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Tuesday, February 19, 2013

Papers on Northern Hemisphere snow cover changes

by Ari Jokimäki, AGW Observer, February 19, 2013

This is a list of papers on snow cover changes with an emphasis on hemispheric and global observational analyses. The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.
Change in snow phenology and its potential feedback to temperature in the Northern Hemisphere over the last three decades – Peng et al. (2013) “Trends in the duration or extent of snow cover are expected to feedback to temperature trends. We analyzed trends in dates of onset and termination of snow cover in relation to temperature over the past 27 years (1980–2006) from over 636 meteorological stations in the Northern Hemisphere. Different trends in snow duration are observed over North America and Eurasia. Over North America, the termination date of snow cover remained stable during the 27 years, whereas over Eurasia it has advanced by 2.6 ± 5.6 d decade−1. Earlier snow cover termination is systematically correlated on a year-to-year basis with a positive temperature anomaly during the snowmelt month with a sensitivity of −0.077 °C d−1. These snow feedbacks to air temperature are more important in spring, because high net radiation is coupled with thin snow cover. Shushi Peng et al 2013 Environ. Res. Lett. 8 014008 doi:10.1088/1748-9326/8/1/014008. [Full text]
Northern Hemisphere spring snow cover variability and change over 1922–2010 including an assessment of uncertainty – Brown & Robinson (2011) “An update is provided of Northern Hemisphere (NH) spring (March, April) snow cover extent (SCE) over the 1922–2010 period incorporating the new climate data record (CDR) version of the NOAA weekly SCE dataset, with annual 95% confidence intervals estimated from regression analysis and intercomparison of multiple datasets. The uncertainty analysis indicates a 95% confidence interval in NH spring SCE of ±5–10% over the pre-satellite period and ±3–5% over the satellite era. The multi-dataset analysis shows larger uncertainties monitoring spring SCE over Eurasia (EUR) than North America (NA) due to the more complex regional character of the snow cover variability and larger between-dataset variability over northern Europe and north-central Russia. Trend analysis of the updated SCE series provides evidence that NH spring snow cover extent has undergone significant reductions over the past ~90 yr and that the rate of decrease has accelerated over the past 40 yr. The rate of decrease in March and April NH SCE over the 1970–2010 period is ~0.8 million km2 per decade corresponding to a 7% and 11% decrease in NH March and April SCE respectively from pre-1970 values. In March, most of the change is being driven by Eurasia (NA trends are not significant) but both continents exhibit significant SCE reductions in April. The observed trends in SCE are being mainly driven by warmer air temperatures, with NH mid-latitude air temperatures explaining ~50% of the variance in NH spring snow cover over the 89-yr period analyzed. However, there is also evidence that changes in atmospheric circulation around 1980 involving the North Atlantic Oscillation and Scandinavian pattern have contributed to reductions in March SCE over Eurasia. Brown, R. D. and Robinson, D. A.: Northern Hemisphere spring snow cover variability and change over 1922–2010 including an assessment of uncertainty, The Cryosphere, 5, 219-229, doi:10.5194/tc-5-219-2011, 2011. [Full text]
Long-term variability in Northern Hemisphere snow cover and associations with warmer winters – McCabe & Wolock (2010) “A monthly snow accumulation and melt model is used with gridded monthly temperature and precipitation data for the Northern Hemisphere to generate time series of March snow-covered area (SCA) for the period 1905 through 2002. The time series of estimated SCA for March is verified by comparison with previously published time series of SCA for the Northern Hemisphere. The time series of estimated Northern Hemisphere March SCA shows a substantial decrease since about 1970, and this decrease corresponds to an increase in mean winter Northern Hemisphere temperature. The increase in winter temperature has caused a decrease in the fraction of precipitation that occurs as snow and an increase in snowmelt for some parts of the Northern Hemisphere, particularly the mid-latitudes, thus reducing snow packs and March SCA. In addition, the increase in winter temperature and the decreases in SCA appear to be associated with a contraction of the circumpolar vortex and a poleward movement of storm tracks, resulting in decreased precipitation (and snow) in the low- to mid-latitudes and an increase in precipitation (and snow) in high latitudes. If Northern Hemisphere winter temperatures continue to warm as they have since the 1970s, then March SCA will likely continue to decrease. Gregory J. McCabe, David M. Wolock, Climatic Change, March 2010, Volume 99, Issue 1-2, pp 141-153, DOI: 10.1007/s10584-009-9675-2.
