Theoretical modeling of dual-frequency scatterometer response: improving ocean wind and rainfall effects

Ocean surface wind is a key parameter of the Earth’s climate system. Occurring at the interface between the ocean and the atmosphere, ocean winds modulate fluxes of heat, moisture and gas exchanges. They reflect the lower branch of the atmospheric circulation and represent a major driver of the ocean circulation. Studying the long-term trends and variability of the ocean surface winds is of key importance in our effort to understand the Earth’s climate system and the causes of its changes. More than three decades of surface wind data are available from spaceborne scatterometer/radiometer missions and there is an ongoing effort to inter-calibrate all these measurements with the aim of building a complete and continuous picture of the ocean wind variability. Currently, spaceborne scatterometer wind retrievals are obtained by inversion algorithms of empirical Geophysical Model Functions (GMFs), which represent the relationship between ocean surface backscattering coefficient and the wind parameters. However, by being measurement-dependent, the GMFs are sensor-specific and, in addition, they may be not properly defined in all weather conditions. This may reduce the accuracy of the wind retrievals in presence of rain and it may also lead to inconsistencies amongst winds retrieved by different sensors. Theoretical models of ocean backscatter have the big potential of providing a more general and understandable relation between the measured microwave backscatter and the surface wind field than empirical models. Therefore, the goal of our research is to understand and address the limitations of the theoretical modeling, in order to propose a new strategy towards the definition of a unified theoretical model able to account for the effects of both wind and rain. In this work, it is described our approach to improve the theoretical modeling of the ocean response, starting from the Ku-band (13.4 GHz) frequency and then broadening the analysis at C-band (5.3 GHz) frequency. This research has revealed the need for new understanding of the frequency-dependent modeling of the surface backscatter in response to the wind-forced surface wave spectrum. Moreover, our ocean wave spectrum modification introduced to include the influences of the surface rain, allows the interpretation/investigation of the scatterometer observations in terms not only of the surface winds but also of the surface rain, defining an additional step needed to improve the wind retrievals algorithms as well as the possibility to jointly estimate wind and rain from scatterometer observations

A Ka-band wind Geophysical Model Function using doppler scatterometer measurements from the Air-Sea Interaction Tower experiment

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Polverari, F., Wineteer, A., Rodríguez, E., Perkovic-Martin, D., Siqueira, P., Farrar, J., Adam, M., Closa Tarrés, M., & Edson, J. A Ka-band wind Geophysical Model Function using doppler scatterometer Measurements from the Air-Sea Interaction Tower experiment. Remote Sensing, 14(9), (2022): 2067, https://doi.org/10.3390/rs14092067.Physical understanding and modeling of Ka-band ocean surface backscatter is challenging due to a lack of measurements. In the framework of the NASA Earth Ventures Suborbital-3 Submesoscale Ocean Dynamics Experiment (S-MODE) mission, a Ka-Band Ocean continuous wave Doppler Scatterometer (KaBODS) built by the University of Massachusetts, Amherst (UMass) was installed on the Woods Hole Oceanographic Institution (WHOI) Air-Sea Interaction Tower. Together with ASIT anemometers, a new data set of Ka-band ocean surface backscatter measurements along with surface wind/wave and weather parameters was collected. In this work, we present the KaBODS instrument and an empirical Ka-band wind Geophysical Model Function (GMF), the so-called ASIT GMF, based on the KaBODS data collected over a period of three months, from October 2019 to January 2020, for incidence angles ranging between 40° and 68°. The ASIT GMF results are compared with an existing Ka-band wind GMF developed from data collected during a tower experiment conducted over the Black Sea. The two GMFs show differences in terms of wind speed and wind direction sensitivity. However, they are consistent in the values of the standard deviation of the model residuals. This suggests an intrinsic geophysical variability characterizing the Ka-band surface backscatter. The observed variability does not significantly change when filtering out swell-dominated data, indicating that the long-wave induced backscatter modulation is not the primary source of the KaBODS backscatter variability. We observe evidence of wave breaking events, which increase the skewness of the backscatter distribution in linear space, consistent with previous studies. Interestingly, a better agreement is seen between the GMFs and the actual data at an incidence angle of 60° for both GMFs, and the statistical analysis of the model residuals shows a reduced backscatter variability at this incidence angle. This study shows that the ASIT data set is a valuable reference for studies of Ka-band backscatter. Further investigations are on-going to fully characterize the observed variability and its implication in the wind GMF development.F.P. research was funded by an appointment to the NASA Postdoctoral Program initially administered by Universities Space Research Association and now administered by Oak Ridge Associated Universities, under a contract with National Aeronautics and Space Administration. A.W., E.R., D.P.-M., P.S., M.A., M.C.T. and J.T.F. received support from the S-MODE project, an EVS-3 Investigation awarded under NASA Research Announcement NNH17ZDA001N-EVS3 (JPL/Cal Tech: 80NM0019F0058, WHOI: 80NSSC19K1256, UMass Amherst: 80NSSC19K1282). J.B.E. acknowledges support from NSF under grant number OCE-1756789

