Kohl Armin

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Kohl
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Armin
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  • Article
    Towards an end-to-end analysis and prediction system for weather, climate, and marine applications in the Red Sea
    (American Meteorological Society, 2021-01-01) Hoteit, Ibrahim ; Abualnaja, Yasser ; Afzal, Shehzad ; Ait-El-Fquih, Boujemaa ; Akylas, Triantaphyllos ; Antony, Charls ; Dawson, Clint N. ; Asfahani, Khaled ; Brewin, Robert J. W. ; Cavaleri, Luigi ; Cerovecki, Ivana ; Cornuelle, Bruce D. ; Desamsetti, Srinivas ; Attada, Raju ; Dasari, Hari ; Sanchez-Garrido, Jose ; Genevier, Lily ; El Gharamti, Mohamad ; Gittings, John A. ; Gokul, Elamurugu ; Gopalakrishnan, Ganesh ; Guo, Daquan ; Hadri, Bilel ; Hadwiger, Markus ; Hammoud, Mohammed Abed ; Hendershott, Myrl ; Hittawe, Mohamad ; Karumuri, Ashok ; Knio, Omar ; Kohl, Armin ; Kortas, Samuel ; Krokos, George ; Kunchala, Ravi ; Issa, Leila ; Lakkis, Issam ; Langodan, Sabique ; Lermusiaux, Pierre F. J. ; Luong, Thang ; Ma, Jingyi ; Le Maitre, Olivier ; Mazloff, Matthew R. ; El Mohtar, Samah ; Papadopoulos, Vassilis P. ; Platt, Trevor ; Pratt, Lawrence J. ; Raboudi, Naila ; Racault, Marie-Fanny ; Raitsos, Dionysios E. ; Razak, Shanas ; Sanikommu, Sivareddy ; Sathyendranath, Shubha ; Sofianos, Sarantis S. ; Subramanian, Aneesh C. ; Sun, Rui ; Titi, Edriss ; Toye, Habib ; Triantafyllou, George ; Tsiaras, Kostas ; Vasou, Panagiotis ; Viswanadhapalli, Yesubabu ; Wang, Yixin ; Yao, Fengchao ; Zhan, Peng ; Zodiatis, George
    The Red Sea, home to the second-longest coral reef system in the world, is a vital resource for the Kingdom of Saudi Arabia. The Red Sea provides 90% of the Kingdom’s potable water by desalinization, supporting tourism, shipping, aquaculture, and fishing industries, which together contribute about 10%–20% of the country’s GDP. All these activities, and those elsewhere in the Red Sea region, critically depend on oceanic and atmospheric conditions. At a time of mega-development projects along the Red Sea coast, and global warming, authorities are working on optimizing the harnessing of environmental resources, including renewable energy and rainwater harvesting. All these require high-resolution weather and climate information. Toward this end, we have undertaken a multipronged research and development activity in which we are developing an integrated data-driven regional coupled modeling system. The telescopically nested components include 5-km- to 600-m-resolution atmospheric models to address weather and climate challenges, 4-km- to 50-m-resolution ocean models with regional and coastal configurations to simulate and predict the general and mesoscale circulation, 4-km- to 100-m-resolution ecosystem models to simulate the biogeochemistry, and 1-km- to 50-m-resolution wave models. In addition, a complementary probabilistic transport modeling system predicts dispersion of contaminant plumes, oil spill, and marine ecosystem connectivity. Advanced ensemble data assimilation capabilities have also been implemented for accurate forecasting. Resulting achievements include significant advancement in our understanding of the regional circulation and its connection to the global climate, development, and validation of long-term Red Sea regional atmospheric–oceanic–wave reanalyses and forecasting capacities. These products are being extensively used by academia, government, and industry in various weather and marine studies and operations, environmental policies, renewable energy applications, impact assessment, flood forecasting, and more.
  • Article
    Seasonal overturning circulation in the Red Sea : 2. Winter circulation
    (John Wiley & Sons, 2014-04-14) Yao, Fengchao ; Hoteit, Ibrahim ; Pratt, Lawrence J. ; Bower, Amy S. ; Kohl, Armin ; Gopalakrishnan, Ganesh ; Rivas, David
    The shallow winter overturning circulation in the Red Sea is studied using a 50 year high-resolution MITgcm (MIT general circulation model) simulation with realistic atmospheric forcing. The overturning circulation for a typical year, represented by 1980, and the climatological mean are analyzed using model output to delineate the three-dimensional structure and to investigate the underlying dynamical mechanisms. The horizontal model circulation in the winter of 1980 is dominated by energetic eddies. The climatological model mean results suggest that the surface inflow intensifies in a western boundary current in the southern Red Sea that switches to an eastern boundary current north of 24°N. The overturning is accomplished through a cyclonic recirculation and a cross-basin overturning circulation in the northern Red Sea, with major sinking occurring along a narrow band of width about 20 km along the eastern boundary and weaker upwelling along the western boundary. The northward pressure gradient force, strong vertical mixing, and horizontal mixing near the boundary are the essential dynamical components in the model's winter overturning circulation. The simulated water exchange is not hydraulically controlled in the Strait of Bab el Mandeb; instead, the exchange is limited by bottom and lateral boundary friction and, to a lesser extent, by interfacial friction due to the vertical viscosity at the interface between the inflow and the outflow.
