Satellite Wind Data Research Articles

Impact of Satellite Wind on Improving Simulation of the Upper Ocean Response to Tropical Cyclones

Accurate modeling of the ocean response to tropical cyclones (TCs) requires high-quality wind fields to force ocean models. In this study, blended wind fields are generated using multi-source satellite data and the Climate Forecast System Reanalysis (CFSR) wind data. We utilize the hybrid wind fields to drive the Regional Ocean Modeling System (ROMS) for simulating oceanic dynamic and thermodynamic parameters. The model’s simulated ocean surface and sub-surface temperatures, as well as current speeds, are generally consistent with satellite and in situ observations collected during TC Winston and Freddy. The results are significantly better than those simulated by ROMS using wind forcing from CFSR alone. These results suggest that incorporating satellite wind data into the atmospheric forcing has the potential to enhance vertical mixing and improve simulations of the upper ocean response to TCs.

Technoeconomic Analysis of a Wind Power Generation System and Wind Resource Mapping Using GIS Tools: The Case of Twelve Locations in the Commune of Evodoula, Cameroon

This paper performs a technoeconomic analysis of the wind power potential and evaluates the cost of wind power generation in Evodoula, comparing two methods, the conventional method and the uncertainty method based on a comparative spatiotemporal approach using the geographic information system (GIS) software tool. This study is based on satellite wind data measured at 10 m above ground level (AGL) over a 40-year period (1980-2019), by the meteorological service NASA (National Aeronautics and Space Administration)/Goddard Space Flight Center (GSFC). The main objectives are to obtain an appropriate design for a proven optimal location and to assess the viability of wind power at Evodoula. For this type of study, there is little literature available. The optimization of an onshore wind farm and deployment in the wind energy development interest area (ZIDEE) is carried out to obtain a minimum and parsimonious discounted cost production unitary (CPU) of the electricity produced. The results showed that in Okok, a location with a large energy deficit, an onshore wind farm with an electricity generation capacity of 12.5 MW with 5 NORDEX N100-2.5MW wind turbines would have a total energy production (TEP) of about 64.0254825 TWh and a selling price of electricity that would be 0.0034 CAD$/kWh, which is very low compared to the utility price (about 98% cheaper). The total cost of the wind farm would be about $11 million, with a net present cost of about $218 million. The annual profit generated by the wind farm would be over $6 billion. The return on investment (ROI) of the project is estimated at 2880.882%. The constructed onshore wind farm would avoid CO2 emission at over 11 MtCO2,eq/year as the energy generated is from the atmosphere. The wind farm would realize an average annual cash flow estimated at nearly $30 million after 20 years of operation. These savings would allow the installation of CO2 capture systems in conventional power plants. In addition, the analysis of uncertainties and risks was identified and quantified to estimate the confidence levels of the project development results. The risks have been assessed, and we recommend that the total uncertainty of the project is around 15%. The energy values in P75 and P90 are 10.08% and 19.22%, respectively, lower than the energy value in P50 of 11.60 GWh/An. Finally, the main policy recommendations for an inclusive design process are highlighted. The contribution of this study is to assist policy makers in making appropriate decisions in the development and implementation of energy and environmental policy in Cameroon and in many continental areas.

Assimilating Aeolus Satellite Wind Data on a Regional Level: Application in a Mediterranean Cyclone Using the WRF Model

This study uses a limited area model to improve the understanding of assimilating Aeolus Level 2B wind profiles on a regional level under severe weather conditions. Aeolus wind profile measurements have offered new insights into weather analysis and applications. The assimilation of Aeolus Level 2B winds has enhanced the observed state of the atmosphere spatially and temporally in global modeling systems. This work is focused on the development and evolution of a Mediterranean tropical-like cyclone that occurred between 27–30 September 2018. Aeolus coverage had a good spatial and temporal alignment with the broader area and time periods during which the cyclone originated and developed, affording the opportunity to explore the direct influence of Aeolus satellite retrievals in model initialization processes. Using the WRF 3DVar modeling system, model results showcase the effects stemming from Aeolus data ingestion, with the main differences presenting after the first 24 h of simulation. Smaller or larger deviations in the runs with and without the Aeolus wind data assimilation are evident in most cyclonic characteristics, extending vertically up to the mid-troposphere. The absence of a consistent trend in cyclone intensification or weakening underlines the unique impact of the Aeolus dataset in each case.