Changing Northern Hemisphere Snow Seasons – Choi et al. (2010) “Spatial and temporal patterns in the onset, offset, and length of the snow season across Northern Hemisphere continents are examined for the period from 1967 to 2008. Full snow seasons (FSS) and core snow seasons (CSS) are defined based on the consistency of snow cover within a location over the course of the cold season. Climatologically, the seasonal onsets of FSS and CSS progress more rapidly across the continents than the slower spring northward offset. Average Northern Hemisphere FSS duration has decreased at a rate of 0.8 week decade−1 (5.3 days decade−1) between the winters of 1972/73 and 2007/08, while there is no significant hemispheric change in CSS duration. Changes in the FSS duration are attributed primarily to a progressively earlier offset, which has advanced poleward at a rate of 5.5 days decade−1. A major change in the trends of FSS offset and duration occurred in the late 1980s. Earlier FSS offsets, ranging from 5 to 25 days, and resultant abbreviated durations are observed in western Europe, central and East Asia, and the mountainous western United States. Where regional changes in CSS were observed, most commonly there were shifts in both onset and offset dates toward earlier dates. Results indicate that it is important to pay close attention to spring snowmelt as an indicator of hemispheric climate variability and change. Choi, Gwangyong, David A. Robinson, Sinkyu Kang, 2010: Changing Northern Hemisphere Snow Seasons. J. Climate, 23, 5305–5310. doi: [Full text]
Recent Northern Hemisphere snow cover extent trends and implications for the snow-albedo feedback – Déry & Brown (2007) “Monotonic trend analysis of Northern Hemisphere snow cover extent (SCE) over the period 1972–2006 with the Mann-Kendall test reveals significant declines in SCE during spring over North America and Eurasia, with lesser declines during winter and some increases in fall SCE. The weekly mean trend attains −1.28, −0.78, and −0.48 × 106 km2 (35 years)−1over the Northern Hemisphere, North America, and Eurasia, respectively. The standardized SCE time series vary and trend coherently over Eurasia and North America, with evidence of a poleward amplification of decreasing SCE trends during spring. Multiple linear regression analyses reveal a significant dependence of the retreat of the spring continental SCE on latitude and elevation. The poleward amplification is consistent with an enhanced snow-albedo feedback over northern latitudes that acts to reinforce an initial anomaly in the cryospheric system. Stephen J. Déry, Ross D. Brown, Geophysical Research Letters, Volume 34, Issue 22, November 2007, DOI: 10.1029/2007GL031474. [Full text]
Variability and trends in the annual snow-cover cycle in Northern Hemisphere land areas, 1972–2000 – Dye (2002)“This study investigated variability and trends in the annual snow-cover cycle in regions covering high-latitude and high-elevation land areas in the Northern Hemisphere. The annual snow-cover cycle was examined with respect to the week of the last-observed snow cover in spring (WLS), the week of the first-observed snow cover in autumn (WFS), and the duration of the snow-free period (DSF). The analysis used a 29-year time-series (1972–2000) of weekly, visible-band satellite observations of Northern Hemisphere snow cover from NOAA with corrections applied by D. Robinson of Rutgers University Climate Laboratory. Substantial interannual variability was observed in WLS, WFS and DSF (standard deviations of 0·8–1·1, 0·7–0·9 and 1·0–1·4 weeks, respectively), which is related directly to interannual variability in snow-cover area in the regions and time periods of snow-cover transition. Over the nearly three-decade study period, WLS shifted earlier by 3–5 days/decade as determined by linear regression analysis. The observed shifts in the annual snow-cover cycle underlie a significant trend toward a longer annual snow-free period. The DSF increased by 5–6 days/decade over the study period, primarily as a result of earlier snow cover disappearance in spring. The observed trends are consistent with reported trends in the timing and length of the active growing season as determined from satellite observations of vegetation greenness and the atmospheric CO2 record.Dennis G. Dye, Hydrological Processes, Volume 16, Issue 15, pages 3065–3077, 30 October 2002, DOI: 10.1002/hyp.1089.
