[1] Long-term thermospheric neutral density trends near 400 km altitude are analyzed using high accuracy satellite drag measurements over the common time period 1970 -2000. Data coverage is over all latitudes and local times and an extensive range of solar and geomagnetic conditions. Densities are compared to empirical models that remove known variations related to solar activity, latitude, local time, day of year and altitude. An average unmodeled secular neutral density decrease of 1.7% per decade is detected. This result is qualitatively consistent with predictions of thermospheric cooling related to anthropogenic causes deduced by theoretical models, and in general agreement with global cooling estimates determined from previous analyses of satellite orbital decay.

[1] Orbit-averaged mass densities r and exospheric temperatures T 1 inferred from measurements by accelerometers on the Gravity Recovery and Climate Experiment (GRACE) satellites are used to investigate global energy E th and power P th inputs to the thermosphere during two complex magnetic storms. Measurements show r, T 1 , and E th rising from and returning to prevailing baselines as the magnetospheric electric field e VS and the Dst index wax and wane. Observed responses of E th and T 1 to e VS driving suggest that the storm time thermosphere evolves as a driven-but-dissipative thermodynamic system, described by a first-order differential equation that is identical in form to that governing the behavior of Dst. Coupling and relaxation coefficients of the E th , T 1 , and Dst equations are established empirically. Numerical solutions of the equations for T 1 and E th are shown to agree with GRACE data during large magnetic storms. Since T 1 and Dst have the same e VS driver, it is possible to combine their governing equations to obtain estimates of storm time thermospheric parameters, even when lacking information about interplanetary conditions. This approach has the potential for significantly improving the performance of operational models used to calculate trajectories of satellites and space debris and is also useful for developing forensic reconstructions of past magnetic storms. The essential correctness of the approach is supported by agreement between thermospheric power inputs calculated from both GRACE-based estimates of E th and the Weimer Poynting flux model originally derived from electric and magnetic field measurements acquired by the Dynamics Explorer 2 satellite.

[1] We have used output from the Weimer Joule heating model (2005) and the Air Force High Accuracy Satellite Drag Model (HASDM) to study the response of the thermosphere to Joule heating. Our study period of 15 January to 29 June 2001 contains a number of large and small magnetic storms during which thermospheric heating events occurred. We find that a new Joule heating model (Weimer, 2005), combined with the energy input provided by precipitating particles (NOAA/TIROS hemispheric power index), can supply more than enough energy to account for the change in total thermospheric internal and gravitational potential energy during magnetic storms. In the smaller storm heating events the energy input is about equally divided, with Joule heating only slightly dominant over particle precipitation. In the larger events, Joule heating clearly dominates. We find that the thermosphere responds globally in just 3-6 hours to an increase in energy input.

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In this paper we present and discuss the cryogenic infrared radiance instrumentation for shuttle (CIRRIS) 15-•m CO2 and 5.3-•m NO data with respect to limb emission variability and within the context of latitudinal, diurnal, and geomagnetic variations during two days of observations onboard shuttle flight STS 39, April 29-30, 1991. About 50 limb emission profiles were examined for the two emissions. Enhancements were observed at high latitudes relative to midlatitudes and low latitudes at 140 km altitude for the 15-•m CO2 emission (factor of 2-5). The high-latitude enhancement in the 5.3-•m NO emission was larger (factor of 11-14). The high-latitude nighttime data were collected in the auroral zone during a class III aurora. Diurnal variations are examined at midlatitudes. A significant enhancement in the 15-•m emission was observed between 0500 and 0700 LT at 140 and 160 km. This effect was modeled by the SHARC atmospheric generator (SAG) which uses the mass spectrometer incoherent scatter (MSIS) model. Species concentrations from the thermosphere-ionospheremesosphere electrodynamics general circulation model (TIME-GCM) and SAG models were input to the SHARC radiance code to simulate the CIRRIS limb emission data.The TIME-GCM predicted the 15-btm CIRRIS radiances generally well for 100 km < z < 120 km but for higher altitudes the data was consistently a factor of 2 higher. For the 5.3-•m simulation the TIME-GCM predicted the data well at low latitudes and midlatitudes, but some significant discrepancies were found at higher latitudes. The altitude of the peak radiance of the 5.3-•m NO emission was found to vary between 110 to 135 km with little systematic global pattern. During high-latitude auroral events the peak of the 5.3-•m emission was consistently observed at higher altitudes than the peak of the 3914• N2 + first negative emission, in agreement with previous observations.

[1] We explore the feasibility of using variations in the horizontal component (DB H ) of the Earth's magnetic field as measured by DMSP satellites while crossing the dip equator to estimate the provisional Dst index and the state of the thermosphere in near real time. Equatorial crossings are identified as locations where the vertical component of the main field measured by DMSP satellites vanishes. Local differences between measured and IGRF (epoch 2005) horizontal components (dB H ) were calculated for the years 2005 to 2009. Each year quiet time (0 ≥ Dst ≥ -7 nT) subsets of dB H were identified to establish offset baselines (dB H B ) as functions of longitude along the magnetic equator ( eq ) for each spacecraft. Year-to-year changes in dB H B reflect variations of the Earth's main field, indicating that baseline calculations must be updated at regular intervals for each spacecraft. Running-averaged values of DB H (t) = dB H ( eq , t) − dB H B ( eq , t) inferred from combined DMSP F16 and F17 data streams are shown to follow variations in Dst during the test interval. The method is also shown to apply during the magnetic superstorms of late 2003. Except during the late main phase, increases in globally averaged exospheric temperatures inferred from DB H and provisional Dst time series are in reasonable agreement with those inferred from measurements by accelerometers on the GRACE satellites.

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