The role of scatterometry in ocean model forcing

VI Expanding Ocean Frontiers Conference, 5-7 July 2021, Barcelona, Spain.-- 25 page

Extrem, o no tan extrem, aquesta és la qüestió

3 pages, 2 figures[EN] This proves to be a question that is difficult to answer, but has far-reaching consequences for satellite meteorology, weather forecasting, oceanography, climate and hurricane advisories. Hurricanes are among the deadliest of the existing natural disasters, moreover causing formidable economic losses (Bevere et al. 2020). Accurate, short- and medium-range forecasting of their intensity and track (among others) are therefore essential to mitigate human and economic losses. In the longer range, it is also important to understand whether extreme weather conditions are becoming more extreme in a changing climate, stirring deeper waters in the ocean and hence affecting climate system dynamics. Unfortunately, tropical circulation conditions, such as El Niño and the Madden Julian Oscillation, are associated with large year-to-year variability in extreme wind speed distribution and their link to climate change is poorly understood, limiting our ability to determine whether the hurricane climatology is actually changing or not. […][ES] Esta es una pregunta difícil de responder, pero que tiene consecuencias de gran alcance para la meteorología satelital, la previsión meteorológica, la oceanografía, el clima y los programas de aviso de huracanes. Los huracanes se encuentran entre los desastres naturales más mortíferos y, además, causan enormes pérdidas económicas (Bevere et al. 2020). Por lo tanto, una predicción precisa de su intensidad y trayectoria a corto y medio plazo son esenciales para mitigar las pérdidas humanas y económicas. A más largo plazo, también es importante comprender si las condiciones meteorológicas extremas se están volviendo más extremas en el contexto del cambio climático, llegando a perturbar aguas más profundas y, por lo tanto, afectando la dinámica del sistema climático entero. Desafortunadamente, fenómenos como El Niño y la Oscilación de Madden-Julian, están asociados a una gran variabilidad interanual en la distribución de la intensidad de vientos extremos, con una dependencia del cambio climático todavía poco clara, limitando así nuestra capacidad para determinar si la climatología de huracanes en realidad está cambiando o no. […][CAT] Aquesta és una pregunta difícil de respondre, però que té conseqüències de gran abast per a la meteorologia satel·litària, la previsió meteorològica, l’oceanografia, el clima i els programes d’avís d’huracans. Els huracans es troben entre els desastres naturals més mortífers i, a més, causen enormes pèrdues econòmiques (Bevere et al. 2020). Per tant, una predicció precisa de la seva intensitat i trajectòria a curt i mitjà termini són essencials per a mitigar les pèrdues humanes i econòmiques. A més llarg termini, també és important comprendre si les condicions meteorològiques extremes s’estan tornant més extremes en el context del canvi climàtic, arribant a pertorbar aigües més profundes i, per tant, afectant la dinàmica del sistema climàtic sencer. Desafortunadament, fenòmens com El Niño i l’Oscil·lació de Madden-Julian estan associats a una gran variabilitat interanual en la distribució de la intensitat de vents extrems, amb una dependència del canvi climàtic encara poc clara, limitant així la nostra capacitat per a determinar si la climatologia d’huracans en realitat està canviant o no. […]Peer reviewe

Intercomparison of ASCAT sea surface winds and NWC/GEO-HRW Atmospheric Motion Vectors

20 pages, 9 figures, 4 tablesIn order to forecast the weather, conventional observations are sparse, whereas satellite based observations provide near global coverage at regular time intervals. [...]Peer Reviewe

Cross Talk between Reactive Nitrogen and Oxygen Species during the Hypersensitive Disease Resistance Response

Review relativa ai ruoli di ossido nitrico e specie reattive dell'ossigeno nella morte cellulare ipersensibile delle piante, come forma estrema di resistenza a patogeni

Are satellite-derived mesoscale sea surface winds useful in the Mediterranean?

