NRLMSISE-00 Atmospheric Model Research Articles

Drag Coefficient Constraints for Space Weather Observations in the Upper Thermosphere

AbstractThe space weather research community relies heavily on thermospheric density data to understand long‐term thermospheric variability, construct assimilative, empirical, and semiempirical global atmospheric models and validate model performance. One of the challenges in resolving accurate thermospheric density data sets from satellite orbital drag measurements is modeling appropriate physical aerodynamic drag force coefficients. The drag coefficient may change throughout the thermosphere due to model dependencies on composition and altitude. As such, existing drag coefficient model errors and corresponding errors in orbit‐derived density data sets and models may be altitude and solar cycle dependent with greater errors at higher altitudes around 500 km near the oxygen‐to‐helium transition region. In this paper, inter‐satellite observed‐to‐modeled density comparisons at ∼500 km are evaluated to constrain drag coefficient modeling assumptions. Observed densities are derived from accelerometer data for the Gravity Recovery and Climate Experiment (GRACE) satellites and Two‐Line Element data for a set of compact satellites, while the NRLMSISE‐00 atmospheric model is used to obtain modeled densities and composition information. Density consistency results indicate that drag coefficient models with incomplete energy and momentum accommodation produce the most consistent densities, while the standard diffuse modeling approach may not be appropriate at these altitudes. Models with momentum accommodation between 0.5 and 0.9 and energy accommodation between 0.83 and 0.96 may be most appropriate at upper thermospheric altitudes. Modeling drag coefficients with diffuse gas‐surface interactions for the GRACE satellites could lead to errors in derived density of ∼25% and in‐track satellite orbit prediction uncertainty during solar maximum conditions on the order of kilometers.

Measurement of mesopause temperature using the mesospheric airglow spectrum photometer (MASP)

This work presents a practical spectrophotometer based on passive remote sensing, the mesospheric airglow spectrum photometer (MASP). Also presented is a detailed description of its data processing. The MASP measures the rotational temperature from nighttime airglow emission of the O2(0–1) band. All components of the MASP are commercial standard components, making it cost-effective and easy to maintain and update. The housing of the MASP has excellent thermal insulation and is equipped with a small semiconductor thermoelectric cooler (TEC) air conditioner that guarantees a constant temperature for the instrument. The calibration of the instrument parameters and the forward model simulation of synthetic spectra are described in detail. Moreover, the data processing is adjusted according to the characteristics of MASP, especially for the removal of background continuum. Observation results show that the MASP is capable of measuring disturbances caused by a small-scale gravity wave and by tidal waves with periods of 4 or 8 h. Comparisons with the NRLMSISE-00 atmospheric model also show a more consistent trend of averaged daily temperature variation. Accordingly, the MASP is suitable for installation at multiple stations to perform long-term and stable synchronous network observation.

Properties of the Ionosphere during an Extreme Storm

Based on an analysis of the F2-layer critical frequency (foF2) at Irkutsk station during the extreme storm of March 13–15, 1989, it is found that geomagnetic activity index aa is a more adequate indicator than ap for foF2 during the maximum of an extreme storm. This is related to the existence of the upper limit of changes in ap (ap = 400) and this fact imposes some limitations on using the ap index for extreme events. In the initial period of the recovery phase of the considered storm, a rapid decrease of geomagnetic activity occurred. A strong deviation of the experimental values of foF2 from the values calculated by the semi-empirical model, which considers the dependences of the thermospheric temperature and composition on geomagnetic activity by the NRLMSISE-00 atmospheric model, was observed during that period. It is assumed that this could be related to the effect of disturbance of thermospheric wind velocity due to the rapid decrease of geomagnetic activity. This assumption is rather qualitative and requires a special study.

