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NASA NTRS2001

Atlantic Tropical Cyclone Monitoring with AMSU-A: Estimation of Maximum Sustained Wind Speeds

The first Advanced Microwave Sounding Unit temperature sounder (AMSU-A) was launched on the NOAA-15 satellite on 13 May 1998. The AMSU-A's higher spatial and radiometric resolutions provide more useful information on the strength of the middle- and upper-tropospheric warm cores associated with tropical cyclones than have previous microwave temperature sounders. The gradient wind relationship suggests that the temperature gradient near the core of tropical cyclones increases nonlinearly with wind speed. The gradient wind equation is recast to include AMSU-A-derived variables, Stepwise regression is used to determine which of these variables is most closely related to maximum sustained winds (V(sub max)). The satellite variables investigated include the radially averaged gradients at two spatial resolutions of AMSU-A channels 1-10 T(sub b) data (delta(sub r)T(sub B)), the squares of these gradients, a channel-15-based scattering index (SI(sub 89)), and area-averaged T(sub B). Calculations of T(sub B) and delta(sub r)T(sub B) from mesoscale model simulations of Andrew reveal the effects of the AMSU spatial sampling on the cyclone warm core presentation. Stepwise regression of 66 AMSU-A terms against National Hurricane Center V(sub max) estimates from the 1998 and 1999 Atlantic hurricane season confirms the existence of a nonlinear relationship between wind speed and radially averaged temperature gradients near the cyclone warm core. Of six regression terms, four are dominated by temperature information, and two are interpreted as correcting for hydrometeor contamination. Jackknifed regressions were performed to estimate the algorithm performance on independent data. For the 82 cases that had in situ measurements of V(sub max), the average error standard deviation was 4.7 m/s. For 108 cases without in situ wind data, the average error standard deviation was 7.5 m/s Operational considerations, including the detection of weak cyclones and false alarm reduction, are also discussed.

Spencer, Roy W.↗
NASA NTRS2001

Simulation of Climatic Changes in the Arctic and North Atlantic During Recent Decades

The interactions of the atmosphere and ice-ocean system in the Arctic will be studied using a coupled ice-ocean model which will also use ice drift derived from microwave observations as forcing. We especially search for linkages between the recent large climatic shifts in the Arctic Ocean and atmosphere for which period we also have microwave sea ice data. The coupled model area covers the whole N. Atlantic thus interactions between the lower latitudes are also investigated because we anticipate that the same large scale atmospheric patterns which dominate the midlatitudes extend their influence on the Arctic. The model hindcast for 1951-1993 shows clear decadal variability in the leading modes of ocean circulation. No specific low-freq modes are expected for the ice drift because its spectrum is white. However, the ice drift exhibits two see-saw patterns in response to the leading atmospheric circulation mode ('Arctic Oscillation'), one of them is the well-known out of phase relationship between Baffin Bay and Barents-Kara Seas, the other one is between Siberian shelf and Alaskan Coast (Hakkinen and Geiger, 2000).

Hakkinen, Sirpa↗
NASA NTRS2001

Modeling Biogeochemical-Physical Interactions and Carbon Flux in the Sargasso Sea (Bermuda Atlantic Time-series Study site)

An ecosystem-carbon cycle model is used to analyze the biogeochemical-physical interactions and carbon fluxes in the Bermuda Atlantic Time-series Study (BATS) site for the period of 1992-1998. The model results compare well with observations (most variables are within 8% of observed values). The sea-air flux ranges from -0.32 to -0.50 mol C/sq m/yr, depending upon the gas transfer algorithm used. This estimate is within the range (-0.22 to -0.83 mol C/sq m/yr) of previously reported values which indicates that the BATS region is a weak sink of atmospheric CO2. The overall carbon balance consists of atmospheric CO2 uptake of 0.3 Mol C/sq m/yr, upward dissolved inorganic carbon (DIC) bottom flux of 1.1 Mol C/sq m/yr, and carbon export of 1.4 mol C/sq m/yr via sedimentation. Upper ocean DIC levels increased between 1992 and 1996 at a rate of approximately 1.2 (micro)mol/kg/yr, consistent with observations. However, this trend was reversed during 1997-1998 to -2.7 (micro)mol/kg/yr in response to hydrographic changes imposed by the El Nino-La Nina transition, which were manifested in the Sargasso Sea by the warmest SST and lowest surface salinity of the period (1992-1998).

