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Movements of Blacknose, Finetooth, and Sharpnose Sharks in the US South Atlantic: Establishing Migration Benchmarks to Assess Future Climate Impacts
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Solar-cycle Variations of South Atlantic Anomaly Proton Intensities Measured with the PAMELA Mission
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Understanding long-term (1982–2013) multi-decadal change in the equatorial and subtropical South Atlantic climate
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Shallow and Deep Eastern Boundary Currents in the South Atlantic at 34.5°S: Mean Structure and Variability
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Carbonate Chemistry and the Potential for Acidification in Georgia Coastal Marshes and the South Atlantic Bight, USA
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Atmospheric Origins of Variability in the South Atlantic Meridional Overturning Circulation
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Biopower: Impact of Biofuels Deployment to Replace Petroleum Liquids in Stationary Power Applications
Petroleum-based liquids are used in a portion of power generation applications in the United States, predominantly in the New England, Middle Atlantic, South Atlantic, and Pacific-Noncontiguous regions. Power plants that burn petroleum liquids, such as distillate or residual fuel oils, are generally used for short periods to accommodate peak electricity demands. The Energy Information Administration (EIA) estimated the U.S. consumption of petroleum liquids for electricity generation at 27 million barrels in 2018, representing a cost of $2.4 billion annually. This study assesses the potential to displace all or part of the petroleum liquids in U.S. power generation with biofuels. The biofuels for this application are assumed to be derived from terrestrial feedstocks, with conversion routes of both fast pyrolysis (bio-oil) and hydrothermal liquefaction (bio-crude). Regional models were used to assess the availability and cost of three different base materials: clean wood, forest residues, and corn stover; each was evaluated in the laboratory at small or experimental scales for conversion to bio-oil or bio-crude. The estimated biofuel production quantities depend on equivalent heating versus the current heavy fuel. In this report, the availability of each type of biomass for each section of the U.S. Census division is estimated using a conservative broker price (in each case) of $ 80 per dry tonne. The results show that the petroleum-liquid power generation in each of the Census Divisions could be supplied by one or more of the feedstocks evaluated. For all regions, clean wood supplies (only) could provide ample supply. For all but two regions (Middle Atlantic and New England), forest residues alone are sufficient. Finally, for all regions but three (Middle Atlantic, New England, and South Atlantic), corn stover alone is adequate. The Minimum Fuel Selling Price (MFSP) of bio-oil and bio-crude were also estimated for each feedstock type and Census Division. This analysis showed that fast pyrolysis bio-oil projections to be lower (14% on average) than current wholesale petroleum-based heating oil prices in each of the regions, assuming 100 dry tonnes/day processing capacity. However, bio-crude predictions were significantly higher (2X) in all cases. The effect of biorefinery size was also quantified. Based on the preliminary results in this study, it is apparent the biofuels could be an economical alternative for current petroleum liquids in U.S. power generation. However, additional research is needed to determine the necessary biofuel characteristics to support existing generation equipment. It is recommended that both power generation and biofuel production stakeholders to be engaged to outline the research and testing needed to identify the technical hurdles to enable the opportunity.
Geoid height versus age for symmetric spreading ridges
Geoid height-age relations have been extracted from Geos 3 altimeter data for large areas in the North Atlantic, South Atlantic, southeast Indian, and southeast Pacific oceans. Except for the southeast Pacific area, geoid height decreases approximately linearly with the age of the ocean floor for ages less than about 80 m.y. in agreement with the prediction of an isostatically compensated thermal boundary layer model (Haxby and Turcotte, 1978). The geoid-age data for 0 to 80 m.y. are consistent with constant slopes of -0.094 + or - -0.131 + or - 0.041, and -0.149 + or - 0.028 m/m.y. for the South Atlantic, southeast Indian, and North Atlantic regions, respectively. For ages greater than 80 m.y. the geoid-age relation for the North Atlantic is nearly flat, indicating a reduction in the rate of boundary layer thickening with age. The uncertainties in the geoid slope-age estimates are positively correlated with spreading velocity.