  • Article
    Putting it all together: Adding value to the global ocean and climate observing systems with complete self-consistent ocean state and parameter estimates.
    (Frontiers Media, 2019-03-04) Heimbach, Patrick ; Fukumori, Ichiro ; Hill, Christopher N. ; Ponte, Rui M. ; Stammer, Detlef ; Wunsch, Carl ; Campin, Jean-Michel ; Cornuelle, Bruce D. ; Fenty, Ian ; Forget, Gael ; Kohl, Armin ; Mazloff, Matthew R. ; Menemenlis, Dimitris ; Nguyen, An T. ; Piecuch, Christopher G. ; Trossman, David S. ; Verdy, Ariane ; Wang, Ou ; Zhang, Hong
    In 1999, the consortium on Estimating the Circulation and Climate of the Ocean (ECCO) set out to synthesize the hydrographic data collected by the World Ocean Circulation Experiment (WOCE) and the satellite sea surface height measurements into a complete and coherent description of the ocean, afforded by an ocean general circulation model. Twenty years later, the versatility of ECCO's estimation framework enables the production of global and regional ocean and sea-ice state estimates, that incorporate not only the initial suite of data and its successors, but nearly all data streams available today. New observations include measurements from Argo floats, marine mammal-based hydrography, satellite retrievals of ocean bottom pressure and sea surface salinity, as well as ice-tethered profiled data in polar regions. The framework also produces improved estimates of uncertain inputs, including initial conditions, surface atmospheric state variables, and mixing parameters. The freely available state estimates and related efforts are property-conserving, allowing closed budget calculations that are a requisite to detect, quantify, and understand the evolution of climate-relevant signals, as mandated by the Coupled Model Intercomparison Project Phase 6 (CMIP6) protocol. The solutions can be reproduced by users through provision of the underlying modeling and assimilation machinery. Regional efforts have spun off that offer increased spatial resolution to better resolve relevant processes. Emerging foci of ECCO are on a global sea level changes, in particular contributions from polar ice sheets, and the increased use of biogeochemical and ecosystem data to constrain global cycles of carbon, nitrogen and oxygen. Challenges in the coming decade include provision of uncertainties, informing observing system design, globally increased resolution, and moving toward a coupled Earth system estimation with consistent momentum, heat and freshwater fluxes between the ocean, atmosphere, cryosphere and land.
  • Article
    Measuring global ocean heat content to estimate the Earth energy Imbalance
    (Frontiers Media, 2019-08-20) Meyssignac, Benoit ; Boyer, Tim ; Zhao, Zhongxiang ; Hakuba, Maria Z. ; Landerer, Felix ; Stammer, Detlef ; Kohl, Armin ; Kato, Seiji ; L’Ecuyer, Tristan S. ; Ablain, Michaël ; Abraham, John Patrick ; Blazquez, Alejandro ; Cazenave, Anny ; Church, John A. ; Cowley, Rebecca ; Cheng, Lijing ; Domingues, Catia M. ; Giglio, Donata ; Gouretski, Viktor ; Ishii, Masayoshi ; Johnson, Gregory C. ; Killick, Rachel E. ; Legler, David ; Llovel, William ; Lyman, John ; Palmer, Matthew D. ; Piotrowicz, Stephen R. ; Purkey, Sarah G. ; Roemmich, Dean ; Roca, Rémy ; Savita, Abhishek ; von Schuckmann, Karina ; Speich, Sabrina ; Stephens, Graeme ; Wang, Gongjie ; Wijffels, Susan E. ; Zilberman, Nathalie
    The energy radiated by the Earth toward space does not compensate the incoming radiation from the Sun leading to a small positive energy imbalance at the top of the atmosphere (0.4–1 Wm–2). This imbalance is coined Earth’s Energy Imbalance (EEI). It is mostly caused by anthropogenic greenhouse gas emissions and is driving the current warming of the planet. Precise monitoring of EEI is critical to assess the current status of climate change and the future evolution of climate. But the monitoring of EEI is challenging as EEI is two orders of magnitude smaller than the radiation fluxes in and out of the Earth system. Over 93% of the excess energy that is gained by the Earth in response to the positive EEI accumulates into the ocean in the form of heat. This accumulation of heat can be tracked with the ocean observing system such that today, the monitoring of Ocean Heat Content (OHC) and its long-term change provide the most efficient approach to estimate EEI. In this community paper we review the current four state-of-the-art methods to estimate global OHC changes and evaluate their relevance to derive EEI estimates on different time scales. These four methods make use of: (1) direct observations of in situ temperature; (2) satellite-based measurements of the ocean surface net heat fluxes; (3) satellite-based estimates of the thermal expansion of the ocean and (4) ocean reanalyses that assimilate observations from both satellite and in situ instruments. For each method we review the potential and the uncertainty of the method to estimate global OHC changes. We also analyze gaps in the current capability of each method and identify ways of progress for the future to fulfill the requirements of EEI monitoring. Achieving the observation of EEI with sufficient accuracy will depend on merging the remote sensing techniques with in situ measurements of key variables as an integral part of the Ocean Observing System.
