<div class="eI0">
  <div class="eI1">Mod&egrave;le:</div>
  <div class="eI2"><h2><a href="http://www.emc.ncep.noaa.gov/gmb/gdas/" target="_blank">GDAS</a>: "Global Data Assimilation System"</h2></div>
 </div>
 <div class="eI0">
  <div class="eI1">Mise &agrave; jour:</div>
  <div class="eI2">4 times per day, from 00:00, 06:00, 12:00 and 18:00 UTC</div>
 </div>
 <div class="eI0">
  <div class="eI1">Greenwich Mean Time:</div>
  <div class="eI2">12:00 UTC = 13:00 CET</div>
 </div>
 <div class="eI0">
  <div class="eI1">R&eacute;solution:</div>
  <div class="eI2">0.25&deg; x 0.25&deg;</div>
 </div>
 <div class="eI0">
  <div class="eI1">Param&egrave;tre:</div>
  <div class="eI2">Geopotential in 850 hPa (solid, black lines) and Vorticity advection in 10<sup>5</sup>/(s*6h) (colored lines)</div>
 </div>
 <div class="eI0">
  <div class="eI1">Description:</div>
  <div class="eI2">
The two types of vorticity advection are positive (PVA) and negative vorticity
advection (NVA). <img border="0" src="//www.wofrance.fr/daten/expertgifs/v_adv_en.jpg" align="left">
The closed circles in the figure show the 850 hPa absolute vorticity
lines, the others the 850 hPa height lines. When an air parcel is moving from
an area higher vorticity to an area lower vorticity this is called: PVA
(red color). The other way around is called: NVA (blue color). PVA is
associated with upper-air divergence, i.e. upward vertical motion. NVA
is associated with down ward vertical motion. Therefore, PVA&nbsp; at 500
hPa is strongest above a surface low, while NVA at 500 hPa is strongest
above a surface high. <br>
In operational meteorology Vorticity advection maps are used to identify areas 
with vertical air motion to see where clouds, precipitation or clear conditions 
are likely to occur. Keep in mind, however, that PVA is not the same as upward
vertical motion. Here temperature advection is important too.<br>

    
  </div>
 </div>
 <div class="eI0">
  <div class="eI1">GDAS</div>
  <div class="eI2">The Global Data Assimilation System (GDAS) is the system used by the National Center for Environmental Prediction (NCEP) Global Forecast System (GFS) model to place observations into a gridded model space for the purpose of starting, or initializing, weather forecasts with observed data. GDAS adds the following types of observations to a gridded, 3-D, model space: surface observations, balloon data, wind profiler data, aircraft reports, buoy observations, radar observations, and satellite observations.
</div></div>
 <div class="eI0">
  <div class="eI1">NWP:</div>
  <div class="eI2">La pr&eacute;vision num&eacute;rique du temps (PNT) est une application de la m&eacute;t&eacute;orologie et de l'informatique. Elle repose sur le choix d'&eacute;quations math&eacute;matiques offrant une proche approximation du comportement de l'atmosph&egrave;re r&eacute;elle. Ces &eacute;quations sont ensuite r&eacute;solues, &agrave; l'aide d'un ordinateur, pour obtenir une simulation acc&eacute;l&eacute;r&eacute;e des &eacute;tats futurs de l'atmosph&egrave;re. Le logiciel mettant en &oelig;uvre cette simulation est appel&eacute; un mod&egrave;le de pr&eacute;vision num&eacute;rique du temps.<br><br>
<br>Pr&eacute;vision num&eacute;rique du temps. (2009, d&eacute;cembre 12). Wikip&eacute;dia, l'encyclop&eacute;die libre. Page consult&eacute;e le 20:48, f&eacute;vrier 9, 2010 &agrave; partir de <a href="http://fr.wikipedia.org/w/index.php?title=Pr%C3%A9vision_num%C3%A9rique_du_temps&oldid=47652746" target="_blank">http://fr.wikipedia.org/w/index.php?title=Pr%C3%A9vision_num%C3%A9rique_du_temps&oldid=47652746</a>.<br>
</div></div>
</div>