7.2.1                 Earth atmosphere

7.2.1.1              General

a.              The NRLMSISE-00 model [RN.4] shall be used for calculating both the neutral temperature, and the detailed composition of the atmosphere.

b.              The JB-2006 model [RN.5] shall be used for calculating the total atmospheric density above an altitude of 120 km.

c.               For altitudes below 120 km, NRLMSISE-00 shall be used for calculating the total air density.

NOTE              This recommendation follows the advice of the CIRA Working Group, sponsored by COSPAR and URSI.

7.2.1.2              Application guidelines

a.              The NRLMSISE-00 model for species densities shall not be mixed with the JB-2006 model for total density.

b.              For worst case high results and analysis periods not exceeding 1 week high daily short-term values given in Table 6‑3 shall be used as input for daily activity together with the high long-term values for the 81-day average activity.

c.               For analysis periods longer than 1 week the long term activities given in Table 6‑3 shall be used as input for both, the daily and the 81-day averaged values.

d.              For analysis periods longer than 1 week and conditions specified in 6.2.3c, the daily and 81-day averaged solar activities given in Table A-1 shall be used.

e.               Short-term daily high solar activity values shall not be used together with low or moderate long-term solar activity values.

NOTE 1      Both models can only predict large scale and slow variations, on the order of 1 000 km (given by the highest harmonic component) and 3 hours. Spacecraft can encounter density variations with smaller temporal and spatial scales partly since they are in motion (for example, +100% or -50% in 30 s), and partly because smaller-scale disturbances certainly occur during periods of disturbed geomagnetic activity.

NOTE 2      Reference values for the key indices needed as inputs for the atmosphere models are given in Clause 6.

NOTE 3      The F10.7 81-day average activity can also be estimated by averaging three successive monthly predicted values.

NOTE 4      Information on density model uncertainties can be found in G.5 and in [RN.4] and [RN.5].

NOTE 5      For high activities the atmosphere models only give realistic results if high short term values are combined with high 81-day averaged values.

NOTE 6      High Ap values can be used with low, moderate or high solar activities.