observed robustness of interannual variability of october eurasian snowcover and its climate linkage...
TRANSCRIPT
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]*