ASSESSMENT OF WIND ENERGY POTENTIAL IN THE BIEN DONG SEA USING CCMP SATELLITE DATA

This study assessesed the wind energy potential in the Bien Dong Sea by using the Cross-Calibrated Multi-Platform (CCMP) satellite wind data from 1991 to 2020. The results showed that the wind energy potential at 10 m height above ground is not high in the offshore areas with annual mean wind speeds ranging from 5 to 8 m/s. At heights of 100 m, 150 m, and 200 m, the greatest wind energy potential is found in the offshore areas of the North Bien Dong Sea Region, Binh Dinh - Ninh Thuan, Binh Thuan - Ca Mau, and the central part of the Gulf of Tonkin. Especially, the wind energy is quite high in the Sea of Ninh Thuan to Ba Ria - Vung Tau with annual mean wind speeds of 8 to 10 m/s, and the annual mean wind power density of 500 to 700 W/m2 at a height of 100 m. On the seasonal scale, the wind energy potential of January and October is greater than that of April and July for the orthern offshore areas while the wind energy potential of January is the greatest, followed by July and transition months for the southern offshore areas.

An FSO-based Optimization Framework for Improved Observation Performance: Theoretical Formulation and Experiments with NAVDAS-AR/NAVGEM

Abstract The forecast sensitivity to observations (FSO) is embedded into a new optimization framework for improving the observation performance in atmospheric data assimilation. Key ingredients are introduced as follows: the innovation-weight parametrization of the analysis equation, the FSO-based evaluation of the forecast error gradient to parameters, a line search approach to optimization, and an efficient mechanism for step length specification. This methodology is tested in preliminary numerical experiments with the Naval Research Laboratory Atmospheric Variational Data Assimilation System-Accelerated Representer (NAVDAS-AR) and the U.S. Navy’s Global Environmental Model (NAVGEM) at a T425L60 resolution. The experimental setup relies on a verification state produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) to estimate the analysis and short-range forecast errors. Parameter tuning is implemented in a training stage valid for April 1-14 of 2018 and aimed at improving the use of assimilated observations in reducing the initial-condition errors. Assessment is carried out for April 15 – May 31 of 2018 to investigate the performance of the weighted assimilation system in reducing the errors in analyses and 24-hour model forecasts. In average, as compared with the control run and verified against the ECMWF analyses, the weighted approach provided 17.4% reduction in analysis errors and 3.1% reduction in 24-hour forecast errors, measured in a dry total energy norm. Observation impacts are calculated to assess the use of various observation types in reducing the analysis and forecast errors. In particular, assimilation of satellite wind data is significantly improved through the innovation-weighting procedure.

Testing of the Multi-Physics Ensemble Kalman filter to Simulate the Track and Intensity of the Typhoon HaiYan (2013)

This paper presents some experimental results of the multi-physics ensemble Kalman filter method which assimilating the satellite wind data in WRF model to simulate the track and intensity of the typhoon HaiYan (2013). The study conducted two experiments.: (1) Ensemble forecast with multi-physics ensemble Kalman filter assimilates the satellite wind data (CIMSS); (2) multi-physics Ensemble forecast (MPH). The results of atmospheric circulation analysis in the simulation started at 12 UTC (international time) until November 7, 2013, showing that the trend and intensity of the general circulation in the CIMSS test are similar to the real development. So the results of the storm trajectory forecast of CIMSS test at the 48-hour forecast limit onwards are better than the MPH test. Moreover, experimental results based on the results of the 6 simulations for simulation error, the track error in the CIMSS test decreased 14% and 14.3% respectively in the 48-hour forecast period and 72 hours compared with the MPH test, and decreased 14% and 23.9% respectively compared to the global GFS forecast. For storm intensity (Pmin and Vmax), the CIMSS test also resulted in significantly improved errors in the 72-hour forecast period compared to MPH testing. These results confirmed that the assimilation of the satellite wind data into the input field of the model has a positive effect on Haiyan storm intensity and trajectory prediction skills. We may use this research to applying the multi-physics ensemble Kalman filter for forecasting storms affecting Vietnam.

