7/2/97
Hi Michiko,
Everything is running smoothly with the Nature data except in regard to the clouds. Sid Wood at SWA was a bit suspicious of the abundance of clouds over the poles. We were wondering if you could take a look at cross-sections of total cloud fraction, especially over the north pole. It may simply be a normal feature of the model but we wanted to make sure it's reasonable. He is currently looking at the first day of the forecast. If you have an opinion about it let us know.
I plotted cloud cover over pole for 6 hour forcast.
I am trying to produce time evolution.
It is taking some time because
the size of the data set often crashes plotting program.
Let me know how you think of these figures.
Time height cross section of cloud cover at north pole
7/30/97
I plotted observed cloud cover from NAVY and posted on Web Page.
I showed the figure to Bob Grunbine and Ken Campana. Following
the comments I received.
- Generally this cloud estimate is not reliable outside of 60S
to 60N.
- During February Cloud cover of the North Pole is about 60% and
fluctuation between 30% and 90%. Therefore, model look more
reasonable than NAVY's estimate, which indicate almost no cloud
over North pole. Probably NAVY estimate is showing only the fact
the North Pole is night during February and no visible light.
- Near South Pole between 90S to 70S, cloud cover look
reversed. Probably because sea ice is reported as no cloud
although it is covered with thick cloud. On the other hand, over
Antarctic continent should be mostly clear. The high cloud cover
over the Antarctica may be confusion with snow drift.
- Disagreement bween ECMWF reanalysis and NCEP/NCAR reanalysis on cloud cover
over poles is about 20%.
As conclusion, the model cloud looks more realistic than "Observed" cloud
we have now. May be we can look into other estimate done by NESDIS.
Any question about observed cloud estimate, contact Kenneth.Campana@noaa.gov.
Michiko
Total Cloud Cover From the Nature Run
February 1993 Observed Cloud Cover
Hamill, T. M., R. P. d'Entremont, and J.T. Bunting, 1992: Description
of the Air Force real-time nephanalysys model, Weather and Forecasting, 7, 288-306.
Joe:
Joe :
Total cloud cover averaged from 6Z 5 Febuuary 1993(6hr fcst) to 00Z7March 1993(720 hr fcst).
White indicates cloud. Dark blue, clear sky.
Cloud cover estimated by Navy using one channel. Cloud cover over polar
regions is not reliable.
