IGARSS 2000. IEEE 2000 International Geoscience and Remote Sensing Symposium. Taking the Pulse of the Planet: The Role of Remote Sensing in Managing the Environment. Proceedings (Cat. No.00CH37120), 2000
Since June 1999, two satellite scatterometers are operational. The European Remote Sensing Satell... more Since June 1999, two satellite scatterometers are operational. The European Remote Sensing Satellite (ERS-2) scatterometer and the NASA Seawind scatterometer onboard the QuikSCAT satellite, provide estimation of surface wind vectors with high spatial and temporal resolutions, using different frequencies and resolution configurations. The paper presents the intercomparison between measurements inferred from the two sensors. On average, the two wind vectors
Since July 1987 the Special Sensor Microwave Imagers (SSM/I) on satellites in the U.S. Defense Me... more Since July 1987 the Special Sensor Microwave Imagers (SSM/I) on satellites in the U.S. Defense Meteorological Satellite Program provide surface wind speed computed from the measurements of the intensity of microwave radiation emitted from the ocean surface. The scatterometer and the altimeter of the European Remote Sensing Satellite (ERS-1) collect global measurements of sea surface winds. The three instruments use empirical models, which have been independently verified, to estimate wind speed in oceanic regions with an accuracy better than 2 m/s. Comparisons are made of scatterometer and altimeter, and of scatterometer and SSM/I wind speed measurements from the Atlantic tropical area during November 1992. The rms values of the differences between scatterometer and altimeter, and between scatterometer and SSM/I are 1.58 m/s and 1.48 m/s, respectively. There is no global bias between scatterometer and SSM/I wind estimates, but between scatterometer and altimeter wind speeds the bias is about 0.84 m/s. In order to assess the cause of the differences, comparisons are made in different environmental conditions. For instance the difference between the scatterometer and altimeter appears to be dependent on the significant wave height and the difference between scatterometer and SSM/I is dependent of the integrated water vapour content
[Proceedings] IGARSS'91 Remote Sensing: Global Monitoring for Earth Management, 1991
The first pre-operational scatterometer will fly onboard the European Space Agency (ESA) satellit... more The first pre-operational scatterometer will fly onboard the European Space Agency (ESA) satellite ERS1 in May 1991. Data will be generated off-line and will be accessible, early in 1992, to users in fields such as climatology, mesoscale meterology, ocean modeling and remote sensing. Specific objectives of the work are: (1) to develop and test algorithms used to infer wind from
Proceedings of IGARSS '94 - 1994 IEEE International Geoscience and Remote Sensing Symposium, 1994
As a result of tests performed since ERS-1 launch, the scatterometer archive was reprocessed usin... more As a result of tests performed since ERS-1 launch, the scatterometer archive was reprocessed using improved algorithms at "Centre ERS d'Archivage et de Traitement" located in the "Institut Francais de Recherche pour l'Exploitation de la MER". A model function based upon buoy and model wind data was developed and the Normalized Radar Cross Section (NRCS) observations are shown to fit
1] The physics of remote sensing sea surface measurements is still poorly understood under severe... more 1] The physics of remote sensing sea surface measurements is still poorly understood under severe weather conditions. Wind vector algorithms are usually developed for non-precipitating atmospheres and for wind speeds less than 20 m/s. In this study, we analyze observations from the QuikSCAT Ku-band scatterometer collocated with the WindSat full polarimetric microwave radiometer to estimate the potential of these two instruments for sea surface wind retrieval under severe weather conditions. The Jason altimeter provides independent measurements of wind speed and rain rate for comparison purposes. The sensitivity of the radar cross-sections and brightness temperatures to the wind speed and direction is directly studied from the observations and compared with semi empirical models. This study clearly demonstrates that wind vector retrieval under extreme condition is feasible. Comparisons between QuikSCAT and WindSat coincident observations evidence a better sensitivity of the active mode to low and moderate winds and more sensitivity to high wind speeds in the passive mode. Although the WindSat observations are affected by water vapor, cloud, and rain, especially at and above 18 GHz, the measurements are sensitive to wind speed even at high wind speeds. Contrarily to the active instrument, there is no saturation at high winds. The sensitivity clearly tends to increase for winds above 15 m/s. For the wind direction, the amplitude of the azimuthal modulation in the active mode decreases with increasing wind speed, while it increases for the passive measurements. The development of specific wind retrievals under severe weather conditions is encouraged and a simple illustration is provided. Citation: Quilfen, Y., C. Prigent, B. Chapron, A. A. Mouche, and N. Houti (2007), The potential of QuikSCAT and WindSat observations for the estimation of sea surface wind vector under severe weather conditions,
Asymptotic models (small perturbation and small slope approximation at first-order, Kirchhoff app... more Asymptotic models (small perturbation and small slope approximation at first-order, Kirchhoff approximation or two-scale model) used to predict the normalized radar cross section of the sea surface generally fail to reproduce in detail backscatter radar measurements. In particular, the predicted polarization ratio versus incidence and azimuth angles is not in agreement with experimental data. This denotes the inability of these
