrieval of the absorption and biomass of two major phytoplankton groups (PhytoDOAS) from data of the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) satellite sensor. SCIAMACHY measures back scattered solar radiation in the UV-Vis-NIR spectral regions with a high spectral resolution (0.2 to 1.5 nm). In order to identify phytoplankton absorption characteristics in the SCIAMACHY data in the range of 430 to 500 nm, phytoplankton absorption spectra measured in-situ during two different RV "Polarstern" expeditions were used. The two spectra have been measured in different ocean regions where different phytoplankton groups (cyanobacteria and diatoms) dominated the phytoplankton composition. Results clearly show distinct absorption characteristics of the two phytoplankton groups in the SCIAMACHY spectra. Using these results in addition to calculations of the light penetration depth derived from DOAS retrievals of the inelastic scattering (developed by Vountas et al., 2007), globally distributed pigment concentrations for these characteristic phytoplankton groups for two monthly periods (FebruaryMarch 2004 and OctoberNovember 2005) were determined. This satellite information on cyanobacteria and diatoms distribution clearly matches the concentrations based on high pressure liquid chromatography (HPLC) pigment analysis of collocated water samples and concentrations derived from a global model analysis with the NASA Ocean Biogeochemical Model (Gregg et al., 2003; Gregg and Casey 2007). The quantitative assessment of the distribution of key phytoplankton groups from space enables various biogeochemical regions to be distinguished and will be of great importance for the global modeling of marine ecosystems and biogeochemical cycles which enables the impact of climate change in the oceanic biosphere to be estimated.

Research areas: Ecosystems
New insights into the spatial variability of the surface water carbon dioxide in varying sea ice conditions in the Arctic Ocean (2009)

In the summer of 2005, continuous surface water measurements of fugacity of CO2 (fCO2sw), salinity and temperature were performed onboard the IB Oden along the Northwest Passage from Cape Farwell (South Greenland) to the Chukchi Sea. The aim was to investigate the importance of sea ice and river runoff on the spatial variability of fCO2 and the seaair CO2 fluxes in the Arctic Ocean. Additional data was obtained from measurements of total alkalinity (AT) by discrete surface water and water column sampling in the Canadian Arctic Archipelago (CAA), on the Mackenzie shelf, and in the Bering Strait. The linear relationship between AT and salinity was used to evaluate and calculate the relative fractions of sea ice melt water and river runoff along the cruise track. High-frequency fCO2sw data showed rapid changes, due to variable sea ice conditions, freshwater addition, physical upwelling and biological processes. The fCO2sw varied between 102 and 678atm. Under the sea ice in the CAA and the northern Chukchi Sea, fCO2sw were largely CO2 undersaturated of approximately 100atm lower than the atmospheric level. This suggested CO2 uptake by biological production and limited seaair CO2 gas exchange due to the ice cover. In open areas, such as the relatively fresh water of the Mackenzie shelf and the Bering Strait, the fCO2sw values were close to the atmospheric CO2 level. Upwelling of saline and relatively warm water at the Cape Bathurst caused a dramatic fCO2sw increase of about 100atm relative to the values in the CAA. At the southern part of the Chukchi Peninsula we found the highest fCO2sw values and the water was CO2 supersaturated, likely due to upwelling. In the study area, the calculated seaair CO2 flux varied between an oceanic CO2 sink of 140mmolm2d1 and an oceanic source of 18mmolm2d1. However, in the CAA and the northern Chukchi Sea, the sea ice cover prevented gas exchange, and the CO2 fluxes were probably negligible at this time of the year. Assuming that the water was exposed to the atmosphere by total melting and gas exchange would be the only process, the CO2 undersaturated water in the ice-covered areas will not have the time to reach the atmospheric CO2 value, before the formation of new sea ice. This study highlights the value of using high-frequency measurements to gain increased insight into the variable and complex conditions, encountered on the shelves in the Arctic Ocean.

