nasa-gesdisc/es-publications-researchareas huggingface dataset:
A Simple Technique for Creating Regional Composites of Sea Surface Temperature from MODIS for Use in Operational Mesoscale NWP (2010)

This paper describes a simple technique for creating regional, high-resolution, daytime and nighttime composites of sea surface temperature (SST) for use in operational numerical weather prediction (NWP). The composites are based on observations from NASAs Moderate Resolution Imaging Spectroradiometer (MODIS) aboard Aqua and Terra. The data used typically are available nearly in real time, are applicable anywhere on the globe, and are capable of roughly representing the diurnal cycle in SST. The composites resolution is much higher than that of many other standard SST products used for operational NWP, including the low- and high-resolution Real-Time Global (RTG) analyses. The difference in resolution is key because several studies have shown that highly resolved SSTs are important for driving the airsea interactions that shape patterns of static stability, vertical and horizontal wind shear, and divergence in the planetary boundary layer. The MODIS-based composites are compared to in situ observations from buoys and other platforms operated by the National Data Buoy Center (NDBC) off the coasts of New England, the mid-Atlantic, and Florida. Mean differences, mean absolute differences, and root-mean-square differences between the composites and the NDBC observations are all within tenths of a degree of those calculated between RTG analyses and the NDBC observations. This is true whether or not one accounts for the mean offset between the skin temperatures of the MODIS dataset and the bulk temperatures of the NDBC observations and RTG analyses. Near the coast, the MODIS-based composites tend to agree more with NDBC observations than do the RTG analyses. The opposite is true away from the coast. All of these differences in point-wise comparisons among the SST datasets are small compared to the 1.0C accuracy of the NDBC SST sensors. Because skin-temperature variations from land to water so strongly affect the development and life cycle of the sea breeze, this phenomenon was chosen for demonstrating the use of the MODIS-based composite in an NWP model. A simulated sea breeze in the vicinity of New York City and Long Island shows a small, net, but far from universal improvement when MODIS-based composites are used in place of RTG analyses. The timing of the sea breezes arrival is more accurate at some stations, and the near-surface temperature, wind, and humidity within the breeze are more realistic.

Research areas: Validation
African Dust over the Northern Tropical Atlantic: 19552008 (2010)

African dust outbreaks are the result of complex interactions between the land, atmosphere, and oceans, and only recently has a large body of work begun to emerge that aims to understand the controls onand impacts ofAfrican dust. At the same time, long-term records of dust outbreaks are either inferred from visibility data from weather stations or confined to a few in situ observational sites. Satellites provide the best opportunity for studying the large-scale characteristics of dust storms, but reliable records of dust are generally on the scale of a decade or less. Here the authors develop a simple model for using modern and historical data from meteorological satellites, in conjunction with a proxy record for atmospheric dust, to extend satellite-retrieved dust optical depth over the northern tropical Atlantic Ocean from 1955 to 2008. The resultant 54-yr record of dust has a spatial resolution of 1 and a monthly temporal resolution. From analysis of the historical dust data, monthly tropical northern Atlantic dust cover is bimodal, has a strong annual cycle, peaked in the early 1980s, and shows minimums in dustiness during the beginning and end of the record. These dust optical depth estimates are used to calculate radiative forcing and heating rates from the surface through the top of the atmosphere over the last half century. Radiative transfer simulations show a large net negative dust forcing from the surface through the top of the atmosphere, also with a distinct annual cycle, and mean tropical Atlantic monthly values of the surface forcing range from 3 to 9 W m2. Since the surface forcing is roughly a factor of 3 larger in magnitude than the top-of-the-atmosphere forcing, there is also a positive heating rate of the midtroposphere by dust.