The absolute calibration of the relationship between air-sea CO2 transfer velocity, k, and wind s... more The absolute calibration of the relationship between air-sea CO2 transfer velocity, k, and wind speed, U, has been a topic of debate for some time, because k global average, <k>, as deduced from Geochemical Ocean Sections Study oceanic 14 C inventory has differed from that deduced from experimental k-U relationships. Recently, new oceanic 14C inventories and inversions have lead to a lower <k>. In addition, new measurements performed at sea in high-wind speed conditions have led to new k-U relationship. Meanwhile, quality and sampling of satellite wind speeds has greatly improved. The QuikSCAT scatterometer has provided high-quality wind speeds for more than 7 years. This allows us to estimate the global distributions of k computed using k-U relationships and temperature dependent Schmidt numbers from 1999 to 2006. Given the difficulty of measuring in situ wind speed very accurately, we performed a sensitivity study of the k uncertainty which results from QuikSCAT U uncertainties. New QuikSCAT-buoy U comparisons in the northern Atlantic Ocean and in the Southern Ocean confirm the excellent precision of QuikSCAT U (RMS difference of about 1 m s −1 ), but it is possible that QuikSCAT overestimates wind speeds by 5%, leading to a possible overestimation of k derived with quadratic relationships by 10%. The <k> values obtained with two recent experimental k-U relationships are very close, between 15.9 and 17.9 cm h −1 , and within the error bar of k average deduced from the new oceanic 14 C inventory.
Satellite wind and wind stress fields at the sea surface, derived from the scatterometers on Euro... more Satellite wind and wind stress fields at the sea surface, derived from the scatterometers on European Remote Sensing satellites 1 and 2 (ERS-1 and ERS-2) are used to drive the ocean general circulation model (OGCM) OPA in the tropical oceans. The results of the impact of ERS winds are ...
This paper presents an analysis of the wind speed dependence of upwind/downwind asymmetry (UDA) a... more This paper presents an analysis of the wind speed dependence of upwind/downwind asymmetry (UDA) and upwind-crosswind anisotropy (UCA) as derived from global C band VV-polarized ERS 1 and 2 and Ku band VV- and HH-polarized NASA scatterometer (NSCAT) data. Interpretation of the results relies on identifying relationships between the differing frequencies and incidence angles that are consistent with Bragg scattering
IEEE Transactions on Geoscience and Remote Sensing, 1999
This study examines the consistency of surface wind-speeds estimated from the European Remote Sen... more This study examines the consistency of surface wind-speeds estimated from the European Remote Sensing Satellite (ERS-1) scatterometer, ERS-1 altimeter, and the special sensor microwave/imager (SSM/I). The goal is to combine these wind estimates to produce surface wind fields. With this in mind, a comparison with buoy wind measurements and comparison among the three sensors is performed. According to the in
The global surface wind fields calculated from scatterometer observations have been updated to co... more The global surface wind fields calculated from scatterometer observations have been updated to cover the decade 1991-2001. This involves an enhancement of the remotely sensed wind retrievals, quality control, and objective method. This paper presents the improvements with respect to the first release and provides the main characteristics of the surface parameter fields. The accuracy of the resulting weekly and monthly surface wind fields is studied through comparisons with buoy and numerical model averaged wind estimates.
Abstract-—Uncertainties in the surface wind field have long been recognized as a major limitation... more Abstract-—Uncertainties in the surface wind field have long been recognized as a major limitation in the interpretation of results obtained by oceanic circulation models. It is especially true in the tropical oceans, where the response to wind forcing is very strong on short time scales. The purpose of this paper is to show that these uncertainties can be greatly reduced by using spaceborne wind sensors that provide accurate measurements on a global basis. Surface winds over the global oceans have been measured by scafterometry since the launch of the European Remote Sensing Satellite (ERS-1) in August 1991 by the European Space Agency, Noordwijk, The Netherlands, and is currently provided by ERS-2, launched in April 1995. The ground-track wind vectors are processed to compute mean weekly surface winds onto a Io square grid at the Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Plouzane, France. These winds are validated by comparison with the buoy array in the tropical Pacific ocean, showing good agreement. In order to further evaluate this wind field, the three-dimensional (3-D) ocean model OPA7 developed at Laboratoire d'Océanographie Dynamique et de Climatologie, Paris, France, is forced over the tropical oceans by the ERS-de-rived wind stress fields and by fields from the atmospheric model Arpege/Climat. Selected ocean parameters are defined in order to validate the ocean model results with measurements of the tropical ocean and global atmosphere (TOGA) buoys in the Pacific ocean. The ability of the model to describe the short scale (a few weeks to a few years) oceanic variability is greatly enhanced when the satellite-derived surface forcing is used. In this paper, we present further comparison of the ocean model results with the TOPEX-Poseidon altimeter measurements. Simulated and measured sea level variability are described over the three tropical oceans. The annual and semi-annual signals, as well as the interannual variability, partly linked to the El Niño southern oscillation (ENSO) phenomenon, are well simulated by the OPA7 model when the satellite winds are used. Furthermore, it shows that the objective method, kriging technique, used to interpolate the mean ERS wind fields, dramatically reduces the effects of the satellite bandlike sampling. In the last part of this paper, we focus on the relationship between the wind stress anomalies and the sea level anomalies in the case of the 1997-1998 El Niño event. It clearly shows that sea level anomalies in the eastern and western parts of the Pacific are strongly linked to wind stress anomalies in the central Pacific. The forthcoming scatterometers aboard the METOP and ADEOS satellites will provide a much better coverage. 11 will enable the wind variability spatial and temporal scales to be resolved better, in order that wind uncertainties no longer blur the interpretation of ocean circulation numerical models results.
