Impacts of Snow Initialization on Subseasonal Forecasts of Surface Air Temperature for the Cold Season

Abstract

The present study examines the impacts of snow initialization on surface air temperature by a number of ensemble seasonal predictability experiments using the NCAR Community Atmosphere Model version 3 (CAM3) AGCM with and without snow initialization. The study attempts to isolate snow signals on surface air temperature. In this preliminary study, any effects of variations in sea ice extent are ignored and do not explicitly identify possible impacts on atmospheric circulation. The Canadian Meteorological Center (CMC) daily snow depth analysis was used in defining initial snow states, where anomaly rescaling was applied in order to account for the systematic bias of the CAM3 snow depth with respect to the CMC analysis. Two suites of seasonal (3 months long) ensemble hindcasts starting at each month in the colder part of the year (September–April) with and without the snow initialization were performed for 12 recent years (1999–2010), and the predictability skill of surface air temperature was estimated. Results show that considerable potential predictability increases up to 2 months ahead can be attained using snow initialization. Relatively large increases are found over East Asia, western Russia, and western Canada in the later part of this period. It is suggested that the predictability increases are sensitive to the strength of snow–albedo feedback determined by given local climate conditions; large gains tend to exist over the regions of strong snow–albedo feedback. Implications of these results for seasonal predictability over the extratropical Northern Hemisphere and future direction for this research are discussed.

Eurasian snow depth in long-term climate reanalyses

“…Reciprocally, as a corresponding component of the climate system, the snow cover influences large-scale climate patterns and has been tapped as a source of predictability at the subseasonal-to-seasonal scale, especially over Eurasia in au-M. Wegmann et al: Eurasian snow depth in long-term climate reanalyses tumn and winter (Cohen and Entekhabi, 1999;Jeong et al, 2013;Orsolini et al, 2013;Wu et al, 2014;Ye et al, 2015,).…”

Influence of the Eurasian snow on the negative North Atlantic Oscillation in subseasonal forecasts of the cold winter 2009/2010

“…Since the land-sea thermal contrast is a strong driver of PWs, it is not surprising that the presence of a continent-wide surface cooling due to an anomalously thick snowpack may modulate their amplitudes. Furthermore, recent studies demonstrate that initialization of the snowpack has an impact on subseasonal forecasts (Jeong et al 2013;Orsolini et al 2013).…”

Medium- and Extended-Range Ensemble Weather Forecasting

“…Initial conditions in the stratosphere can affect the circulation in the troposphere over the following month, providing another source for sub-seasonal predictability (Baldwin and Dunkerton 2001). Other potential sources of predictability at this timescale include the land surface (Koster et al 2010) and snow cover (Jeong et al 2013) conditions at the start of the forecast.…”