Research areas: Atmospheric/Ocean Indicators
Aerosol remote sensing in polar regions (2015)

Multi-year sets of ground-based sun-photometer measurements conducted at 12 Arctic sites and 9 Antarctic sites were examined to determine daily mean values of aerosol optical thickness () at visible and near-infrared wavelengths, from which best-fit values of Angstrom's exponent  were calculated. Analysing these data, the monthly mean values of (0.50 m) and  and the relative frequency histograms of the daily mean values of both parameters were determined for winterspring and summerautumn in the Arctic and for austral summer in Antarctica. The Arctic and Antarctic covariance plots of the seasonal median values of  versus (0.50 m) showed: (i) a considerable increase in (0.50 m) for the Arctic aerosol from summer to winterspring, without marked changes in ; and (ii) a marked increase in (0.50 m) passing from the Antarctic Plateau to coastal sites, whereas  decreased considerably due to the larger fraction of sea-salt aerosol. Good agreement was found when comparing ground-based sun-photometer measurements of () and  at Arctic and Antarctic coastal sites with Microtops measurements conducted during numerous AERONET/MAN cruises from 2006 to 2013 in three Arctic Ocean sectors and in coastal and off-shore regions of the Southern Atlantic, Pacific, and Indian Oceans, and the Antarctic Peninsula.

Lidar measurements were also examined to characterise vertical profiles of the aerosol backscattering coefficient measured throughout the year at Ny-Alesund. Satellite-based MODIS, MISR, and AATSR retrievals of () over large parts of the oceanic polar regions during spring and summer were in close agreement with ship-borne and coastal ground-based sun-photometer measurements. An overview of the chemical composition of mode particles is also presented, based on in-situ measurements at Arctic and Antarctic sites. Fourteen log-normal aerosol number size-distributions were defined to represent the average features of nuclei, accumulation and coarse mode particles for Arctic haze, summer background aerosol, Asian dust and boreal forest fire smoke, and for various background austral summer aerosol types at coastal and high-altitude Antarctic sites. The main columnar aerosol optical characteristics were determined for all 14 particle modes, based on in-situ measurements of the scattering and absorption coefficients. Diurnally averaged direct aerosol-induced radiative forcing and efficiency were calculated for a set of multimodal aerosol extinction models, using various Bidirectional Reflectance Distribution Function models over vegetation-covered, oceanic and snow-covered surfaces. These gave a reliable measure of the pronounced effects of aerosols on the radiation balance of the surfaceatmosphere system over polar regions.

Research areas: Validation
An improved understanding of the Alaska Coastal Current: The application of a bivalve growth-temperature model to reconstruct freshwater-influenced paleoenvironments (2011)

Shells of intertidal bivalve mollusks contain sub-seasonally to interannually resolved records of temperature and salinity variations in coastal settings. Such data are essential to understand changing land-sea interactions through time, specifically atmospheric (precipitation rate, glacial meltwater, river discharge) and oceanographic circulation patterns; however, independent temperature and salinity proxies are currently not available. We established a model for reconstructing daily water temperatures with an average standard error of ,1.3 6C based on variations in the width of lunar daily growth increments of Saxidomus gigantea from southwestern Alaska, United States. Temperature explains 70% of the variability in shell growth. When used in conjunction with stable oxygen isotope data, this approach can also be used to identify changes in past seawater salinity. This study provides a better understanding of the hydrological changes related to the Alaska Coastal Current (ACC). In combination with d18Oshell values, increment-derived temperatures were used to estimate salinity changes with an average error of 1.4  1.1 PSU. Our model was calibrated and tested with modern shells and then applied to archaeological specimens. As derived from the model, the time interval of 9881447 cal yr BP was characterized by ,12 6C colder and much drier (25 PSU) summers. During that time, the ACC was likely flowing much more slowly than at present. In contrast, between 5991014 cal yr BP, the Aleutian low may have been stronger, which resulted in a 3 6C temperature decrease during summers and 12 PSU fresher conditions than today; the ACC was probably flowing more quickly at that time. The shell growthtemperature model can be used to estimate seasonal to interannual salinity and temperature changes in freshwater-influenced environments through time.