Research areas: Atmospheric/Ocean Indicators
Investigations of an intense aerosol loading during 2007 cyclone SIDR  A study using satellite data and ground measurements over Indian region (2009)

Tropical cyclones are prominent weather systems characterized by high atmospheric pressure gradients and wind speeds. Intense tropical cyclones occur in India during the pre-monsoon (spring), early monsoon (early summer), or post-monsoon (fall) periods. Originating in both the Bay of Bengal (BoB) and the Arabian Sea (AS), these tropical cyclones often attain velocities of more than 100 km h1 and are notorious for causing intense rain and storm surge as they cross the Indian coast. In this study, we examine the changes in the aerosol properties associated with an intense tropical cyclone SIDR, that occurred during 1116 November 2007 over BoB. This cyclone, accompanied with very strong surface winds reaching 223 km h1, caused extensive damage over Bangladesh. Ground-based measurements of Aerosol Optical Depth (AOD) in the neighboring urban environment of Hyderabad, India, showed significant variations due to changes in wind velocity and direction associated with the cyclone passage. The Terra-MODIS and AVHRR satellite images showed prevalence of dust particles mixed with emissions from anthropogenic sources and biomass-burning AS, while the aerosol loading over BoB was significantly lower. The positive values of Aerosol index (AI) obtained from the Ozone Monitoring Instrument (OMI) suggested the presence of an elevated aerosol layer over the West coast of India, AS and Thar Desert during and after the cyclone episode. Meteorological parameters from the MM5 mesoscale model were used to study the variations in winds associated with the cyclonic activity. Particulate matter loading over the region during the cyclone period increased by 45% with an accompanying decrease in columnar aerosol optical depth. The variations in Angstrom parameters suggested coarse-mode particle loading due to dust aerosols as observed in satellite data.

Research areas: Severe Storms, Environmental Impacts
Direct measurements of the effect of biomass burning over the Amazon on the atmospheric temperature profile (2009)

Abstract. Aerosols suspended in the atmosphere interact with solar radiation and clouds, thus change the radiation energy fluxes in the atmospheric column. In this paper we measure changes in the atmospheric temperature profile as a function of the smoke loading and the cloudiness, over the Amazon basin, during the dry seasons (August and September) of 20052008. We show that as the aerosol optical depth (AOD) increases from 0.02 to a value of ~0.6, there is a decrease of ~4C at 1000 hPa, and an increase of ~1.5C at 850 hPa. The warming of the aerosol layer at 850 hPa is likely due to aerosol absorption when the particles are exposed to direct illumination by the sun. The large values of cooling in the lower layers could be explained by a combination of aerosol extinction of the solar flux in the layers aloft together with an aerosol-induced increase of cloud cover which shade the lower atmosphere. We estimate that the increase in cloud fraction due to aerosol contributes about half of the observed cooling in the lower layers.

Research areas: Atmospheric/Ocean Indicators, Environmental Impacts
High Latitude Changes in Ice Dynamics and Their Impact on Polar Marine Ecosystems (2008)

Polar regions have experienced significant warming in recent decades. Warming has been most pronounced across the Arctic Ocean Basin and along the Antarctic Peninsula, with significant decreases in the extent and seasonal duration of sea ice. Rapid retreat of glaciers and disintegration of ice sheets have also been documented. The rate of warming is increasing and is predicted to continue well into the current century, with continued impacts on ice dynamics. Climate-mediated changes in ice dynamics are a concern as ice serves as primary habitat for marine organisms central to the food webs of these regions. Changes in the timing and extent of sea ice impose temporal asynchronies and spatial separations between energy requirements and food availability for many higher trophic levels. These mismatches lead to decreased reproductive success, lower abundances, and changes in distribution. In addition to these direct impacts of ice loss, climate-induced changes also facilitate indirect effects through changes in hydrography, which include introduction of species from lower latitudes and altered assemblages of primary producers. Here, we review recent changes and trends in ice dynamics and the responses of marine ecosystems. Specifically, we provide examples of ice-dependent organisms and associated species from the Arctic and Antarctic to illustrate the impacts of the temporal and spatial changes in ice dynamics.

