Key developments have been made to the NCAR Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X). Among them, the most important are the self‐consistent solution of global electrodynamics, and transport of O+ in the F‐region. Other ionosphere developments include time‐dependent solution of electron/ion temperatures, metastable O+ chemistry, and high‐cadence solar EUV capability. Additional developments of the thermospheric components are improvements to the momentum and energy equation solvers to account for variable mean molecular mass and specific heat, a new divergence damping scheme, and cooling by O(3P) fine structure. Simulations using this new version of WACCM‐X (2.0) have been carried out for solar maximum and minimum conditions. Thermospheric composition, density, and temperatures are in general agreement with measurements and empirical models, including the equatorial mass density anomaly and the midnight density maximum. The amplitudes and seasonal variations of atmospheric tides in the mesosphere and lower thermosphere are in good agreement with observations. Although global mean thermospheric densities are comparable with observations of the annual variation, they lack a clear semiannual variation. In the ionosphere, the low‐latitude E × B drifts agree well with observations in their magnitudes, local time dependence, seasonal, and solar activity variations. The prereversal enhancement in the equatorial region, which is associated with ionospheric irregularities, displays patterns of longitudinal and seasonal variation that are similar to observations. Ionospheric density from the model simulations reproduces the equatorial ionosphere anomaly structures and is in general agreement with observations. The model simulations also capture important ionospheric features during storms.

[1] In atmospheric and space environment studies it is key to understand and to quantify the coupling of atmospheric regions and the solar impacts on the whole atmosphere system. There is thus a need for a numerical model that encompasses the whole atmosphere and can self-consistently simulate the dynamic, physical, chemical, radiative, and electrodynamic processes that are important for the Sun-Earth system. This is the goal for developing the National Center for Atmospheric Research (NCAR) Whole Atmosphere Community Climate Model (WACCM). In this work, we report the development and preliminary validation of the thermospheric extension of WACCM (WACCM-X), which extends from the Earth's surface to the upper thermosphere. The WACCM-X uses the finite volume dynamical core from the NCAR Community Atmosphere Model and includes an interactive chemistry module resolving most known neutral chemistry and major ion chemistry in the middle and upper atmosphere, and photolysis and photoionization. Upper atmosphere processes, such as nonlocal thermodynamic equilibrium, radiative transfer, auroral processes, ion drag, and molecular diffusion of major and minor species, have been included in the model. We evaluate the model performance by examining the quantities essential for the climate and weather of the upper atmosphere: the mean compositional, thermal, and wind structures from the troposphere to the upper thermosphere and their variability on interannual, seasonal, and daily scales. These quantities are compared with observational and previous model results.

[1] The High Resolution Dynamics Limb Sounder (HIRDLS) experiment was designed to provide global temperature and composition data on the region from the upper troposphere to the mesopause with vertical and horizontal resolution not previously available. The science objectives are the study of small-scale dynamics and transports, including stratosphere-troposphere exchange, upper troposphere/lower stratosphere chemistry, aerosol, cirrus and PSC distributions, and gravity waves. The instrument features 21 channels, low noise levels, high vertical resolution, and a mechanical cooler for long life. During launch most of the optical aperture became obscured, so that only a potion of an optical beam width at a large azimuth from the orbital plane on the side away from the Sun can see the atmosphere. Irrecoverable loss of capabilities include limitation of coverage to the region 65°S-82°N and inability to obtain longitudinal resolution finer than an orbital spacing. While this optical blockage also impacted radiometric performance, extensive effort has gone into developing corrections for the several effects of the obstruction, so that radiances from some of the channels can be put into retrievals for temperature. Changes were also necessary for the retrieval algorithm. The validation of the resulting temperature retrievals is presented to demonstrate the effectiveness of these corrections. The random errors range from $0.5 K at 20 km to $1.0 at 60 km, close to those predicted. Comparisons with high-resolution radiosondes, lidars, ACE-FTS, and ECMWF analyses give a consistent picture of HIRDLS temperatures being 1-2 K warm from 200 to 10 hPa and within ±2 K of standards from 200 to 2 hPa (but warmer in the region of the tropical tropopause), above which HIRDLS appears to be cold. Comparisons show that both COSMIC and HIRDLS can see small vertical features down to about 2 km