Research areas: Atmospheric/Ocean Indicators, Ecosystems
Aerosol optical and radiative properties during summer and winter seasons over Lahore and Karachi (2012)

The study of aerosol optical and radiative properties presented here focuses on a geographic region in which there exist significant gaps in our knowledge. These properties have been analyzed through the ground-based Aerosol Robotic Network (AERONET) over the two megacities of Lahore and Karachi for summer (AprilJune) and winter (DecemberFebruary) of 201011. During the study period the monthly mean aerosol optical depth (AOD) at 500 nm over Lahore ranged from 0.57  0.18 to 0.76  0.38, and the monthly mean Angstrom exponent () ranged from 0.39  0.17 to 1.22  0.13. Likewise, over Karachi the monthly mean AOD ranged from 0.33  0.11 to 0.63  0.28 and the  values varied between 0.29  0.08 to 0.95  0.22. The average AOD values in summer and winter are 0.66  0.30, 0.50  0.18 and 0.67  0.40, 0.34  0.12 in Lahore and Karachi respectively. The relationship between the Absorption Angstrom Exponent (AAE) and the Extinction Angstrom Exponent (EAE) provided an indication of the relative proportions of urban-industrial and mineral dust aerosols over the two sites. The volume size distributions were higher over Lahore than over Karachi during both seasons. The single scattering albedo (SSA) ranged from 0.83  0.02 (440 nm) to 0.91  0.05 (1020 nm) over Lahore and from 0.88  0.02 (440 nm) to 0.97  0.01 (1020 nm) over Karachi. The lower SSA values over Lahore suggest that absorbing aerosols are more dominant over Lahore than over Karachi. The average aerosol radiative forcing (ARF) values in summer at the surface and the top of atmosphere (TOA) are 101.6  8.2, 63.3  9.5 and 19  4.35, 20  3.1 over Lahore and Karachi respectively. Likewise, the average ARF values in winter at the surface and TOA are 90.3  21.03, 57  6.35 and 26  7, 16  2.3 over Lahore and Karachi respectively. The averaged aerosol ARF values over Lahore and Karachi for the entire period covered by the observations were 22.5  5.9 W m2 and 18  2.2 W m2 at the TOA and 96  13 W m2 and 60  6.8 W m2 at the surface, respectively, giving an averaged atmospheric forcing of 74.56  16.8 W m2 over Lahore and 41.85  6.4 W m2 over Karachi, which indicates significant heating of the atmosphere at both sites. The average heating rate during summer was 2.3  0.1 and 1.2  0.2 K day1 and during winter was 1.8  0.4 and 1.1  0.1 K day1 over Lahore and Karachi respectively.

Research areas: Atmospheric/Ocean Indicators
Dust emission and transport associated with a Saharan depression: February 2007 case (2010)

The dust activity over North Africa associated with the Saharan depression event in February 2007 is investigated by mean of spaceborne observations, ground-based measurements, and mesoscale simulation with Meso-NH. The main characteristics of the cyclone as well as the meteorological conditions during this event are described using the European Centre for Medium-Range Weather Forecasts (ECMWF). The dust storm and cloud cover over North Africa is thoroughly described combining for the first time Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) images for the spatiotemporal evolution and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) and CloudSat observations for the vertical distribution. The Saharan depression formed over Algeria in the lee of the Atlas Mountains on the afternoon of 20 February in response to midlatitude trough intrusion. It migrated eastward with a speed of 11 m s1 and reached Libya on 22 February before exiting the African continent toward the Mediterranean Sea on 23 February. The horizontal scale of the cyclone at the surface varied between 800 and 1000 km during its lifetime. On the vertical the cyclone extended over 8 km, and a potential vorticity of 2 potential vorticity units (PVU) was reported at its center at 3 km in altitude. The cyclone was characterized by a surface pressure anomaly of about 9 hPa with respect to the environment, a warm front typified at the surface by an increase in surface temperature of 5C, and a sharp cold front characterized by a drop in surface temperature of 8C and an increase in 10 m wind speed of 15 m s1. The cyclone provided dynamical forcing that led to strong near-surface winds and produced a major dust storm over North Africa. The dust was transported all around the cyclone leaving a clear eye at its center and was accompanied by a deep cloud band along the northwestern edge of the cyclone. On the vertical, slanted dust layers were consistently observed during the event over North Africa. Furthermore, the dust was lofted to altitudes as high as 7 km, becoming subject to long-range transport. The model was able to reasonably reproduce the structure, lifetime, and trajectory of the cyclone. Also, comparison with Moderate Resolution Imaging Spectrometer (MODIS) deep blue aerosol optical depths and CALIPSO-CloudSat observations suggests that the model can be reliably used to quantify the dust emissions associated with this event. The mean daily dust loads over the area influenced by the cyclone were simulated to range between 2 and 8 Tg during the lifetime of the Sharav cyclone (i.e., 5 days). This study suggests that dust emissions linked with Saharan cyclones may contribute significantly to the total dust load over West and North Africa observed annually.