Research areas: Cryospheric Indicators, Ecosystems
Spatial variability of regional model simulated JuneSeptember mean precipitation over West Africa (2007)

The study examines the spatial variability of JuneSeptember 2003 mean precipitation rates (Pr03) simulated by a regional climate model on a horizontal grid with 0.5 spacing. In particular, it evaluates the relative impact of different initial conditions versus the influence of the lateral boundary conditions (LBC), and it compares small spatial scale distributions of modeled Pr03 to data from the Tropical Rainfall Measuring Mission (TRMM) and the NOAA Climate Prediction Center data for the African Famine Early Warning System (FEWS). Simulations over West Africa were made with the CCSR/GISS RM3, driven by synchronous data from NCEP reanalysis. A five-member ensemble for a single season was generated by staggering the initial conditions of each member by 36 hr within the period May 915, 2003. Results showed that the LBC influence dominated over that of differing initial conditions, implying that the precipitation simulations suffered little contamination of random noise. In a second evaluation, small spatial scale distributions of Pr03 were computed as the difference between Pr03 and spatially smoothed fields. Spatial correlations between the RM3 product versus the TRMM and FEWS small-scale components of Pr03 were highest using TRMM data provided at 1 elements. Results suggest that the model may be challenged to simulate realistic small-scale features of the seasonal mean precipitation field, and/or that observational data sets do not adequately capture these fine spatial features.

Research areas: Validation
Spatial and temporal operation of the Scotia Sea ecosystem: a review of large-scale links in a krill centred food web (2007)

The Scotia Sea ecosystem is a major component of the circumpolar Southern Ocean system, where productivity and predator demand for prey are high. The eastward-flowing Antarctic Circumpolar Current (ACC) and waters from the WeddellScotia Confluence dominate the physics of the Scotia Sea, leading to a strong advective flow, intense eddy activity and mixing. There is also strong seasonality, manifest by the changing irradiance and sea ice cover, which leads to shorter summers in the south. Summer phytoplankton blooms, which at times can cover an area of more than 0.5 million km2, probably result from the mixing of micronutrients into surface waters through the flow of the ACC over the Scotia Arc. This production is consumed by a range of species including Antarctic krill, which are the major prey item of large seabird and marine mammal populations. The flow of the ACC is steered north by the Scotia Arc, pushing polar water to lower latitudes, carrying with it krill during spring and summer, which subsidize food webs around South Georgia and the northern Scotia Arc. There is also marked interannual variability in winter sea ice distribution and sea surface temperatures that is linked to southern hemisphere-scale climate processes such as the El NinoSouthern Oscillation. This variation affects regional primary and secondary production and influences biogeochemical cycles. It also affects krill population dynamics and dispersal, which in turn impacts higher trophic level predator foraging, breeding performance and population dynamics. The ecosystem has also been highly perturbed as a result of harvesting over the last two centuries and significant ecological changes have also occurred in response to rapid regional warming during the second half of the twentieth century. This combination of historical perturbation and rapid regional change highlights that the Scotia Sea ecosystem is likely to show significant change over the next two to three decades, which may result in major ecological shifts.