Large Scale Covariability in the Aerosol-SST-Precipitation Relation: A Satellite Perspective
Although large scale aerosol effects on precipitation have attracted increasing attention in recent years, significant uncertainties still remain in the current understanding of'such effects. One of the factors contributing to these uncertainties is the availability of aerosol data sets that are sufficiently long, stable, and comprehensive to be used for climate analysis. Such data sets are crucial for any long-term studies that are needed to demonstrate the statistical significance of large scale aerosol effects on precipitation when compared to the effects from other climate factors, such as remote or local sea surface temperature (SST) variability (ENSO. etc.). A longterm consistent aerosol product that complements the existing MODIS and AVHRR aerosol products is therefore needed to minimize aerosol data uncertainty issues for such Studies. The SeaWiFS instrument was primarily designed to measure ocean color, and it has been the mayor source for providing a comprehensive global data set of such measurements since its launch in 1997. Besides being used in this capacity, however, the well-calibrated set of radiances measured in the wavelength range from the visible (0.41 m) to the near infrared (0.87 m) is also well suited to creating long-term climate data records of aerosols. Recently, a new 13-year SeaWiFS aerosol optical depth dataset has been developed that expands its capacity to be used for such atmospheric studies. This SeaWiFS aerosol product provides us with an unprecedented opportunity to examine the covariability of aerosol, SST and precipitation on both a regional and global scale. We also use concurrent independent SST (NOAA Optimum Interpolation, OI, SST V2) and precipitation (GPCP V2) datasets for this study. We will present and discuss results from this study over several aerosol hot spot regions ( -,North Atlantic. South Atlantic, Western Pacific, Indian Ocean etc.) during the SeaWIFS data period (1997 -- current) from this study will be presented and discussed. These results will highlight the value and impact of this unique product to climate studies
Impacts of ENSO on the South American Summer Monsoon During 1997-1999
Using the National Center for Environmental Prediction (NCEP) Reanalysis, and CPC Merged Analysis Product (CMAP) rainfall, we have compared and contrasted the anomalies of the South American Summer Monsoon (SASM) during two extreme years of 1997/98 (EI Nino) and 1998/99 (La Nina). The results are assessed against a "canonical" ENSO response (CER) pattern for the SASM obtained from empirical mode decomposition based on a previous period (1980-1995). Overall, the SASM anomalies compare well with CER, but with some important differences. Anomalies occurring in the warm phase of the 1997-98 El Nino are very significant and robust, while those occurring in 1998/99 La Nina, appear to be reversed from 1997/98, but are relatively weak and less well-defined. The most pronounced signal in DJF 1997/98 is the development of drought conditions in northern Brazil, excessive rainfall over northern Peru and Ecuador, and over Uruguay and southern Brazil. The tropical rainfall anomalies are associated with the eastward shift of the Walker circulation, which is represented by pronounced low-level anomalous westerlies over the equatorial eastern Pacific and easterlies over northern Brazil. The easterlies are deflected sharply southeastward by the steep topography of the Andes, enhancing the low-level jet (LLJ) along the eastern foothills of the Andes near 15-20 S. The LLJ penetrates deep into the extratropics, yielding rainfall anomalies further poleward compared to CER. During DJF 1997/98, the eastward expansion of the warm tropospheric temperature over the Nino-3 region causes anomalous geopotential height to develop in the upper troposphere above the Altiplano, leading to a strengthened Bolivian High. An upper-tropospheric jet anomaly maximum is found over the subtropical continent near 30 S, due to increasing meridional gradient of tropospheric temperature, as well as teleconnection patterns linking the South Pacific and the South Atlantic. Consistent with the CER, the South Pacific High is weakened, and the South Atlantic High is strengthened in DJF 1997/98. However, rather than appearing as a coherent large scale signal over the entire Atlantic as in CER, the South Atlantic High anomalies in DJF 1997/98 split into two separate high pressure centers; one located south of the Amazon basin, and another over the southeastern South Atlantic. The former is induced as a Rossby-wave response by ENSO-Induced sinking motion over nor-them and eastern Brazil, and the latter may be associated with extratropical teleconnection signals. Anomalous convection observed over equatorial western Africa may also have contributed to the different circulation response over the Atlantic in DFJ 1997/99 compared to the CER. Comparison of the evolution of the SASM anomalies in 1997-99 with their corresponding annual cycles, suggest that the anomalies are phase-locked to and represent either enhancement or reduction of the annual variations. Results suggest that, from a system perspective the SASM was strengthened during the 1997/98 El Nino and weakened, albeit to a lesser extent, during the 1998/99 La Nina.
