The UARS satellite describes a non-sun-synchronous orbit. If the orbit were sun-synchronous, then the observation of each latitude in each orbit would correspond to two fixed local times (one for ascending and one for descending orbits). This is not the case and each day corresponds to a drift in local time of some 20 minutes.
In some 30 days, then, ascending and descending node observations
will cover all local times. In practice, the geometry is not that
simple, but most local times will be sampled at most latitudes.
If all variation in the signal were diurnal, these monthly observations
would directly show the local time dependence of the NO2
signal. In practice, this local time variation is combined with other
time variation of the signal and is
If we take the results of a Grose model run and evaluate the field at longitude zero over the course of a month or so, we see the basic results:
So, we see that at least in the Grose model case, the diurnal variation of NO2 is easily recovered from asynoptic data such as we can obtain from a satellite. We can then apply this to the CLAES instrument aboard the UARS satellite:
We see qualitatively that the actual and model data agree well in their diurnal signal.