Unprecedented views of surface wind fields in tropical cyclones (hereafter TCs) are provided by t... more Unprecedented views of surface wind fields in tropical cyclones (hereafter TCs) are provided by the European Remote Sensing Satellite (ERS) C band scatterometer. Scatterometer measurements at C band are able to penetrate convective storms clouds, observing the surface wind fields with good accuracy. However the resolution of the measurements (50x50 km 2) limits the interpretation of the scatterometer signals in such mesoscale events. The strong gradients of the surface wind existing at scales of a few kms are smoothed in the measured features such as the intensity and location of the wind maxima, and the position of the center. Beyond the ERS systems, the scatterometers on-board the ADEOS and METOP satellites, designed by the Jet Propulsion Laboratory and by the European Space Agency, respectively, will be able to produce measurements of the backscattering coefficient at about 25x25 km 2 resolution. A few sets of ERS-1 orbits sampling TC events were produced with an experimental 25x25 km 2 resolution. Enhancing the resolution by a factor of 2 allows location of the wind maxima and minima in a TC with a much better accuracy than at 50 km resolution. In addition, a better resolution reduces the geophysical noise (variability of wind speed within the cell and effect of rain) that dominates the radiometric noise and hence improves the definition of the backscattering measurements. A comprehensive analysis of the backscattering measurements in the case of high winds and high sea states obtained within TCs is proposed in order to refine the interpretation of the wind vector derived from a backscattering model that is currently only calibrated up to moderate winds (< 20 m/s) in neutral conditions. Observations of the TOPEX-POSEIDON dual-frequency altimeter are also used for that purpose. Patterns of the surface winds in TCs are described and characteristic features concerning asymmetries in the maximum winds and in the divergence field are discussed.
An analysis is presented for the spatial and intensity distributions of North Atlantic extreme
at... more An analysis is presented for the spatial and intensity distributions of North Atlantic extreme atmospheric events crossing the buoyant Amazon-Orinoco freshwater plume. The sea surface cooling amplitude in the wake of an ensemble of storm tracks traveling in that region is estimated from satellite products for the period 1998–2012. For the most intense storms, cooling is systematically reduced by 50% over the plume area compared to surroundings open-ocean waters. Historical salinity and temperature observations from in situ profiles indicate that salt-driven vertical stratification, enhanced oceanic heat content, and barrier-layer presence within the plume waters are likely key oceanic factors to explain these results. Satellite SMOS surface salinity data combined with in situ observations are further used to detail the oceanic response to category 4 hurricane Igor in 2010. Argo and satellite measurements confirm the haline stratification impact on the cooling inhibition as the hurricane crossed the river plume. Over this region, the SSS mapping capability is further tested and demonstrated to monitor the horizontal distribution of the vertical stratification parameter. SMOS SSS data can thus be used to consistently anticipate the cooling inhibition in the wake of TCs traveling over the Amazon-Orinoco plume region
Sea surface estimates of local winds, waves, and rain-rate conditions are crucial to complement i... more Sea surface estimates of local winds, waves, and rain-rate conditions are crucial to complement infrared/ visible satellite images in estimating the strength of tropical cyclones (TCs). Satellite measurements at microwave frequencies are thus key elements of present and future observing systems. Available for more than 20 years, passive microwave measurements are very valuable but still suffer from insufficient resolution and poor wind vector retrievals in the rainy conditions encountered in and around tropical cyclones. Scatterometer and synthetic aperture radar active microwave measurements performed at the C and Ku band on board the European Remote Sensing (ERS), the Meteorological Operational (MetOp), the Quick Scatterometer (QuikSCAT), the Environmental Satellite (Envisat), and RadarSat satellites can also be used to map the surface wind field in storms. Their accuracy is limited in the case of heavy rain and possible saturation of the microwave signals is reported. Altimeter dual-frequency measurements have also been shown to provide along-track information related to surface wind speed, wave height, and vertically integrated rain rate at about 6-km resolution. Although limited for operational use by their dimensional sampling, the dual-frequency capability makes altimeters a unique satellite-borne sensor to perform measurements of key surface parameters in a consistent way. To illustrate this capability two Jason-1 altimeter passes over Hurricanes Isabel and Wilma are examined. The area of maximum TC intensity, as described by the National Hurricane Center and by the altimeter, is compared for these two cases. Altimeter surface wind speed and rainfall-rate observations are further compared with measurements performed by other remote sensors, namely, the Tropical Rainfall Measuring Mission instruments and the airborne Stepped Frequency Microwave Radiometer.