7th International Conference on Meteorology and Climatology of the Mediterranean (MetMed), 4-6 March 2019, Palm

Modeling the Polarimetric Response to Atmospheric Precipitation on Synthetic Aperture Radar Imagery over Ocean

The polarimetric synthetic aperture radar (SAR) response at frequencies above the C-band, has proved to be affected by atmospheric events so that they can be used to extract information useful for studying weather conditions and climate changes. A microwave model for simulating the Normalized Radar Cross Section (NRCS) over sea surface, due to atmospheric precipitation, has been developed based on the model set up over bare soil. In this work, the main results obtained by considering a realistic scenario, using the wind vectors extracted by the System for Atmospheric Modeling (SAM) data to realize the synthetic surface model, are shown. The sea surface response has been performed using the SEAWIND2 software, which is able to simulate the scatterometer backscattering coefficient

On Dropsonde Surface-Adjusted Winds and Their Use for the Stepped Frequency Microwave Radiometer Wind Speed Calibration

8 pages, 7 figuresThe airborne stepped frequency microwave radiometer (SFMR) provides the measurements of 10-m ocean surface wind speed in high and extreme wind conditions. These winds are calibrated using the surface-adjusted wind estimates from the so-called dropsondes. The surface-adjusted winds are obtained from layer-averaged winds scaled to 10-m altitude to eliminate the local surface variability not associated with the storm strength. The SFMR measurements and, consequently, the surface-adjusted dropsonde winds represent a possible reference for satellite instrument and model calibration/validation at high and extreme wind conditions. To this end, representativeness errors that those measurements may introduce need to be taken into account to ensure that the storm variability is correctly resolved in satellite retrievals and modeling. In this work, we compare the SFMR winds with the dropsonde surface-adjusted winds derived from the so-called WL150 algorithm, which uses the lowest 150-m layer between 10 and 350 m. We use nine years of data from 2009 to 2017. We focus on the effects of the layer altitude and thickness. Our analysis shows that the layer altitude has a significant impact on dropsonde/SFMR wind comparisons. Moreover, the averaged winds obtained from layers thinner than the nominal 150 m and closer to the surface are more representative of the SFMR surface wind speed than the WL150 speeds. We also find that the surface-adjusted winds are more representative of 10-km horizontally averaged SFMR winds. We conclude that for calibration/validation purposes, the WL150 algorithm can introduce noise, and the use of actual 10-m dropsonde measurements should be further investigatedThis work was supported in part by the MCIN/AEI/10.13039/501100011033 and ERDF A way of making Europe through the Spanish Research and Development Project L-BAND under Grant ESP2017-89463-C3-1-R, in part by the MCIN/AEI/10.13039/501100011033 through the Project INTERACT under Grant PID2020-114623RB-C31, in part by the Spanish Government through the Severo Ochoa Center of Excellence Accreditation under Grant CEX2019-000928-S, in part by the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) through the Tender 16_166-STC under C-band High and Extreme- Force Speeds (CHEFS) Project EUM/CO/16/4600001953, and in part by the Jet Propulsion Laboratory, California Institute of Technology, through the National Aeronautics and Space Administration (NASA) Postdoctoral Program (NPP), initially administered by Universities Space Research Association and now administered by Oak Ridge Associated Universities, under a contract with NASAPeer reviewe

Precipitating cloud effects on the radar polarimetric signature at Ka band

In this work we will introduce a simulation framework developed to characterize precipitating clouds effects on spaceborne X- and Ka-Band spaceborne Synthetic Aperture Radar (SAR) systems. The work has been accomplished in the framework of an ESA project aiming at supporting instrument parametric analyses and establishing system requirements of spaceborne Ka polarimetric/interferometric radar. Preliminary results will be discussed