Northern Hemisphere Snow Cover Variability and Change, 1915–97 – Brown (2000) “Historical and reconstructed snow cover data from stations in Canada, the United States, the former Soviet Union, and the People’s Republic of China were used to reconstruct monthly snow cover extent (SCE) fluctuations over midlatitudinal (40°–60°N) regions of North America (NA) and Eurasia back to the early 1900s using an areal snow index approach. The station distribution over NA allowed SCE to be reconstructed back to 1915 for 6 months (November–April), along with estimates of monthly mean snow water equivalent (SWE) from gridded daily snow depth data. Over Eurasia, SCE was able to be reconstructed back to 1922, but major gaps in the station network limited the approach to 3 months (October, March, and April). The reconstruction provided evidence of a general twentieth century increase in NA SCE, with significant increases in winter (December–February) SWE averaging 3.9% per decade. The results are consistent with an observed increasing trend in winter snow depth over Russia and provide further evidence for systematic increases in precipitation over NH midlatitudes. North American spring snow cover was characterized by rapid decreases during the 1980s and early 1990s with a significant long-term decrease in April SWE averaging 4.4% per decade. Eurasia was characterized by a significant reduction in April SCE over the 1922–97 period associated with a significant spring warming. The snow cover reduction was significant at the hemispheric scale with an estimated average NH SCE loss of 3.1 × 106 km2 (100 yr)−1 associated with significant warming of 1.26°C (100 yr)−1 over NH midlatitudinal land areas (40°–60°N). The computed temperature sensitivity of NH April SCE was −2.04 × 106 km2 °C−1. Since 1950, March SCE decreases have become more important than those in April with significant reductions over both continents averaging 8.5 × 106 km2 (100 yr)−1. March was also observed to have experienced the largest warming during the November–April snow season with significant post-1950 warming trends in both continents averaging 4.1°C (100 yr)−1. The hemisphere-wide elevated March snow cover–temperature response is consistent with the position of the snowline over continental grassland vegetation zones where snow cover is relatively shallow and the potential snow cover area–albedo feedback is large.” Brown, Ross D., 2000: Northern Hemisphere Snow Cover Variability and Change, 1915–97. J. Climate, 13, 2339–2355. doi:;2. [Full text]
Northern Hemisphere snow extent: regional variability 1972–1994 – Frei & Robinson (1999) “Snow cover is an important hydrologic and climatic variable due to its effects on water supplies, and on energy and mass exchanges at the surface. We investigate the kinematics and climatology of Northern Hemisphere snow extent between 1972 and 1994, and associated circulation patterns. Interannual fluctuations of North American and Eurasian snow extents are driven by both hemispheric scale signals, as well as signals from smaller ‘coherent’ regions, within which interannual fluctuations of snow extent are highly correlated. These regions cover only 2–6% of the continental land area north of 20°N, yet during many months they explain more than 60% of the variance in continental snow extent. They are identified using Principal Components Analysis (PCA) of digitized snow extent charts obtained from the National Oceanic and Atmospheric Administration (NOAA). Significant month-to-month persistence is found over western North America and Europe during winter and spring. Geographically and seasonally dependent associations are identified between North American snow extent and atmospheric circulation patterns, surface air temperature, and snowfall. Over western North America, snow extent is associated with the longitudinal position of the North American ridge. Over eastern North America, snow extent is associated with a meridional oscillation in the 500-mb geopotential height field. These teleconnection patterns, derived using composite analyses, are associated with secondary modes of tropospheric variability during autumn and winter. During spring, snow extent becomes effectively decoupled from tropospheric dynamics. These results are useful for understanding the natural variability of the climate system, reconstructing pre-satellite era climate variability, evaluating climate models, and detecting climate change. Allan Frei, David A. Robinson, International Journal of Climatology, Volume 19, Issue 14, pages 1535–1560, 30 November 1999, DOI: 10.1002/(SICI)1097-0088(19991130)19:143.0.CO;2-J. [Full text]
Recent variations and regional relationships in Northern Hemisphere snow cover – Robinson et al. (1995) Abstract doesn’t seem to be available online. Robinson, David A.; Frei, Allan; Serreze, Mark C., Annals of Glaciology, vol.21, pp.71-76.
