AGU Articles - Query Results

2003 - 2005 Space Weather Papers making use of ACE Data in their Investigations. No ACE team members on author list.

(18 Papers as of November 10 2005. Note: search is incomplete due to AGU search engine problems)

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Space weather effects on midlatitude HF propagation paths: Observations and a data-driven D region model Eccles J. V., R. D. Hunsucker, D. Rice, J. J. Sojka (2005), Space weather effects on midlatitude HF propagation paths: Observations and a data-driven D region model, Space Weather, 3, S01002, doi:10.1029/2004SW000094. 2005-01-06 Abstract: A two-pronged study is under way to improve understanding of the D region response to space weather and its effects on HF propagation. One part, the HF Investigation of D region Ionospheric Variation Experiment (HIDIVE), is designed to obtain simultaneous, quantitative propagation and absorption data from an HF signal monitoring network along with solar X-ray flux from the NOAA GOES satellites. Observations have been made continuously since late December 2002 and include the severe disturbances of October–November 2003. GOES satellite X-ray observations and geophysical indices are assimilated into the Data-Driven D Region (DDDR) electron density model developed as the second part of this project. ACE satellite proton observations, the HIDIVE HF observations, and possibly other real-time space weather data will be assimilated into DDDR in the future. Together with the Ionospheric Forecast Model developed by the Space Environment Corporation, DDDR will provide improved specification of HF propagation and absorption characteristics when supplemented by near-real-time propagation observations from HIDIVE. Copyright 2005 by the American Geophysical Union.	[HTML] [PDF]

Determining shock velocities for inputs to Sun-to-Earth models from radio and coronagraph data Smith Z., M. Dryer, C. D. Fry (2005), Determining shock velocities for inputs to Sun-to-Earth models from radio and coronagraph data, Space Weather, 3, S07002, doi:10.1029/2004SW000136. 2005-07-28 Abstract: The speed of a shock that precedes ejecta from a solar energetic eruption is one of the key parameters used for input by many numerical models that predict the arrival of interplanetary shocks at Earth. These shocks are likely to be followed by significant geomagnetic activity. Near-real-time “fearless forecasts” of shock arrival times at the L1 libration point have been made for more than 6 years with several models. Initially, these models used, for input speeds near the Sun, speeds obtained from observations of metric type II radio bursts that are signatures of shocks propagating out through the solar corona. More recently, speeds of halo/partial halo coronal mass ejections (CMEs) were also considered in these models as another measure of shock speeds close to the Sun. During the period of high solar activity in October–November 2003, the data required for input into the models were often available in near real time from a number of observing stations. Therefore the fearless forecasts were issued in some cases with alternative inputs. These forecasts provided a basis on which to compare the success of the predictions (in terms of how close each prediction of the shock arrival time was to the observed time). The results of the analysis of this data set provide guidelines for selecting the input speed for shock propagation models. Both CME and metric type II radio burst measurements are shown to be useful and complementary. In general, the highest speed gave the best predictions. This demonstrates the desirability of having coronagraph data available for operational use. Copyright 2005 by the American Geophysical Union.	[HTML] [PDF]

An overview of the impulsive geomagnetic field disturbances and power grid impacts associated with the violent Sun-Earth connection events of 29–31 October 2003 and a comparative evaluation with other contemporary storms Kappenman J. G. (2005), An overview of the impulsive geomagnetic field disturbances and power grid impacts associated with the violent Sun-Earth connection events of 29–31 October 2003 and a comparative evaluation with other contemporary storms, Space Weather, 3, S08C01, doi:10.1029/2004SW000128. 2005-08-02 Abstract: An overview is provided of the geomagnetic storms and impacts on electric power grids associated with the violent Sun-Earth events of October 2003. During the period from 29 to 31 October 2003, two large geomagnetic storms were observed, as measured by periods of high Kp, Ap, and Dst indices. In fact, these storms had Ap rankings of 6th and 16th all time. This ranking would suggest that the October 2003 storms would be significant with regard to geomagnetically induced currents (GIC) in power grids. However, the resulting geomagnetic storms were much lower in delta B and dB / dt intensity than other historically large geomagnetic storms. A variety of geomagnetic storm processes drove observed GIC. For example, ground observations indicated the presence of large dB / dt pulsations and GIC at North American midlatitude locations on 29 October 2003 that may be due to unusually intense Kelvin-Helmholtz shearing. Sustained disturbance conditions at low-latitude and equatorial latitude locations that are likely linked to ring current intensifications may be the source of sustained GIC at these locations and the cause of large power transformer failures. Comparative evaluations will be provided for the 29–31 October 2003 storms and other important and contemporary storms, such as those observed on 13–14 March 1989, 13–14 July 1982, and 15–16 July 2001. Rather than an index-based evaluation method, the comparative evaluations presented in this paper are based on comparisons of storm morphology. This approach provides a more meaningful comparison of geomagnetic field disturbance dynamics that are important to characterize large GIC threats to power grid infrastructures. Copyright 2005 by the American Geophysical Union.	[HTML] [PDF]