In the North Atlantic, there are more than 10
extratropical storms every year with hurricaneforce... more In the North Atlantic, there are more than 10 extratropical storms every year with hurricaneforce winds (Fig. 1). Observing the dynamics and effects of these storms is a particular challenge because in-situ observations are scarce and opportunities to apply and validate remote-sensing techniques for wind speeds above hurricane force and for phenomenal sea states are rare. We show here that a suite of data from different sources—a combination that may not be typical in forecasting environments—can give a remarkably coherent characterization of an extreme storm event and associated wave fields. In February 2011, the North Atlantic storm Quirin produced the ideal conditions to illustrate this synergetic approach.
IGARSS 2000. IEEE 2000 International Geoscience and Remote Sensing Symposium. Taking the Pulse of the Planet: The Role of Remote Sensing in Managing the Environment. Proceedings (Cat. No.00CH37120), 2000
Since June 1999, two satellite scatterometers are operational. The European Remote Sensing Satell... more Since June 1999, two satellite scatterometers are operational. The European Remote Sensing Satellite (ERS-2) scatterometer and the NASA Seawind scatterometer onboard the QuikSCAT satellite, provide estimation of surface wind vectors with high spatial and temporal resolutions, using different frequencies and resolution configurations. The paper presents the intercomparison between measurements inferred from the two sensors. On average, the two wind vectors
Since July 1987 the Special Sensor Microwave Imagers (SSM/I) on satellites in the U.S. Defense Me... more Since July 1987 the Special Sensor Microwave Imagers (SSM/I) on satellites in the U.S. Defense Meteorological Satellite Program provide surface wind speed computed from the measurements of the intensity of microwave radiation emitted from the ocean surface. The scatterometer and the altimeter of the European Remote Sensing Satellite (ERS-1) collect global measurements of sea surface winds. The three instruments use empirical models, which have been independently verified, to estimate wind speed in oceanic regions with an accuracy better than 2 m/s. Comparisons are made of scatterometer and altimeter, and of scatterometer and SSM/I wind speed measurements from the Atlantic tropical area during November 1992. The rms values of the differences between scatterometer and altimeter, and between scatterometer and SSM/I are 1.58 m/s and 1.48 m/s, respectively. There is no global bias between scatterometer and SSM/I wind estimates, but between scatterometer and altimeter wind speeds the bias is about 0.84 m/s. In order to assess the cause of the differences, comparisons are made in different environmental conditions. For instance the difference between the scatterometer and altimeter appears to be dependent on the significant wave height and the difference between scatterometer and SSM/I is dependent of the integrated water vapour content
[Proceedings] IGARSS'91 Remote Sensing: Global Monitoring for Earth Management, 1991
The first pre-operational scatterometer will fly onboard the European Space Agency (ESA) satellit... more The first pre-operational scatterometer will fly onboard the European Space Agency (ESA) satellite ERS1 in May 1991. Data will be generated off-line and will be accessible, early in 1992, to users in fields such as climatology, mesoscale meterology, ocean modeling and remote sensing. Specific objectives of the work are: (1) to develop and test algorithms used to infer wind from
Proceedings of IGARSS '94 - 1994 IEEE International Geoscience and Remote Sensing Symposium, 1994
As a result of tests performed since ERS-1 launch, the scatterometer archive was reprocessed usin... more As a result of tests performed since ERS-1 launch, the scatterometer archive was reprocessed using improved algorithms at &quot;Centre ERS d&#39;Archivage et de Traitement&quot; located in the &quot;Institut Francais de Recherche pour l&#39;Exploitation de la MER&quot;. A model function based upon buoy and model wind data was developed and the Normalized Radar Cross Section (NRCS) observations are shown to fit
1] The physics of remote sensing sea surface measurements is still poorly understood under severe... more 1] The physics of remote sensing sea surface measurements is still poorly understood under severe weather conditions. Wind vector algorithms are usually developed for non-precipitating atmospheres and for wind speeds less than 20 m/s. In this study, we analyze observations from the QuikSCAT Ku-band scatterometer collocated with the WindSat full polarimetric microwave radiometer to estimate the potential of these two instruments for sea surface wind retrieval under severe weather conditions. The Jason altimeter provides independent measurements of wind speed and rain rate for comparison purposes. The sensitivity of the radar cross-sections and brightness temperatures to the wind speed and direction is directly studied from the observations and compared with semi empirical models. This study clearly demonstrates that wind vector retrieval under extreme condition is feasible. Comparisons between QuikSCAT and WindSat coincident