Changes of Snow Cover, Temperature, and Radiative Heat Balance over the Northern Hemisphere – Groisman et al.(1994) “Contemporary large-scale changes in satellite-derived snow cover were examined over the Northern Hemisphere extratropical land (NEL) areas. These areas encompass 55% of the land in the Northern Hemisphere. Snow cover (S) transient regions, the “centers of action” relative to interannual variations of snow cover, were identified for the years 1972–1992. During these years a global retreat in snow cover extent (SE) occurred in the second half of the hydrologic year (April–September). Mean annual SE has decreased by 10% (2.3 × 106 km2). Negative trends account for one-third to one-half of the interannual continental variance of SE. The historical influence of S on the planetary albedo and outgoing longwave radiation (OLR) is investigated. The mean annual response of the S feedback on the radiative balance (RB) is negative and suggests a large-scale heat redistribution. During autumn and early winter (up to January), however, the feedback of S on the planetary RB may he positive. Only by February does the cooling effect of S (due to albedo increase) dominate the planetary warming due to reduced OLR over the S. Despite a wintertime maximum in SF, the feedback in spring has the greatest magnitude. The global retreat of spring SE should lead to a positive feedback on temperature. Based on observed records of S, changes in RB are calculated that parallel an observed increase of spring temperature during the past 20 years. The results provide a partial explanation of the significant increase in spring surface air temperature observed over the land areas of the Northern Hemisphere during the past century. The mean SE in years with an El Niño and La Niña were also evaluated. El Niño events are generally accompanied by increased SE over the NEL during the first half of the hydrological year. In the second half of the hydrologic year (spring and summer), the El Niño events are accompanied by a global retreat of SE. Groisman, Pavel Ya, Thomas R. Karl, Richard W. Knight, Georgiy L. Stenchikov, 1994: Changes of Snow Cover, Temperature, and Radiative Heat Balance over the Northern Hemisphere. J. Climate, 7, 1633–1656. doi:;2. [Full text]
Global Snow Cover Monitoring: An Update – Robinson et al. (1993) “Accurate monitoring of the large-scale dimensions of global snow cover is essential for understanding details of climate dynamics and climate change. Presently, such information is gathered individually from ground station networks and satellite platforms. Efforts are in progress to consolidate and analyze long-term station records from a number of countries. To gain truly global coverage, however, satellite-based monitoring techniques must be employed. A 27-year record of Northern Hemisphere continental snow cover produced by the National Oceanic and Atmospheric Administration (NOAA) is the longest such environmental record available. Records of Southern Hemisphere continental cover and snow on top of Arctic sea ice have been produced by similar means for a portion of this interval. The visible imagery charting technique used to generate these data provides information on snow extent but not on snow volume. Satellite microwave analyses over Northern Hemisphere lands show some promise in this regard, however, large-scale monitoring of snow extent with microwave data remains less accurate than visible charting. This paper updates the status of global snow cover monitoring, concentrating on the weekly snow charts prepared by NOAA and discussing a new and consistent record of monthly snow cover generated from these weekly charts. The NOAA charts show a reduction of hemispheric snow cover over the past five years, particularly in spring. Snow areas from the NOAA product are then compared with values derived using passive microwave data. The latter consistently reports less snow cover than the more accurate visible product. Finally, future snow monitoring initiatives are recommended. These include continuing the consistent NOAA product until an all-weather all-surface product is developed. The latter would use multiple data sources and geographic information systems techniques. Such an integrative product would need extensive comparisons with the NOAA product to ensure the continued utility of the lengthy NOAA observations in studies of climate change. In a retrospective sense, satellite charts from the middle 1960s to early 1970s need reevaluation and techniques to merge satellite products with historic station time series must be developed. Robinson, David A., Kenneth F. Dewey, Richard R. Heim, 1993: Global Snow Cover Monitoring: An Update. Bull. Amer. Meteor. Soc., 74, 1689–1696. doi:;2. [Full text]
