Arctic in Nature Run

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Arctic in Nature Run
Nikki Privé NOAA/ESRL
February 2008
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We have interests in doing OSSE investigations
for UAS projects over the Arctic. I have done a
little bit of work looking at the characteristics
of the arctic in the Nature Run in comparison to
obs (limited obs are available).  I've attached a
powerpoint with some plots of different fields. 
So far I have only looked at the temperature
fields to compare the upper atmosphere with obs,
and also comparison of some soundings both over
the sea ice (russian ice stations/sheba) and over
land (BRW, I also have some data from YLT
(Alert)). The early results are that 1. The
Nature Run has problems with the low-level
inversion usually found over the arctic, esp in
winter (too weak). 2. Something is weird with
the surface temperatures, they are too high and
seem disconnected with the rest of the
temperature profiles. 3. The Nature Run has a
'cold pole' in arctic winter, with a too-strong
polar vortex. The summer temperature fields are
much better than the winter fields. In winter,
there is no incoming shortwave radiation, and
there are complicated interactions between
clouds, sea ice, winds, and other variables that
all affect the troposphere, esp. at low levels. 
I haven't had a chance yet to look at bigger
synoptic/dynamic behaviors. I know there was a
study with the ECMWF during the Sheba project
(1997-1998) that looked at how the model handled
the arctic, and found some problems, particularly
with the near-surface fields.  There was a paper
in JGR on the results (Beesley et al 2000). Maybe
someone at ECMWF has looked at arctic fields with
the newer version of the model, as I think they
have changed many of the parametrizations for sea
ice/etc. -Nikki
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Nature Run
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ECMWF 1990-2001
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NR (blue)
SHEBA (red)
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I used the 1x1 fields from T511 run. I wanted to
look at winter and summer because they avoid big
changes in incoming radiation (esp winter).  I am
working on extracting the sea ice and radiation
variables from the T511 run. Slide 7 looks at
the Sheba data compared to the NR data. Sheba is
a very high quality data set, with frequent
observations (including fluxes and clouds), but
there is only one year of data available. I took
the observed temperatures from sheba at 975 mb 
and at the surface, and binned them to make
frequency bars, then did the same thing with the
NR for points near where the sheba camp was (it
moved).  At 975 mb, the NR has more frequent
occurrence of cold temperatures (-25 to -30C),
while the sheba camp had more occurrences of warm
temperatures (-10 to 0 C). The warm sheba
temperatures occurred when there was cloudiness,
the lack of warm temperatures in the NR means
that either there were not as many clouds in the
NR, or that the longwave radiation does not
interact with the clouds properly in the NR.  In
the bottom panel, I compared the same thing with
the 2m surface air temperatures, but now the NR
is much warmer than the Sheba data. This is
something that was found and written up in the
Beesley paper, that the ECMWF operational model
strongly underestimated surface temperature
fluctuations, especially cold conditions. They
thought this was due to problems with the sea ice
parametrization and surface turbulent heat flux.
-Nikki
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Blue drifting Russian ice stations Red NR at
points over Arctic Ocean
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Red NR Blue BRW Green BRW ens mean
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Arctic in NR

• Stratospheric cold pole - without input from
  obs, model develops abnormally cold polar region
  in winter with strong polar vortex. Common
  problem with global models.
• Surface temperatures are strangely high over the
  arctic
• Disconnect with temperatures above surface layer?
  
• Low level inversion too weak - impacted by many
  processes
• What is energy balance over ice?
  SHF/LHF/longwave/cloud impacts?
• Sea ice and SST are applied from 2005/6 fields,
  not interactive with model atmosphere