Richard Allard

Studies of the Arctic ice cover and upper ocean with a coupled ice-ocean model

An ice-ocean model has been developed by coupling the Hibler ice model to a three-dimensional ocean model that consists of a turbulent mixed layer model and an inverse geostrophic model. The coupled model has a horizontal grid spacing of 127 km and has 17 vertical levels extending to the ocean bottom. The model is forced with 12-hourly general circulation model-derived atmospheric fluxes for the year 1986, for which good quality ice edge analyses and buoy tracks were available for comparisons. The results are presented for the fifth year of a repetitive simulation with the 1986 fluxes, at which time the system has reached a statistical equilibrium. The seasonal and geographical variations of the ice cover and the upper few hundred meters of the ocean have been examined, including the heat and salt budgets. The computed heat fluxes and mixed layer depths (MLDs) fall in the observed seasonal ranges, with winter heat fluxes ranging from 15 W m−2 in the central Arctic to about 500 W m−2 in the Barents Sea area, and summer fluxes from about 5 W m−2 under the ice to about 30 W m−2 in the various marginal ice zone (MIZ) edge areas. The corresponding winter MLDs are found to be about 25–75 m in the central Arctic to a deep 800 m in the Greenland Sea; typical summer MLDs are between 5 and 30 m. In all seasons, the MIZ was found to be the center of flux activity for both heat and salt, with the processes of advection, diffusion, atmospheric forcing, and vertical oceanic fluxes having their largest values here, and of comparable magnitudes. Values of the heat flux components in the MIZ exceed those found under the ice by an order of magnitude or more, and those in the open water region by a factor of 2. For salt, the situation is similar except in the summer (June through September), when a lot of salt flux activity takes place under the ice. Comparisons are made with Naval Polar Oceanography Center (NPOC) analyses for ice concentration and ice edge, and with observed Arctic buoy tracks, in the same 1986 time period. The computed ice edge positions have comparable accuracy to previous three-dimensional coupled ice-ocean studies, with too much ice growth during the winter in the Barents Sea and too little ice east of Greenland. The ice thickness distributions, however, are much better, with a monotonic increase of the ice thickness from the Siberian coast east toward the Canadian archipelago with maximum winter values of about 5–6 m.

Short‐term sea ice forecasting: An assessment of ice concentration and ice drift forecasts using the U.S. Navy's Arctic Cap Nowcast/Forecast System

In this study the forecast skill of the U.S. Navy operational Arctic sea ice forecast system, the Arctic Cap Nowcast/Forecast System (ACNFS), is presented for the period Feb 2014 – June 2015. ACNFS is designed to provide short term, 1-7 day forecasts of Arctic sea ice and ocean conditions. Many quantities are forecast by ACNFS; the most commonly used include ice concentration, ice thickness, ice velocity, sea surface temperature, sea surface salinity, and sea surface velocities. Ice concentration forecast skill is compared to a persistent ice state and historical sea ice climatology. Skill scores are focused on areas where ice concentration changes by ±5% or more, and are therefore limited to primarily the marginal ice zone. We demonstrate that ACNFS forecasts are skillful compared to assuming a persistent ice state, especially beyond 24 hours. ACNFS is also shown to be particularly skillful compared to a climatologic state for forecasts up to 102 hours. Modeled ice drift velocity is compared to observed buoy data from the International Arctic Buoy Programme. A seasonal bias is shown where ACNFS is slower than IABP velocity in the summer months and faster in the winter months. In February 2015 ACNFS began to assimilate a blended ice concentration derived from Advanced Microwave Scanning Radiometer 2 (AMSR2) and the Interactive Multisensor Snow and Ice Mapping System (IMS). Preliminary results show that assimilating AMSR2 blended with IMS improves the short-term forecast skill and ice edge location compared to the independently derived National Ice Center Ice Edge product. This article is protected by copyright. All rights reserved.

Integrated Modeling of the Battlespace Environment

The goal of the Battlespace Environments Institute (BEI) is to integrate Earth and space modeling capabilities into a seamless, whole-Earth common modeling infrastructure that facilitates interservice development of multiple, mission-specific environmental simulations and supports battlefield decisions, improves interoperability, and reduces operating costs.

Validation of the Global Relocatable Tide/Surge Model PCTides

The Naval Research Laboratory (NRL) has developed a global, relocatable, tide/surge forecast system called PCTides. This system was designed in response to a U.S. Navy requirement to rapidly produce tidal predictions anywhere in the world. The system is composed of a two-dimensional barotropic ocean model driven by tidal forcing only or in conjunction with surface wind and pressure forcing. PCTides is unique in its ability to forecast tidal parameters for a user-specified latitude/longitude domain easily and quickly, and is especially useful in areas where observations are nonexistent. PCTides provides short-term (daily to weekly) predictions of water-level elevation and depth-averaged ocean currents. The system has been tested in numerous regions and validated against observations collected in conjunction with several navy exercises.

The Distributed Integrated Ocean Prediction System (DIOPS)

The Distributed Integrated Ocean Prediction System (DIOPS) is a complete wave, tide and surf prediction system that can be run on a Unix platform or personal computer. Operational Navy meteorological numerical modeled winds and sea level pressure are used to initialize and force the system. An improved graphical user interface allows for efficient model setup, configuration, and visualization. DIOPS is being designed to be operated by junior enlisted personnel.