The HALogen Occultation Experiment (HALOE) instrument on UARS observes vertical profiles of ozone and other gases of interest for atmospheric chemistry using the solar occultation technique. A broadband radiometer in the 9.6-ttm band is used for ozone measurements. Version 17 ozone retrieved by HALOE is intercompared successfully with about 400 profiles of other sounders, including ozonesondes, lidars, balloons, rocketsondes, and other satellites. Usually, the HALOE data are within the error range of the correlative measurements between about 100 and 0.03 mbar atmospheric pressure. Between about 30 and 1 mbar, HALOE agrees typically within 5%, with a tendency to be low. In the first year of data, larger errors sometimes occur in the lower stratosphere due to the necessary correction for Pinatubo aerosol effects, but these differences do not exceed 20%. The data show internal consistency for sunrise and sunset events at the same locations. Some examples of observed ozone distributions, including polar regions, are given.

For the first time a mesoscale-resolving whole atmosphere general circulation model has been developed, using the National Center for Atmospheric Research Whole Atmosphere Community Climate Model with ∼0.25 • horizontal resolution and 0.1 scale height vertical resolution above the middle stratosphere (higher resolution below). This is made possible by the high accuracy and high scalability of the spectral element dynamical core from the High-Order Method Modeling Environment. For the simulated January-February period, the latitude-height structure and the magnitudes of the temperature variance compare well with those deduced from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) observations. The simulation reveals the increasing dominance of gravity waves (GWs) at higher altitudes through both the height dependence of the kinetic energy spectra, which display a steeper slope (∼ −3) in the stratosphere and an increasingly shallower slope above, and the increasing spatial extent of GWs (including a planetary-scale extent of a concentric GW excited by a tropical cyclone) at higher altitudes. GW impacts on the large-scale flow are evaluated in terms of zonal mean zonal wind and tides: with no GW drag parameterized in the simulations, forcing by resolved GWs does reverse the summer mesospheric wind, albeit at an altitude higher than climatology, and only slows down the winter mesospheric wind without closing it. The hemispheric structures and magnitudes of diurnal and semidiurnal migrating tides compare favorably with observations.

We simulated anthropogenic global change through the entire atmosphere, including the thermosphere and ionosphere, using the Whole Atmosphere Community Climate Model‐eXtended. The basic result was that even as the lower atmosphere gradually warms, the upper atmosphere rapidly cools. The simulations employed constant low solar activity conditions, to remove the effects of variable solar and geomagnetic activity. Global mean annual mean temperature increased at a rate of +0.2 K/decade at the surface and +0.4 K/decade in the upper troposphere but decreased by about −1 K/decade in the stratosphere‐mesosphere and −2.8 K/decade in the thermosphere. Near the mesopause, temperature decreases were small compared to the interannual variation, so trends in that region are uncertain. Results were similar to previous modeling confined to specific atmospheric levels and compared favorably with available measurements. These simulations demonstrate the ability of a single comprehensive numerical model to characterize global change throughout the atmosphere.

