The Schatten-predicted solar flux files are used to compute the atmospheric density in the Jacchia-Roberts (JR) atmospheric model and are generally used for long term analysis due to their extended time spans.

They are updated twice per year, once in the spring and then again in the fall.

These files provide daily predicted minimum global exospheric temperatures (Tc) along with weighted planetary geomagnetic indices (Kp) which are used as inputs to the JR model to produce atmospheric density values, which can then be used in the calculation of the atmospheric drag on a spacecraft.

The solar cycle is a nearly periodic 11-year change in solar activity due to the inversion of the Sun's magnetic field. But the exact period and amplitude of these cycles are not known precisely and vary somewhat.

As a result, the Schatten files are not a single file of solar activity but instead 9 different files - each with a different assumption about the period and amplitude of the solar cycle.

There are three predictions of the solar cycle period - early, nominal and late - corresponding to the occurence of the solar flux peak amplitude occuring before, at, or later than the nominal 11-year solar cyle.

And for each of these three predictions of solar cycle periods there are three predictions of solar cycle peak amplitude - "+2 sigma (plus)" , "mean" and "-2 sigma (minus)" - corresponding to the solar flux peak being 2 standard deviations above the historical mean value, 0 standards above the mean value or -2 standard deviation below the mean values.

Hence, the set of Schatten files consists of the 9 files :

minusearl.dat = -2 sigma amplitude, early peak period
meanearl.dat  = mean amplitude, early peak period
plusearl.dat  = +2 sigma amplitude, early peak period

minusnom.dat  = -2 sigma amplitude, nominal peak period
meannom.dat   = mean amplitude, nominal peak period
plusnom.dat   = +2 sigma amplitude, nominal peak period

minulate.dat  = -2 sigma amplitude, late peak period
meanlate.dat  = mean amplitude, late peak period
pluslate.dat  = +2 sigma amplitude, late peak period


The format of each file is identical, consisting of a header record followed by the data records.

The header record consists of 16 bytes

bytes  1- 4 = IJDF = Modified Julian Date - 0.5 of the first day of available data in the file
bytes  5- 8 = IJDL = Modified Julian Date - 0.5 of the last day of the available data in the file
bytes  9-12 = NREC = Number of records in the file
bytes 13-16 = IJDG = Modified Julian Date of the last good data point in the file

Each data record consists of 252 bytes

byte    1-  4 = IT = Modified Juliand data of the first day in this record
bytes   5-172 = {KP(I,J), I=1,21, J=1,4} = 21 days of packed 3-hour (I*2) Kp geomagentic indices starting with day (IT-1)
bytes 173-252 = {TC(I), I=1,20} = 20 days of  night time minimum global temperatures (Tc), starting with day IT    

Here's a snippet of sample Fortran code to read these files :

        INTEGER*4 IJDF, IJDL, NREC, IJDG, IT
        INTEGER*2 KP (21,4)
        REAL*4 TC(20)        

        OPEN (75, FILE = 'meannom.dat')

        READ(75, REC=1) IJDF, IJDL, NREC, IJDG

        DO 100 K = 1,NREC

             READ(75, REC=K) IT, KP, TC

        100 CONTINUE

THE SIGMAS DO NOT REPRESENT VARIATIONS ASSOCIATED WITH THE DAILY/MONTHLY/YEARLY VARIATIONS IN 
ACTIVITY, BUT RATHER THE ESTIMATE OF OUR UNCERTAINTY IN THE PREDICTED AVERAGE BEHAVIOR.

The author bears no responsibility for the resultant use or misuse of the predicted solar data.