AN MPI QUASI TIME-ACCURATE APPROACH FOR NEARSHORE WAVE PREDICTION USING THE SWAN CODE : PART II : APPLICATIONS TO WAVE HINDCASTS

This study compares the quasi time-accurate method in Part I: Method, with the time-accurate version of SWAN for a simulation of 1995 Hurricane Luis and a Gulf of Mexico storm that occurred in September 2000. Using the quasi time-accurate method, significant reductions in wall times were achieved relative to time-accurate computations. Examination of the error norms show that the quasi time-accurate method agrees well with the time-accurate results. Thus, the MPI quasi time-accurate method, because of its efficiency, can play an important role for cases where the time-dependent forcing terms are the dominant influence on wave conditions.

Synoptic and Seasonal Variations of the Ice-Ocean Circulation in the Arctic: A Numerical Study

Abstract : The circulations of the Arctic ice cover and ocean are investigated using a coupled ice-ocean model. The coupling is strong and two-way for synoptic time scales, but is limited on seasonal time scales: the geostrophic ocean currents are not changed by the computed heat and salt fluxes. The ice-drift motion, Ekman transports and the wind-driven part of the barotropic circulation are examined for the months of February and August 1986, representing different atmospheric forcing, ice thickness and ice-strength regimes. Initial examination of the results revealed no significant seasonal dependence of ice-drift response on the synoptic time scale, other than larger velocities with larger wind stresses. Daily maximum ice-drift velocities range from 20-40 cm/s in February, and 15-30 cm/s in August. The corresponding mean monthly maximum drifts were 11 and 9 cm, respectively. The drag associated with the geostrophic currents plays a much bigger role in the summer because of the lighter atmospheric stresses. The well-known reversal of the normally clockwise Beaufort Gyre to a cyclonic system in August takes place in a few days and lasts well into September. In February, the Beaufort Gyre varies between a large, clockwise system covering all the Canadian Basin to a small, tight gyre centered over the southern Beaufort Sea, without any hint of reversal or disappearance. Large areas of strong divergence were found in the Ekman transport patterns, as well as the ice-divergence fields, indicating areas where ice thinning, openings and new ice formation might occur. In August this occurred in the Chukchi Sea, and in February just north of Novaya Zemlya.

The Navy's coupled atmosphere-ocean-wave prediction system

An air-ocean-wave modeling system has been developed by the Naval Research Laboratory to provide improved predictive capabilities to the warfighter in regions that include an oceanic component. Each of the three operational models, run in a standalone mode, have provided 48 to 96 hour forecast guidance for the past several years. Utilizing the Earth System Modeling Framework, a model coupler exchanges needed information between the model components and interpolates between the model grids. This paper will discuss the model coupling and provide a brief overview of validation studies that have been performed in the Adriatic Sea, Ligurian Sea and Kuroshio extension, with a particular emphasis on air-sea interactions. Model studies presented here focus on the upper ocean (mixed layer) heat fluxes, near surface winds, temperature, moisture, the air-sea interaction, and the marine boundary layer characteristics. Validation studies presented here show the most improvements in ocean heat fluxes, due to a more realistic sea surface temperature. The coupled system is scheduled for operational implementation at Navy production centers beginning in 2011.

Coupled ocean-atmosphere forecasting at short and medium time scales

Recent technological advances over the past few decades have enabled the development of fully coupled atmosphere-ocean modeling prediction systems that are used today to support short-term (days to weeks) and medium-term (10–21 days) needs for both the operational and research communities. We overview the coupling framework, including model components and grid resolution considerations, as well as the coupling physics by examining heat fluxes between atmosphere and ocean, momentum transfer, and freshwater fluxes. These modeling systems can be run as fully coupled atmosphere-ocean and atmosphere-ocean-wave configurations. Examples of several modeling systems applied to complex coastal regions including Madeira Island, Adriatic Sea, Coastal California, Gulf of Mexico, Brazil, and the Maritime Continent are presented. In many of these studies, a variety of field campaigns have contributed to a better understanding of the underlying physics associated with the atmosphere-ocean feedbacks. Examples of improvements in predictive skill when run in coupled mode versus standalone are shown. Coupled model challenges such as model initialization, data assimilation, and earth system prediction are discussed.

Wave-current interaction in the Florida Current in a coupled atmosphere-ocean-wave model

The interaction of waves and currents are investigated in the Florida Current region in two events in early April 2005 using a state-of-the-art coupled atmosphere-ocean forecast model that includes assimilation of observations. During the first event, strong northerly winds force swell southward opposing the Florida Current. Current-wave interaction results in larger significant wave heights than found without currents. The second event has south-easterly winds with a significant component along the current direction. In that case, significant wave heights are smaller for the simulation that includes wave-current interaction than without that feed-back. Wave heights at buoy locations near the coast is generally in good agreement with the models results, which implies that inclusion of wave-current interaction may not be important near the shore. The simulation includes events where the maximum winds reach 20 m/s and significant wave heights exceed 2 m.