The Halogen Occultation Experiment (HALOE) experiment on Upper Atmosphere Research Satellite (UARS) performs solar occultation (sunrise and sunset) measurements to infer the composition and structure of the stratosphere and mesosphere. Two of the HALOE channels, centered at 5.26 gm and 6.25 gm, are designed to infer concentrations of nitric oxide and nitrogen dioxide respectively. The NO measurements extend from the lower stratosphere up to 130 km, while the NO2 results typically range from the lower stratosphere to 50 km and higher near the winter terminator. Comparison with results from various instruments are presented, including satellite-, balloon-, and ground-based measurements. Both NO and NO2 can show large percentage errors in the presence of heavy aerosol concentrations, confined to below 25 km and before 1993. The NO2 measurements show mean differences with correlative measurements of about 10 to 15% over the middle stratosphere. The NO2 precision is about 7.5x10 '13 arm, degrading to 2x10 -12 arm in the lower stratosphere. The NO differences are similar in the middle stratosphere but sometimes show a low bias (as much as 35%) between 30 and 60 km with some correlative measurements. NO precision when expressed in units of density is nearly constant at lx10 '12 atmospheres, or approximately 0.1 ppbv at 10.0 mb or, 1.0 ppbv at 1.0 mb, and so forth when expressed in mixing ratio. Above 65 km, agreement in the mean with Atmospheric Trace Molecule Spectroscopy (ATMOS) NO results is very good, typically + 15%. Model comparisons are also presented, showing good agreement with both expected morphology and diurnal behavior for both NO2 and NO. hydrogen chloride (HCI), hydrogen fluoride (HF), methane (CH4), water vapor (H20), nitric oxide (NO), nitrogen dioxide (NOy), and aerosol extinction. Retrieved profiles cover an altitude range from the upper troposphere, in some cases, to the lower thermosphere for nitric oxide. Fifteen spacecraft sunrises and sunsets are observed daily and usually in opposite hemispheres, although at certain times these measurements occur on the same day and almost overlap in space. Details of the HALOE experiment, including geographic coverage, discussion of the experiment and instrument techniques, instrument ground test results, error mechanisms, in-orbit performance, initial pressure versus latitude cross sections, and orthographic projections are included in the HALOE overview by Russell et. al. [1993]. The purpose of 'this paper is to describe steps taken and 'the status of efforts to validate data from the NO gas correlation channel and the NO2 radiometer channel. All results were inferred using the most current archived HALOE data, version 17, released in November 1994. Version numbers were liberally changed during the continuous validation and evolution of the HALOE processing system. Attainment of research quality results coincided with version 16 in late summer of 1994, which was the first version released to the general science community. However, a second general processing ...

Global distributions of CH 4 in the mesosphere and stratosphere have been measured continuously since October 11, 1991, by the Halogen Occultation Experiment (HALOE) onboard the UARS. CH 4 mixing ratio is obtained using the gas filter correlation technique operating in the 3.3-grn region. Since measurements are made during solar occultation in the 57 ø inclination orbit, data are collected 15 times daily for both sunrises and sunsets. This provides coverage of one hemisphere in a month period. One complete hemispheric sweep (from equator to -80 ø latitude) is made during the spring and summer seasons of two hemispheres, and a partial sweep (from equator to around 50 ø latitude) is made during the fall and winter seasons of two hemispheres. HALOE CH 4 measurements are validated using direct comparisons with correlative data and internal consistency checks using other HALOE-measured tracers, HF, and aerosols. It is estimated for the 0.3-to 50-mbar region that the total error, including systematic and random components, is less than 15 % and that the precision is better than 7%. The CH4 gas filter channel does not depend significantly on the Pinatubo aerosol extinction. An experimentally accurate measurement of CH 4 is very important because CH 4 is a primary interfering gas in the HALOE HC1 channel and, subsequently, can cause HC1 measurement error. Simultaneous measurements of CH4 and other HALOE species (03, H20, NO, NO2, HC1, HF, and aerosol extinction coefficients) provide important information on atmospheric dynamic and chemical processes, since CH4 can be used as a tracer and an indicator of atmospheric transport processes. Several new pieces of infolsnation on previously unreported HALOE-observed features are also presented. Introduction Atmospheric methane, CH 4, naturally produced and released from the surface, has an important role in the greenhouse effect, causing a global warming, and in atmospheric chemistry, by removing hydroxyl radicals in the troposphere and in the stratosphere by converting reactive chlorine atoms to HC1 and producing hydrogen species to form water vapor by oxidation (see summary [World Meteorological Organization (WMO), 1982]). Methane can be used as a tracer to study atmospheric transport processes when enough measurements are made on a regional or global scale. For example, the features of CH 4 and other species observed by the Halogen Occultation Experiment (HALOE) were reported by Russell et al. [1993a] for the springtime Antarctic and by Park and Russell [1994] for the summertime polar region. Both papers used CH 4 as a tracer, and in the latter paper it was used to separate dynamical effects and to assess the importance of chemical processes for ozone deficiency in the polar regions. Methane measurements in the stratosphere before the Upper Atmosphere Research Satellite (UARS) [Reber, 1993] include the 1979 global measurements by stratospheric and mesospheric sounder (SAMS) on Nimbus 7 [Rodgers et al., 1984] and otherwise sparse individual profiles obtained by in situ sampli...