Comparison Study of HY-2A, WindSat, ASCAT Satellite Wind Data with In-situ Measurement Data

Lee, J. and Kim, T., 2019. Comparison study of HY-2A, WindSat, ASCAT satellite wind data with in-situ measurement data. In: Lee, J.L.; Yoon, J.-S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp. 341-345. Coconut Creek (Florida), ISSN 0749-0208.This paper compares HY-2A, WindSat, ASCAT satellite wind data collected over six years from 2012 to 2017 with observed wind data from Ieodo Ocean Research Station (IORS) and Buoy located in the south sea of Jeju Island(BSJI), and analyzes the accuracy and characteristics of satellite wind data. The three satellites can measure wind speed and direction by remotely sensing the ocean surface. Specially, HY-2A scatterometer data produced by Chinese satellite were recently open to research users. The error analysis shows that RMSE of the three satellites are between 1.3 and 2.2 m/s, and correlations are between 0.84 and 0.92, and accuracy is high in the order of ASCAT, WindSat and HY-2A. Accuracy analysis in different wind speed ranges is also performed to find the characteristics of each satellite wind data. The satellite wind data are to be used for verification and assimilation data for wind forecasting model which produces input data for wave prediction numerical model.

Application of ensemble Kalman filter in WRF model to forecast rainfall on monsoon onset period in South Vietnam

Application of ensemble Kalman filter in WRF model to forecast rainfall on monsoon onset period in South Vietnam

Correction to: Influence of summer conditions on surface water properties and phytoplankton productivity in embayments of the South Shetland Islands

Phytoplankton productivity in glaciomarine embayments of the West Antarctic Peninsula is constrained because of extensive thermohaline variability, which is due to seasonal sea-ice and glacial melting. To determine whether or not this affects the biology of the water column, we explored the influence of surface water properties on phytoplankton productivity in four embayments of the South Shetland Islands (SSI) during late summer of 2013. We analyzed hydrographic, climatic, and primary productivity satellite data (wind velocity, sea-ice cover, and chlorophyll-a), in situ CTD measurements of physical and chemical characteristics, new estimates of net primary production (NPP), and surface water samples for chlorophyll-a, nutrients, biogenic silica, and plankton composition. Sea-ice cover at the SSI was ~ 20% during February. Long-term satellite wind data (2010–2015) showed that during February 2013 the average wind velocity was ~ 2 m s−1 higher than the long-term mean with two low sea surface temperature events occurring simultaneously at all sites. The CTD profiles did not show vertical salinity changes, although salinity was highly correlated with the percentage of integrated nanoplankton Chl-a, which represented > 50% of the total integrated Chl-a in all the embayments. Phytoplankton was the major contributor to the integrated carbon biomass of the upper water column, where centric diatoms predominated. The contribution of microzooplankton and bacterioplankton at the different sites explained NPP values and the trophic mode at each site. Specifically, NPP at Fildes Bay exhibited an autotrophic productivity mode in contrast to Collins Bay, where both heterotrophic and autotrophic modes alternated, mainly due to weekly changes in community respiration rates.

Impact of using scatterometer and altimeter data on storm surge forecasting

Satellite data are rarely used in storm surge models because of the lack of established methodologies. Nevertheless, they can provide useful information on surface wind and sea level, which can potentially improve the forecast. In this paper satellite wind data are used to correct the bias of wind originating from a global atmospheric model, while satellite sea level data are used to improve the initial conditions of the model simulations. In a first step, the capability of global winds (biased and unbiased) to adequately force a storm surge model are assessed against that of a high resolution local wind. Then, the added value of direct assimilation of satellite altimeter data in the storm surge model is tested. Eleven storm surge events, recorded in Venice from 2008 to 2012, are simulated using different configurations of wind forcing and altimeter data assimilation. Focusing on the maximum surge peak, results show that the relative error, averaged over the eleven cases considered, decreases from 13% to 7%, using both the unbiased wind and assimilating the altimeter data, while, if the high resolution local wind is used to force the hydrodynamic model, the altimeter data assimilation reduces the error from 9% to 6%. Yet, the overall capabilities in reproducing the surge in the first day of forecast, measured by the correlation and by the rms error, improve only with the use of the unbiased global wind and not with the use of high resolution local wind and altimeter data assimilation.