Interannual and Decadal Variability of Summer Rainfall over South America
Using the CPC (Climate Prediction Center) Merged Analysis of Precipitation product along with the Goddard Earth Observing System reanalysis and the Climate Analysis Center sea surface temperature (SST) data, we conduct a diagnostic study of the interannual and decadal scale variability of summer rainfall over South America. Results show three leading modes of rainfall variation identified with interannual, decadal, and long-term trend variability. Together, these modes explain more than half the total variance. The first mode is highly correlated with El Nino/southern oscillation (ENSO), showing severe drought over Northeast Brazil and copious rainfall over the Ecuador coast and the area of Uruguay-Southern Brazil in El Nino years. This pattern is attributed to the large scale zonal shift of the Walker circulation and local Hadley cell anomaly induced by positive (negative) SST anomaly over the eastern (western) equatorial Pacific. In El Nino years, two convective belts indicated by upper tropospheric velocity potential trough and mid-tropospheric rising motion, which are somewhat symmetric about the equator, extend toward the northeast and the southeast into the tropical North and South Atlantic respectively. Sandwiched between the ascent is a region of descending motion over Northeast Brazil. The southern branch of the anomalous Hadley cell is dynamically linked to the increase of rainfall over Uruguay-Southern Brazil. The regional response of anomalous circulation shows a stronger South American summer monsoon and an enhanced (weakened) subtropical high over the South Atlantic (South Pacific) Ocean. The decadal variation displays a meridional shift of the Intertropical Convergence Zone (ITCZ), which is tie to the anomalous cross-equatorial SST gradient over the Atlantic and the eastern Pacific. In conjunction with this mode is a large scale mass swing between the polar regions and midlatitudes in both hemispheres. Over the South Atlantic and the South Pacific, the changes of the strength of the subtropical high and the associated surface wind are dynamically consistent with the distribution of local SST anomalies, suggesting the importance of the atmospheric forcing in the decadal time scale. The decadal mode also presents a weak summer monsoon in its positive phase, which reduces the moisture supply from the equatorial Atlantic and the Amazon Basin and results in negative rainfall anomalies over the central Andes and Gran Chaco. The long-term trend shows decrease of rainfall from the northwest coast to the southeast subtropical region and a southward shift of Atlantic ITCZ that leads to increased rainfall over northern and eastern Brazil. Our result shows a close link of this mode to the observed SST warming trend over the subtropical South Atlantic and a remote connection to the interdecadal SST variation over the extratropical North Atlantic found in previous studies.
