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  • 1
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    Sea-surface salinity fronts and associated salinity-minimum zones in the tropical ocean (2015)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 120 (2015): 4205–4225, doi:10.1002/2015JC010790.
    Description: The Intertropical Convergence Zone (ITCZ) is a major source of the surface freshwater input to the tropical open ocean. Under the ITCZ, sea-surface salinity (SSS) fronts that extend zonally across the basins are observed by the Aquarius/SAC-D mission and Argo floats. This study examined the evolution and forcing mechanisms of the SSS fronts. It is found that, although the SSS fronts are sourced from the ITCZ-freshened surface waters, the formation, structure, and propagation of these fronts are governed by the trade wind driven Ekman processes. Three features characterize the governing role of Ekman forcing. First, the SSS fronts are associated with near-surface salinity-minimum zones (SMZs) of 50–80 m deep. The SMZs are formed during December–March when the near-equatorial Ekman convergence zone concurs with an equatorward displaced ITCZ. Second, after the formation, the SMZs are carried poleward away at a speed of ∼3.5 km d−1 by Ekman transport. The monotonic poleward propagation is a sharp contrast to the seasonal north/south oscillation of the ITCZ. Lastly, each SMZ lasts about 12–15 months until dissipated at latitudes beyond 10°N/S. The persistence of more than 1 calendar year allows two SMZs to coexist during the formation season (December–March), with the newly formed SMZ located near the equator while the SMZ that is formed in the previous year located near the latitudes of 10–15° poleward after 1 year's propagation. The contrast between the ITCZ and SMZ highlights the dominance of Ekman dynamics on the relationship between the SSS and the ocean water cycle.
    Description: The study was supported by the NASA Ocean Salinity Science Team (OSST) under grant NNX12AG93G. Support from the NOAA Office of Climate Observation (OCO) under grant NA09OAR4320129 and NASA Ocean Vector Wind Science Team (OVWST) under grant NNA10AO86G in developing OAFlux evaporation and surface wind stress used in the study is gratefully acknowledged.
    Description: 2015-12-08
    Keywords: Sea-surface salinity fronts ; Salinity-minimum zones ; Tropical water cycle and salinity ; Aquarius salinity observations
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    Assessing high-resolution analysis of surface heat fluxes in the Gulf Stream region (2014)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 118 (2013): 5353–5375, doi:10.1002/jgrc.20386.
    Description: A satellite-based global analysis of high-resolution (0.25°) ocean surface turbulent latent and sensible heat fluxes was developed by the objectively analyzed air-sea fluxes (OAFlux) project. Resolving air-sea flux down to the order to 0.25° is critical for the description of the air-sea interaction on mesoscale scales. In this study, we evaluate the high-resolution product in depicting air-sea exchange in the eddy-rich Gulf Stream region. Two approaches were used for evaluation, one is point-to-point validation based on six moored buoys in the region, and another is basin-scale analysis in terms of wave number spectra and probability density functions. An intercomparison is also carried out between OAFlux-0.25°, OAFlux-1°, and four atmospheric reanalyses. Results indicate that OAFlux-0.25° is able to depict sharp oceanic fronts and has the best performance among the six participating products in comparison with buoy measurements. The mean OAFlux-0.25° differences in latent and sensible heat flux with respect to the buoy are 7.6 Wm−2 (7.7%) with root-mean-square (RMS) difference of 44.9 Wm−2, and 0.0 Wm−2 with RMS difference of 19.4 Wm−2, respectively. Large differences are primarily due to mismatch in SST between gridded data and point measurements when strong spatial gradients are presented. The wave number spectra and decorrelation length scale analysis indicate OAFlux-0.25° depicts eddy variability much better than OAFlux-1° and the four reanalyses; however, its capability in detecting eddies with smaller scale still needs to be improved. Among the four reanalyses, CFSR stands out as the best in comparison with OAFlux-0.25°.
    Description: This study was supported by NOAA Ocean Climate Observations program (OCO) under grant NA09OAR4320129 and the NASA Ocean Vector Wind Science Team (OVWST) under grant NNA10AO86G.
    Description: 2014-04-15
    Keywords: OAFlux ; Latent and sensible heat flux ; Satellite-based ; High resolution ; Flux analysis
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    Air-sea interaction regimes in the sub-Antarctic Southern Ocean and Antarctic marginal ice zone revealed by icebreaker measurements (2017)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 6547–6564, doi:10.1002/2016JC012281.
