Help Topics
About the NCEP Annual Data GraphsThe grey shading in these figures indicates the range of values for each date in previous years' data (e.g., all Jan.15ths, all Jan. 16ths, all Jan. 17ths...). Hence, a record cold temperature on a particular date will lie below the grey shading. The mean temperature for each date is indicated by the green line in the middle of the grey shading.
The Type I PSC and Type II PSC lines refer to temperatures at which
nitric acid and water saturate to form nitric acid trihydrate particles
and water ice particles respectively. These saturation temperatures
depend on the concentration of water and nitric acid in the
stratosphere (the approximate
Graphs for the current year are updated daily.
Variable DescriptionsThere are 17 variables available for graphic display or downloading. These are:Minimum TemperaturesThese represent the minimum temperature between 50° and 90° latitude for each day.Temperatures at 90°Temperatures at the Pole.Temperatures at 80°Temperatures at 80° are indicative of the mean temperature in the polar region.Temperatures at 50°Temperatures at 50° are indicative of the mean temperature in the mid-latitudes region.Temperatures between 60° and 90°Temperatures in the polar cap, poleward of 60°.Temperatures between 55° and 75°Same as Temperatures at 50° (or 80°), but averaged between 55° and 75°.Balanced Zonal Wind at 60°The longitudinally averaged zonal wind at 60° is an indicator of the strength of the polar vortex. Stratospheric warmings act to decelerate this wind. The zonal wind is predominantly westerly (that is that winds blow from the west) during the winter and flips to easterly during the summer. The breakdown of the polar vortex occurs in the spring, when these wind values drop below about 20 m/s.Heat Flux at 60°The longitudinally averaged heat flux at 60° is another indicator of a disturbed stratosphere. The heat flux is calculated by correlating the meridional wind (north-south wind) and temperature. The heat flux is almost always poleward. That is, in the Northern Hemisphere the warm temperatures are transported northward by the merdional wind, while cold temperatures are transported southward. This polar warming by the heat flux is compensated by an upward Eulerian circulation that acts to cool the polar region.Heat Flux between 45° and 75°Same as Heat Flux at 60°, but averaged between 45° and 75°. The two should track very well together.Heat Flux (Waves 1-3) between 45° and 75°Same as Heat Flux between 45° and 75°, but using only the first three wavenumbers. These lower wave numbers usually contain most of the wave energy.45-Day Mean Heat Flux between 45° and 75°These are the Heat Flux between 45° and 75° averaged for the 45-day period prior to the date plotted. This quantity is the most important factor in modifying the polar cap temperatures (Temperatures between 60° and 90°). Increasing values of the pervious 45-day averaged heat flux indicates an increase in wave activity and corresponds very strongly with an increase in the polar cap termperatures.45-Day Mean Heat Flux (Waves 1-3) between 45° and 75°Same as Heat Flux between 45° and 75°, but using only the first three wavenumbers. These lower wave numbers usually contain most of the wave energy and have an even stronger relationship to the polar cap temperatures (Temperatures between 60° and 90°).Momentum Flux at 60°The longitudinally averaged momentum flux at 60° is yet again another indicator of a disturbed stratosphere. The momentum flux is calculated by correlating the meridional wind (north-south wind) and the longitudinal asymmetries of the zonal wind (east-west wind). While the heat flux is almost always poleward, the momentum flux is more variable in direction, albeit the momentum flux is generally poleward.Momentum Flux between 45 and 75°Same as Momentum Flux at 60°, but averaged between 45 and 75°.Momentum Flux (Waves 1-3) between 45° and 75°Same as Momentum Flux between 45° and 75°, but using only the first three wavenumbers. These lower wave numbers usually contain most of the wave energy.Wave 1 Amplitude of Geopotential Height at 60°The amplitude of the zonal wavenumber one Fourier component of the geopotential height at 60° is also an indicator of a disturbed stratosphere (see the heat flux).Wave 2 Amplitude of Geopotential Height at 60°The amplitude of the zonal wavenumber two Fourier component of the geopotential height at 60° is also an indicator of a disturbed stratosphere (see the heat flux and momentum flux).Data Request FormYou can request a copy of the data behind these graphs by using the data request form. You will need to provide the following 4 pieces of information:Time PeriodThere are three possible ways to specify the time period that you are interested in. You must select one and only one of these methods; the default is "Date Range"
VariablesThe variables available are described in the Variables section above. You must select at least 1 variable, you may select more than 1.HemisphereData is available for the northern and southern hemispheres. You must select at least 1 hemisphere, you may select both.Pressure LevelsData is available at the 150 hPa, 100 hPa, 70 hPa, 50 hPa, 30 hPa, and 10 hPa pressure levels. (hPa is hectaPascal; 1 hPa = 1 millibar). You must select at least 1 pressure level, you may select more than 1.
Note that you will get all possible combinations of the variables, hemispheres, and pressure levels you select - selecting all 17 variables for both hemispheres and all 6 pressure levels will result in 204 columns of data per day. Selecting this for all days results in almost 10 MB of data being returned - this takes a bit of time (at least 15 seconds per year of data on a good network connection). Selecting only the data values you need for the time periods you need them will significantly improve your download time. Data Request OutputAssuming that you have submitted a valid request via the Data Request Form, the data will be returned to you as a text file via your web browser. You can opt to save this file locally via your browser's "Save" facility once it has completed downloading.The data is formatted as an ascii file with fixed-width columns. The first column contains the date in YYYY-MM-DD format; following this is a column of data for each variable / hemisphere / pressure level combination selected. All data values are in "F10.2" floating point format. The data columns are ordered by variable name, then by hemisphere, then finally by pressure level. Depending on the combinations of parameters selected, you will have anywhere from 1 to 204 columns of data plus the date column; each column is 10 characters wide. The first 5 lines of the file are column header information. Line 1 is the Variable specifier (see table below); Line 2 indicates the latitude range and hemisphere; Line 3 is the pressure level, and Line 4 specifies the units the data values are presented in. Line 5 is a separator.
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Sample output:
Tmin Tmin Tmin Tmin U U U U
50-90 N 50-90 N 50-90 S 50-90 S 60 N 60 N 60 S 60 S
100 hPa 50 hPa 100 hPa 50 hPa 100 hPa 50 hPa 100 hPa 50 hPa
Date (K) (K) (K) (K) (m/s) (m/s) (m/s) (m/s)
---------- --------- --------- --------- --------- --------- --------- --------- ---------
2001-01-15 197.64 189.98 211.73 217.90 9.77 14.83 10.41 2.43
2001-01-16 197.65 191.69 211.36 217.39 10.46 14.87 8.83 1.23
2001-01-17 198.93 193.67 210.93 218.50 12.09 16.36 7.39 0.71
2001-01-18 199.41 193.58 213.45 218.90 10.26 15.92 7.98 1.24
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Web Curator: Michael K. Heney (SSAI) ( mheney@code916.gsfc.nasa.gov)
Responsible NASA organization/official: Last Updated: Thu Feb 3 10:15:34 EST 2005 (graphs updated daily) |
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