Global Modeling of the Low and Mid-Latitude Ionospheric D and Lower E Regions and Implications for HF Radiowave Absorption

We present a global comparison of D and lower E region ionospheric model calculations driven by the Whole Atmosphere Community Climate Model (WACCM) with a selection of electron density profiles made by sounding rockets. WACCM, in turn, is nudged by winds and tem peratures for the years 2008 and 2009 from the Navy Operational Global Atmospheric Prediction System- Advanced Level Physics High Altitude (NOGAPS-ALPHA). This nudging has been shown to greatly improve the representation of key neutral constituents, such as nitric oxide (NO), that are used as inputs to the ionospheric model. Here we show that we improve the comparison between calculated and observed electron densities relative to older studies. At mid-latitudes, both for winter and equinoctal conditions, the model agrees well with the data. At tropical latitudes, our results confirm a previous suggestion that there is a model deficit in the calculated electron density in the lowermost D region. We then apply the calculated electron densities to examine the variation of HF absorption with altitude, latitude, season and from 2008 to 2009. For low latitudes, our results agree with recent studies showing a primary peak absorption in the lower E region with a secondary peak below 75 km. For mid-to-high latitudes, the absorption contains a significant contribution from the middle D region where ioniziation of NO drives the ion chemistry. The difference in mid-to-high latitude absorption from 2008 to 2009 is due to changes in the NO abundance near 80 km which we explain in terms of the changes in the wintertime mesospheric residual circulation.