    Description: This study analyzed shipboard air-sea measurements acquired by the icebreaker Aurora Australis during its off-winter operation in December 2010 to May 2012. Mean conditions over 7 months (October–April) were compiled from a total of 22 ship tracks. The icebreaker traversed the water between Hobart, Tasmania, and the Antarctic continent, providing valuable in situ insight into two dynamically important, yet poorly sampled, regimes: the sub-Antarctic Southern Ocean and the Antarctic marginal ice zone (MIZ) in the Indian Ocean sector. The transition from the open water to the ice-covered surface creates sharp changes in albedo, surface roughness, and air temperature, leading to consequential effects on air-sea variables and fluxes. Major effort was made to estimate the air-sea fluxes in the MIZ using the bulk flux algorithms that are tuned specifically for the sea-ice effects, while computing the fluxes over the sub-Antarctic section using the COARE3.0 algorithm. The study evidenced strong sea-ice modulations on winds, with the southerly airflow showing deceleration (convergence) in the MIZ and acceleration (divergence) when moving away from the MIZ. Marked seasonal variations in heat exchanges between the atmosphere and the ice margin were noted. The monotonic increase in turbulent latent and sensible heat fluxes after summer turned the MIZ quickly into a heat loss regime, while at the same time the sub-Antarctic surface water continued to receive heat from the atmosphere. The drastic increase in turbulent heat loss in the MIZ contrasted sharply to the nonsignificant and seasonally invariant turbulent heat loss over the sub-Antarctic open water.
    Description: NOAA Climate Observation Division Grant Number: NA09OAR4320129
    Description: 2018-02-23
    Keywords: Air-sea interaction ; Sub-Antarctic Southern Ocean ; Antarctic marginal ice zone ; Icebreaker measurements
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
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    Coherent evidence from Aquarius and Argo for the existence of a shallow low-salinity convergence zone beneath the Pacific ITCZ (2015)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 119 (2014): 7625–7644, doi:10.1002/2014JC010030.
    Description: Aquarius observations feature a prominent zonal sea-surface salinity (SSS) front that extends across the tropical Pacific between 2–10°N. By linking to Argo subsurface salinity observations and satellite-derived surface forcing datasets, the study discovered that the SSS front is not a stand-alone feature; it is in fact the surface manifestation of a low-salinity convergence zone (LSCZ) located within 100 m of the upper ocean. The near-surface salinity budget analysis suggested that, although the LSCZ is sourced from the rainfall in the Inter-tropical convergence zone (ITCZ), its generation and maintenance are governed by the wind-driven Ekman dynamics, not the surface evaporation-minus-precipitation flux. Three distinct features highlight the relationship between the oceanic LSCZ and the atmospheric ITCZ. First, the seasonal movement of the LSCZ is characterized by a monotonic northward displacement starting from the near-equatorial latitudes in boreal spring, unlike the ITCZ that is known for its seasonal north-south displacement. Second, the lowest SSS waters in the LSCZ are locked to the northern edge of the Ekman salt convergence throughout the year, but have no fixed relationship with the ITCZ rain band. Collocation between the LSCZ and ITCZ occurs only during August-October, the time that the ITCZ rain band coincides with the Ekman convergence zone. Lastly, the SSS front couples with the Ekman convergence zone but not the ITCZ. The evidence reinforces the findings of the study that the Ekman processes are the leading mechanism of the oceanic LSCZ and the SSS front is the surface manifestation of the LSCZ.
    Description: The study was supported by the NASA Ocean Salinity Science Team (OSST) under grant NNX12AG93G. Support from the NOAA Office of Climate Observation (OCO) under grant NA09OAR4320129 and NASA Ocean Vector Wind Science Team (OVWST) under grant NNA10AO86G in developing OAFlux evaporation and surface wind stress used in the study is gratefully acknowledged.
    Description: 2015-05-18
    Keywords: Aquarius/SAC-D mission ; Sea surface salinity front ; Surface freshwater flux ; Ekman dynamics ; Tropical low-salinity waters
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
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    Insights on the OAFlux ocean surface vector wind analysis merged from scatterometers and passive microwave radiometers (1987 onward) (2014)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 119 (2014): 5244–5269, doi:10.1002/2013JC009648.