Seasonal and interannual variability of the Eastern Tropical Pacific Fresh Pool

AbstractThe Eastern Pacific Fresh Pool (EPFP) is a large region of low sea surface salinity (SSS) defined by values lower than 34 practical salinity scale within (5°S–30°N, 75°W–180°W). The fresh pool dynamically responds to strong regional and seasonally varying ocean‐atmosphere‐land interactions (including monsoon rain, trade and gap winds, and strong currents). Using more than 5 years of Soil Moisture and Ocean Salinity (SMOS) satellite sea surface salinity (SSS) and complementary satellite wind, rain, currents, and sea surface temperature data together with a historical ensemble of in situ products, the present study explores the seasonal and interannual dynamics of the fresh pool over the period 2004–2015. An important interannual variability of the maximal surface extension of the EPFP over the past decade is revealed with two extreme events (2012, 2015) occurring during the SMOS satellite period. These extremes are found to be related to the El Niño‐Southern Oscillation (ENSO) phases and associated anomalies of precipitation, surface currents, and trade wind in the central Pacific. In 2012 (La Niña), stronger trade winds coupled with a deficit of precipitation induced a minimum extension of the pool during the rainy season. Whereas, during the strong El Niño 2014–2015, the EPFP extension reached an unprecedented maximum value. A modification of the atmospheric freshwater fluxes and ocean surface currents during winter 2014 is found to have favored the onset of this abnormal fresh event.

Variability of ChlorophyllaConcentration and Halocline Depth in La Paz Bay (Gulf of California, Mexico) and the Relationship to Pacific Large-Scale Climatic Phenomena

ABSTRACT Guevara-Guillen, C.; Shirasago-German, B.; Perez-Lezama, E.L., and Obeso-Nieblas, M., 2018. Variability of chlorophyll a concentration and Halocline depth in La Paz Bay (Gulf of California, Mexico) and the relationship to Pacific large-scale climatic phenomena. Variability of the chlorophyll a (Chl a) concentration and halocline depth in La Paz Bay were analyzed and compared against the variability of North Pacific (NP) large-scale phenomena and local winds during 1999–2009. Chl a data were obtained from satellite images, and halocline depth was obtained from in situ data. Eight large-scale phenomenon climate indices and satellite wind data were also used in this work. Chl a was processed on three timescales—interannual, mean annual cycle, and monthly time series. The halocline depth was processed as a time series. The Chl a interannual analysis revealed a high variability in the study period, with the highest concentration in 2001 and the lowest in 2005. The Pacific Decadal Oscillation (PDO) was...

Seasonal air–sea CO2 fluxes in the southern California Current off the Baja California Peninsula (Mexico)

Seasonal climatology of air–sea CO2 exchange was estimated from in situ sea surface CO2 partial pressure, temperature, salinity, and satellite wind data obtained from 2004 to 2011 in the southern region of the California Current, off the Baja California Peninsula (Mexico). The average annual CO2 flux indicates that the study area is a source of CO2 to the atmosphere (0.65 mmol m–2 d–1). It changes from being a source in summer (2.33 mmol m–2 d–1) and autumn (0.92 mmol m–2 d–1) to acting as a sink in winter (–0.26 mmol m–2 d–1) and spring (–0.37 mmol m–2 d–1). The area to the north of latitud 28ºN (off Punta Eugenia) is a CO2 sink (–0.42 mmol m–2 d–1), whereas the area to the south of this latitude is a source of CO2 to the atmosphere (1.80 mmol m–2 d–1), mostly due to thermodynamic effects. The northern coastal zone is a permanent CO2 sink (–1.29 mmol m–2 d–1). During the 2004 El Niño event the whole area contributed 2.00 mmol m–2 d–1 of CO2 to the atmosphere, but during the 2011 La Niña the ocean absorbed 5.30 mmol m–2 d–1 as a result of physical and biological dynamics. The seasonalcycle is dominated by temperature rather than biological effects, except in the northern coastal area. It is necessary to continue with in situ measurements of the CO2 system to have solid foundations to estimate the effect of the long-term increase in dissolved inorganic carbon onmarine organisms.