observations evidence a better sensitivity of the active mode to low and moderate winds and more sensitivity to high wind speeds in the passive mode. Although the WindSat observations are affected by water vapor, cloud, and rain, especially at and above 18 GHz, the measurements are sensitive to wind speed even at high wind speeds. Contrarily to the active instrument, there is no saturation at high winds. The sensitivity clearly tends to increase for winds above 15 m/s. For the wind direction, the amplitude of the azimuthal modulation in the active mode decreases with increasing wind speed, while it increases for the passive measurements. The development of specific wind retrievals under severe weather conditions is encouraged and a simple illustration is provided. Citation: Quilfen, Y., C. Prigent, B. Chapron, A. A. Mouche, and N. Houti (2007), The potential of QuikSCAT and WindSat observations for the estimation of sea surface wind vector under severe weather conditions,
Asymptotic models (small perturbation and small slope approximation at first-order, Kirchhoff app... more Asymptotic models (small perturbation and small slope approximation at first-order, Kirchhoff approximation or two-scale model) used to predict the normalized radar cross section of the sea surface generally fail to reproduce in detail backscatter radar measurements. In particular, the predicted polarization ratio versus incidence and azimuth angles is not in agreement with experimental data. This denotes the inability of these
The absolute calibration of the relationship between air-sea CO2 transfer velocity, k, and wind s... more The absolute calibration of the relationship between air-sea CO2 transfer velocity, k, and wind speed, U, has been a topic of debate for some time, because k global average, <k>, as deduced from Geochemical Ocean Sections Study oceanic 14 C inventory has differed from that deduced from experimental k-U relationships. Recently, new oceanic 14C inventories and inversions have lead to a lower <k>. In addition, new measurements performed at sea in high-wind speed conditions have led to new k-U relationship. Meanwhile, quality and sampling of satellite wind speeds has greatly improved. The QuikSCAT scatterometer has provided high-quality wind speeds for more than 7 years. This allows us to estimate the global distributions of k computed using k-U relationships and temperature dependent Schmidt numbers from 1999 to 2006. Given the difficulty of measuring in situ wind speed very accurately, we performed a sensitivity study of the k uncertainty which results from QuikSCAT U uncertainties. New QuikSCAT-buoy U comparisons in the northern Atlantic Ocean and in the Southern Ocean confirm the excellent precision of QuikSCAT U (RMS difference of about 1 m s −1 ), but it is possible that QuikSCAT overestimates wind speeds by 5%, leading to a possible overestimation of k derived with quadratic relationships by 10%. The <k> values obtained with two recent experimental k-U relationships are very close, between 15.9 and 17.9 cm h −1 , and within the error bar of k average deduced from the new oceanic 14 C inventory.
Satellite wind and wind stress fields at the sea surface, derived from the scatterometers on Euro... more Satellite wind and wind stress fields at the sea surface, derived from the scatterometers on European Remote Sensing satellites 1 and 2 (ERS-1 and ERS-2) are used to drive the ocean general circulation model (OGCM) OPA in the tropical oceans. The results of the impact of ERS winds are ...
This paper presents an analysis of the wind speed dependence of upwind/downwind asymmetry (UDA) a... more This paper presents an analysis of the wind speed dependence of upwind/downwind asymmetry (UDA) and upwind-crosswind anisotropy (UCA) as derived from global C band VV-polarized ERS 1 and 2 and Ku band VV- and HH-polarized NASA scatterometer (NSCAT) data. Interpretation of the results relies on identifying relationships between the differing frequencies and incidence angles that are consistent with Bragg scattering
IEEE Transactions on Geoscience and Remote Sensing, 1999
This study examines the consistency of surface wind-speeds estimated from the European Remote Sen... more This study examines the consistency of surface wind-speeds estimated from the European Remote Sensing Satellite (ERS-1) scatterometer, ERS-1 altimeter, and the special sensor microwave/imager (SSM/I). The goal is to combine these wind estimates to produce surface wind fields. With this in mind, a comparison with buoy wind measurements and comparison among the three sensors is performed. According to the in
The global surface wind fields calculated from scatterometer observations have been updated to co... more The global surface wind fields calculated from scatterometer observations have been updated to cover the decade 1991-2001. This involves an enhancement of the remotely sensed wind retrievals, quality control, and objective method. This paper presents the improvements with respect to the first release and provides the main characteristics of the surface parameter fields. The accuracy of the resulting weekly and monthly surface wind fields is studied through comparisons with buoy and numerical model averaged wind estimates.
