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A comparison of the regional Arctic System Reanalysis* and the global ERA-Interim
Reanalysis for the Arctic David H. Bromwich, Aaron B. Wilson, Le-sheng Bai, G.W. Kent Moore, Bill Kuo,
Zhiquan Liu, Hui-Chuan Lin, and Michael Barlage
AGU FALL MEETING Wednesday 17 December 2014
*http://polarmet.osu.edu/ASR/
INTRODUCTION
Arctic Climate System
Complex Interactions Rapidly Changing Amplified warming with
multiple feedbacks
Comprehensive picture of the changing Arctic climate Improved temporal and spatial resolution over existing global reanalyses A system-oriented approach focusing on the atmosphere, land surface
and sea ice
What is needed?
What is the Arctic System Reanalysis? • Key Characteristics
Regional reanalysis that merges observations with model forecasts
High-Resolution in Space (ASRv1-30km /ASRv2-15 km) and Time (3hr)
Fine-Scale Terrain Features Well Captured
Period: 2000 - 2012
• Key Components Polar WRF with fractional sea ice,
and variable sea ice thickness, albedo, and snow cover
WRFDA: 3D-Var
High Resolution Land Data Assimilation System (HRLDAS) – assimilates snow cover/depth, observed vegetation fraction and albedo
ASR available online at the NCAR CISL Research Data Archive
Aqua (AMSU, AIRS)
NOAA (HIRS, AMSU)
Conventional Observations: synoptic, metar, ship, buoy, and radiosonde Satellite Radiances: AMSUA, AMSUB, MHS, HIRS3, HIRS4 Other Satellite Observations: QuickSCAT, SSMI-sea surface wind speed, SSMI-precipitable water
GPS: GPSRO, GPSPW
Atmospheric Data Assimilation in ASR
GPSRO
RESULTS
Annual Surface Analysis
ASRv1
ASRv1
ERAI
ERAI
2 m Temperature ASRv1: 0.10/1.33/0.96 ERAI: 0.29/1.99/0.92 Cool in high latitudes of
Eurasia and N. America Warm in central Asia and
western N. America
10 m Wind Speed ASRv1: -0.24/1.78/0.70 ERAI: 0.41/2.13/0.64 Improved biases in ASRv1
over ERAI across much of Eurasia
Other Variables
2 m Dewpoint similar to 2 m Temperature
Surface Pressure well captured in both reanalyses
Compared to ~5000 surface stations
Mesoscale Features Power Spectra for 10 m wind
speed near Greenland Averaged for Dec-Feb 2000-12 ASRv1 has spatial energy in
the mesoscale than global reanalyses
ERAI NCEP ASRv1 3D Turbulence Scatterometer Winds
Features tied to the terrain (e.g., katabatic flow and tip jets) as well as polar lows are well captured by ASRv1
60⁰-70⁰N, 45⁰-10⁰W
Annual Upper-Air Analysis
~300 radiosondes (25% in the
Arctic)
Temperature Mean biases are ±0.2⁰C throughout
most of the column ASRv1 is slightly cold in the lower
atmosphere; ERAI is less so Minimal seasonal differences in biases
(poorest in summer) Horizontal Wind Speed Weaker than observed wind speed at
nearly all levels ASRv1 mean biases are lower
(statistically significant) than ERAI between 925-100 hPa
Negative biases nearly domain-wide
Other Variables Small RH biases in both ASRv1 and ERAI;
Dry over the high-latitudes Geopotential height biases < ±1 gpm at
all levels except 100 hPa
Monthly & Annual Precipitation Biases
Mid-latitude annual bias in ASRv1 is smaller then ERAI, but due to large compensation between warm/cool season precipitation
Too much precipitation in ASRv1 from Apr-Aug (4.9-25.2%)-too much convective precipitation
Mid-latitude dry precipitation biases from Sept-Mar, somewhat present in the Arctic, most notably across the Canadian Arctic Archipelago
Dry in the Arctic during summer (-17.2 to -23.7%) – moist physics issues
~400 stations (20% in the Arctic)
Monthly and Annual Incident Radiation
ASRv1 SW biases are positive and larger than ERAI (statistically significant) for mid-latitude and polar regions; RMSEs - smaller; Correlations - higher
ASRv1 Spring /Summer SW biases are seasonally the largest
Annual negative longwave biases in ASRv1 and ERAI are similar
Issues with amount of cloud as well as cloud optical properties in the model physics (e.g., convective cloud fraction)
Shortwave Radiation
Shortwave Radiation with ASRv2 15km
Bias (W m-2) RMSE Correlation
ASR 30km 15km 30km 15km 30km 15km
SW 52.3 17.6 122.6 111.4 0.93 0.93
LW -22.5 -6.9 31.4 25.6 0.72 0.68
SW and LW biases are significantly improved for most stations
Summary and Future Endeavors
ASRv1 surface analysis of temperature, dewpoint, and pressure are better than ERAI with a particular improvement in the wind field
ASRv1 improves on ERAI winds throughout the troposphere
ASRv1 forecast fields (precipitation, radiation) need further improvement of model physics
ERAI’s strength remains in the forecast fields as 4DVAR leads to greater temporal consistency between assimilated observations and the initialized state
ASRv1’s strength lies in the depiction of mesoscale processes in the Arctic
ASRv2 (30 km and 15 km) are currently being refined with improvements to radiation (convective cloud fraction decreases SW biases) and summer precip.
Precipitation Intensity Distribution
Polar Region (ASRv1/ERAI)
January dry days in ASRv1 (72) much lower than ERAI (357)
Very light precipitation (<0.1 mm day-1) on more days in ASRv1
Mid-latitude Region (ASRv1/ERAI)
January difference between dry days in ERAI (> 2000) much higher than ASRv1 (276) while light precipitation (< 0.1 mm day-1) higher in ASRv1
In July, ASRv1 produces greater rainfall in higher amounts (> 10 mm day-1)
2 m Temperature 2 m Dewpoint Surface Pressure 10 m Wind Speed
B R C B R C B R C B R C
ERAI 0.28 1.87 0.91 -0.03 1.81 0.85 -0.21 0.90 0.98 0.29 1.93 0.60
ASRv1 30km
0.05 1.25 0.95 -0.15 1.53 0.90 0.0 0.77 0.99 -0.27 1.63 0.66
ASRv2 15 km
0.01 1.13 0.96 0.01 1.40 0.91 0.01 0.74 0.99 -0.04 1.62 0.67
State Variables with ASRv2 15km For August 2007
Compared to ~5000 surface stations