  • Article
    Seasonal overturning circulation in the Red Sea : 1. Model validation and summer circulation
    (John Wiley & Sons, 2014-04-14) Yao, Fengchao ; Hoteit, Ibrahim ; Pratt, Lawrence J. ; Bower, Amy S. ; Kohl, Armin ; Gopalakrishnan, Ganesh ; Rivas, David
    The overturning circulation in the Red Sea exhibits a distinct seasonally reversing pattern and is studied using high-resolution MIT general circulation model simulations. In the first part of this study, the vertical and horizontal structure of the summer overturning circulation and its dynamical mechanisms are presented from the model results. The seasonal water exchange in the Strait of Bab el Mandeb is successfully simulated, and the structures of the intruding subsurface Gulf of Aden intermediate water are in good agreement with summer observations in 2011. The model results suggest that the summer overturning circulation is driven by the combined effect of the shoaling of the thermocline in the Gulf of Aden resulting from remote winds in the Arabian Sea and an upward surface slope from the Red Sea to the Gulf of Aden set up by local surface winds in the Red Sea. In addition, during late summer two processes associated, respectively, with latitudinally differential heating and increased salinity in the southern Red Sea act together to cause the reversal of the contrast of the vertical density structure and the cessation of the summer overturning circulation. Dynamically, the subsurface northward pressure gradient force is mainly balanced by vertical viscosity resulting from the vertical shear and boundary friction in the Strait of Bab el Mandeb. Unlike some previous studies, the three-layer summer exchange flows in the Strait of Bab el Mandeb do not appear to be hydraulically controlled.
  • Article
    The mean state and variability of the North Atlantic circulation: a perspective from ocean reanalyses
    (American Geophysical Union, 2019-11-06) Jackson, Laura ; Dubois, Clotilde ; Forget, Gael ; Haines, Keith ; Harrison, Matthew ; Iovino, Doroteaciro ; Toyoda, Takahiro ; Kohl, Armin ; Mignac, Davi ; Masina, Simona ; Peterson, K. Andrew ; Piecuch, Christopher G. ; Roberts, Chris ; Robson, Jon ; Storto, Andrea ; Toyoda, Takahiro ; Valdivieso, Maria ; Wilson, Christopher G. ; Wang, Yiguo ; Zuo, Hao
    The observational network around the North Atlantic has improved significantly over the last few decades with subsurface profiling floats and satellite observations and the recent efforts to monitor the Atlantic Meridional Overturning Circulation (AMOC). These have shown decadal time scale changes across the North Atlantic including in heat content, heat transport, and the circulation. However, there are still significant gaps in the observational coverage. Ocean reanalyses integrate the observations with a dynamically consistent ocean model and can be used to understand the observed changes. However, the ability of the reanalyses to represent the dynamics must also be assessed. We use an ensemble of global ocean reanalyses to examine the time mean state and interannual‐decadal variability of the North Atlantic ocean since 1993. We assess how well the reanalyses are able to capture processes and whether any understanding can be gained. In particular, we examine aspects of the circulation including convection, AMOC and gyre strengths, and transports. We find that reanalyses show some consistency, in particular showing a weakening of the subpolar gyre and AMOC at 50°N from the mid‐1990s until at least 2009 (related to decadal variability in previous studies), a strengthening and then weakening of the AMOC at 26.5°N since 2000, and impacts of circulation changes on transports. These results agree with model studies and the AMOC observations at 26.5°N since 2005. We also see less spread across the ensemble in AMOC strength and mixed layer depth, suggesting improvements as the observational coverage has improved.