Abstract-—Uncertainties in the surface wind field have long been recognized as a major limitation... more Abstract-—Uncertainties in the surface wind field have long been recognized as a major limitation in the interpretation of results obtained by oceanic circulation models. It is especially true in the tropical oceans, where the response to wind forcing is very strong on short time scales. The purpose of this paper is to show that these uncertainties can be greatly reduced by using spaceborne wind sensors that provide accurate measurements on a global basis. Surface winds over the global oceans have been measured by scafterometry since the launch of the European Remote Sensing Satellite (ERS-1) in August 1991 by the European Space Agency, Noordwijk, The Netherlands, and is currently provided by ERS-2, launched in April 1995. The ground-track wind vectors are processed to compute mean weekly surface winds onto a Io square grid at the Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Plouzane, France. These winds are validated by comparison with the buoy array in the tropical Pacific ocean, showing good agreement. In order to further evaluate this wind field, the three-dimensional (3-D) ocean model OPA7 developed at Laboratoire d'Océanographie Dynamique et de Climatologie, Paris, France, is forced over the tropical oceans by the ERS-de-rived wind stress fields and by fields from the atmospheric model Arpege/Climat. Selected ocean parameters are defined in order to validate the ocean model results with measurements of the tropical ocean and global atmosphere (TOGA) buoys in the Pacific ocean. The ability of the model to describe the short scale (a few weeks to a few years) oceanic variability is greatly enhanced when the satellite-derived surface forcing is used. In this paper, we present further comparison of the ocean model results with the TOPEX-Poseidon altimeter measurements. Simulated and measured sea level variability are described over the three tropical oceans. The annual and semi-annual signals, as well as the interannual variability, partly linked to the El Niño southern oscillation (ENSO) phenomenon, are well simulated by the OPA7 model when the satellite winds are used. Furthermore, it shows that the objective method, kriging technique, used to interpolate the mean ERS wind fields, dramatically reduces the effects of the satellite bandlike sampling. In the last part of this paper, we focus on the relationship between the wind stress anomalies and the sea level anomalies in the case of the 1997-1998 El Niño event. It clearly shows that sea level anomalies in the eastern and western parts of the Pacific are strongly linked to wind stress anomalies in the central Pacific. The forthcoming scatterometers aboard the METOP and ADEOS satellites will provide a much better coverage. 11 will enable the wind variability spatial and temporal scales to be resolved better, in order that wind uncertainties no longer blur the interpretation of ocean circulation numerical models results.
Unprecedented views of surface wind fields in tropical cyclones (hereafter TCs) are provided by t... more Unprecedented views of surface wind fields in tropical cyclones (hereafter TCs) are provided by the European Remote Sensing Satellite (ERS) C band scatterometer. Scatterometer measurements at C band are able to penetrate convective storms clouds, observing the surface wind fields with good accuracy. However the resolution of the measurements (50x50 km 2) limits the interpretation of the scatterometer signals in such mesoscale events. The strong gradients of the surface wind existing at scales of a few kms are smoothed in the measured features such as the intensity and location of the wind maxima, and the position of the center. Beyond the ERS systems, the scatterometers on-board the ADEOS and METOP satellites, designed by the Jet Propulsion Laboratory and by the European Space Agency, respectively, will be able to produce measurements of the backscattering coefficient at about 25x25 km 2 resolution. A few sets of ERS-1 orbits sampling TC events were produced with an experimental 25x25 km 2 resolution. Enhancing the resolution by a factor of 2 allows location of the wind maxima and minima in a TC with a much better accuracy than at 50 km resolution. In addition, a better resolution reduces the geophysical noise (variability of wind speed within the cell and effect of rain) that dominates the radiometric noise and hence improves the definition of the backscattering measurements. A comprehensive analysis of the backscattering measurements in the case of high winds and high sea states obtained within TCs is proposed in order to refine the interpretation of the wind vector derived from a backscattering model that is currently only calibrated up to moderate winds (< 20 m/s) in neutral conditions. Observations of the TOPEX-POSEIDON dual-frequency altimeter are also used for that purpose. Patterns of the surface winds in TCs are described and characteristic features concerning asymmetries in the maximum winds and in the divergence field are discussed.
