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Betts A.K.,U.S. National Center for Atmospheric Research | Desjardins R.,Agriculture and Agri Food Canada | Beljaars A.C.M.,The European Center for Medium Range Weather Forecasts | Tawfik A.,U.S. National Center for Atmospheric Research | Tawfik A.,George Mason University
Frontiers in Earth Sciences | Year: 2015

Our aim is to provide an observational reference for the evaluation of the surface and boundary layer parameterizations used in large-scale models using the remarkable long-term Canadian Prairie hourly dataset. First we use shortwave and longwave data from the Baseline Surface Radiation Network (BSRN) station at Bratt's Lake, Saskatchewan, and clear sky radiative fluxes from ERA-Interim, to show the coupling between the diurnal cycle of temperature and relative humidity and effective cloud albedo and net longwave flux. Then we calibrate the nearby opaque cloud observations at Regina, Saskatchewan in terms of the BSRN radiation fluxes. We find that in the warm season, we can determine effective cloud albedo to ±0.08 from daytime opaque cloud, and net long-wave radiation to ±8 W/m2 from daily mean opaque cloud and relative humidity. This enables us to extend our analysis to the 55 years of hourly observations of opaque cloud cover, temperature, relative humidity, and daily precipitation from 11 climate stations across the Canadian Prairies. We show the land-surface-atmosphere coupling on daily timescales in summer by stratifying the Prairie data by opaque cloud, relative humidity, surface wind, day-night cloud asymmetry and monthly weighted precipitation anomalies. The multiple linear regression fits relating key diurnal climate variables, the diurnal temperature range, afternoon relative humidity and lifting condensation level, to daily mean net longwave flux, windspeed and precipitation anomalies have R2-values between 0.61 and 0.69. These fits will be a useful guide for evaluating the fully coupled system in models. © 2015 Betts, Desjardins, Beljaars and Tawfik.

Dirmeyer P.A.,Center for Ocean Land Atmosphere Studies | Cash B.A.,Center for Ocean Land Atmosphere Studies | Kinter III J.L.,Center for Ocean Land Atmosphere Studies | Kinter III J.L.,George Mason University | And 16 more authors.
Climate Dynamics | Year: 2012

The effects of horizontal resolution and the treatment of convection on simulation of the diurnal cycle of precipitation during boreal summer are analyzed in several innovative weather and climate model integrations. The simulations include: season-long integrations of the Non-hydrostatic Icosahedral Atmospheric Model (NICAM) with explicit clouds and convection; year-long integrations of the operational Integrated Forecast System (IFS) from the European Centre for Medium-range Weather Forecasts at three resolutions (125, 39 and 16 km); seasonal simulations of the same model at 10 km resolution; and seasonal simulations of the National Center for Atmospheric Research (NCAR) low-resolution climate model with and without an embedded two-dimensional cloud-resolving model in each grid box. NICAM with explicit convection simulates best the phase of the diurnal cycle, as well as many regional features such as rainfall triggered by advancing sea breezes or high topography. However, NICAM greatly overestimates mean rainfall and the magnitude of the diurnal cycle. Introduction of an embedded cloud model within the NCAR model significantly improves global statistics of the seasonal mean and diurnal cycle of rainfall, as well as many regional features. However, errors often remain larger than for the other higher-resolution models. Increasing resolution alone has little impact on the timing of daily rainfall in IFS with parameterized convection, yet the amplitude of the diurnal cycle does improve along with the representation of mean rainfall. Variations during the day in atmospheric prognostic fields appear quite similar among models, suggesting that the distinctive treatments of model physics account for the differences in representing the diurnal cycle of precipitation. © 2011 The Author(s).

Benestad R.E.,Norwegian Meteorological Institute | Senan R.,Norwegian Meteorological Institute | Balmaseda M.,The European Center for Medium range Weather Forecasts | Ferranti L.,The European Center for Medium range Weather Forecasts | And 2 more authors.
Tellus, Series A: Dynamic Meteorology and Oceanography | Year: 2011

Current seasonal forecast models involve simple schemes for representing sea ice, such as imposing climatological values. The spread of ensemble forecasts may in principle be biased due to common boundary conditions prescribed in the high latitudes. The degree of sensitivity in the 2-metre temperature, associated with seasonal time scales and the state of the June-August sea ice, is examined through a set of experiments with a state-of-the-art coupled ocean-atmosphere model. Here we present a suite of numerical experiments examining the effect of different sea ice configurations on the final ensemble distribution. We also compare the sensitivity of the 2-metre temperature to sea ice boundary conditions and sea surface temperature perturbation in the initial conditions. One objective of this work was to test a simple scheme for a more realistic representation of sea ice variations that allows for a spread in the Polar surface boundary conditions, captures the recent trends and doesn't smudge the sea ice edges. We find that the use of one common set of boundary conditions in the polar regions has little effect on the subsequent seasonal temperatures in the low latitudes, but nevertheless a profound influence on the local temperatures in the mid-to-high latitudes. © 2010 The Authors Tellus A©2010 International Meteorological Institute in Stockholm.

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