nasa-gesdisc/es-publications-researchareas huggingface dataset:
Empirical and semi-analytical chlorophyll a algorithms for multi-temporal monitoring of New Zealand lakes using Landsat (2015)

The concentration of chlorophyll a (chl a; as a proxy for phytoplankton biomass) provides an indication of the water quality and ecosystem health of lakes. An automated image processing method for Landsat images was used to derive chl a concentrations in 12 Rotorua lakes of North Island, New Zealand, with widely varying trophic status. Semi-analytical and empirical models were used to process 137 Landsat 7 Enhanced Thematic Mapper (ETM+) images using records from 1999 to 2013. Atmospheric correction used radiative transfer modelling, with atmospheric conditions prescribed with Moderate Resolution Imaging Spectroradiometer (MODIS) Terra and AIRS data. The best-performing semi-analytical and empirical equations resulted in similar levels of variation explained (r2 = 0.68 for both equations) and root-mean-square error (RMSE = 10.69 and 10.43 g L1, respectively) between observed and estimated chl a. However, the symbolic regression algorithm performed better for chl a concentrations <5 g L1. Our Landsat-based algorithms provide a valuable method for synoptic assessments of chl a across the 12 lakes in this region. They also provide a basis for assessing changes in chl a individual lakes through time. Our methods provide a basis for cost-effective hindcasting of lake trophic status at a regional scale, informing on spatial variability of chl a within and between lakes.

Research areas: Validation
Effect of Cloud Fraction on Near-Cloud Aerosol Behavior in the MODIS Atmospheric Correction Ocean Color Product (2015)

Characterizing the way satellite-based aerosol statistics change near clouds is important for better understanding both aerosol-cloud interactions and aerosol direct radiative forcing. This study focuses on the question of whether the observed near-cloud increases in aerosol optical thickness and particle size may be explained by a combination of two factors: (i) Near-cloud data coming from areas with higher cloud fractions than  far-from-cloud data and (ii) Cloud fraction being correlated with aerosol optical thickness and particle size. This question is addressed through a statistical analysis of aerosol parameters included in the MODIS (MODerate resolution Imaging Spectroradiometer) ocean color product. Results from ten Septembers (20022011) over part of the northeast Atlantic Ocean confirm that the combination of these two factors working together explains a significant but not dominant part (in our case, 15%30%) of mean optical thickness changes near clouds. Overall, the findings show that cloud fraction plays a large role in shaping the way aerosol statistics change with distance to clouds. This implies that both cloud fraction and distance to clouds are important to consider when aerosol-cloud interactions or aerosol direct radiative effects are examined in satellite or modeling studies.

Research areas: Validation
Drought or humidity oscillations? The case of coastal zone of Lebanon (2015)

There is discrepancy in classifying Lebanon according to the different climatic zones; however, it is often described as a semi-arid region. Lately, Lebanon has been witnessing climatic oscillations in the meteorological parameters. The impact of these oscillations on water sector has been reflected also on energy-food nexus. Yet, there are a number of studies obtained to identify the climate of Lebanon, and they show contradictory results; especially these studies elaborated different datasets and applied diverse methods which often modeled only on large-scale regions. Therefore, the analysis of climatic data depended on complete and long-term climatic records that can be applied to assess the existing climatic status of Lebanon, as well as to assure whether Lebanon is under drought, humidity or it is oscillating between both. This study utilized considerable datasets, from different sources including the remotely sensed systems (e.g. TRMM). These datasets were interpolated and analyzed statistically according to De Martonne Aridity Index. Aiming to affirm the climatic attribute of Lebanon; however, ten climatic stations were investigated. They are with representative geographic setting and diverse time series in the coastal zone of Lebanon were investigated. Even though, Lebanon is known as a semi-arid region, yet results in this study show that the studied zone does not evidence any drought, since around 70% of the investigated years are characterized by semi-humid to humid climate. This climatic figure is well pronounced since rainfall rate exceeds 900mm, average temperature rate is about 19C, and snow remains for a couple of months annually.