    Description: A high-resolution global daily analysis of ocean surface vector winds (1987 onward) was developed by the Objectively Analyzed air-sea Fluxes (OAFlux) project. This study addressed the issues related to the development of the time series through objective synthesis of 12 satellite sensors (two scatterometers and 10 passive microwave radiometers) using a least-variance linear statistical estimation. The issues include the rationale that supports the multisensor synthesis, the methodology and strategy that were developed, the challenges that were encountered, and the comparison of the synthesized daily mean fields with reference to scatterometers and atmospheric reanalyses. The synthesis was established on the bases that the low and moderate winds (〈15 m s−1) constitute 98% of global daily wind fields, and they are the range of winds that are retrieved with best quality and consistency by both scatterometers and radiometers. Yet, challenges are presented in situations of synoptic weather systems due mainly to three factors: (i) the lack of radiometer retrievals in rain conditions, (ii) the inability to fill in the data voids caused by eliminating rain-flagged QuikSCAT wind vector cells, and (iii) the persistent differences between QuikSCAT and ASCAT high winds. The study showed that the daily mean surface winds can be confidently constructed from merging scatterometers with radiometers over the global oceans, except for the regions influenced by synoptic weather storms. The uncertainties in present scatterometer and radiometer observations under high winds and rain conditions lead to uncertainties in the synthesized synoptic structures.
    Description: The project is sponsored by the NASA Ocean Vector Wind Science Team (OVWST) activities under grant NNA10AO86G.
    Description: 2015-02-19
    Keywords: Remote sensing ; Climate record of ocean surface vector wind ; Scatterometer ; Passive microwave radiometer ; Mesoscale air-sea interaction
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 6
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    Confidence and sensitivity study of the OAFlux multisensor synthesis of the global ocean surface vector wind from 1987 onward (2015)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 119 (2014): 6842–6862, doi:10.1002/2014JC010194.
    Description: This study presented an uncertainty assessment of the high-resolution global analysis of daily-mean ocean-surface vector winds (1987 onward) by the Objectively Analyzed air-sea Fluxes (OAFlux) project. The time series was synthesized from multiple satellite sensors using a variational approach to find a best fit to input data in a weighted least-squares cost function. The variational framework requires the a priori specification of the weights, or equivalently, the error covariances of input data, which are seldom known. Two key issues were investigated. The first issue examined the specification of the weights for the OAFlux synthesis. This was achieved by designing a set of weight-varying experiments and applying the criteria requiring that the chosen weights should make the best-fit of the cost function be optimal with regard to both input satellite observations and the independent wind time series measurements at 126 buoy locations. The weights thus determined represent an approximation to the error covariances, which inevitably contain a degree of uncertainty. Hence, the second issue addressed the sensitivity of the OAFlux synthesis to the uncertainty in the weight assignments. Weight perturbation experiments were conducted and ensemble statistics were used to estimate the sensitivity. The study showed that the leading sources of uncertainty for the weight selection are high winds (〉15 ms−1) and heavy rain, which are the conditions that cause divergence in wind retrievals from different sensors. Future technical advancement made in wind retrieval algorithms would be key to further improvement of the multisensory synthesis in events of severe storms.
    Description: The project is sponsored by the NASA Ocean Vector Wind Science Team (OVWST) activities under grant NNA10AO86G. The database of 126 buoys was established during the development of the OAFlux surface turbulent latent and sensible heat fluxes under the auspices of the NOAA grant NA09OAR4320129.
    Description: 2015-04-15
    Keywords: Remote sensing of ocean surface winds ; Scatterometer ; Passive microwave radiometer ; Error analysis
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 7
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    Air-sea heat flux climatologies in the Mediterranean Sea : surface energy balance and its consistency with ocean heat storage Authors (2017)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 4068–4087, doi:10.1002/2016JC012254.