Research areas: Severe Storms
Diving seabirds share foraging space and time within and among species (2010)

Ecological theory predicts that animals with similar foraging strategies should not be able to co-exist without segregating either in space, time or diet. In communities, intra-specific competition is thought to be more intense than the competition among species, because of the lack of niche partitioning between conspecifics. Hence, while different seabird species can overlap in their foraging distribution, intra-specific competition can drive the neighboring populations of the same species to spatial segregation of foraging areas. To investigate ecological segregation within and among species of diving seabirds, we used a multi-species GPS-tracking approach of seabirds of four species on a small island in the Southwest Atlantic. The present study goes beyond previous work by analyzing simultaneous effects of species and colonies. We observed strikingly strong spatial foraging segregation among birds of the same species, breeding in colonies as close as 2 km from each other. Conspecifics from neighboring colonies used foraging places adjacent to their own colony, and there was little or no overlap with birds from the other colony. A zone with increased predator concentration was completely avoided during foraging trips, likely contributing to the spatial segregation. In addition to spatial segregation, we also observed intra-specific differences in other components of foraging behavior, such as time of day, dive depth and diet. These were most likely caused by optimal foraging of individuals in relation to habitat differences on a local scale, leading to a complex pattern of interactions with environmental covariates, in particular foraging daytime, foraging water layer temperature and depth, distance to coast and bathymetric depth of foraging areas. As mechanisms leading to the spatial segregation we propose a combination of optimal foraging and avoidance of predation.

Research areas: Ecosystems
Distribution of dissolved iron in Antarctic sea ice: Spatial, seasonal, and inter-annual variability (2010)

Results from recent field studies in Antarctic sea ice show no clear differences in dissolved iron (dFe) concentrations between pack ice sampled in East Antarctica (2.620.5 nmol/L), in the Weddell Sea (0.736.8 nmol/L), and in the Bellingshausen Sea (1.130.2 nmol/L). Dissolved Fe concentrations were also similar in land-fast ice collected in East Antarctica (0.74.3 nmol/L) and in the Ross Sea (1.16.0 nmol/L). In contrast, we observed a remarkable seasonal drawdown of dFe in sea ice for all reported studies. Furthermore, large inter-annual variations in depth-averaged dFe and organic matter concentrations were observed in sea ice collected in the East Antarctic sector between expeditions in late austral winter-spring of 2003 and 2007. Variability in the water column productivity and in the magnitude of the new Fe supply (e.g., upwelling, resuspended shelf sediments) at the time of sea ice formation could explain such differences.

Research areas: Ecosystems
Distribution and diversity of open-ocean, near-bottom macroplankton in the western Mediterranean: Analysis at different spatio-temporal scales (2010)

We analyzed the distribution, diversity, and composition of western Mediterranean macroplankton (excluding gelatinous taxa) in the water column over depths of ca. 550850m, with special attention to near-bottom (01.5 and ca. 577m above the bottom, mab) levels, and including data from three areas (off the coasts of Catalonia, and to the NW, and SE of Mallorca, Balearic Islands) in the period 19912008. Spatio-temporal changes in macroplankton abundance were evaluated as follows: (i) by seasonal sampling in 2007 off the Catalonian coast, (ii) by comparing Catalonian and Balearic Island slopes, and (iii) by comparing a fixed station on the Catalonian slope (at 550800m depth) at decadal (1991/19922007/2008) time scales. Diversity (in terms of species richness, S) was greater (i) at ca. 577 mab than at 01.5mab, (ii) over the insular slopes of the Balearic Island (around Mallorca) than over the mainland Catalonian slopes, and (iii) in the period 1991/1992 than in 2007, likely related to higher values of the North Atlantic Oscillation (NAO) index in 1991/1992. In most analyses species composition was strongly influenced by the degree of stratification and homogenization of the water column in summerautumn and winterspring respectively and by location (longitude). Changes consisted mainly of higher density of macroplankton (e.g. abundance of the dominant euphausiids Nematoscelis megalops, Meganyctiphanes norvegica and Euphausia krohni and of the fish Cyclothone braueri) between June and October, parallel to an increase in the T and S close to the bottom. This coincided with changes in the flow of Levantine intermediate water (LIW) in the area. Aggregation of adult forms of the dominant species close to the bottom in summerautumn could be favored because summer is the period of highest density of food  copepods, mainly Calanus helgolandicus  near the bottom off the Catalan slope. The formation of a thermocline in the water column and the reinforcement of the permanent thermohaline front at the shelf-slope break during summer at ca. 400m in the Balearic Basin may also enhance this tendency toward greater aggregation of deep macroplankton under stratified water column conditions.

