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Aaron B. WilsonG. W. K. Moore, D. H. Bromwich, I. Renfrew, L. Bai, S.-H. Wang, K. M. Hines, B. Kuo, Z. Liu, H.-C. Lin, M. Barlage
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?
Arctic System Reanalysis• Regional reanalysis of the Greater Arctic for 2000 – 2012 where rapid climate change is
occurring (http://polarmet.osu.edu/ASR/)• Uses Polar WRF model with WRFDA (3D-VAR)
• Fractional sea ice and variable sea ice thickness, albedo, and snow cover• High Resolution Land Data Assimilation System (HRLDAS) – assimilates snow
cover/depth, observed vegetation fraction and albedo at frequent intervals• Assimilated Atmospheric Observations
• Conventional (e.g., Surface and Radiosondes) • Satellite (e.g., Radiances, QuikSCAT, SSMI-sea
surface wind speed & precipitable water)• GPS: GPSRO, GPSPW
• High-Resolution (Currently two versions)• ASRv1-30km & ASRv2-15 km• 71 Vertical Levels (1st level – 4m)• 3 Hour temporal resolution
ASRv1 30 km available online at the NCAR CISL Research Data ArchiveASRv2 – 15 km Coming Very Soon!
• High complex topography
• Proximity to North Atlantic storm track
• Yield topographically forced weather systems (tip jets, barrier winds & katabatic flow)
• Roles in local weather/global climate(sea ice transport, polynyas, ocean circulation)
Greenland’s Place in Arctic/Global System
Tracks of 100 most intense winter extra-tropical cyclones 1989-2008 (Courtesy U. of Reading)
Tip Jets & Barrier Winds
Occurrence Frequency (%) of 10m QuikSCAT Winds in excess of 20m/s(Sampe & Xie, BAMS 2007)
Easterly TipJet
Note: Buoy data from the Cape Farewell region indicates that QuikSCAT winds are biased high (Moore et al GRL 2008)
Three basic types of topographically forced systems: 1-Tip Jets
Form near Cape Farewell and can be either easterly or westerly
Note: Buoy data from the Cape Farewell region indicates that QuikSCAT winds are biased high (Moore et al GRL 2008)
Three basic types of topographically forced systems: 2-Barrier Winds
NE winds that form along SE coast of Greenland
BarrierWind
Note: Buoy data from the Cape Farewell region indicates that QuikSCAT winds are biased high (Moore et al GRL 2008)
Three basic types of topographically forced systems: 3-Katabatic Winds
NW winds that flow down fjords and out over the ocean
KatabaticWinds
WesterlyTip Jet
• Assess the representation of low-level winds in the ASR:• Across the Arctic• Near Greenland
• ERA-Interim (~80km) and 2 versions of ASR: • ASRv1 (30km) and ASRv2 (15km)
• Observations:• Operational met stations in SE Greenland (surface and
radiosonde) • Aircraft observations (low-level and dropsonde) made during
the Greenland Flow Distortion Experiment (GFDex) that was held during Feb/Mar 2007.
Motivation
SurfaceCompared to ~4500
surface stations
10 m Wind SpeedASRv1: -0.24/1.78/0.70ERAI: 0.41/2.13/0.64
Wind Speed Comparison
ASRv1 ERAI
Upper AirCompared to 300 radiosondes
(25% in the Arctic)
• Weaker than observed wind speeds ASRv1 mean biases closer to observed between 925-100 hPa
• Negative biases nearly domain-wide
ASR improves depictions of Polar Lows…
Wind Speed
m s-1
31 January 200812 UTC 18 UTC
ASRv1
ERA-Interim
ASRv1
ERA-Interim
… and other mesoscale weather phenomena!Intense Barrier Wind in Denmark Strait
10 m Wind
03UTC Mar 03, 2007
ASR 30kmASR 15kmWind Speed
m/s
Iceland
Greenland
Mesoscale Features
• 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
G. W. Kent Moore (Moore et al., 2015: GRL)
ERAINCEPASRv13D TurbulenceScatterometer Winds
• Power Spectra for 10 m wind speed near Greenland
• Averaged for Dec-Feb 2000-12
• ASRv1 has more spatial energy in the mesoscale than global reanalyses
Topography of Southern Greenland (km) as represented in the ERA-I (80km) andASRv2 (15km)
DMI stations in the region are indicated
Greenland Topography
Mean 10 m Wind• Both capture enhanced barrier flow
along Denmark Strait (DS) and NE flow near Cape Farewell (CF)
• Increased resolution ≈ higher wind
• ASR demonstrates • Enhanced wind speed gradient
along ice edge• Low wind speeds downwind of
Sermilik and Kangerdlugssuaq Fjords (topographic sheltering effect Moore et al. GRL 2015)
• Onshore extension of high wind speed near CF
DS
DS
CF
CF
10 m Wind Speeds at DMI Sites• Winds generally stronger in the
southern sites during first half
• B268 flight investigated Easterly Tip Jet near Ikerasassuaq (CF); ERAI winds too low – better captured by ASR
• Stronger winds in North during second half
• B274, B276, B277, and B278 captured Barrier Wind Event
• Observed winds at Tasillaq lower than reanalyses (sheltering)
DMI 04390 Ikerasassuaq (near CF – South)
ERA-I
ASRv2
Scatter Plots of the DMI Stations• ERA-I has high/low wind speed
bias that is reduced in the ASRv2.