    Description: This study provides an analysis of the Mediterranean Sea surface energy budget using nine surface heat flux climatologies. The ensemble mean estimation shows that the net downward shortwave radiation (192 ± 19 W m−2) is balanced by latent heat flux (−98 ± 10 W m−2), followed by net longwave radiation (−78 ± 13 W m−2) and sensible heat flux (−13 ± 4 W m−2). The resulting net heat budget (Qnet) is 2 ± 12 W m−2 into the ocean, which appears to be warm biased. The annual-mean Qnet should be −5.6 ± 1.6 W m−2 when estimated from the observed net transport through the Strait of Gibraltar. To diagnose the uncertainty in nine Qnet climatologies, we constructed Qnet from the heat budget equation by using historic hydrological observations to determine the heat content changes and advective heat flux. We also used the Qnet from a data-assimilated global ocean state estimation as an additional reference. By comparing with the two reference Qnet estimates, we found that seven products (NCEP 1, NCEP 2, CFSR, ERA-Interim, MERRA, NOCSv2.0, and OAFlux+ISCCP) overestimate Qnet, with magnitude ranging from 6 to 27 W m−2, while two products underestimate Qnet by −6 W m−2 (JRA55) and −14 W m−2 (CORE.2). Together with the previous warm pool work of Song and Yu (2013), we show that CFSR, MERRA, NOCSv2.0, and OAFlux+ISCCP are warm-biased not only in the western Pacific warm pool but also in the Mediterranean Sea, while CORE.2 is cold-biased in both regions. The NCEP 1, 2, and ERA-Interim are cold-biased over the warm pool but warm-biased in the Mediterranean Sea.
    Description: National Natural Science Foundation of China (NSFC) Grant Number: 41306003 and 41430963; Fundamental Research Funds for the Central Universities Grant Number: 0905-841313038, 1100-841262028, and 0905-201462003; China Postdoctoral Science Foundation Grant Number: 2013M531647; Natural Science Foundation of Shandong Grant Number: BS2013HZ015; Qingdao National Laboratory for Marine Science and Technology
    Description: 2017-11-16
    Keywords: Air-sea heat flux ; Mediterranean Sea ; Heat content changes ; Heat budget analysis
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 8
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    Poleward shift in ventilation of the North Atlantic subtropical underwater (2018)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 45 (2018): 258–266, doi:10.1002/2017GL075772.
    Description: We report the findings that the sea surface salinity maximum (SSS-max) in the North Atlantic has poleward expanded in recent decades and that the expansion is a main driver of the decadal changes in subtropical underwater (STUW). We present observational evidence that the STUW ventilation zone (marked by the location of the 36.7 isohaline) has been displaced northward by1.2 ± 0.36° latitude for the 34 year (1979–2012) period. As a result of the redistribution of the SSS-max water, the ventilation zone has shifted northward and expanded westward into the Sargasso Sea. The ventilation rate of STUW has increased, which is attributed to the increased lateral induction of the sloping mixed layer. STUW has become broader, deeper, and saltier, and the changes are most pronounced on the northern and western edges of the high-saline core.
    Description: NOAA Ocean Observation and Monitoring Division (OOMD) Grant Number: NA14OAR4320158
    Description: 2018-07-15
    Keywords: North Atlantic salinity maximum ; Subtropical underwater ; Poleward expansion ; Ventilation ; Decadal variability
    Repository Name: Woods Hole Open Access Server
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  • 9
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    Unexpected impacts of the Tropical Pacific array on reanalysis surface meteorology and heat fluxes (2014)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 41 (2014): 6213–6220, doi:10.1002/2014GL061302.
    Description: The Tropical Pacific mooring array has been a key component of the climate observing system since the early 1990s. We identify a pattern of strong near surface humidity anomalies, colocated with the array, in the widely used European Center for Medium Range Weather Forecasting Interim atmospheric reanalysis. The pattern generates large, previously unrecognized latent and net air-sea heat flux anomalies, up to 50 Wm−2 in the annual mean, in reanalysis derived data sets employed for climate studies (TropFlux) and ocean model forcing (the Drakkar Forcing Set). As a consequence, uncertainty in Tropical Pacific ocean heat uptake between the 1990s and early 2000s at the mooring sites is significant with mooring colocated differences in decadally averaged ocean heat uptake as large as 20 Wm−2. Furthermore, these results have major implications for the dual use of air-sea flux buoys as reference sites and sources of assimilation data that are discussed.
    Description: SKG and NT were supported by the Russian Science Foundation project 14-17-00697.
    Description: 2015-03-03
    Keywords: Tropical Pacific ; Heat flux ; Mooring array ; Reanalysis
    Repository Name: Woods Hole Open Access Server
    Type: Article
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