Interannual Variability of Wintertime Snow Cover across the Northern Hemisphere – Gutzler & Rosen (1992)“Digitized maps of Northern Hemisphere snow cover derived from visible satellite imagery are examined to assess the interannual variability of snow cover in winter months for years 1972–90. The secular trend of winter snow cover over the landmasses of Eurasia and North America during this period is extremely small in December and January. A decreasing trend of somewhat larger magnitude is observed in Eurasian snow cover in February. Fluctuations of detrended interannual snow-cover anomalies averaged over the Eurasian and North American continents are positively correlated. By subdividing the continents into longitudinal sectors it is determined that this intercontinental relationship is due to high correlations between European and North American sectors. The relationship of snow-cover fluctuations to large-scale circulation anomalies is described using lime series of teleconnection pattern indices derived from monthly mean geopotential height fields. A pattern of height anomalies resembling the North Atlantic Oscillation is correlated with snow-cover anomalies in North America and Europe. The Pacific-North American teleconnection pattern is highly correlated with snow-cover anomalies in western North America but has limited influence on intercontinental snow-cover fluctuations.” Gutzler, David S., Richard D. Rosen, 1992: Interannual Variability of Wintertime Snow Cover across the Northern Hemisphere. J. Climate, 5, 1441–1447. doi:;2. [Full text]
Recent secular variations in the extent of Northern Hemisphere snow cover – Robinson & Dewey (1990) “Northern hemisphere snow cover during 1988 and 1989 was at its lowest extent since the advent of reliable satellite snow-cover monitoring in 1972; running some 8–10% below the eighteen-year annual mean of 25.7 million km2. Monthly minima for the period of record occurred six times during these two years. In general, the last nine years of the satellite record had less extensive cover than the 1972–80 interval. Negative anomalies during the 1980s were largest over Eurasia in all seasons, and in the Spring over North America. Hemispheric seasonal means for the most recent nine years were 3.7% to 8.4% lower than those between 1972 and 1980. Results are based on analyses of National Oceanic and Atmospheric Administration weekly snow charts, which are produced from visible satellite imagery.” David A. Robinson, Kenneth F. Dewey, Geophysical Research Letters, Volume 17, Issue 10, pages 1557–1560, September 1990, DOI: 10.1029/GL017i010p01557. [Full text]
A Digital Archive of Northern Hemisphere Snow Cover, November 1966 through December 1980 – Dewey & Heim (1982) “The purpose of this article is to acquaint the research community with a new data base—a digitized archive of Northern Hemisphere snow cover. Historically, those researchers who needed snow cover data for climatic and atmospheric boundary layer studies have had to rely on the irregularly spaced (and in some regions, sparse)grid of point observations. Northern Hemisphere Weekly Snow and Ice Cover Charts, which are created from analyzed satellite imagery at the National Earth Satellite Service (NESS), have been available on an operational basis since late 1966. Each of these weekly charts for the period November 1966 through December 1980 was digitized and stored in a new data archive. Snow cover area and snow cover frequency climatologies were created and examples are presented. The significance of this unique data archive is examined by comparing the 14-year mean annual snow cover frequency climatology with several published snow cover climatologies. The potential uses for this data archive in meteorological and climatological studies also are reviewed. Dewey, Kenneth F., Richard Heim, 1982: A Digital Archive of Northern Hemisphere Snow Cover, November 1966 through December 1980. Bull. Amer. Meteor. Soc., 63, 1132–1141. doi:;2. [Full text]

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