An analysis is presented for the spatial and intensity distributions of North Atlantic extreme
at... more An analysis is presented for the spatial and intensity distributions of North Atlantic extreme atmospheric events crossing the buoyant Amazon-Orinoco freshwater plume. The sea surface cooling amplitude in the wake of an ensemble of storm tracks traveling in that region is estimated from satellite products for the period 1998–2012. For the most intense storms, cooling is systematically reduced by 50% over the plume area compared to surroundings open-ocean waters. Historical salinity and temperature observations from in situ profiles indicate that salt-driven vertical stratification, enhanced oceanic heat content, and barrier-layer presence within the plume waters are likely key oceanic factors to explain these results. Satellite SMOS surface salinity data combined with in situ observations are further used to detail the oceanic response to category 4 hurricane Igor in 2010. Argo and satellite measurements confirm the haline stratification impact on the cooling inhibition as the hurricane crossed the river plume. Over this region, the SSS mapping capability is further tested and demonstrated to monitor the horizontal distribution of the vertical stratification parameter. SMOS SSS data can thus be used to consistently anticipate the cooling inhibition in the wake of TCs traveling over the Amazon-Orinoco plume region
Sea surface estimates of local winds, waves, and rain-rate conditions are crucial to complement i... more Sea surface estimates of local winds, waves, and rain-rate conditions are crucial to complement infrared/ visible satellite images in estimating the strength of tropical cyclones (TCs). Satellite measurements at microwave frequencies are thus key elements of present and future observing systems. Available for more than 20 years, passive microwave measurements are very valuable but still suffer from insufficient resolution and poor wind vector retrievals in the rainy conditions encountered in and around tropical cyclones. Scatterometer and synthetic aperture radar active microwave measurements performed at the C and Ku band on board the European Remote Sensing (ERS), the Meteorological Operational (MetOp), the Quick Scatterometer (QuikSCAT), the Environmental Satellite (Envisat), and RadarSat satellites can also be used to map the surface wind field in storms. Their accuracy is limited in the case of heavy rain and possible saturation of the microwave signals is reported. Altimeter dual-frequency measurements have also been shown to provide along-track information related to surface wind speed, wave height, and vertically integrated rain rate at about 6-km resolution. Although limited for operational use by their dimensional sampling, the dual-frequency capability makes altimeters a unique satellite-borne sensor to perform measurements of key surface parameters in a consistent way. To illustrate this capability two Jason-1 altimeter passes over Hurricanes Isabel and Wilma are examined. The area of maximum TC intensity, as described by the National Hurricane Center and by the altimeter, is compared for these two cases. Altimeter surface wind speed and rainfall-rate observations are further compared with measurements performed by other remote sensors, namely, the Tropical Rainfall Measuring Mission instruments and the airborne Stepped Frequency Microwave Radiometer.
In the North Atlantic, there are more than 10
extratropical storms every year with hurricaneforce... more In the North Atlantic, there are more than 10 extratropical storms every year with hurricaneforce winds (Fig. 1). Observing the dynamics and effects of these storms is a particular challenge because in-situ observations are scarce and opportunities to apply and validate remote-sensing techniques for wind speeds above hurricane force and for phenomenal sea states are rare. We show here that a suite of data from different sources—a combination that may not be typical in forecasting environments—can give a remarkably coherent characterization of an extreme storm event and associated wave fields. In February 2011, the North Atlantic storm Quirin produced the ideal conditions to illustrate this synergetic approach.
Uploads
Papers by yves quilfen
Surface winds over the global oceans have been measured by scafterometry since the launch of the European Remote Sensing Satellite (ERS-1) in August 1991 by the European Space Agency, Noordwijk, The Netherlands, and is currently provided by ERS-2, launched in April 1995. The ground-track wind vectors are processed to compute mean weekly surface winds onto a Io square grid at the Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Plouzane, France. These winds are validated by comparison with the buoy array in the tropical Pacific ocean, showing good agreement. In order to further evaluate this wind field, the three-dimensional (3-D) ocean model OPA7 developed at Laboratoire d'Océanographie Dynamique et de Climatologie, Paris, France, is forced over the tropical oceans by the ERS-de-rived wind stress fields and by fields from the atmospheric model Arpege/Climat. Selected ocean parameters are defined in order to validate the ocean model results with measurements of the tropical ocean and global atmosphere (TOGA) buoys in the Pacific ocean. The ability of the model to describe the short scale (a few weeks to a few years) oceanic variability is greatly enhanced when the satellite-derived surface forcing is used.
In this paper, we present further comparison of the ocean model results with the TOPEX-Poseidon altimeter measurements. Simulated and measured sea level variability are described over the three tropical oceans. The annual and semi-annual signals, as well as the interannual variability, partly linked to the El Niño southern oscillation (ENSO) phenomenon, are well simulated by the OPA7 model when the satellite winds are used. Furthermore, it shows that the objective method, kriging technique, used to interpolate the mean ERS wind fields, dramatically reduces the effects of the satellite bandlike sampling. In the last part of this paper, we focus on the relationship between the wind stress anomalies and the sea level anomalies in the case of the 1997-1998 El Niño event. It clearly shows that sea level anomalies in the eastern and western parts of the Pacific are strongly linked to wind stress anomalies in the central Pacific. The forthcoming scatterometers aboard the METOP and ADEOS satellites will provide a much better coverage. 11 will enable the wind variability spatial and temporal scales to be resolved better, in order that wind uncertainties no longer blur the interpretation of ocean circulation numerical models results.
