Kirtman Benjamin

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  • Article
    Challenges and prospects for reducing coupled climate model SST biases in the eastern tropical Atlantic and Pacific Oceans : the U.S. CLIVAR Eastern Tropical Oceans Synthesis Working Group
    (American Meteorological Society, 2017-01-12) Zuidema, Paquita ; Chang, Ping ; Medeiros, Brian ; Kirtman, Benjamin ; Mechoso, Roberto ; Schneider, Edwin K. ; Toniazzo, Thomas ; Richter, Ingo ; Small, R. Justin ; Bellomo, Katinka ; Brandt, Peter ; de Szoeke, Simon ; Farrar, J. Thomas ; Jung, Eunsil ; Kato, Seiji ; Li, Mingkui ; Patricola, Christina ; Wang, Zaiyu ; Wood, Robert ; Xu, Zhao
    Well-known problems trouble coupled general circulation models of the eastern Atlantic and Pacific Ocean basins. Model climates are significantly more symmetric about the equator than is observed. Model sea surface temperatures are biased warm south and southeast of the equator, and the atmosphere is too rainy within a band south of the equator. Near-coastal eastern equatorial SSTs are too warm, producing a zonal SST gradient in the Atlantic opposite in sign to that observed. The U.S. Climate Variability and Predictability Program (CLIVAR) Eastern Tropical Ocean Synthesis Working Group (WG) has pursued an updated assessment of coupled model SST biases, focusing on the surface energy balance components, on regional error sources from clouds, deep convection, winds, and ocean eddies; on the sensitivity to model resolution; and on remote impacts. Motivated by the assessment, the WG makes the following recommendations: 1) encourage identification of the specific parameterizations contributing to the biases in individual models, as these can be model dependent; 2) restrict multimodel intercomparisons to specific processes; 3) encourage development of high-resolution coupled models with a concurrent emphasis on parameterization development of finer-scale ocean and atmosphere features, including low clouds; 4) encourage further availability of all surface flux components from buoys, for longer continuous time periods, in persistently cloudy regions; and 5) focus on the eastern basin coastal oceanic upwelling regions, where further opportunities for observational–modeling synergism exist.
  • Article
    Effects of grid spacing on high-frequency precipitation variance in coupled high-resolution global ocean–atmosphere models
    (Springer, 2022-03-29) Light, Charles X. ; Arbic, Brian K. ; Martin, Paige E. ; Brodeau, Laurent ; Farrar, J. Thomas ; Griffies, Stephen M. ; Kirtman, Benjamin ; Laurindo, Lucas ; Menemenlis, Dimitris ; Molod, Andrea ; Nelson, Arin D. ; Nyadjro, Ebenezer ; O’Rourke, Amanda K. ; Shriver, Jay F. ; Siqueira, Leo ; Small, R. Justin ; Strobach, Ehud
    High-frequency precipitation variance is calculated in 12 different free-running (non-data-assimilative) coupled high resolution atmosphere–ocean model simulations, an assimilative coupled atmosphere–ocean weather forecast model, and an assimilative reanalysis. The results are compared with results from satellite estimates of precipitation and rain gauge observations. An analysis of irregular sub-daily fluctuations, which was applied by Covey et al. (Geophys Res Lett 45:12514–12522, 2018. to satellite products and low-resolution climate models, is applied here to rain gauges and higher-resolution models. In contrast to lower-resolution climate simulations, which Covey et al. (2018) found to be lacking with respect to variance in irregular sub-daily fluctuations, the highest-resolution simulations examined here display an irregular sub-daily fluctuation variance that lies closer to that found in satellite products. Most of the simulations used here cannot be analyzed via the Covey et al. (2018) technique, because they do not output precipitation at sub-daily intervals. Thus the remainder of the paper focuses on frequency power spectral density of precipitation and on cumulative distribution functions over time scales (2–100 days) that are still relatively “high-frequency” in the context of climate modeling. Refined atmospheric or oceanic model grid spacing is generally found to increase high-frequency precipitation variance in simulations, approaching the values derived from observations. Mesoscale-eddy-rich ocean simulations significantly increase precipitation variance only when the atmosphere grid spacing is sufficiently fine (< 0.5°). Despite the improvements noted above, all of the simulations examined here suffer from the “drizzle effect”, in which precipitation is not temporally intermittent to the extent found in observations.
  • Article
    Understanding ENSO diversity
    (American Meteorological Society, 2015-06) Capotondi, Antonietta ; Wittenberg, Andrew T. ; Newman, Matthew ; Di Lorenzo, Emanuele ; Yu, Jin-Yi ; Braconnot, Pascale ; Cole, Julia ; Dewitte, Boris ; Giese, Benjamin ; Guilyardi, Eric ; Jin, Fei-Fei ; Karnauskas, Kristopher B. ; Kirtman, Benjamin ; Lee, Tong ; Schneider, Niklas ; Xue, Yan ; Yeh, Sang-Wook
    El Niño–Southern Oscillation (ENSO) is a naturally occurring mode of tropical Pacific variability, with global impacts on society and natural ecosystems. While it has long been known that El Niño events display a diverse range of amplitudes, triggers, spatial patterns, and life cycles, the realization that ENSO’s impacts can be highly sensitive to this event-to-event diversity is driving a renewed interest in the subject. This paper surveys our current state of knowledge of ENSO diversity, identifies key gaps in understanding, and outlines some promising future research directions.
  • Article
    Ocean 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, Qing
    Abstract 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.