OBSERVED ROBUSTNESS OF INTERANNUAL VARIABILITY OF OCTOBER EURASIAN SNOWCOVER AND ITS CLIMATE LINKAGE

CanSISE conference, VictoriaYara MohajeraniMay 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 AOCohen 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 AnomalyBrown 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 Type Name Monthly 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

Dataset SCF Change (%)

MERRA -8.2

BROWN -11.4

NOAA 16.7

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, 5335-5343, 1

NOVEMBER 2007. 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, 3337-3352. SEPTEMBER 2005. 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, 6185- 6202. DOI: 10.1175/JCLI-D-11-00055.1 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:10.1029/2012JD017587, 2012 Brown R. D., Derksen, C. (2013) Is Eurasian October snow cover extent increasing? Environ. Res. Lett. 8, doi: 10.1088/1748-9326/8/2/024006 Brown R. D., Robinson D. (2011) Northern Hemisphere spring snow cover variability and change over 1922–2010 including an assessment of

uncertainty. Cryosphere. 5 219–29. 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 113.12 (2009): 2661-669. 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: 10.1029/2000GL012556 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):

3624-648. 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) 045026 (6pp) doi:10.1088/1748-9326/4/4/045026 Reichle, R.H. (2011) Assessment and Enhancement of MERRA Land Surface Hydrology Estimates, Journal of Climate, 6322-6338, DOI:

10.1175/JCLI-D-10-05033.1 Buygina O. N. et al. (2011) Changes in snow cover characteristics over Northern Eurasia since 1966. Environ. Res. Lett. 6 (2011) 045204

(10pp). doi:10.1088/1748-9326/6/4/045204 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 115. 3517–3529. doi:10.1016/j.rse.2011.08.014 Reichle et al (2011) Assessment and Enhancement of MERRA Land Surface Hydrology Estimates. Journal of Climate. Volume 24, 6322-6338.

DOI: 10.1175/JCLI-D-10-05033.1

Supplementary Material

SCF Histogram

Regression: Zonally Asymmetric geopotential [Z]*