Seasonal variations in fire conditions are important drivers in the trend of aerosol optical properties over the south-eastern Atlantic
Abstract. From June to October, southern Africa produces one-third of the global biomass burning (BB) emissions by widespread fires. BB aerosols are transported westward over the south-eastern Atlantic with the mid-tropospheric winds, resulting in significant radiative effects. Ascension Island (ASI) is located midway between Africa and South America. From June 2016 to October 2017, a 17-month in situ observation campaign on ASI found a low single-scattering albedo (SSA) as well as a high mass absorption cross-section of black carbon (MACBC), demonstrating the strong absorbing marine boundary layer in the south-eastern Atlantic. Here we investigate the monthly variations of critical optical properties of BB aerosols, i.e. SSA and MACBC, during the BB seasons and the driving factors behind these variations. Both SSA and MACBC increase from June to August and decrease in September and October. The average SSA during the BB seasons is 0.81 at 529 nm wavelength, with the highest mean ∼ 0.85 in October and the lowest ∼ 0.78 in August. The absorption enhancement (Eabs) derived from the MACBC shows similar trends with SSA, with the average during the whole of the BB seasons at ∼ 1.96 and ∼ 2.07 in 2016 and 2017, respectively. As the Eabs is higher than the ∼ 1.5 commonly adopted value by climate models, this result suggests the marine boundary layer in the south-eastern Atlantic is more absorbing than model simulations. We find the enhanced ratio of BC to CO (ΔBC/ΔCO, equal to BC/ΔCO as the BC background concentration is considered to be 0) is well correlated with SSA and MACBC, providing a simple way to estimate the aerosol optical characteristics in the south-eastern Atlantic. The exponential function we proposed can approximate SSA and MACBC with BC/ΔCO, and when BC/ΔCO is small it can capture the rapid growth of SSA as BC/ΔCO decreases. BC/ΔCO is influenced by combustion conditions and aerosol scavenging. From the analysis of the location of BB, the primary source fuel, the water content in the fuel, combined with the mean cloud cover and precipitation in the transport areas of the BB plume, we conclude that the increase in BC/ΔCO from June to August is likely to be caused by burning becoming more flaming. The reduction in the water content of fuels may be responsible for the change in the burning conditions from June to August. The decrease in BC/ΔCO in September and October may be caused by two factors, one being a lower proportion of flaming conditions, possibly associated with a decrease in mean surface wind speed in the burning area, and the other being an increase in precipitation in the BB transport pathway, leading to enhanced aerosol scavenging, which ultimately results in an increase in SSA and MACBC.
Elevated Tropospheric Ozone Over the South Tropical Atlantic in January-February 1999: An Ozone Paradox Due to Interhemispheric Transport, Lightning, or Stratospheric Exchange?
On this first North American to southern African oceanographic cruise with ozonesonde launches (January and February 1999 on board the NOAA Research Vessel Ronald H Brown between Norfolk, VA, and Cape Town, South Africa) we found: (1) high ozone, CO, and aerosols off northern equatorial Africa from biomass burning, but even higher ozone concentrations off southern Africa which was not burning - an "ozone paradox"; (2) TOMS satellite evidence that south Atlantic elevated ozone in January-February 1999 was a regional feature similar in extent to the well-known September-October ozone maximum. Several mechanisms are considered to explain the "ozone paradox." Convection transporting air from the lower troposphere rich in ozone and/or ozone precursors to the upper troposphere through the ITCZ (intertropical Convergence Zone) may lead to cross-hemisphere transport of pollution. This is supported by trajectory linkage of lower-tropospheric ozone maxima with smoke seen by the TOMS satellite. Lightning-generated NO (nitric oxide) leading to ozone peaks of > 100 ppbv observed at 7-10 km altitude is another explanation. The TRMM (Tropical Rainfall Measuring Mission) Lightning Imaging Sounder shows many lightning flashes over southern Africa, which trajectories link to the high-ozone layers south of the ITCZ. The highest ozone peaks in the middle troposphere correspond to very low water vapor, which may point to photochemical destruction of ozone or subsidence from the upper troposphere which had interacted with stratospheric ozone.
