<div class="eI0">
  <div class="eI1">Modell:</div>
  <div class="eI2"><h2><a href="http://www.emc.ncep.noaa.gov/GFS/doc.php" target="_blank">GFS</a> (Global Forecast System) Global Model from the "National Centers for Environmental Prediction" (NCEP)</h2></div>
 </div>
 <div class="eI0">
  <div class="eI1">Aktualisierung:</div>
  <div class="eI2">4 times per day, from 3:30, 09:30, 15:30 and 21:30 UTC</div>
 </div>
 <div class="eI0">
  <div class="eI1">Greenwich Mean Time:</div>
  <div class="eI2">12:00 UTC = 13:00 MEZ</div>
 </div>
 <div class="eI0">
  <div class="eI1">Aufl&ouml;sung:</div>
  <div class="eI2">0.25&deg; x 0.25&deg;</div>
 </div>
 <div class="eI0">
  <div class="eI1">Parameter:</div>
  <div class="eI2">Maximum wind velocity of convective wind gusts</div>
 </div>
 <div class="eI0">
  <div class="eI1">Beschreibung:</div>
  <div class="eI2">

The method of Ivens (1987) is used by the forecasters at KNMI to predict the
maximum wind velocity associated with heavy showers or thunderstorms. The
method of Ivens is based on two multiple regression equations that were
derived using about 120 summertime cases (April to September) between 1980 and 1983.
The upper-air data were derived from the soundings at De Bilt, and
observations of
thunder by synop stations were used as an indicator of the presence of
convection.
The regression equations for the maximum wind velocity (w<sub>max</sub> ) in m/s
according
to Ivens (1987) are:<br>
<ul type="square">
<li>if T<sub>x</sub> - &#952;<sub>w850</sub> &lt; 9&deg;C
<dl>
<dd>w<sub>max</sub> = 7.66 + 0.653&sdot;(&#952;<sub>w850</sub> - &#952;<sub>w500</sub> ) + 0.976&sdot;U<sub>850</sub><br></dd>
</dl>
<li>if T<sub>x</sub> - &#952;<sub>w850</sub> &ge; 9&deg; C</li>
<dl>
<dd>w<sub>max</sub> = 8.17 + 0.473&sdot;(&#952;<sub>w850</sub> - &#952;<sub>w500</sub> ) + (0.174&sdot;U<sub>850</sub> + 0.057&sdot;U<sub>250</sub>)&sdot;&radic;(T<sub>x</sub> - &#952;<sub>w850</sub>)<br></dd>
</dl>
</ul>
<br>
where 
<ul>
<li>T<sub>x</sub> is the maximum day-time temperature at 2 m in K
<li>&#952;<sub>wxxx</sub> the potential wet-bulb temperature at xxx hPa in K
<li>U<sub>xxx</sub> the wind velocity at xxx hPa in m/s.
</ul>
The amount of negative buoyancy, which is estimated in these
equations
by the difference of the potential wet-bulb temperature at 850 and at 500 hPa,
and horizontal wind velocities at one or two fixed altitudes are used to estimate
the maximum wind velocity. The effect of precipitation loading is not taken into
account by the method of Ivens.
(Source: <a href="http://www.knmi.nl/" target="_blank">KNMI</a>)

    
  </div>
 </div>
 <div class="eI0">
  <div class="eI1">GFS:</div>
  <div class="eI2">The Global Forecast System (<a href="http://www.emc.ncep.noaa.gov/gmb/moorthi/gam.html" target="_blank">GFS</a>) is a global numerical weather prediction computer model run by NOAA. This mathematical model is run four times a day and produces forecasts up to 16 days in advance, but with decreasing spatial and temporal resolution over time it is widely accepted that beyond 7 days the forecast is very general and not very accurate.<br>
<br>
The resolution of the model horizontally, it divides the surface of the earth into 20 kilometre grid squares; vertically, it divides the atmosphere into 64 layers and temporally, it produces a forecast for every 3rd hour for the first 240 hours, after that they are produced for every 12th hour.
</div></div>
 <div class="eI0">
  <div class="eI1">NWP:</div>
  <div class="eI2">Numerische Wettervorhersagen sind rechnergest&uuml;tzte Wettervorhersagen. Aus dem Zustand der Atmosph&auml;re zu einem gegebenen Anfangszeitpunkt wird durch numerische L&ouml;sung der relevanten Gleichungen der Zustand zu sp&auml;teren Zeiten berechnet. Diese Berechnungen umfassen teilweise mehr als 14 Tage und sind die Basis aller heutigen Wettervorhersagen.<br><br>
In einem solchen numerischen Vorhersagemodell wird das Rechengebiet mit Gitterzellen und/oder durch eine spektrale Darstellung diskretisiert, so dass die relevanten physikalischen Gr&ouml;&szlig;en, wie vor allem Temperatur, Luftdruck, Windrichtung und Windst&auml;rke, im dreidimensionalen Raum und als Funktion der Zeit dargestellt werden k&ouml;nnen. Die physikalischen Beziehungen, die den Zustand der Atmosph&auml;re und seine Ver&auml;nderung beschreiben, werden als System partieller Differentialgleichungen modelliert. Dieses dynamische System wird mit Verfahren der Numerik, welche als Computerprogramme meist in Fortran implementiert sind, n&auml;herungsweise gel&ouml;st. Aufgrund des gro&szlig;en Aufwands werden hierf&uuml;r h&auml;ufig Supercomputer eingesetzt.<br><br>
<br>Seite „Numerische Wettervorhersage“. In: Wikipedia, Die freie Enzyklop&auml;die. Bearbeitungsstand: 21. Oktober 2009, 21:11 UTC. URL: <a href="http://de.wikipedia.org/w/index.php?title=Numerische_Wettervorhersage&amp;oldid=65856709" target="_blank">http://de.wikipedia.org/w/index.php?title=Numerische_Wettervorhersage&oldid=65856709</a> (Abgerufen: 9. Februar 2010, 20:46 UTC) <br>
</div></div>
</div>