Role of winds and tides in timing of beach strandings, occurrence, and significance of swarms of the jellyfish Crambione mastigophora Mass 1903 (Scyphozoa: Rhizostomeae: Catostylidae) in north-western Australia

Very large swarms of the red jellyfish Crambione mastigophora in north-western Australia disrupt swimming on tourist beaches causing economic impacts. In October 2012, jellyfish stranding on Cable Beach (density 2.20 ± 0.43 ind. m−2) was estimated at 52.8 million individuals or 14,172 t wet weight along 15 km of beach. Reports of strandings after this period and up to 250 km south of this location indicate even larger swarm biomass. Strandings of jellyfish were significantly associated with a 2-day lag in conditions of small tidal ranges (<5 m). More than 90% of strandings occurred 2 days after winds were blowing onshore, but with the small number of days when satellite wind data were available during the study period, this result was not statistically significant. Dedicated instrument measurements of meteorological parameters, rather than the indirect measures used in this study (satellite winds and modelled currents) may improve the predictability of such events and help authorities to plan for and manage swimming activity on beaches. We also show a high incidence of predation by C. mastigophora on bivalve larvae which may have a significant impact on the reproductive output of pearl oyster broodstock in the region.

VecStatGraphs2D, A Tool for the Analysis of Two-Dimensional Vector Data: An Example Using QuikSCAT Ocean Winds

Circular or directional data are used in disciplines such as meteorology, geomatics, biology, and geology. The analysis of angular data requires special methods that are available in some statistical packages. However, these tools analyze only the angular values and do not include the vector modules, assuming unit vectors in all cases. In this letter, an open-source graphic and statistical package, i.e., VecStatGraphs2D, is described. It works in the R environment and provides statistics and graphics for modules (linear) and azimuths (circular), as well as graphics for the joint analysis of modules and azimuths. QuikSCAT satellite wind data are used to demonstrate some features of the package. QuikSCAT data are non-unit-length vectors, where both azimuth and magnitude (speed) are derived from u and v vector components (vector projections over the x- and y-axes). The example is used to show the seasonal change of winds in the Intertropical Convergence Zone, a key area in the ocean bird migration from the North to South Atlantic oceans.

The supply of excess phosphate across the Gulf Stream and the maintenance of subtropical nitrogen fixation

with estimated rates between 1 and 20 × 10 11 mol nitrogen fixed annually. However, the region’s nutrient reservoir beneath the euphotic zone is so enriched in nitrate relative to phosphate that it is perplexing how fixation might be sustained there. Here, we investigate whether the physical transport of excess phosphate into the subtropical gyre is sufficient to sustain nitrogen fixation in the gyre. Specifically, we assess the Ekman advection and isopycnal mixing of excess phosphate to the subtropical North Atlantic, using detailed hydrographic and nutrient sections occupied across the Gulf Stream combined with satellite wind data. Ekman advection and along‐isopycnal mixing provide a source of approximately 2 × 10 10 mol yr −1 of excess phosphate in the northwestern subtropics, a physical mechanism that has the potential to support more than 3 × 10 11 mol yr −1 of biological nitrogen fixation, after accounting for alternative sinks of excess phosphate. This excess phosphate supply across the gyre’s northern boundary and high nitrogen fixation there offers a mechanism that can explain both the maintenance of subtropical North Atlantic nitrogen fixation in a phosphate‐poor environment and help account for the weak gradients in the proxies of fixation observed along interior circulation pathways of the gyre.