Chlorophyll Variability in the Oligotrophic Gyres: Mechanisms, Seasonality and Trends
A 16-year (1998-2013) analysis of trends and seasonal patterns was conducted for the 5 subtropical ocean gyres using chlorophyll-a (Chl-a) retrievals from ocean color satellite data, sea surface temperature (SST) obtained from optimally interpolated Advanced Very High Resolution Radiometer (AVHRR) data, and sea-level anomaly (SLA) from Aviso multi-sensor altimetry data. Trend analysis was also performed on mixed-layer data derived from gridded temperature and salinity profiles (1998-2010) from the Simple Ocean Data Assimilation (SODA) model. The Chl-a monthly composites were constructed from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and Moderate-resolution Imaging Spectroradiometer (MODIS) on Aqua using two different algorithms: the standard algorithm (STD) that has been in use since the start of the SeaWiFS mission in 1997, and a more recently developed Ocean Color Index (OCI) algorithm that is purported to provide improved accuracy in low chlorophyll waters such as the oligotrophic regions of the subtropical gyres. Trends were obtained for all gyres using both STD and OCI algorithms, which demonstrated generally consistent results. The North Pacific, Indian Ocean, North Atlantic and South Atlantic gyres showed significant downward trends in Chl-a, while the South Pacific gyre has a much weaker upward trend with no statistical significance. Time series of satellite-derived net primary production (NPP) showed downward trends for all the gyres, while all 5 gyres exhibited positive trends in SST and SLA. The seasonal variability of Chl-a in each gyre is tightly coupled to the variability in mixed layer depth (MLD) with peak values in winter in both hemispheres when vertical mixing is more vigorous, reaching depths approaching the nutricline (ZNO3, here defined as the depth of the 0.2 micron nitrate concentration). On a seasonal basis, Chl-a concentrations increase when the MLD approaches or is deeper than the nutricline depth, in agreement with the concept that vertical mixing is the major driving mechanism for phytoplankton photosynthesis in the interior of the gyres. In addition, MLD and SST seasonal changes are well correlated indicating that SST is a reasonable index of vertical mixing in the gyres. The combination of surface warming trends and biomass reduction over the 16-year period has the potential to reduce atmospheric CO2 uptake by the gyres and therefore influence the global carbon cycle.
Global analysis of January and July sea level pressure
A global analysis of monthly mean sea level pressure for January and July over a 16 year period (1961 through 1976) is presented. For both hemispheres, the summer circulation is characterized by continental lows and oceanic highs. The prominent features of the Northern Hemispheric winter circulation, forced by diabatic heat sources and orography, are Aleutian low, Icelandic low and Siberian high. The interannual variability is small over the tropics and large over the extratropics. Maximum variability occurs over the locations of Icelandic and Aleutian lows in the Northern Hemispheric winter. The locations and intensities of the Southern Hemispheric subtropical highs, which occur over the oceans, are remarkably similar in January and July and show small interannual variability. The north Atlantic and south Atlantic subtropical highs attain their maximum intensity at the same time, during July.
Eastern U.S. Continental Shelf Carbon Budget: Integrating Models,Data Assimilation, and Analysis
The U.S. East Coast Continental Shelf (USECoS) project was initiated in 2004 with the overall goal of developing carbon budgets for Mid-Atlantic and South Atlantic regions of the eastern U.S. coast. We addressed this goal through a series of specific research questions that were designed to understand carbon inputs and fates in the two regions, dominant food web pathways for carbon cycling, and similarities/differences in carbon cycling in the two continental shelf systems. The USECoS project represents a major effort to simultaneously synthesize and integrate diverse data sets, field measurements, models, and modeling approaches. We expect that the type of approach taken here will result in more insight than would be possible if each component of the program moved forward independently. The primary significance of this project is in providing a strong quantitative basis for the development of future observational and modeling studies of carbon budgets of continental shelf systems. A strong aspect of the USECoS project is the integration of modeling and extensive physical, chemical, and biological data sets, which provides an opportunity for modeling and data analyses to inform one another from the outset. This research is particularly germane to NASA's carbon cycle research focus and coastal research initiative and the U.S. Climate Change Research Program, all of which support the goals of the North American Carbon Program. We highlight primary approaches that have been used, and some of the challenges and results that have come from interactions among our team of investigators. The global scale and interdisciplinary nature of the science questions that we now face in Earth Science are such that integrated teams of investigators are needed to address them.