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About the Annual Meteorological Statistics Graphs

The 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 emperature 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 H20 and HNO3 values are noted at the top left).

Graphs for the current year are updated daily.

Data Sources

MERRA-2, the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) provides data beginning in 1980. It was introduced to replace the original MERRA dataset because of the advances made in the assimilation system that enable assimilation of modern hyperspectral radiance and microwave observations, along with GPS-Radio Occultation datasets. It also uses NASA ozone observations after 2005. Additional advances in both the Goddard Earth Observing System Data Assimilation System Version 5 (GEOS-5) model and the GSI assimilation system are included in MERRA-2. Along with the enhancements in the meteorological assimilation, MERRA-2 takes some significant steps towards GMAO's target of an Earth System reanalysis. MERRA-2 is the first long-term global reanalysis to assimilate space-based observations of aerosols and represent their interactions with other physical processes in the climate system. Since these data are from a reanalysis, they are not up-to-date. So, we supplement with the GEOS-5 FP data that are also produced by the GEOS-5 model in near real time. These products are produced by the NASA Global Modeling and Assimilation Office (GMAO).

Disclaimers

All of the data available are subject to being updated at any point. Different data may be substituted or the data-processing and image-rendering algorithms may be changed. The main purpose of this site is to provide a historical view of stratospheric development, but that purpose does not extend to keeping a historical archive of all the data versions and processing algorithms used.

Forecasts are provided for some data sets from the NASA GMAO GEOS system. These forecasts are experimental and are produced for research purposes only. Use of these forecasts for purposes other than research is not recommended.

Variable Descriptions

There are 17 variables available for graphic display or downloading. These are:

Minimum Temperatures

These 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°.

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 15 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 Form

You 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 Period

There 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”:
  • All Data: This will return data for each day from the start of the data set (01 January 1979) through the most recent day data has been received, which is presumed to be yesterday. Please avoid using this if possible—use a more restrictive date range when practical.
  • Date Range (default): This will return data for each day between the specified start date and end date, inclusively. The default date range is set up to be from the most recent 1 July to the most recent day for which data has been received, which is presumed to be yesterday. This corresponds to the current “year” of data centered on Northern Hemisphere winter. You may change these as desired, with the requirement that the end date not be less than the start date. “Impossible” dates, such as 31 April, will be interpreted to mean the last valid day of the specified month and year.
  • Seasonal: This option allows you to specify a “time slice” for multiple years. A season is defined as the period of time beginning on the specified start date and ending on the next occurrence of the specified end date. The year range is applied to the season start date. Thus:
    • 1 May through 1 September for seasons beginning 1995–1997 would return data for
      • 1 May 1995 through 1 September 1995
      • 1 May 1996 through 1 September 1996
      • 1 May 1997 through 1 September 1997
    • 15 November through 15 February for seasons beginning 1990–1992 would return data for
      • 15 Nov 1990 through 15 Feb 1991
      • 15 Nov 1991 through 15 Feb 1992
      • 15 Nov 1992 through 15 Feb 1993
    • 1 July through 1 July for seasons beginning 1979–2001 would return data for only 1 July of each year specified

Variables

The variables available are described above. You must select at least one variable, you may select more than one.

Hemisphere

Data is available for the Northern and Southern Hemispheres. You must select at least one hemisphere, you may select both.

Pressure Levels

Data 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 one pressure level, you may select more than one.

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 Output

Assuming 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 CCYY-MM-DD format; following this is a column of data for each variable, hemisphere, and 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 five 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.

Header Tag Variable
Tmin Minimum temperature in latitude range
T Temperature at latitude or latitude range
U Zonal wind at latitude
VT Heat flux at latitude or latitude range
VT (w1-3) Heat flux (waves 1–3) at latitude or latitude range
45-day VT 45-Day mean heat flux at latitude or latitude range
45dVTw1-3 45-Day mean heat flux (waves 1–3) at latitude or latitude range
UV Momentum flux at latitude or latitude range
UV (w1-3) Momentum flux (waves 1–3) at latitude or latitude range
Z1 Wave 1 amplitude of geopotential height at latitude
Z2 Wave 2 amplitude of geopotential height at latitude

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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