Seasonal Evolution of Aleutian Low Pressure Systems: Implications for the North Pacific Subpolar Circulation*

Abstract The seasonal change in the development of Aleutian low pressure systems from early fall to early winter is analyzed using a combination of meteorological reanalysis fields, satellite sea surface temperature (SST) data, and satellite wind data. The time period of the study is September–December 2002, although results are shown to be representative of the long-term climatology. Characteristics of the storms were documented as they progressed across the North Pacific, including their path, central pressure, deepening rate, and speed of translation. Clear patterns emerged. Storms tended to deepen in two distinct geographical locations—the Gulf of Alaska in early fall and the western North Pacific in late fall. In the Gulf of Alaska, a quasi-permanent “notch” in the SST distribution is argued to be of significance. The signature of the notch is imprinted in the atmosphere, resulting in a region of enhanced cyclonic potential vorticity in the lower troposphere that is conducive for storm development. Later in the season, as winter approaches and the Sea of Okhotsk becomes partially ice covered and cold, the air emanating from the Asian continent leads to enhanced baroclinicity in the region south of Kamchatka. This corresponds to enhanced storm cyclogenesis in that region. Consequently, there is a seasonal westward migration of the dominant lobe of the Aleutian low. The impact of the wind stress curl pattern resulting from these two regions of storm development on the oceanic circulation is investigated using historical hydrography. It is argued that the seasonal bimodal input of cyclonic vorticity from the wind may be partly responsible for the two distinct North Pacific subarctic gyres.

Physical and bio-optical observations of oceanic cyclones west of the island of Hawai’i

Abstract Interdisciplinary observations of mesoscale eddies were made to the west of the island of Hawai’i. A central goal of the studies is to improve our understanding of the coupling of physical, biological, and biogeochemical processes that occur within these eddies. A specific objective was to test the hypothesis that the physical mechanisms of mesoscale eddies result in increases in nutrient availability to the euphotic layer, increases in primary production, changes in biological community compositions and size distributions, and increases in carbon flux to the deep sea. Data were obtained from ships, surface drifters, and satellite sensors during three separate field experiments. Variability was associated with two well-developed cyclonic, cold-core mesoscale eddies, Cyclone Noah and Cyclone Opal, which were observed during the E-Flux I (survey November 6–20, 2004) and E-Flux III (survey March 10–27, 2005) field campaigns, respectively. No mesoscale eddies were found during E-Flux II (survey January 10–19) when winds were erratic in magnitude and direction, supporting the hypothesis that persistent trade winds drive the production of cold-core mesoscale eddies in the lee of the Hawaiian Islands. Cold-core eddies were present in the E-Flux study area for about 2/3 of a year beginning May 1, 2004 and trade winds prevailed for about 3/4 of the same year. Both Cyclone Noah and Cyclone Opal were generated during strong, persistent northeasterly trade wind conditions and appeared downwind of the ’Alenuihaha Channel separating the islands of Maui and Hawai’i. The likely production mechanism for both mesoscale cold-core eddies involves localized wind-stress-curl-induced upwelling produced by trade wind forcing. Cyclone Noah was likely spun up by strong trade winds just to the southwest of the ’Alenuihaha Channel ( ∼ 20 . 10 ∘ N , 156 . 40 ∘ W ) between August 13 and 21, 2004 based on MODIS satellite sea-surface temperature (SST) imagery and QuikScat satellite wind data, and apparently began to dissipate by mid-December 2004. Cyclone Opal was likely spun up by strong trade winds between February 2 and 18, 2005 southwest of the ’Alenuihaha Channel ( ∼ 20 . 30 ∘ N , 156 . 30 ∘ W ), but was no longer evident in April 2005. Both Cyclone Noah and Cyclone Opal had strong physical, chemical, and biological expressions and displayed similar maximum tangential current speeds of ∼ 60 cm s - 1 . However, Cyclone Opal was more symmetric and larger in scale (roughly 180–200 km in diameter compared to ∼ 160 km in horizontal scale for Cyclone Noah). Both mesoscale eddies displayed significant doming in their centers and in some cases outcroppings of isothermal, isopycnal, nutrient, and chlorophyll a isopleths. After formation and a slow drift southward, Cyclone Noah remained in nearly the same location (roughly 19 . 60 ∘ N , 156 . 50 ∘ W ) during the 3-week in situ sampling period, whereas Cyclone Opal drifted southward by ∼ 165 km over a similar time span of sampling. Interestingly, the physical manifestations of both features were relatively unchanged during the ship-based surveys; however, the biology appears to have evolved within Cyclone Opal. The present report sets the context for several other E-Flux studies.