Research areas: Ecosystems, Cryospheric Indicators
Assessing posttsunami effects on ocean colour at eastern Indian Ocean using MODIS Aqua satellite (2007)

The 2004 Indian Ocean tsunami had been reported to cause vast destruction on marine environment, but its effect on the primary production and upwelling event was unknown. Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua ocean colour imageries were used to assess the tsunami effects on the chlorophylla (chla) and turbidity variations. Chlorophylla and normalized water leaving radiance at 551 nm (nLw 551) before and after the tsunami event were processed using SeaWiFS data analysis system (SeaDAS), and the variations were examined. Results showed a sudden increase of chla and nLw 551 at the northwestern Sumatra and middle of Malacca Straits (MS) after the tsunami. At western Sumatra, high sedimentation caused by the backwash resulted in overestimation of the chla values. However, the chla in the upwelling area in the northern MS did not exhibit any significant changes. The chla variation in the northern MS was found to be related to the monsoon wind with about one week time lag. At the seriously eroded coastline along western Sumatra, continuous sedimentation was observed. The sedimentation problem became more severe during higher rainfall periods in April 2005. We strongly suggest a long term monitoring of this sedimentation problem.

Research areas: Earthquakes
Changes of surface recovery at coseismic landslides and their driving factors in the Wenchuan earthquake-affected area (2022)

A major earthquake can trigger numerous landslides, which exert severe impacts on regional vegetation coverage. In some years following an earthquake, rainstorms can easily reactivate coseismic deposits and unstable hillslopes. Vegetation can improve the post-seismic slope instability by the root reinforcement effect, and it is significant to investigate the changes of surface recovery at coseismic landslides for a long-term assessment of post-earthquake geohazards. However, due to limited earth observations, it remains elusive that how long the surface vegetation of coseismic landslides caused by the 2008 Wenchuan earthquake will recover to the pre-earthquake level. We studied the long-term evolution of surface recovery in coseismic landslide-affected areas using multi-temporal Landsat images from 2000 to 2020. We calculated the vegetation recovery rates in different periods, which were used to quantify the rate of vegetation regrowth and landslide activity intensity. We found that 71.34% of the affected areas have been properly revegetated, and the area percentage of landslides in high activity, middle activity, low activity and dormant were 17.6%, 12.4%, 17.7% and 52.3%, respectively in 2020. To examine the factors controlling the surface recovery at coseismic landslides, we further analyzed the relationships between landslide recovery and eighteen influencing factors, and we found that elevation, peak ground acceleration, rainfall, lithology and gully density are the key factors that control landslide surface recovery over all others. Overall the trend of surface recovery at coseismic landslides suggests that the impact of the Wenchuan earthquake on the activities of shallow landslides almost ceases within 17 years in the Wenchuan earthquake-affected areas.

Research areas: Earthquakes, Land Surface/Agriculture Indicators
Surface ozone in Indian urban region (2022)

Atmospheric ozone has witnessed a steady increase attributable to anthropogenic activities aligned with the socioeconomic development of cities. Primary pollutants such as particulate matter, carbon monoxide, and nitrogen oxides have been given utmost priority in the air quality assessment studies conducted in the past. Ozone, one of the most important greenhouse gases, has been regarded as a major global concern due to its adverse impacts on the environment, human health, and vegetation. An understanding about the long-term as well as the short-term trends, underlying chemistry and prominent contributing factors for the accumulation of ozone in urban environments, is one of the key aspects that requires due consideration while developing the strategy for restricting its accumulation in the environment. In view of this, the present study aims to enrich the existing literature on ozone accumulation in urban settings by assessing the variability in ozone levels in Delhi city over a period of 10 years between 2008 and 2018 using satellite observations. The analysis in the present study has been restricted to assess the variations in the levels of total columnar ozone (TOC), nitrogen dioxide (NO2), and solar radiation (SR) over Delhi to assess the variations in surface ozone. The results of the analysis revealed that the pollutant has followed an increasing trend over the study region between 2008 and 2018, which is sure to increase in the future. TOC has witnessed an irregular trend over Delhi city between 2008 and 2018 with a significant rise from 2013 to 2015, indicating the need to restrain these levels. Furthermore, numerous studies have highlighted that the increasing levels of surface ozone pose various environmental, human health, and agricultural challenges. Thus, in view of this, the present study provides a preliminary analysis of long-term trends of surface ozone over Delhi city to strategize interventions and actions to restrict the increase in this new-age pollutant.

Research areas: Air Quality