Czaja
Arnaud
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Arnaud
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ArticleA simple diagnostic for the detection of atmospheric fronts(John Wiley & Sons, 2017-05-14) Parfitt, Rhys ; Czaja, Arnaud ; Seo, HyodaeIn this article, a simple diagnostic to identify atmospheric fronts objectively from gridded data sets is presented. For this diagnostic, fronts are identified as regions where the normalized product of the isobaric relative vorticity and horizontal temperature gradient exceeds a threshold value. The purpose is to introduce a method that is both robust and particularly straightforward in calculation. A climatology of atmospheric fronts, as well as the identification of an individual frontal system, is computed using this diagnostic. These are subsequently compared to a more traditional frontal detection method and the similarities and differences discussed.
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ArticleThe impact of SST resolution change in the ERA-Interim reanalysis on wintertime Gulf Stream frontal air-sea interaction(John Wiley & Sons, 2017-04-01) Parfitt, Rhys ; Czaja, Arnaud ; Kwon, Young-OhThis paper examines the sensitivity to a change in sea surface temperature (SST) resolution of the interaction between atmospheric and oceanic fronts in the Gulf Stream region in the ERA-Interim reanalysis data set. Two periods are considered, January 1979 to December 2001 (SST resolution 1° × 1°) and December 2010 to February 2016 (SST resolution 0.05° × 0.05°). The winter season from the latter 6 years of high-resolution SST is compared against six random periods of six wintertime seasons from the low-resolution SST period, to assess the robustness of the result against natural climate variability. In all comparisons, a significant change in frontal air-sea sensible heat flux exchange is found that is highly correlated to the change in mean SST gradient. This leads to both increases and decreases in occurrence of atmospheric fronts and mean precipitation of up to 30%. These results reemphasize the importance of high SST resolution in resolving the influence of oceanic fronts on weather and climate.
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ArticleOcean mesoscale and frontal-scale ocean–atmosphere interactions and influence on large-scale climate: a review(American Meteorological Society, 2023-03-01) Seo, Hyodae ; O’Neill, Larry W. ; Bourassa, Mark A. ; Czaja, Arnaud ; Drushka, Kyla ; Edson, James B. ; Fox-Kemper, Baylor ; Frenger, Ivy ; Gille, Sarah T. ; Kirtman, Benjamin P. ; Minobe, Shoshiro ; Pendergrass, Angeline G. ; Renault, Lionel ; Roberts, Malcolm J. ; Schneider, Niklas ; Small, R. Justin ; Stoffelen, Ad ; Wang, QingAbstract Two decades of high-resolution satellite observations and climate modeling studies have indicated strong ocean–atmosphere coupled feedback mediated by ocean mesoscale processes, including semipermanent and meandrous SST fronts, mesoscale eddies, and filaments. The air–sea exchanges in latent heat, sensible heat, momentum, and carbon dioxide associated with this so-called mesoscale air–sea interaction are robust near the major western boundary currents, Southern Ocean fronts, and equatorial and coastal upwelling zones, but they are also ubiquitous over the global oceans wherever ocean mesoscale processes are active. Current theories, informed by rapidly advancing observational and modeling capabilities, have established the importance of mesoscale and frontal-scale air–sea interaction processes for understanding large-scale ocean circulation, biogeochemistry, and weather and climate variability. However, numerous challenges remain to accurately diagnose, observe, and simulate mesoscale air–sea interaction to quantify its impacts on large-scale processes. This article provides a comprehensive review of key aspects pertinent to mesoscale air–sea interaction, synthesizes current understanding with remaining gaps and uncertainties, and provides recommendations on theoretical, observational, and modeling strategies for future air–sea interaction research. Significance Statement Recent high-resolution satellite observations and climate models have shown a significant impact of coupled ocean–atmosphere interactions mediated by small-scale (mesoscale) ocean processes, including ocean eddies and fronts, on Earth’s climate. Ocean mesoscale-induced spatial temperature and current variability modulate the air–sea exchanges in heat, momentum, and mass (e.g., gases such as water vapor and carbon dioxide), altering coupled boundary layer processes. Studies suggest that skillful simulations and predictions of ocean circulation, biogeochemistry, and weather events and climate variability depend on accurate representation of the eddy-mediated air–sea interaction. However, numerous challenges remain in accurately diagnosing, observing, and simulating mesoscale air–sea interaction to quantify its large-scale impacts. This article synthesizes the latest understanding of mesoscale air–sea interaction, identifies remaining gaps and uncertainties, and provides recommendations on strategies for future ocean–weather–climate research.
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PreprintMechanisms controlling the SST air-sea heat flux feedback and its dependence on spatial scale( 2016-04-05) Hausmann, Ute ; Czaja, Arnaud ; Marshall, John C.The turbulent air-sea heat flux feedback (α, in W m-2 K-1) is a major contributor to setting the damping timescale of sea surface temperature (SST) anomalies. In this study we compare the spatial distribution and magnitude of α in the North Atlantic and the Southern Ocean, as estimated from the ERA-Interim reanalysis dataset. The comparison is rationalized in terms of an upper bound on the heat flux feedback, associated with \fast" atmospheric export of temperature and moisture anomalies away from the marine boundary layer, and a lower bound associated with "slow" export. It is found that regions of cold surface waters (≤10°C) are best described as approaching the slow export limit. This conclusion is not only valid at the synoptic scale resolved by the reanalysis data, but also on basin scales. In particular, it applies to the heat flux feedback acting as circumpolar SST anomaly scales are approached in the Southern Ocean, with feedbacks of ≤10 W m-2 K-1. In contrast, the magnitude of the heat flux feed-back is close to that expected from the fast export limit over the Gulf Stream and its recirculation with values on the order of ≈40 W m-2 K-1. Further analysis suggests that this high value reflects a compensation between a moderate thermo-dynamic adjustment of the boundary layer, which tends to weaken the heat flux feedback, and an enhancement of the surface winds over warm SST anomalies, which tend to enhance the feedback.