Space–time variability of the Plata plume inferred from ocean color

Satellite ocean color and surface salinity data are used to characterize the space–time variability of the Río de la Plata plume. River outflow and satellite wind data are also used to assess their combined effect on the plume spreading over the Southwestern South Atlantic continental shelf. Over the continental shelf satellite-derived surface chlorophyll- a (CSAT) estimated by the OC4v4 SeaWiFS retrieval algorithm is a good indicator of surface salinity. The log (CSAT) distribution over the shelf presents three distinct modes, each associated to: Subantarctic Shelf Water, Subtropical Shelf Water and Plata Plume water. The log (CSAT) 0.4–0.8 range is associated with a sharp surface salinity transition across the offshore edge of the Plata plume from 28.5 to 32.5. Waters of surface salinity <31, derived from mixtures of Plata waters with continental shelf waters, are associated to log (CSAT)>0.5. In austral winter CSAT maxima extend northeastward from the Plata estuary beyond 30°S. In summer the high CSAT waters along the southern Brazil shelf retreat to 32°S and extend south of the estuary to about 37.5°S, only exceeding this latitude during extraordinary events. The seasonal CSAT variations northeast of the estuary are primarily controlled by reversals of the along-shore wind stress and surface currents. Along-shore wind stress and CSAT variations in the inner and mid-shelves are in phase north of the estuary and 180° out of phase south of the estuary. At interannual time scales northernmost Plata plume penetrations in winter (∼1200 km from the estuary) are associated with more intense and persistent northeastward wind stress, which in the period 2000–2003, prevailed over the shelf south of 26°S. In contrast, in winter 1999, 2004 and 2005, characterized by weaker northeastward wind stress, the plume only reached between 650 and 900 km. Intense southwestward plume extensions beyond 38°S are dominated by interannual time scales and appear to be related to the magnitude of the river outflow. The plume response to large river outflow fluctuations observed at interannual time scales is moderate, except offshore from the estuary mouth, where outflow variations lead CSAT variations by about 2 months.

The Impact of Aircraft Dropsonde and Satellite Wind Data on Numerical Simulations of Two Landfalling Tropical Storms during the Tropical Cloud Systems and Processes Experiment

Abstract Dropwindsonde, Geostationary Operational Environmental Satellite-11 (GOES-11) rapid-scan atmospheric motion vectors, and NASA Quick Scatterometer (QuikSCAT) near-surface wind data collected during NASA’s Tropical Cloud Systems and Processes (TCSP) field experiment in July 2005 were assimilated into an advanced research version of the Weather Research and Forecasting (WRF) model using its three-dimensional variational data assimilation (3DVAR) system. The impacts of the mesoscale data assimilation on WRF numerical simulation of Tropical Storms Cindy and Gert (2005) near landfall are examined. Sensitivity of the forecasts to the assimilation of each single data type is investigated. Specifically, different 3DVAR strategies with different analysis update cycles and resolutions are compared in order to identify the better methodology for assimilating the data from research aircraft and satellite for tropical cyclone study. The results presented herein indicate the following. 1) Assimilation of dropwindsonde and satellite wind data into the WRF model improves the forecasts of the two tropical storms up to the landfall time. The QuikSCAT wind information is very important for improving the storm track forecast, whereas the dropwindsonde and GOES-11 wind data are also necessary for improved forecasts of intensity and precipitation. 2) Data assimilation also improves the quantitative precipitation forecasts (QPFs) near landfall of the tropical storms. 3) A 1-h rapid-update analysis cycle at high resolution (9 km) provides more accurate tropical cyclone forecasts than a regular 6-h analysis cycle at coarse (27 km) resolution. The high-resolution rapidly updated 3DVAR analysis cycle might be a practical way to assimilate the data collected from tropical cyclone field experiments.