Atmospheric ionization induced by precipitating electrons: Comparison of CRAC:EPII model with a parametrization model

Results of a comparison of a new model CRAC:EPII (Cosmic Ray Atmospheric Cascade: Electron Precipitation Induced Ionization) with a commonly used parametric model of atmospheric ionization is presented. The CRAC:EPII is based on a Monte Carlo simulation of precipitating electrons propagation and interaction with matter in the Earth's atmosphere. It explicitly considers energy deposit: ionization, pair production, Compton scattering, generation of Bremsstrahlung high energy photons, photo-ionization and annihilation of positrons, multiple scattering as physical processes accordingly. Propagation of precipitating electrons and their interactions with air is simulated with the GEANT4 simulation tool PLANETOCOSMICS code using NRLMSISE-00 atmospheric model. Ionization yields are computed and compared with a parametrization model for different energies of incident precipitating energetic electrons, using simulated fluxes of mono-energetic particles. A good agreement between the two models is achieved in the mesosphere but the contribution of Bremsstrahlung in the stratosphere, which is not accounted for in the parametric models, is found significant. As an example, we calculated profiles of the ion production rates in the middle and upper atmosphere (below 100km) on the basis of balloon-born measured spectra of precipitating electrons for 30-October-2002 and 07-January-2004.

Monitoring the global-scale winter anomaly of total electron contents using GPS data

Abstract The winter anomaly phenomenon of Total Electron Contents (TEC) at latitudes 15°–60°N and 15°S–60°S is presented using GPS carrier-phase data obtained from GPS stations during 2002. The correlation between the [O/N2] ratio estimated using the NRLMSISE-00 atmospheric model and the TEC winter anomaly is also investigated. The numerical results show that the TEC winter anomaly in different regions of the world tends to be dominated by different factors. In North America, the TEC winter anomaly is strongly affected by the magnetospheric processes in high latitudes and the [O/N2] ratio. In the Euro-Africa and Russia-Asia regions, the TEC winter anomaly depends mainly on the [O/N2] ratio at the latitude band of 30°–60°N, and the extent of the TEC winter anomaly gradually decreases from 60°N to 30°N. The extent of the TEC winter anomaly increases at the latitude band of 15°–30°N due to the influence of the meridional neutral wind and the seasonal changes of the subsolar point. However, the TEC winter anomaly was not observed in southern hemisphere in 2002. The TEC equinoctial asymmetries in the northern and southern hemisphere are also presented using GPS TEC values collected in March and September 2002.

Thermospheric winds and temperatures above Mawson, Antarctica, observed with an all-sky imaging, Fabry-Perot spectrometer

Abstract. A new all-sky imaging Fabry-Perot spectrometer has been installed at Mawson station (67°36' S, 62°52' E), Antarctica. This instrument is capable of recording independent spectra from many tens of locations across the sky simultaneously. Useful operation began in March 2007, with spectra recorded on a total of 186 nights. Initial analysis has focused on the large-scale daily and average behavior of winds and temperatures derived from observations of the 630.0 nm airglow line of atomic oxygen, originating from a broad layer centered around 240 km altitude, in the ionospheric F-region. The 1993 Horizontal Wind Model (HWM93), NRLMSISE-00 atmospheric model, and the Coupled Thermosphere/Ionosphere Plasmasphere (CTIP) model were used for comparison. During the geomagnetically quiet period studied, observed winds and temperatures were generally well modelled, although temperatures were consistently higher than NRLMSISE-00 predicted, by up to 100 K. CTIP temperatures better matched our data, particularly later in the night, but predicted zonal winds which were offset from those observed by 70–180 ms−1 westward. During periods of increased activity both winds and temperatures showed much greater variability over time-scales of less than an hour. For the active night presented here, a period of 45 min saw wind speeds decrease by around 180 ms−1, and temperatures increase by approximately 100 K. Active-period winds were poorly modelled by HWM93 and CTIP, although observed median temperatures were in better agreement with NRLMSISE-00 during such periods. Average behavior was found to be generally consistent with previous studies of thermospheric winds above Mawson. The collected data set was representative of quiet geomagnetic and solar conditions. Geographic eastward winds in the afternoon/evening generally continued until around local midnight, when winds turned equatorward. Geographic meridional and zonal winds in the afternoon were approximately 50 ms−1 weaker than expected from HWM93, as was the transition to equatorward flow around midnight. There was also a negligible geographic zonal component to the post-midnight wind where HWM93 predicted strong westward flow. Average temperatures between 19:00 and 04:00 local solar time were around 60 K higher than predicted by NRLMSISE-00.