Signorini, Sergio R.↗
NASA NTRS2001

Dynamical Interpolation of Mesoscale Flows in the TOPEX/Poseidon Diamond Surrounding the U.S. Joint Global Ocean Flux Study Bermuda Atlantic Time-Series Study Site

An open boundary ocean model is configured in a domain bounded by the four TOPEX/Poseidon (T/P) ground tracks surrounding the US Joint Global Ocean Flux Study Bermuda Atlantic Time-Series Study (BATS) site. This implementation facilitates prescription of model boundary conditions directly from altimetric measurements (both TIP and ERS-2). The expected error characteristics for a domain of this size with periodically updated boundary conditions are established with idealized numerical experiments using simulated data. A hindcast simulation is then constructed using actual altimetric observations during the period October 1992 through September 1998. Quantitative evaluation of the simulation suggests significant skill. The correlation coefficient between predicted sea level anomaly and ERS observations in the model interior is 0.89; that for predicted versus observed dynamic height anomaly based on hydrography at the BATS site is 0.73. Comparison with the idealized experiments suggests that the main source of error in the hindcast is temporal undersampling of the boundary conditions. The hindcast simulation described herein provides a basis for retrospective analysis of BATS observations in the context of the mesoscale eddy field.

McGillicuddy, Dennis J., Jr.↗
NASA NTRS2002

Comparison of Aerosol Single Scattering Albedos Derived by Diverse Techniques In Two North Atlantic Experiments

Aerosol single scattering albedo omega (the ratio of scattering to extinction) is important in determining aerosol climatic effects, in explaining relationships between calculated and measured radiative fluxes, and in retrieving aerosol optical depths from satellite radiances. Recently, two experiments in the North Atlantic region, the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) and the Second Aerosol Characterization Experiment (ACE-2), determined aerosol omega by a variety of techniques. The techniques included fitting of calculated to measured radiative fluxes; retrievals of omega from skylight radiances; best fits of complex refractive index to profiles of backscatter extinction, and size distribution; and in situ measurements of scattering and absorption at the surface and aloft. Both TARFOX and ACE-2 found a fairly wide range of values for omega at midvisable wavelengths approx. 550 nm, with omega(sub midvis) greater than or equal to 0.85 and less than or equal to 0.99 for the marine aerosol impacted by continental pollution. Frequency distributions of omega could usually be approximated by lognormals in omega(sub max) - omega, with some occurrence of bimodality, suggesting the influence of different aerosol sources or processing. In both TARFOX and ACE-2, closure tests between measured and calculated radiative fluxes yielded best-fit values of omega(sub midvis) 0.90 +/- 0.04 for the polluted boundary layer. Although these results have the virtue of describing the column aerosol unperturbed by sampling, they are subject to questions about representativeness and other uncertainties (e.g., thermal offsets, unknown gas absorption) The other techniques gave larger values for omega(sub midvis) for the polluted boundary layer, with a typical result of omega(sub midvis) = 0.95 +/- 0.04. Current uncertainties in omega are large in terms of climate effects More tests are needed of the consistency among different methods and of humidification effects on omega.

Russell, P. B.↗
NASA NTRS2001

Dynamical Interpolation of Mesoscale Flows in the TOPEX/ Poseidon Diamond Surrounding the U.S. Joint Global Ocean Flux Study Bermuda Atlantic Time-Series Study Site

An open boundary ocean model is configured in a domain bounded by the four TOPEX/Poseidon (TIP) ground tracks surrounding the U.S. Joint Global Ocean Flux Study Bermuda Atlantic Time-series Study (BATS) site. This implementation facilitates prescription of model boundary conditions directly from altimetric measurements (both TIP and ERS-2). The expected error characteristics for a domain of this size with periodically updated boundary conditions are established with idealized numerical experiments using simulated data. A hindcast simulation is then constructed using actual altimetric observations during the period October 1992 through September 1998. Quantitative evaluation of the simulation suggests significant skill. The correlation coefficient between predicted sea level anomaly and ERS observations in the model interior is 0.89; that for predicted versus observed dynamic height anomaly based on hydrography at the BATS site is 0.73. Comparison with the idealized experiments suggests that the main source of error in the hindcast is temporal undersampling of the boundary conditions. The hindcast simulation described herein provides a basis for retrospective analysis of BATS observations in the context of the mesoscale eddy field.

