Simulations of the effects of vertical transport on the thermosphere and ionosphere using two coupled models

摘要

We have explored the sensitivity of the thermosphere and ionosphere to dynamical forcing from altitudes near the mesopause (～95 km). We performed five simulations, all for the year 2009, with the National Center for Atmospheric Research (NCAR)/Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM). Two simulations were driven with the NCAR Global Scale Wind Model, and three used output from the Advanced Level Physics High Altitude (ALPHA) version of the Navy’s Operational Global Atmospheric Prediction System (NOGAPS). Use of NOGAPS-ALPHA allows for realistic meteorological variability from the lower atmosphere to propagate up into the TIEGCM, including a rich spectrum of nonmigrating tides. We find that the additional vertical transport from these tides causes a significant reduction in the calculated peak electron density of the ionospheric F2 layer (NmF2). The mechanism for this effect is the enhanced downward transport of atomic oxygen to the base of the thermosphere. In turn, this yields a greater relative abundance of N2 and hence enhanced recombination of ions and electrons. To get improved agreement with observed electron densities, we must reduce (K_(zz)) by a factor of 5. However, even with lower K_(zz), our calculation still underestimates the NmF2 compared with radio occultation observations by the Constellation Observing System for Meteorology, Ionosphere and Climate satellite system. This underestimate of NmF2 may be linked to an overestimate of the nonmigrating tides in the coupled TIEGCM-NOGAPS calculations or to uncertainties in the bottom boundary for atomic oxygen in the TIEGCM.