atmospheric events crossing the buoyant Amazon-Orinoco freshwater plume. The sea surface cooling
amplitude in the wake of an ensemble of storm tracks traveling in that region is estimated from satellite
products for the period 1998–2012. For the most intense storms, cooling is systematically reduced by 50%
over the plume area compared to surroundings open-ocean waters. Historical salinity and temperature
observations from in situ profiles indicate that salt-driven vertical stratification, enhanced oceanic heat content,
and barrier-layer presence within the plume waters are likely key oceanic factors to explain these
results. Satellite SMOS surface salinity data combined with in situ observations are further used to detail the
oceanic response to category 4 hurricane Igor in 2010. Argo and satellite measurements confirm the haline
stratification impact on the cooling inhibition as the hurricane crossed the river plume. Over this region, the
SSS mapping capability is further tested and demonstrated to monitor the horizontal distribution of the vertical
stratification parameter. SMOS SSS data can thus be used to consistently anticipate the cooling inhibition
in the wake of TCs traveling over the Amazon-Orinoco plume region
extratropical storms every year with hurricaneforce
winds (Fig. 1). Observing the dynamics
and effects of these storms is a particular challenge
because in-situ observations are scarce and opportunities
to apply and validate remote-sensing
techniques for wind speeds above hurricane force
and for phenomenal sea states are rare. We show
here that a suite of data from different sources—a
combination that may not be typical in forecasting
environments—can give a remarkably coherent
characterization of an extreme storm event and
associated wave fields. In February 2011, the North
Atlantic storm Quirin produced the ideal conditions
to illustrate this synergetic approach.
Surface winds over the global oceans have been measured by scafterometry since the launch of the European Remote Sensing Satellite (ERS-1) in August 1991 by the European Space Agency, Noordwijk, The Netherlands, and is currently provided by ERS-2, launched in April 1995. The ground-track wind vectors are processed to compute mean weekly surface winds onto a Io square grid at the Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Plouzane, France. These winds are validated by comparison with the buoy array in the tropical Pacific ocean, showing good agreement. In order to further evaluate this wind field, the three-dimensional (3-D) ocean model OPA7 developed at Laboratoire d'Océanographie Dynamique et de Climatologie, Paris, France, is forced over the tropical oceans by the ERS-de-rived wind stress fields and by fields from the atmospheric model Arpege/Climat. Selected ocean parameters are defined in order to validate the ocean model results with measurements of the tropical ocean and global atmosphere (TOGA) buoys in the Pacific ocean. The ability of the model to describe the short scale (a few weeks to a few years) oceanic variability is greatly enhanced when the satellite-derived surface forcing is used.
In this paper, we present further comparison of the ocean model results with the TOPEX-Poseidon altimeter measurements. Simulated and measured sea level variability are described over the three tropical oceans. The annual and semi-annual signals, as well as the interannual variability, partly linked to the El Niño southern oscillation (ENSO) phenomenon, are well simulated by the OPA7 model when the satellite winds are used. Furthermore, it shows that the objective method, kriging technique, used to interpolate the mean ERS wind fields, dramatically reduces the effects of the satellite bandlike sampling. In the last part of this paper, we focus on the relationship between the wind stress anomalies and the sea level anomalies in the case of the 1997-1998 El Niño event. It clearly shows that sea level anomalies in the eastern and western parts of the Pacific are strongly linked to wind stress anomalies in the central Pacific. The forthcoming scatterometers aboard the METOP and ADEOS satellites will provide a much better coverage. 11 will enable the wind variability spatial and temporal scales to be resolved better, in order that wind uncertainties no longer blur the interpretation of ocean circulation numerical models results.
atmospheric events crossing the buoyant Amazon-Orinoco freshwater plume. The sea surface cooling
amplitude in the wake of an ensemble of storm tracks traveling in that region is estimated from satellite
products for the period 1998–2012. For the most intense storms, cooling is systematically reduced by 50%
over the plume area compared to surroundings open-ocean waters. Historical salinity and temperature
observations from in situ profiles indicate that salt-driven vertical stratification, enhanced oceanic heat content,
and barrier-layer presence within the plume waters are likely key oceanic factors to explain these
results. Satellite SMOS surface salinity data combined with in situ observations are further used to detail the
oceanic response to category 4 hurricane Igor in 2010. Argo and satellite measurements confirm the haline
stratification impact on the cooling inhibition as the hurricane crossed the river plume. Over this region, the
SSS mapping capability is further tested and demonstrated to monitor the horizontal distribution of the vertical
stratification parameter. SMOS SSS data can thus be used to consistently anticipate the cooling inhibition
in the wake of TCs traveling over the Amazon-Orinoco plume region
extratropical storms every year with hurricaneforce
winds (Fig. 1). Observing the dynamics
and effects of these storms is a particular challenge
because in-situ observations are scarce and opportunities
to apply and validate remote-sensing
techniques for wind speeds above hurricane force
and for phenomenal sea states are rare. We show
here that a suite of data from different sources—a
combination that may not be typical in forecasting
environments—can give a remarkably coherent
characterization of an extreme storm event and
associated wave fields. In February 2011, the North
Atlantic storm Quirin produced the ideal conditions
to illustrate this synergetic approach.