SA51C-01 INVITED
The Emergence of a Pattern of Global Change in the Upper Atmosphere and Ionosphere
In the upper atmosphere, greenhouse gases produce a cooling effect, instead of a warming effect. Increases in greenhouse gas concentrations are expected to induce substantial changes in the mesosphere, thermosphere, and ionosphere, including a thermal contraction of these layers. Here we present the first global pattern of the observed long-term change in the upper atmosphere and ionosphere, based on trend studies of various parameters. The picture we obtained is qualitative, and contains several gaps and a few discrepancies, but the overall pattern of observed long-term changes throughout the upper atmosphere is mutually consistent and qualitatively consistent with model predictions of the effect of greenhouse gas increases. The upper atmosphere as a whole is cooling and contracting, and changes in temperature and related changes in minor constituents are responsible for changes of the ionosphere. Together with the large body of lower atmospheric trend research, our synthesis indicates that anthropogenic emissions of greenhouse gases are affecting the atmosphere at nearly all altitudes between ground and space.
SA51C-02 INVITED
Middle Atmosphere Climate Changes From Transient Runs With the Canadian Middle Atmosphere Model
The Canadian Middle Atmosphere Model (CMAM) is a general circulation model which extends from the surface up to about 95 km. It contains an interactive photochemical module and includes realistic parameterizations of the major physical processes necessary to represent the complexity of interactions throughout the model domain. The model has been run from 1960 to 2100 to investigate the atmospheric response to transient forcings in sea surface temperatures, CFCs and greenhouse gases, including CO2, CH4, and N2O. The major effect in the middle atmosphere is a cooling caused by the CO2 increase. This cooling is modulated by long-term changes in ozone concentrations: ozone depletion in the past leads to an additional cooling whereas ozone recovery in the future reduces the CO2 effect. The focus of this paper is on processes in the upper stratosphere and mesosphere. Results from the transient numerical experiments with the CMAM are discussed and comparison with available long-term observations of the recent past is shown.
SA51C-03
Interpretation of Hydroxyl Airglow Temperatures for Global Change Trends in the Mesosphere
Traditionally, the hydroxyl (OH) night airglow has been measured to infer the neutral temperature near 87 km, the nominal height of the OH emission. This atmospheric region has been predicted to show appreciable trends associated with the effects of anthropogenic climate change, but is also subject to solar and wave forcing. Although several long-term data sets of mesospheric temperature are available, these have yielded conflicting evidence for temperature trends. We have examined high-latitude hydroxyl airglow temperature data for solar forcing and residual trends, and have used a steady-state photo-chemical model to interpret the results. We find that the observed hydroxyl temperature time-series depends critically on the atomic-oxygen concentration profile and the particular OH band being observed. We will present the model results with prescribed temperature trends associated with solar forcing and climate change, and will identify the hydroxyl airglow response to these changes for different bands. A brief survey of trends observed using different hydroxyl airglow bands will be presented to support the model results.
SA51C-04 INVITED
Secular Change in the Coupled Thermosphere and Ionosphere System
Observed long-term changes in the upper atmosphere have been attributed to increasing of greenhouse gases, mainly CO2, which cools the mesosphere and thermosphere. There has also been evidence [e.g., Lastovica et al., Science, 314, 1253, 2006] indicating that changes in the ionosphere accompany the neutral atmosphere changes, including a slight decrease in E-region altitude and small increases in the maximum electron density of E-region and F1-region. However, trends in the peak electron density and peak electron density height of F2- region have been controversial. Using a global mean upper atmosphere model, CO2 concentration measured at Mauna Loa Observatory, and solar variation based on a proxy model, we have calculated the secular change of thermosphere neutral density. The model result is compared to trend estimates of thermosphere density derived from satellite drag observations, showing good agreement. Sensitivity studies show that in the upper thermosphere, the effect of CO2 increases is much greater than effects from changes in CH4, H2O and O3, etc., accounting for nearly 90% of upper thermosphere density change. We have also used the model to confirm the expected trends in the ionosphere E-region and F1-region. The non-geomagnetic trend of the height of peak electron density in the F2-region is predicted to be negative but the non-geomagnetic trend of the peak electron density of the F2-region can be either positive or negative, depending on solar activity.
SA51C-05 INVITED
Trends in the E and F1 Regions of the Earth's Ionosphere
Ground based ionosonde measurements are a very important source for investigations of long-term variations in the ionospheric E and F1 regions. Data of such observations are available at many different ionospheric stations all over the world since partly more than 50 years. Here mainly standard parameters foE, h'E, and foF1 are used for trend analyses. Two main problems have to be taken into consideration in these analyses. Firstly, the data series have to be homogeneous, i. e. the observations should not be disturbed by artificial steps due to changes in the used technical equipment or in the evaluation algorithm. Secondly, the strong solar and geomagnetic influences upon the ionospheric data have carefully to be removed by an appropriate regression analysis. Otherwise it is impossible to detect the small trends in the different ionospheric parameters. The trends derived at individual stations differ markedly. Nevertheless, the mean global trends estimated from the trends at the different stations are statistically significant different from zero (positive trends in foE and foF1, negative trend in h'E). These mean trends can at least qualitatively be explained by an increasing atmospheric greenhouse effect (increase of CO2 content or of other greenhouse gases) and decreasing ozone values. The positive foE trend is also in qualitative agreement with rocket mass spectrometer observations of ion densities in the E region. Furthermore first indications could be found that the changing ozone trend (before about 1979, between 1979 until 1995, and after about 1995) can modify the estimated long-term variations at least in foE.
SA51C-06
Modeling the Effect of Changes in the Terrestrial Magnetic Field on the Climatology of the Mid- and Low-Latitude Ionosphere.
A new model of the global ionosphere has been developed which utilizes a magnetic field structure derived directly from the full International Geomagnetic Reference Field (IGRF) - as opposed to earlier, dipolar approximations to the IGRF. Using this new model, a series of runs has been undertaken to investigate how the ionosphere has been influenced by changes in the Terrestrial magnetic field over the 40 years from 1965 to 2005. For each run, all inputs to the model, such as thermospheric composition and winds, and the Solar EUV flux are kept the same. The only change comes from the magnetic field, with values taken from the IGRF at the relevant year. The results are very interesting: In most regions the changes to the ionosphere since 1965 are fairly insignificant. However within the equatorial region of South America and the South Atlantic it is a different story. Here the changes are very significant and therefore need to be considered in any analysis of long term trends within the ionosphere. Results from the modeling study will be presented and an analysis, in terms of changes in the location of the magnetic equator and the magnetic declination and inclination, will be discussed.