Research areas: Ecosystems
Distribution and burial of organic carbon in sediments from the Indian Ocean upwelling region off Java and Sumatra, Indonesia (2010)

Sediments were sampled and oxygen profiles of the water column were determined in the Indian Ocean off west and south Indonesia in order to obtain information on the production, transformation, and accumulation of organic matter (OM). The stable carbon isotope composition (13Corg) in combination with C/N ratios depicts the almost exclusively marine origin of sedimentary organic matter in the entire study area. Maximum concentrations of organic carbon (Corg) and nitrogen (N) of 3.0% and 0.31%, respectively, were observed in the northern Mentawai Basin and in the Savu and Lombok basins. Minimum 15N values of 3.7 were measured in the northern Mentawai Basin, whereas they varied around 5.4 at stations outside this region. Minimum bottom water oxygen concentrations of 1.1mLL1, corresponding to an oxygen saturation of 16.1%, indicate reduced ventilation of bottom water in the northern Mentawai Basin. This low bottom water oxygen reduces organic matter decomposition, which is demonstrated by the almost unaltered isotopic composition of nitrogen during early diagenesis. Maximum Corg accumulation rates (CARs) were measured in the Lombok (10.4gCm2yr1) and northern Mentawai basins (5.2gCm2yr1). Upwelling-induced high productivity is responsible for the high CAR off East Java, Lombok, and Savu Basins, while a better OM preservation caused by reduced ventilation contributes to the high CAR observed in the northern Mentawai Basin. The interplay between primary production, remineralisation, and organic carbon burial determines the regional heterogeneity. CAR in the Indian Ocean upwelling region off Indonesia is lower than in the Peru and Chile upwellings, but in the same order of magnitude as in the Arabian Sea, the Benguela, and Gulf of California upwellings, and corresponds to 0.17.1% of the global ocean carbon burial. This demonstrates the relevance of the Indian Ocean margin off Indonesia for the global OM burial.

Research areas: Ecosystems, Atmospheric/Ocean Indicators
Dissolved inorganic carbon dynamics and air-sea carbon dioxide fluxes during coccolithophore blooms in the northwest European continental margin (northern Bay of Biscay) (2010)

We report a data set of dissolved inorganic carbon (DIC) obtained during three cruises in the northern Bay of Biscay carried out in June 2006, May 2007, and May 2008. During these cruises, blooms of the coccolithophore Emiliania huxleyi occurred, as indicated by patches of high reflectance on remote sensing images, phytoplankton pigment signatures, and microscopic examinations. Total alkalinity showed a nonconservative behavior as a function of salinity due to the cumulative effect of net community calcification (NCC) on seawater carbonate chemistry during bloom development. The cumulative effect of NCC and net community production (NCP) on DIC and the partial pressure of CO2 (pCO2) were evaluated. The decrease of DIC (and increase of pCO2) due to NCC was overwhelmingly lower than the decrease of DIC (and decrease of pCO2) due to NCP (NCC:NCP  1). During the cruises, the northern Bay of Biscay acted as a sink of atmospheric CO2 (on average 9.7 mmol C m2 d1 for the three cruises). The overall effect of NCC in decreasing the CO2 sink during the cruises was low (on average 12% of total air-sea CO2 flux). If this is a general feature in naturally occurring phytoplankton blooms in the North Atlantic Ocean (where blooms of coccolithophores are the most intense and recurrent), and in the global ocean, then the potential feedback on increasing atmospheric CO2 of the projected decrease of pelagic calcification due to thermodynamic CO2 production from calcification is probably minor compared to potential feedbacks related to changes of NCP.

Research areas: Ecosystems