Research areas: Atmospheric/Ocean Indicators
Distribution of gymnosomatous pteropods in western Antarctic Peninsula shelf waters: influences of Southern Ocean water masses (2015)

Distributions of gymnosomatous pteropods, Spongiobranchaea australis and Clione antarctica, were determined at six sites along a latitudinal gradient in western Antarctica Peninsula shelf waters using vertically stratified trawls. Hydrographic data were collected at the same sites with conductivity-temperature-depth casts, and correlations of explanatory variables to gymnosome distributions were determined using statistical analyses performed in Matlab, a high level programming software to conduct numerical computation and visualisation. Explanatory variables included sampling site, latitude, longitude and depth, seawater temperature, salinity and density, Southern Ocean Antarctic Surface Water, Winter Water, Upper Circumpolar Deep Water and warm transitional waters, as well as oceanographic remote sensing data for coloured dissolved organic matter, chlorophyll a concentration, normalised fluorescence line height, nighttime sea surface temperature, photosynthetically active radiation, particulate inorganic carbon, particulate organic carbon, daytime sea surface temperature and daily sea ice concentration. Hydrographic data revealed that warmer water masses were prevalent along the western Antarctic Peninsula, and the distributions of both gymnosome species were primarily influenced by water masses, temperature, sampling site and latitude. As a consequence, distributional shifts of gymnosomes are predicted in response to the current warming trends.

Research areas: Ecosystems
Dissolved Oxygen Sensor in Animal-Borne Instruments: An Innovation for Monitoring the Health of Oceans and Investigating the Functioning of Marine Ecosystems (2015)

The current decline in dissolved oxygen concentration within the oceans is a sensitive indicator of the effect of climate change on marine environment. However the impact of its declining on marine life and ecosystems health is still quite unclear because of the difficulty in obtaining in situ data, especially in remote areas, like the Southern Ocean (SO). Southern elephant seals (Mirounga leonina) proved to be a relevant alternative to the traditional oceanographic platforms to measure physical and biogeochemical structure of oceanic regions rarely observed. In this study, we use a new stage of development in biologging technology to draw a picture of dissolved oxygen concentration in the SO. We present the first results obtained from a dissolved oxygen sensor added to Argos CTD-SRDL tags and deployed on 5 female elephant seals at Kerguelen. From October 2010 and October 2011, 742 oxygen profiles associated with temperature and salinity measurements were recorded. Whether a part of the data must be considered cautiously, especially because of offsets and temporal drifts of the sensors, the range of values recorded was consistent with a concomitant survey conducted from a research vessel (Keops-2 project). Once again, elephant seals reinforced the relationship between marine ecology and oceanography, delivering essential information about the water masses properties and the biological status of the Southern Ocean. But more than the presentation of a new stage of development in animal-borne instrumentation, this pilot study opens a new field of investigation in marine ecology and could be enlarged in a near future to other key marine predators, especially large fish species like swordfish, tuna or sharks, for which dissolved oxygen is expected to play a crucial role in distribution and behaviour.

Research areas: Ecosystems
Direct radiative effect by brown carbon over the Indo-Gangetic Plain (2015)

