Global ionospheric climatology

Friday, November 2, 2012

Extensive analyses of COSMIC data for 2007–2010 have revealed a number of features concerning seasonal and solar-cycle variation. Low-latitude ionospheric peak density NmF2 was dominated by the semi-annual anomaly, the equatorial anomaly and the annual asymmetry. The second equinoctial maximum is not centered on the September equinox, but occurred in October. There is an annual variation at high latitudes in which maximum values of NmF2 occur in summer, unlike analyses of earlier periods that showed a winter anomaly. Elevated height of the peak, hmF2, also occurs in summer at high latitudes, with a distinct seasonal and hemispheric asymmetry.

NmF2 climatology for 2007 to 2010 image
NmF2 climatology for 2007 to 2010 in magnetic latitude bins. Units are in per cubic centimeters. Each bin is calculated using the median of data from all longitudes for local times between 0900 and 1500 local solar time. The data were then further processed by taking a 30 day running median for each bin to remove short term variability like geomagnetic activity and any possible short term “breathing” modes of the atmosphere.

Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) data were analyzed to study the climatological variations of the F2-region ionosphere. A 30 day running median was applied to the daily medians of each geomagnetic latitude bin (100) to remove the short-term variability of the data. This permitted a better description of the long-term daytime climatology across the most recent solar minimum to be obtained. Several significant features appeared in this climatology: 1) low-latitude NmF2 was dominated by the semi-annual anomaly, the equatorial anomaly and the annual asymmetry (anomaly); 2) Semi-annual and annual anomalies extended into the middle latitudes; 3) this extension into the middle latitudes appears to be dependent on variations of solar radiation over the solar cycle, as the variations did not reach as far poleward in 2008 as they did in 2010; 4) The second equinoctial maximum is not centered on the September equinox, but occurred in October; 5) there is an annual variation at high latitudes in which maximum values of NmF2 occur in summer there is no indication of a winter anomaly and, in fact, when hemispheres are compared, maximum NmF2 at middle latitudes always occurs in the summer hemisphere rather than the winter one; 6) the highest values of hmF2 at low latitudes occur on the summer side of the magnetic equator throughout the four year period, probably resulting from winds blowing from the summer to the winter; 7) minimum values of hmF2 at middle latitudes occur in winter, when hmF2 is typically 30 to 50 km lower than it is in summer; 8) elevated hmF2 also occurs in summer at high latitudes, with a distinct seasonal and hemispheric asymmetry.

Reference: Burns, A.G., S.C. Solomon, W. Wang, L. Qian, Y. Zhang, and L.J. Paxton (2012a), Daytime climatology of ionospheric NmF2 and hmF2 from COSMIC data, J. Geophys. Res., 117, A09315, doi:10.1029/2012JA017529.