<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">MON 28SEP09: 1055PDT<div><br></div><div>Dear Emily,</div><div><br></div><div>Not sure what dataset you are using, but here is a ncdump of a NCEP Reanalysis netcdf file of SLP: </div><div><br></div><div><div> ncdump -c slp.2009.nc </div><div>netcdf slp.2009 {</div><div>dimensions:</div><div> lon = 144 ;</div><div> lat = 73 ;</div><div> time = UNLIMITED ; // (261 currently)</div><div>variables:</div><div> float lat(lat) ;</div><div> lat:units = "degrees_north" ;</div><div> lat:actual_range = 90.f, -90.f ;</div><div> lat:long_name = "Latitude" ;</div><div> float lon(lon) ;</div><div> lon:units = "degrees_east" ;</div><div> lon:long_name = "Longitude" ;</div><div> lon:actual_range = 0.f, 357.5f ;</div><div> double time(time) ;</div><div> time:units = "hours since 1-1-1 00:00:0.0" ;</div><div> time:long_name = "Time" ;</div><div> time:actual_range = 17601816., 17608056. ;</div><div> time:delta_t = "0000-00-01 00:00:00" ;</div><div> time:avg_period = "0000-00-01 00:00:00" ;</div><div> short slp(time, lat, lon) ;</div><div> slp:long_name = "mean Daily Sea Level Pressure" ;</div><div> slp:valid_range = 87000.f, 115000.f ;</div><div> slp:actual_range = 93602.5f, 110540.f ;</div><div> slp:units = "Pascals" ;</div><div><b> slp:add_offset = 119765.f ;</b></div><div><b> slp:scale_factor = 1.f ;</b></div><div> slp:missing_value = 32766s ;</div><div> slp:precision = 0s ;</div><div> slp:least_significant_digit = -1s ;</div><div> slp:GRIB_id = 2s ;</div><div> slp:GRIB_name = "PRMSL" ;</div><div> slp:var_desc = "Sea Level Pressure\n",</div><div> "P" ;</div><div> slp:dataset = "NCEP Reanalysis Daily Averages" ;</div><div> slp:level_desc = "Sea Level\n",</div><div> "I" ;</div><div> slp:statistic = "Mean\n",</div><div> "M" ;</div><div> slp:parent_stat = "Individual Obs\n",</div><div> "I" ;</div><div><br></div><div>// global attributes:</div><div> :Conventions = "COARDS" ;</div><div> :title = "mean daily NMC reanalysis (2009)" ;</div><div> :history = "created 2009/01 by Hoop (netCDF2.3)" ;</div><div> :description = "Data is from NMC initialized reanalysis\n",</div><div> "(4x/day). It consists of most variables interpolated to\n",</div><div> "pressure surfaces from model (sigma) surfaces." ;</div><div> :platform = "Model" ;</div><div><br></div><div>What one has to do to get the correct value is apply both the scale factor and offset value to the data, so for example, if I wanted to display SLP, I'd need to do this for example: </div><div><br></div><div><br></div><div>'define mslp1 = slp + 119765'</div><div><br></div><div>actual value = value * scaling factor + offset, in the example above, the scaling factor is 1, hence I merely added the offset.</div><div><br></div><div>Your netcdf file probably has these values which you merely need to apply as shown above.</div><div><br></div><div><span class="Apple-style-span" style="font-size: 14px; ">Regards,</span></div></div><div><div><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Calibri; font-size: 14px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; "><div><div><div><div><div><br></div><div>Kevin M Levey, MSc in Oceans and Atmospheric Sciences (University of Cape Town)</div><div>Director of Meteorological Operations</div><div>CustomWeather, Inc.</div><div>San Francisco, California, USA</div><div><br></div><div>"Taking the World by Storm!"</div><div><br></div><div><a href="http://www.customweather.com">http://www.customweather.com</a></div><div><a href="http://www.myforecast.com">http://www.myforecast.com</a></div><div><a href="http://www.1stweather.com">http://www.1stweather.com</a></div><div><br></div><div>cell: 415-794-0411</div><div>work: 415-777-3566</div><div>email: <a href="mailto:klevey@customweather.com">klevey@customweather.com</a></div></div></div></div></div></span>
</div>
<br><div><div>On Sep 28, 2009, at 09/28/09 - 10:47 AM, Emily wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><table cellspacing="0" cellpadding="0" border="0"><tbody><tr><td valign="top" style="font: inherit;">Hi group members,<br><br>I face a problem when I display 500 hpa geopotential height chart, it shows wrong data.<br><br>My gs file is:<br>'reinit'<br>'open d:\gradsfile\ncdata\hgt200812.ddf'<br>'set grads off'<br>'set grid off'<br>'set lon 220 310'<br>'set lat 20 60'<br>'set lev 500'<br>'set time 09z28dec2008'<br>'d hgt'<br>====================<br>My ddf is as below:<br>DSET d:\gradsfile\ncdata\hgt.200812.nc<br>DTYPE netcdf<br>TITLE NARR 4D field Lambert Conformal Conic projection<br>UNDEF 32766 missing_value<br>UNPACK scale_factor add_offset<br>PDEF 349 277 lcc 1 -145.5 1 1 50 50 -107 32463.41 32463.41<br>XDEF 615 linear 150 0.3333<br>YDEF 255 linear 2 0.3333<br>ZDEF 29 levels 1000, 975, 950, 925, 900, 875, 850, 825, 800, 775, 750, 725, 700,<br> 650, 600, 550, 500, 450, 400, 350, 300, 275, 250, 225, 200, 175, 150, 125, 100<br>tdef 248 linear
00:00z01dec2008 3hr<br>vars 3<br>hgt 29 t,z,y,x geopotential_height<br>lat=>glat 0 y,x Latitude<br>lon=>glon 0 y,x Longitude<br>endvars<br>=============<br>My grads version: Grads 2.0 a3,<br>window xp<br><br>I notice that the contours laber values are like -25900, -25800..... I think the value is wrong. Then I check ncdump information, the hgt value from ncdump also shows like -25900,.....<br><br>Is there some one knowing what wrong with this?Thanks very much.<br><br>Regards,<br><br>Emily<br>York University, Toronto, Canada.<br> <br><br></td></tr></tbody></table></blockquote></div><br></div></body></html>