Abstract. The importance of light-absorbing organic aerosols, often called brown carbon (BrC), has become evident in recent years. However, there have been relatively few measurement-based estimates for the direct radiative effect of BrC so far. In earlier studies, the AErosol RObotic NETwork (AERONET)-measured aerosol absorption optical depth (AAOD) and absorption Angstrom exponent (AAE) were exploited. However, these two pieces of information are clearly not sufficient to separate properly carbonaceous aerosols from dust, while imaginary indices of refraction would contain more and better justified information for this purpose. This is first time that the direct radiative effect (DRE) of BrC is estimated by exploiting the AERONET-retrieved imaginary indices. We estimated it for four sites in the Indo-Gangetic Plain (IGP), Karachi, Lahore, Kanpur and Gandhi College. We found a distinct seasonality, which was generally similar among all the sites, but with slightly different strengths. The monthly warming effect up to 0.5 W m2 takes place during the spring season. On the other hand, BrC results in an overall cooling effect in the winter season, which can reach levels close to 1 W m2. We then estimated similarly also the DRE of black carbon and total aerosol, in order to assess the relative significance of the BrC radiative effect in the radiative effects of other components. Even though BrC impact seems minor in this context, we demonstrated that it is not insignificant. Moreover, we demonstrated that it is crucial to perform spectrally resolved radiative transfer calculations to obtain good estimates for the DRE of BrC.

Research areas: Atmospheric/Ocean Indicators
Dimming over the oceans: Transient anthropogenic aerosol plumes in the twentieth century (2015)

Anthropogenic aerosols reduce incoming surface solar radiation (SSR), but the magnitude of this effect for reducing sea surface temperatures (SST) is still debated. Using simulations from the global climate model ECHAM5 with the Hamburg Aerosol Module and prescribed SSTs, we quantify anthropogenic aerosol dimming over sea surfaces by comparing ensembles, which only differ in anthropogenic aerosol emissions. We isolate the anthropogenic aerosol effect on SSR with sufficiently large ensemble sizes to provide statistically significant results. The following simulation results are obtained: Dimming plumes extend from their source regions with clear seasonality. The latter is predominantly shaped by atmospheric circulation, while interdecadal changes follow the gradual increase in anthropogenic aerosol emissions. Comparing the 1990s with the 1870s, on average, 9.4% (clear-sky SSR) or 15.4% (all-sky SSR) of the entire ocean surface was affected by anthropogenic aerosol dimming larger than 4 Wm2 (decadal mean). Comparing the same time periods, global average anthropogenic dimming over oceans is 2.3 Wm2 and 3.4 Wm2 for clear-sky and all-sky SSR, respectively. Surface dimming is hemispherically asymmetrical with stronger Northern Hemispheric dimming by 2.3 Wm2 and 4.5 Wm2 for clear-sky and all-sky SSR, respectively. Zonal average clear-sky dimming reaches its maximum (5.5 Wm2) near the equator. All-sky dimming peaks at 40N (8 Wm2) and is regionally larger than clear-sky dimming. Regionally, surface dimming can reach values up to 9.5 Wm2 (clear-sky) and 25 Wm2 (all-sky). Results are a contribution toward better quantifying spatially heterogeneous and time-dependent anthropogenic dimming effects on SSTs.

Research areas: Sun-Earth Interactions
Diffuse sky radiation influences the relationship between canopy PRI and shadow fraction (2015)

The Photochemical Reflectance Index (PRI) of green leaves is an indicator of photosynthetic downregulation: when the photosynthetic apparatus is close to the saturation limit, PRI becomes dependent on light conditions. Therefore, by measuring the PRI of leaves under different local irradiance conditions, it should be possible to determine the saturation level of the leaves and obtain information on the light use efficiency (LUE) of a vegetation canopy. The dependence of PRI on the ratio of sunlit to shaded foliage (quantified by the canopy shadow fraction) in the field of view of an instrument has been used to remotely measure canopy LUE on clear days. However, besides photosynthetic downregulation, the dependence of canopy PRI on shadow fraction is affected by the blue sky radiation caused by scattering in the atmosphere. To quantify this effect on remotely sensed PRI, we present the underlying definitions relating leaf and canopy PRI and perform the required calculations for typical midsummer conditions in Central Finland. We demonstrate that the effect of blue sky radiation on the variation of PRI with canopy shadow fraction is similar in shape and magnitude to that of LUE variations reported in literature.

