OBSERVED ROBUSTNESS OF INTERANNUAL VARIABILITY OF OCTOBER EURASIAN SNOWCOVER AND ITS CLIMATE LINKAGE CanSISE conference, Victoria Yara Mohajerani May 9, 2014

Outline  Background  Eurasian October snow and wintertime climate  Snow cover datasets  Evaluation of snow cover datasets  Climate linkage  Conclusion

Snow-Climate Connection  Vast and highly variable snow cover  Positive October snow anomaly  negative AO phase in the following winter Effect of October snow on AO Cohen et al 2007, Figure 6, page 5342

Inconsistencies in snow data  Known inconsistencies in snowcover data  NOAA shows false positive trend  NOAA widely used in climate- connection studies Snow Cover Extent Anomaly Brown and Derksen (2013) Figure 2, page 4

Project Overview 1. Validation and evaluation of satellite and reanalysis datasets against ground measurements (for ground station locations) Need global coverage, but can only validate data with local observations 2. Application of revised datasets to the issue of relationships between October Eurasian snow cover and northern hemisphere winter circulation (sea level pressure and free atmospheric geopotential) from 1980 to 2011.

Snow Cover Fraction (SCF) datasets Measurement TypeNameMonthly SCF Definition Reanalysis (based on ERAint temperature and precipitation) BROWN % of days in a month with ≥ 2cm snow depth Reanalysis MERRA % of days in a month with SWE ≥4mm Passive Microwave Satellite Measurements PMW % of days in a month with SWE ≥7.5mm Visible Satellite Measurements NOAA % of days in month that a cell has more than 50% snow covered Ground Measurements of snow depth over Russia RU % of days in a month with >=2 cm snow depth.

Consistency

Consistency (15%)

S(t) time series DatasetSCF Change (%) MERRA-8.2 BROWN-11.4 NOAA16.7 RU-7.5

Correlation of snow indices

Snow-Climate Connection

Regression: 2-meter Temperature

Regression: Sea Level Pressure

Regression: Zonal mean geopotential [Z]

Snowcover and AO index

Snow climate connection discussion  MERRA has weaker correlation than NOAA  BROWN has very weak correlation  Time frame matters: MERRA and NOAA more similar in JF than DJF

Conclusions  Internal inconsistencies in NOAA: false positive trend  MERRA and BROWN have best agreement with in- situ data (respectively)  Dataset bias (NOAA) possible in previous climate linkage studies  Relationship still evident between October Eurasian snow and wintertime circulation  The extent of this relationship should be taken with caution due to inconsistencies in snowcover data

Acknowledgements  Professor Paul J. Kushner  Dr. Chris Derksen  Dr. Ross Brown  Centre for Global Change Science, University of Toronto  The Canadian Sea Ice and Snow Evolution (CanSISE)  Department of Physics, University of Toronto

References  Watanabe, M., and T. Nitta (1998): Relative impacts of snow and sea surface temperature anomalies on an extreme phase in the winter atmospheric circulation. J. Climate, 11, 2837–2857.  Cohen J., and D. Entekhabi (1999): Eurasian snow cover variability and Northern Hemisphere climate predictability. Geophys. Res. Lett., 26, 345–348.  Cohen J. et al (2007) Stratosphere–Troposphere Coupling and Links with Eurasian Land Surface Variability. J. Climate, Volume 20, , 1 NOVEMBER  Wallace, J. M., Hobbs, P. V. (2006): Atmospheric Science: An Introductory Survey. Second Edition, University of Washington. Copyright ©2006 Elsevier Inc.  Reichler, T. et al (2005): The Coupled Stratosphere–Troposphere Response to Impulsive Forcing from the Troposphere. JOURNAL OF THE ATMOSPHERIC SCIENCES. Volume 62, SEPTEMBER  Polvani, L. M., and D. W. Waugh, 2004: Upward wave activity flux as a precursor to extreme stratospheric events and sub- sequent anomalous surface weather regimes. J. Climate, 17, 3548–3554.  Smith K. L. et al (2011) The Role of Linear Interference in Northern Annular Mode Variability Associated with Eurasian Snow Cover Extent. J. Climate, Volume 24, DOI: /JCLI-D  Smith K. L., Kushner P. J. (2012) Linear interference and the initiation of extratropical stratosphere-troposphere interactions. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 117, D13107, doi: /2012JD017587, 2012  Brown R. D., Derksen, C. (2013) Is Eurasian October snow cover extent increasing? Environ. Res. Lett. 8, doi: / /8/2/  Brown R. D., Robinson D. (2011) Northern Hemisphere spring snow cover variability and change over 1922–2010 including an assessment of uncertainty. Cryosphere –29.  Savoie, Matthew H., Richard L. Armstrong, Mary J. Brodzik, and James R. Wang. "Atmospheric Corrections for Improved Satellite Passive Microwave Snow Cover Retrievals over the Tibet Plateau." Remote Sensing of Environment (2009):  Armstrong, R.L. and M.J. Brodzik, 2001: Recent northern hemisphere snow extent: A comparison of data derived from visible and microwave satellite sensors. Geophys. Res. Lett., 28: 3673–3676. doi: /2000GL  Dee, D.P., “The ERA-Interim reanalysis: configuration and performance of the data assimilation system.” Q.J.R.Meteorol.Soc.137:553–597, April 2011  Rienecker, Michele M. et al., "MERRA: NASA’s Modern-Era Retrospective Analysis for Research and Applications." Journal of Climate 24 (2011):  Bulygina O.N., Razuvaev V.N., Korshunova N.N. (2009) Changes in snow cover over Northern Eurasia in the last few decades. Environ. Res. Lett. 4 (2009) (6pp) doi: / /4/4/  Reichle, R.H. (2011) Assessment and Enhancement of MERRA Land Surface Hydrology Estimates, Journal of Climate, , DOI: /JCLI-D  Buygina O. N. et al. (2011) Changes in snow cover characteristics over Northern Eurasia since Environ. Res. Lett. 6 (2011) (10pp). doi: / /6/4/  Takala, M. et al. (2011) Estimating northern hemisphere snow water equivalent for climate research through assimilation of space-borne radiometer data and ground- based measurements. Remote Sensing of Environment –3529. doi: /j.rse  Reichle et al (2011) Assessment and Enhancement of MERRA Land Surface Hydrology Estimates. Journal of Climate. Volume 24, DOI: /JCLI-D

Supplementary Material

SCF Histogram

Regression: Zonally Asymmetric geopotential [Z]*