McGillicuddy, D. J.↗
NASA NTRS2002

Linking Horizontal And Vertical Transports of Biomass Fire Emissions to the Tropical Atlantic Ozone Paradox during the Northern Hemisphere Winter Season: II. 1998-1999.

The horizontal and vertical transport of biomass fire emissions in West Africa during November 1998 through February 1999, are examined using all available data including wind, fire, aerosol, precipitation, lightning and outgoing longwave radiation. Ozonesonde data from the Aerosols99 Trans-Atlantic cruise are also included with rain and wind analyses. The results here support earlier studies that ozone and ozone precursors associated with biomass burning are confined to the lower troposphere primarily due to the lack of deep convection over land areas. Ozone and its precursors are horizontally transported equatorward or towards the west by winds in the 1000-700 hPa layers. However, rising adiabatic motions associated with the diurnal evolution of the West African n can transport ozone and its precursors vertically into the free troposphere above the marine boundary layer. Moreover, lightning from South America, Central Africa and mesoscale convective systems in the Gulf of Guinea can lead to elevated ozone mixing ratios in the middle and upper troposphere.

Jenkins, Gregory S.↗
NASA NTRS2003

Elevated Ozone in the Troposphere over the Atlantic and Pacific Oceans in the Northern Hemisphere

Tropospheric column ozone (TCO) is derived from differential measurements of total column ozone from Nimus-7 and Earth Probe TOMS, and stratospheric column ozone from the Microwave Limb Sounder instrument on the Upper Atmospheric Research Satellite. It is shown that TCO during summer months over the Atlantic and Pacific Oceans at northern mid-latitudes is about the same (50-60 Dobson Units) as over the continents of North America, Europe and Asia, where surface emissions of nitrogen oxides from industrial sources, biomass and biofuel burning and biogenic emissions are significantly larger. This nearly uniform zonal variation in TCO is modulated by surface topography of the Rocky and Himalayan mountains and Tibetan Plateau where TCO is reduced by 20-30 Dobson Units. The zonal characteristics of TCO derived from satellite measurements are well simulated by a global chemical transport model called MOZART-2 (Model of Ozone and Related Chemical Tracers, version 2). The model results are analyzed to delineate the relative importance of various processes contributing to observed zonal characteristics of TCO, and they are shown that the surface emission of NOx contributes about 50% of the TCO at northern mid-latitudes, especially over the continents of North America, Europe and Asia. The result of TCO derived from TOMS and the analysis from MOZART-2 indicate that TCO is a very useful tool to study tropospheric O3 pollution resulting from surface emissions of pollutants.

Chandra, S.↗
NASA NTRS2003

Elevated Tropospheric Ozone over the Atlantic

Tropospheric column ozone (TCO) is derived from differential measurements of TOMS total column ozone and Microwave Limb Sounder stratospheric column ozone. It is shown that TCO during summer months over the Atlantic and Pacific Oceans in northern midlatitudes is about the same (50 to 60 Dobson Units) as over the continents of North America, Europe, and Asia, where surface emissions of nitrogen oxides from industrial sources, biomass and biofuel burning and biogenic emissions are significantly larger. This nearly uniform zonal variation in TCO is modulated by surface topography of the Rocky and Himalayan mountains, and Tibetan plateau where TCO is reduced by 20 to 30 Dobson Units. The zonal variation in TCO is well simulated by a global chemical transport model called MOZART-2 (Model of Ozone and Related Chemical Tracers, version 2). The model results are analyzed to delineate the relative importance of various processes contributing to observed zonal characteristics of TCO.

Chandra, S.↗
NASA NTRS2004

Simulation of Spatial and Temporal Radiation Exposures for ISS in the South Atlantic Anomaly

The International Space Station (ISS) living areas receive the preponderance of ionizing radiation exposure from Galactic Cosmic Rays (GCR) and geomagnetically trapped protons. Practically all trapped proton exposure occurs when the ISS passes through the South Atlantic Anomaly (SAA) region. The fact that this region is in proximity to a trapping mirror point indicates that the proton flux is highly directional. The inherent shielding provided by the ISS structure is represented by a recently-developed CAD model of the current 11-A configuration. Using modeled environment and configuration, trapped proton exposures have been analytically estimated at selected target points within the Service and Lab Modules. The results indicate that the directional flux may lead to substantially different exposure characteristics than the more common analyses that assume an isotropic environment. Additionally, predictive capability of the computational procedure should allow sensitive validation with corresponding on-board directional dosimeters.