• Both regression slope and correlation coefficient approach 1 as one transitions from the ERA-I to ASRv2.
• ASRv2 still overestimates wind speeds during weak wind regimes – likely tied to the sheltering situations
ERA-I
ASRv2
Scatter Plots of the GFDex Low-Level Flight Legs
• Both reanalyses have a systematic low wind speed bias
• No significant difference between the ERA-I and ASRv2
• There is a reduction in RMSE and increase in correlation between ASRv1 and ASRv2: perhaps better spatial gradients
• Model parameterizations (Renfrew et al. 2009)
Scatter Plots of the GFDex Dropsondes
• Both reanalyses are similar with respect to the winds from the GFDex dropsondes
• The ASRv2 does a better job with the high winds (> 40 m s-1) but these are not numerous enough to influence the statistics.
• => Representation of the vertical structure of off shore jets is marginally improved in the ASRv2
• Resolution may play a bigger role near shore
ERA-I
ASRv2
Sea-level pressure (mb-contours), 10m wind (m/s-vectors) and 10m wind speed (m/s-shading) for the easterly tip jet (ETJ) flight (B268- flight track in white with
dropsondes indicated) at 12 UTC on February 21 2007
ERA-I
ASRv2
Easterly Tip Jet during Flight B268• Synoptic Low SE of CF, region under NE
flow, broad scale captured well in reanalyses.
• ASRv2 captures the mesoscale low that forms on the lee side of the barrier as well as generally having higher wind speeds.
• ASRv2 also identifies a new feature of ETJ, downslope onshore flow that may play a role in erosion and aerosol dispersion.
Observed and model wind speed profiles during GFDex flight B268
Narsarsuaq(onshore)
GFDex sonde # 9(jet core)
Vertical Structure of the Tip Jet
• ERA-I missing onshore extension of tip jet
• ASRv2 is able to better represent the onshore and offshore vertical structure of the observed easterly tip jet.
Sea-level pressure (mb-contours), 10m wind (m/s-vectors) and 10m wind speed (m/s-shading) for the katabatic flow event at Køge Bugt Fjord at 12 UTC on February 16 2007
Katabatic Wind Flow at Ikermit –Køgt Bugt Fjord
ERA-I ASRv2
• At DMI station at Ikermit, observed 10m wind speed was 28 m/s, ERA-I had a wind speed of 12 m/s, while ASRv2 had a wind speed of 27 m/s.
•Global reanalyses/models: Advanced knowledge of Greenland’s topographically-forced winds but features are under-resolved.
•These mesoscale features are important across scales (Local Weather to Global Climate)
• Air-sea interactions• Ocean model forcing with higher resolution atmospheric model improved
surface and deep ocean circulation (Jung et al., 2014)
•In general, the higher resolution of the ASR improves representation compared to observations (lower rmse, higher correlation coefficients and regression slopes closer to 1).
•However, underlying parameterizations used in the models have a significant impact on the agreement with observations (e.g., off-shore story is inconsistent).
•Opportunity – Further Validation and Room for improvement in this regard. ASRv2 will soon be publically available
Closing Thoughts
Bromwich, D. H., A. B. Wilson, L. Bai, G. W. K. Moore, and P. Bauer, 2016: A comparison of the regional Arctic System Reanalysis and the global ERA-Interim Reanalysis for the Arctic. Q. J. R. Meteorol. Soc., 142, 644-658, doi:10.1002/qj.2527.
DuVivier, A. K., and J. J. Cassano, 2013: Evaluation of WRF Model resolution on simulated mesoscale winds and surface fluxes near Greenland. Mon. Wea. Rev., 141, 941–963, doi:10.1175/MWR-D-12-00091.1
Jung, T., S. Serrar, and Q. Wang, 2014: The oceanic response to mesoscale atmospheric forcing. Geophys. Res. Lett., 41, 1255-1260.
Moore, G. W. K., R. S. Pickart, and I. A. Renfrew, 2008: Buoy observations from the windiest location in the world ocean, Cape Farewell, Greenland. Geophys. Res. Lett., 35, L18802, doi:10.1029/2008GL034845.
Moore, GWK, IA Renfrew, BE Harden, and SH Mernild, 2015: The impact of resolution on the representation of southeast Greenland barrier winds and katabatic flows. Geophys. Res. Lett., 42, 3011–3018. doi:10.1002/2015GL063550.
Moore, G. W. K., D. H. Bromwich, A. B. Wilson, I, Renfrew, and L. Bai, 2016: Arctic System Reanalysis improvements in topographically-forced winds near Greenland. Q. J. R. Meteorol. Soc., doi: 10.1002/qj.2798, in press.
Renfrew, I. A., G. N. Petersen, D. A. J. Sproson, G. W. K. Moore, H. Adiwidjaja, S. Zhang, and R. North, 2009: A comparison of aircraft-based surface-layer observations over Denmark Strait and the Irminger Sea with meteorological analyses and QuikSCAT winds. Q. J. R. Meteorol. Soc., 135, 2046-2066.
Sampe T, Xie SP. 2007. Mapping high sea winds from space: A global climatology. Bull. Am. Meteorol. Soc. 88: 1965–1978.
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