Alice K. DuVivier

Evaluation of WRF Model Resolution on Simulated Mesoscale Winds and Surface Fluxes near Greenland

AbstractSouthern Greenland has short-lived but frequently occurring strong mesoscale barrier winds and tip jets that form when synoptic-scale atmospheric features interact with the topography of Greenland. The influence of these mesoscale atmospheric events on the ocean, particularly deep ocean convection, is not yet well understood. Because obtaining observations is difficult in this region, model simulations are essential for understanding the interaction between the atmosphere and ocean during these wind events. This paper presents results from the Weather Research and Forecasting (WRF) Model simulations run at four different resolutions (100, 50, 25, and 10 km) and forced with the ECMWF Re-Analysis Interim (ERA-Interim) product. Case study comparisons between WRF output at different resolutions, observations from the Greenland Flow Distortion Experiment (GFDex), which provides valuable in situ observations of mesoscale winds, and Quick Scatterometer (QuikSCAT) satellite data highlight the importance o...

Simulating transient ice-ocean Ekman transport in the Regional Arctic System Model and Community Earth System Model

Abstract This work evaluates the fidelity of the polar marine Ekman layer in the Regional Arctic System Model (RASM) and Community Earth System Model (CESM) using sea-ice inertial oscillations as a proxy for ice-ocean Ekman transport. A case study is presented that demonstrates that RASM replicates inertial oscillations in close agreement with motion derived using the GPS. This result is obtained from a year-long case study pre-dating the recent decline in perennial Arctic sea ice, using RASM with sub-hourly coupling between the atmosphere, sea-ice and ocean components. To place this work in context, the RASM coupling method is applied to CESM, increasing the frequency of oceanic flux exchange from once per day in the standard CESM configuration, to every 30 min. For a single year simulation, this change causes a considerable increase in the median inertial ice speed across large areas of the Southern Ocean and parts of the Arctic sea-ice zone. The result suggests that processes associated with the passage of storms over sea ice (e.g. oceanic mixing, sea-ice deformation and surface energy exchange) are underestimated in Earth System Models that do not resolve inertial frequencies in their marine coupling cycle.

Winter Atmospheric Buoyancy Forcing and Oceanic Response during Strong Wind Events around Southeastern Greenland in the Regional Arctic System Model (RASM) for 1990–2010*

AbstractStrong, mesoscale tip jets and barrier winds that occur along the southeastern Greenland coast have the potential to impact deep convection in the Irminger Sea. The self-organizing map (SOM) training algorithm was used to identify 12 wind patterns that represent the range of winter [November–March (NDJFM)] wind regimes identified in the fully coupled Regional Arctic System Model (RASM) during 1990–2010. For all wind patterns, the ocean loses buoyancy, primarily through the turbulent sensible and latent heat fluxes; haline contributions to buoyancy change were found to be insignificant compared to the thermal contributions. Patterns with westerly winds at the Cape Farewell area had the largest buoyancy loss over the Irminger and Labrador Seas due to large turbulent fluxes from strong winds and the advection of anomalously cold, dry air over the warmer ocean. Similar to observations, RASM simulated typical ocean mixed layer depths (MLD) of approximately 400 m throughout the Irminger basin, with indi...

Exploration of turbulent heat fluxes and wind stress curl in WRF and ERA‐Interim during wintertime mesoscale wind events around southeastern Greenland

The strong, mesoscale tip jets and barrier winds that occur off the coast of southeastern Greenland drive large surface turbulent heat fluxes that may impact deep ocean convection. The turbulent fluxes and wind stress curl associated with 10 m wind patterns identified using the self-organizing map technique are investigated for 10 winters (1997–2007, November-December-January-February-March) in the European Centre for Medium-Range Weather Forecasts Interim Reanalysis (ERA-I) and a regional simulation using the Weather Research and Forecasting (WRF) model at 50 km. Sensible heat flux differences between WRF and ERA-I are primarily due to differences in near-surface temperature, while latent heat flux differences are driven by both moisture and wind speed differences. The largest turbulent flux differences occur over the marginal ice zone where the fluxes in WRF are larger than in ERA-I due to specified sea ice thickness that influences the near-surface atmospheric temperature and moisture; WRF has larger magnitude wind stress curl over the Irminger Sea. Patterns of strong westerly tip jet with barrier flow are most likely to impact preconditioning and convection in the Irminger Sea compared to other manifestations of westerly tip jets, and easterly tip jets are expected to have localized ocean impacts south of Cape Farewell.

Land Surface Climate in the Regional Arctic System Model

AbstractThe Regional Arctic System Model (RASM) is a fully coupled, regional Earth system model applied over the pan-Arctic domain. This paper discusses the implementation of the Variable Infiltration Capacity land surface model (VIC) in RASM and evaluates the ability of RASM, version 1.0, to capture key features of the land surface climate and hydrologic cycle for the period 1979–2014 in comparison with uncoupled VIC simulations, reanalysis datasets, satellite measurements, and in situ observations. RASM reproduces the dominant features of the land surface climatology in the Arctic, such as the amount and regional distribution of precipitation, the partitioning of precipitation between runoff and evapotranspiration, the effects of snow on the water and energy balance, and the differences in turbulent fluxes between the tundra and taiga biomes. Surface air temperature biases in RASM, compared to reanalysis datasets ERA-Interim and MERRA, are generally less than 2°C; however, in the cold seasons there are ...

Development of the Regional Arctic System Model (RASM): Near-Surface Atmospheric Climate Sensitivity

AbstractThe near-surface climate, including the atmosphere, ocean, sea ice, and land state and fluxes, in the initial version of the Regional Arctic System Model (RASM) are presented. The sensitivity of the RASM near-surface climate to changes in atmosphere, ocean, and sea ice parameters and physics is evaluated in four simulations. The near-surface atmospheric circulation is well simulated in all four RASM simulations but biases in surface temperature are caused by biases in downward surface radiative fluxes. Errors in radiative fluxes are due to biases in simulated clouds with different versions of RASM simulating either too much or too little cloud radiative impact over open ocean regions and all versions simulating too little cloud radiative impact over land areas. Cold surface temperature biases in the central Arctic in winter are likely due to too few or too radiatively thin clouds. The precipitation simulated by RASM is sensitive to changes in evaporation that were linked to sea surface temperature...

A Case Study of Observed and Modeled Barrier Flow in the Denmark Strait in May 2015

AbstractMesoscale barrier jets in the Denmark Strait are common in winter months and have the capability to influence open ocean convection. This paper presents the first detailed observational study of a summertime (21 May 2015) barrier wind event in the Denmark Strait using dropsondes and observations from an airborne Doppler wind lidar (DWL). The DWL profiles agree well with dropsonde observations and show a vertically narrow (~250–400 m) barrier jet of 23–28 m s−1 near the Greenland coast that broadens (~300–1000 m) and strengthens farther off coast. In addition, otherwise identical regional high-resolution Weather Research and Forecasting (WRF) Model simulations of the event are analyzed at four horizontal grid spacings (5, 10, 25, and 50 km), two vertical resolutions (40 and 60 levels), and two planetary boundary layer (PBL) parameterizations [Mellor–Yamada–Nakanishi–Niino, version 2.5 (MYNN2.5) and University of Washington (UW)] to determine what model configurations best simulate the observed jet ...