Anderson, Brooke M.↗
NASA NTRS2005

Oceanic Situational Awareness over the North Atlantic Corridor

Air traffic control (ATC) mandated, aircraft separations over the oceans impose a limitation on traffic capacity for a given corridor, given the projected traffic growth over the oceanic domain. The separations result from a lack of acceptable situational awareness over oceans where radar position updates are not available. This study considers the use of Automatic Dependent Surveillance (ADS) data transmitted over a commercial satellite communications system as an approach to provide ATC with the needed situational awareness and thusly allow for reduced aircraft separations. This study uses Federal Aviation Administration data from a single day for the North Atlantic Corridor to analyze traffic loading to be used as a benchmark against which to compare several approaches for coordinating data transmissions from the aircraft to the satellites.

Welch, Bryan↗
NASA NTRS2005

Oceanic Situational Awareness Over the Western Atlantic Track Routing System

Air traffic control (ATC) mandated, aircraft separations over the oceans impose a limitation on traffic capacity for a given corridor, given the projected traffic growth over the Western Atlantic Track Routing System (WATRS). The separations result from a lack of acceptable situational awareness over oceans where radar position updates are not available. This study considers the use of Automatic Dependent Surveillance (ADS) data transmitted over a commercial satellite communications system as an approach to provide ATC with the needed situational awareness and thusly allow for reduced aircraft separations. This study uses Federal Aviation Administration data from a single day for the WATRS corridor to analyze traffic loading to be used as a benchmark against which to compare several approaches for coordinating data transmissions from the aircraft to the satellites.

Welch, Bryan↗
NASA NTRS2003

Emissions of Trace Gases and Particles from Two Ships in the Southern Atlantic Ocean

Measurements were made of the emissions of particles and gases from two diesel-powered ships in the southern Atlantic Ocean off the coast of Namibia. The measurements are used to derive emission factors from ships of three species not reported previously, namely, black carbon, accumulation-mode particles, and cloud condensation nuclei (CCN), as well as for carbon dioxide, carbon monoxide (CO), methane (CH4), non-methane hydrocarbons, sulfur dioxide (SO2), nitrogen oxides (NOx), and condensation nuclei. The effects of fuel grade and engine power on ship emissions are discussed. The emission factors are combined with fuel usage data to obtain estimates of global annual emissions of various particles and gases from ocean-going ships. Global emissions of black carbon, accumulation- mode particles, and CCN from ocean-going ships are estimated to be 19-26 Gg yr(sup -1), (4.4-6.1) x 10(exp 26) particles yr(sup -1), and (1.0-1.5) x l0(exp 26) particles yr(sup -1), respectively. Black carbon emissions from ocean-going ships are approximately 0.2% of total anthropogenic emissions. Emissions of NOx and SO2 from ocean-going ships are approximately 10-14% and approximately 3-4%, respectively, of the total emissions of these species from the burning of fossil fuels, and approximately 40% and approximately 70%, respectively, of the total emissions of these species from the burning of biomass. Global annual emissions of CO and CH4 from ocean-going ships are approximately 2% and approximately 2-5%, respectively, of natural oceanic emissions of these species.

Sinha, Parikhit↗
NASA NTRS2005

Variability of particulate organic carbon concentration in the north polar Atlantic based on ocean color observations with Sea-viewing Wide Field-of-view Sensor (SeaWiFS)

