An analysis of Russian Sea Ice Charts for 1933-2006

A. Mahoney, R.G. Barry and F. FettererNational Snow and Ice Data Center, University of Colorado

Boulder, Colorado, 80303, USA

AARI ice chart April 8-11, 2006

Outline

• Introduction

• Background on AARI ice charts

• Method• Locating discontinuous pack ice edges

• Results• 20th Century sea ice extent variability

• Comparison with other data• Meteorological data• Other ice charts

• Summary and conclusions

Introduction and

Background

About the AARI* ice charts

• Operational sea ice charts generated approximately every 10 days, dating back as far as 1933

• Charts produced by assimilation of different observations:• satellite active / passive microwave• airborne radar and infrared• visual observations from aircraft, ships and coastal stations• coastal radar installations• buoy-mounted instrumentation• automatic ice stations

• Provide information on:• sea ice concentration• stages of development• ice forms

*Arctic and Antarctic Research InstituteSt Petersburg, Russia

Airborne radar flightlines

• Standard pattern of airborne radar observations

• Carried out periodically through the year since 1970s

• Highest concentration along Northern Sea Route

From: Remote Sensing of the Sea

Ice in the Northern Sea Route, Studies and Applications,

Johannessen et al, 2007

AARI ice charts in EASE grid

• Ice charts are provided in SIGRID* format and converted to EASE-Grid**

• Separate charts for eastern and western Russian Arctic

• Spatial and temporal coverage is variable and discontinuous

* Sea Ice Grid (World Meteorological Organization)**Equal Area Scalable Earth Grid – details at http://www.nsidc.org/ease

Examples of early AARI ice charts

• Chart coverage is poor

• Mostly limited to reconnaissance flights within range of coastal stations

• Still possible to identify and locate the ice edge

Method

Coast-to-pole vectors

• 360 vectors along meridians from the coast to the pole

• Used for locating the edge of the pack ice

• Can cope with discontinuous edges

Locating the edge of the pack ice

1) Transition to <15% ice concentration

2) Pack ice / landfast ice boundary

3) The coast

Algorithm looks for ice edge along every coast-to-pole vector

Ice edge is defined by either:

Manual inspection of algorithm

• Algorithm can be confused around islands and polynyas

• In these cases, the edge is corrected manually

• The edge on every chart will be manually inspected

Results

Spatio-temporal coverage of results

• Only spring and summer months charted in early years

• Frequency of charts increases through record

• Continuity of ice edges improves over time

Changes in sea ice extent

• Much regional variability

• Reduced autumn ice extent in early 20th century

• Increasingly negative anomalies in both spring and autumn since 1970s

• Missing data during key period (1993-1996)

Manually inspected

Changes in sea ice concentration

• Comparison of decadal monthly means

• Increase from 1940s – 1970s is mostly matched by the loss between 1970s and 2000s

Comparison with other

data

Temperature and pressure anomalies

• Derived from station data North of 65°N

• Early and late part of record warmer than middle

• Evidence of decadal variability

Ice and temperature variability

• No significant interannual correlation between ice and air temperature

• Adjacent seas show similar temperature trends, but different trends in ice extent

• Similarly weak relationship to station SLP observations

• No consistent correlations with Arctic Oscillation index

Comparison with NIC* charts

• Overall mean difference is close to zero

• AARI charts report higher concentration in autumn and winter

• NIC charts report higher concentration in summer

• No apparent long-term differences though number of common cells between chart sets increases with time

* National Ice Center

AARI>

NIC

NIC>

AARI

Summary

AARI ice charts provide a long timeseries of ice extent variability in Russian Arctic

• Manual inspection of ice edges required throughout record

Ice edge results so far indicate:

• Reduced ice extent in 1930s – 40s

• greatest reduction in Barents Sea

• Most evident in fall minimum extent

• Greater reduction in ice extent since 1970s

• Evident in both spring and autumn

Hi-latitude observations show cooling in mid 20th Century

• No direct correlations with ice extent variability

Future work

Finish manual inspection of ice edgesFinish manual inspection of ice edges

More detailed analysis of sea ice variabilityMore detailed analysis of sea ice variability

• Both temporal and spatialBoth temporal and spatial

• Include landfast sea iceInclude landfast sea ice

• Statistical analysis of atmospheric forcingStatistical analysis of atmospheric forcing

Extend comparisons with other datasetsExtend comparisons with other datasets

• Derive an optimal, merged sea ice record from different Derive an optimal, merged sea ice record from different chartscharts

AcknowledgementsVasily SmolyanitskyArctic and Antarctic Research Institute (AARI)St. Petersburg, Russia

• Providing the AARI data in SIGRID format with near-EASE-grid regridding software

Joey ComeauxNational Center for Atomspheric Research (NCAR)Boulder, Colorado, USA

• Assistance acquiring meteorological station data

NASA

• Award NNG04GH03G, “Twentieth Century Sea Ice Conditions in the Eurasian Arctic from a Comprehensive Reconstitution and Synthesis of Russian Data Sources with Modern Satellite Data”