Research areas: Validation
Development of Flood Forecasting System for the Wangchhu River Basin in Bhutan (2015)

In mountainous countries like Bhutan, floods are potentially serious dangers for communities since they triggersubsequent hazards such as landslides. The countries lying in the Himalayan Mountain are exposed to floodsowing to the heavy rainfall and glacial lake outburst floods. The forecasting of catastrophic flood hazards iscrucial for the sustainability of these mountainous countries. At the same time, the hydro-met observation systemis inadequate to set up a robust flood-forecasting model in Bhutan. This paper focuses on developing a floodforecasting model for the Wangchhu river basin in Bhutan, by assimilating the hydrological gauge data andsatellite rainfall, and by providing stream flow frequency, rating curve and stream characteristics of theWangchhu basin. The study depicts the poor efficiency without upstream rainfall gauges. Using satellite databasewith proxy stations in the upper catchments increase the accuracy of the model. The Weather Research Forecast(WRF) model generated 3-day rainfall forecasts, which were used to generate flow forecasting. The WRF resultfor Bhutan is poor; thus, other sources of rainfall prediction need to be incorporated in the model. The model hasbeen calibrated for 2003-2004 and validated for 2005, 2009 and 2010 data.

Research areas: Floods
Detecting CDOM Fluorescence Using High Spectrally Resolved Satellite Data: A Model Study (2015)

Absorption and fluorescence of CDOM are widely used to characterize its concentration and composition, both in situ and with remote sensing techniques. As fluorescence is an inelastic scattering process, it can potentially be observed in filling-in of Fraunhofer lines with the DOAS method in high spectrally resolved satellite data. Here, we perform a theoretical model study and preliminary DOAS retrieval on SCIAMACHY data in order to test the feasibility of such an approach. Our results show that retrieving CDOM fluorescence is difficult, due to its relatively weak signal in global oceans (in comparison to Raman scattering of clear water) and varying broad spectral features. Detailed studies of the synergistic use of narrow and broad fluorescence features, and an appropriate scheme to account for disturbance effects of Raman scattering, are needed for further investigating the retrieval of CDOM fluorescence.

Research areas: Validation
Decomposing the variance in southern elephant seal weaning mass: partitioning environmental signals and maternal effects (2015)

Predator populations are likely to respond to bottom-up processes, but there remains limited understanding of how wide-ranging marine predators respond to environmentally driven temporal variation in food availability. Widespread declines of several Southern Ocean predators, including southern elephant seals Mirounga leonina, have been attributed to decreases in food availability following environmental changes. We used linear mixed models to examine temporal process variance in weaning mass (a key fitness component) of southern elephant seals at Marion Island over a 27-year period (19862013). We quantified the contribution of within- and between-year covariates to the total phenotypic variance in weaning mass and determined whether the observed reversal of population decline was associated with a continued increase in weaning mass, suggesting improvement in per capita food availability to adult females. Weaning mass initially increased rapidly with maternal age, but reached an asymptote when females were nine years old. Longitudinal data examining between-individual maternal differences suggested latent, age-independent maternal influences on weaning mass. Between-year differences accounted for only 6% of the total phenotypic variance in weaning mass. We found no evidence for a systematic trend in weaning mass, but model predicted weaning mass was 8.70 kg (95% CI = 2.1414.73) lower during the 1980s, suggesting that food limitation may have been most severe during these years when the population was declining. Model support for a population size effect was entirely driven by the low weaning mass and comparatively high (but declining) population size from 1986 to 1988; subsequent variation in population size had no detectable influence on weaning mass. Remotely sensed chlorophyll-a concentration within the seals' foraging distribution explained 45% of the between-year variation (19982013, n = 9) in weaning mass, with higher weaning mass in years of positive chlorophyll-a anomalies. Environmental variation associated with variability in the Southern Annular Mode poorly predicted temporal variation in weaning mass. Our long-term data on elephant seal weaning mass provides a perspective on variation in food availability in a pelagic environment which is poorly known. Examining the long-term regionally specific effects of environmental variability aids our understanding of how these predators interact with their environment.