We use satellite data from Sea-viewing Wide Field-of-view Sensor (SeaWiFS) to investigate distributions of particulate organic carbon (POC) concentration in surface waters of the north polar Atlantic Ocean during the spring summer season (April through August) over a 6-year period from 1998 through 2003. By use of field data collected at sea, we developed regional relationships for the purpose of estimating POC from remote-sensing observations of ocean color. Analysis of several approaches used in the POC algorithm development and match-up analysis of coincident in situ derived and satellite-derived estimates of POC resulted in selection of an algorithm that is based on the blue-to-green ratio of remote-sensing reflectance R(sub rs) (or normalized water-leaving radiance L(sub wn)). The application of the selected algorithm to a 6-year record of SeaWiFS monthly composite data of L(sub wn) revealed patterns of seasonal and interannual variability of POC in the study region. For example, the results show a clear increase of POC throughout the season. The lowest values, generally less than 200 mg per cubic meters, and at some locations often less than 50 mg per cubic meters, were observed in April. In May and June, POC can exceed 300 or even 400 mg per cubic meters in some parts of the study region. Patterns of interannual variability are intricate, as they depend on the geographic location within the study region and particular time of year (month) considered. By comparing the results averaged over the entire study region and the entire season (April through August) for each year separately, we found that the lowest POC occurred in 2001 and the highest POC occurred in 2002 and 1999.

Stramska, Malgorzata↗
NASA NTRS1996

Age Dependent 3-D Magnetic Modeling of the North Pacific and North Atlantic Oceanic Crust at Intermediate Wavelengths

Three-dimensional magnetic modeling of the North Atlantic and Northeast pacific is performed at intermediate wavelengths using three models for the acquisition of a natural remanent magnetization. It is shown that a remanent magnetization which is dependent on the rustal age is the dominant source for the intermediate wavelength pattern in both basins.

magnetic modeling tectonics plate tectonics oceani↗
NASA NTRS2006

Remote Versus Local Forcing of Chlorophyll Variability in the South Atlantic Bight

This TM documents results of analyses addressing the local versus remote forcing of chlorophyll variability on the shelf and slope regions of the South Atlantic Bight (SAB) based on satellite-derived products and a limited amount of in situ data. This study is part of a larger multi-disciplinary, multi-institutional effort to study the Eastern U.S. Continental Shelf carbon budget (U.S. Eastern Continental Shelf Carbon Budget: Modeling, Data Assimilation, and Analysis, U.S. ECoS), a project funded by the NASA Earth System Enterprise Interdisciplinary Science Program that started in the summer of 2004.

Signorini, Sergio R.↗
NASA NTRS2006

Processes Influencing Ozone Levels in Alaskan Forest Fires Plumes during Long-Range Transport over the North Atlantic

A case of long-range transport of a biomass burning plume from Alaska to Europe is analyzed using a Lagrangian approach. This plume was sampled several times in the free troposphere over North America, the North Atlantic and Europe by 3 different aircraft during the IGAC Lagrangian 2K4 experiment which was part of the ICARTT/ITOP measurement intensive in summer 2004. Measurements in the plume showed enhanced values of CO, VOCs and NOy, mainly in form of PAN. Observed O3 levels increased by 17 ppbv over 5 days. A photochemical trajectory model, CiTTyCAT, is used to examine processes responsible for the chemical evolution of the plume. The model was initialized with upwind data, and compared with downwind measurements. The influence of high aerosol loading on photolysis rates in the plume is investigated using in-situ aerosol measurements in the plume and lidar retrievals of optical depth as input into a photolysis code (Fast-J), run in the model. Significant impacts on photochemistry are found with a decrease of 18 percent in O3 production and 24 percent in O3 destruction over 5 days when including aerosols. The plume is found to be chemically active with large O3 increases attributed primarily to PAN decomposition during descent of the plume towards Europe. The predicted O3 changes are very dependent on temperature changes during transport, and also, on water vapor levels in the lower troposphere which can lead to O3 destruction. Simulation of mixing/dilution was necessary to reproduce observed pollutants level in the plume. Mixing was simulated using background concentrations from measurements in air masses in close proximity to the plume, and mixing timescales (averaging 6.25 days) were derived from CO changes. Observed and simulated O3/CO correlations in the plume are also compared in order to evaluate the photochemistry in the model. Observed slopes changed from negative to positive over 5 days. This change, which can be attributed largely to photochemistry, is well reproduced by multiple model runs even if slope values are slightly underestimated suggesting small underestimation of photochemical processes. The possible impact of this biomass burning plume on O3 levels in the Europe boundary layer is also examined by running the model for a further 5 days, and comparing with data collected at surface sites, such as Jungfraujoch, which showed small O3 increases and elevated CO levels. The model predicts significant changes in O3 over this 10 days due to photochemistry but the signal is largely lost due to the effects of dilution. However, measurement in several others BB plumes over Europe show that O3 impact of Alaskan fires can be punctually significant over Europe.

Real, E.↗