Research areas: Ecosystems
Correlation between the spatio-temporal distributions of aerosols, sulphur dioxide, and formaldehyde using MODIS and SCIAMACHY satellite data for China (2015)

The spatial and temporal relationship between fine-mode aerosol optical depth (AOD) observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) and tropospheric columns of SO2 and formaldehyde (HCHO) from the Scanning Imaging Absorption Chartography (SCIAMACHY) are used to infer information on the variability of sulphate aerosol, which is a major determinant of fine-mode AOD (AODf) in east China. When averaging the satellite data over specific regions of China and for longer time periods (from 2005 to 2011), we find obvious similar trends between AODf and SO2, HCHO columns for southern and eastern China. The results of satellite observations show the high spatial and temporal correlation between AODf and SO2 over the Yangtze River Delta (R2), the Pearl River Delta (R3), and the ChongqingChengdu region (R4), with the coefficients of determination (R2) of 0.376, 0.438, and 0.837, respectively. These regions are performing with the huge amount of anthropogenic SO2 emissions by traffic, industry, and domestic heating. The trend is consistent with fine-mode aerosol and SO2 appearing in summer because AODf is often correlated with enhanced HCHO concentrations, reflecting the importance of secondary aerosol formation over industrialized regions in that season. Over the North China Plain, distinct maximum values of AODf and HCHO were observed and the minimum value for SO2 was observed in summer. The decrease in the mean SO2 column was 35.5%, which has been attributed to the strict security measures by the government during the 2008 Olympic Games period while there was a decrease of 46% in AODf at the same time. As sulphate aerosol occurs seasonally in the North China Plain, the strong correlation between anomalies of AODf and SO2 can be used to estimate and analyse the distribution of sulphate aerosol. Singular value decomposition (SVD) analysis showed the same variation between AODf and SO2 over eastern China and Sichuan Province, and a distinct negative value of SVD variables over comparably industrialized regions in southern and eastern China and Sichuan Province. The results for SO4 from the Model for Ozone and Related chemical Tracers model for southern and eastern China and the Sichuan regions suggest much stronger sulphate contributions to aerosol formation than for other areas of China. We propose that the SVD variables between AODf and SO2, which can be inferred from the satellite data, can be used as indicators for regional pollution control.

Research areas: Air Quality
Correlation Analysis between AOD and Cloud Parameters to Study Their Relationship over China Using MODIS Data (2003-2013): Impact on Cloud Formation and Climate Change (2015)

ABSTRACTIn the present study, we examined the spatial and temporal variations in aerosol optical depth (AOD) at 550 nm and its relationship with various cloud parameters derived from the Moderate resolution Imaging Spectroradiometer (MODIS) sensor onboard Terra satellite. The data have been analyzed for the period of 10-years between March 2003 and February 2013 over 12 major cities in China. The results revealed that high AOD noticed over low latitude regions influenced with high anthropogenic activities and the low AOD observed for the high altitude and mountainous areas, since AOD accounts for the slant path which reduces the aerosol emissions. In addition, the aerosol variations in the atmosphere are complicated by several factors in emissions (natural and anthropogenic) as well as stagnant synoptic meteorology. From the temporal studies, it is clear that the maximum AOD was found during summer followed by spring and autumn with a minimum AOD in winter season for all the regions of study in China. Furthermore, we studied the relationship between AOD versus water vapor (WV), cloud fraction (CF), cloud optical thickness (COT), cloud effective radius (CER), cloud top pressure (CTP), and cloud top temperature (CTT) for the selected regions in China. Additionally, regression analysis and one paired students t-Test were applied to represent the probability of data significant at 95% confidence for the derived AOD values and cloud parameters in order to provide a better understanding of aerosol-cloud interaction.

Research areas: Atmospheric/Ocean Indicators