Structure of magnetic fields in NOAA active regions 0486 and 0501 and in the associated interplanetary ejecta Yurchyshyn V., Q. Hu, V. Abramenko (2005), Structure of magnetic fields in NOAA active regions 0486 and 0501 and in the associated interplanetary ejecta, Space Weather, 3, S08C02, doi:10.1029/2004SW000124. 2005-08-17 Abstract: Spectacular burst of solar activity in October–November 2003, when large solar spots and intense solar flares dominated the solar surface for many consecutive days, caused intense geomagnetic storms. In this paper we analyze solar and interplanetary magnetic fields associated with the storms in October–November 2003. We used space- and ground-based data in order to compare the orientations of the magnetic fields on the solar surface and at 1 AU as well as to estimate parameters of geomagnetic storms during this violent period of geomagnetic activity. Our study further supports earlier reports on the correlation between the coronal mass ejection speed and the strength of the magnetic field in an interplanetary ejecta. A good correspondence was also found between directions of the helical magnetic fields in interplanetary ejecta and in the source active regions. These findings are quite significant in terms of their potential to predict the severity of geomagnetic activity 1–2 days in advance, immediately after an Earth directed solar eruption. Copyright 2005 by the American Geophysical Union.	[HTML] [PDF]

Geomagnetic storm of 29–31 October 2003: Geomagnetically induced currents and their relation to problems in the Swedish high-voltage power transmission system Pulkkinen A., S. Lindahl, A. Viljanen, R. Pirjola (2005), Geomagnetic storm of 29–31 October 2003: Geomagnetically induced currents and their relation to problems in the Swedish high-voltage power transmission system, Space Weather, 3, S08C03, doi:10.1029/2004SW000123. 2005-08-25 Abstract: On 30 October 2003, an ongoing geomagnetic superstorm knocked down a part of the high-voltage power transmission system in southern Sweden. The blackout lasted for an hour and left about 50,000 customers without electricity. The incident was probably the most severe geomagnetically induced current (GIC) failure observed since the well-known March 1989 Québec blackout. The “three-phase” storm produced exceptionally large geomagnetic activity at the Fennoscandian auroral region. Although the diversity of the GIC drivers is addressed in the study, the problems in operating the Swedish system during the storm are attributed geophysically to substorms, storm sudden commencement, and enhanced ionospheric convection, all of which created large and complex geoelectric fields capable of driving large GIC. On the basis of the basic twofold nature of the failure-related geoelectric field characteristics, a semideterministic approach for forecasting GIC-related geomagnetic activity in which average overall activity is supplemented with statistical estimations of the amplitudes of GIC fluctuations is suggested. The study revealed that the primary mode of GIC-related failures in the Swedish high-voltage power transmission system were via harmonic distortions produced by GIC combined with too sensitive operation of the protective relays. The outage in Malmö on 30 October 2003 was caused by a combination of an abnormal switching state of the system and tripping of a low-set residual overcurrent relay that had a high sensitivity for the third harmonic of the fundamental frequency. Copyright 2005 by the American Geophysical Union.	[HTML] [PDF]

Modeling the radiation belt electrons with radial diffusion driven by the solar wind Barker A. B., X. Li, R. S. Selesnick (2005), Modeling the radiation belt electrons with radial diffusion driven by the solar wind, Space Weather, 3, S10003, doi:10.1029/2004SW000118. 2005-10-13 Abstract: On the basis of the correlation between the solar wind and radiation belt electron fluxes, we develop a model to simulate the MeV electron phase space density variations from L = 3 to L = 8 by extending the Li et al. (2001) radial diffusion model for geosynchronous electrons. We add L dependence to the Li et al. model and allow for comparison with measurements at more than one L shell while retaining a similar form of their diffusion coefficient. The extended model achieves a prediction efficiency (PE) of 0.61 at L = 4 and 0.52 at L = 6 when the phase space density is converted to differential flux and compared with orbit-averaged Polar 2 MeV measurements at L = 4 and daily averaged LANL 0.7–1.8 MeV geosynchronous measurements for the year 1998. These results indicate that radial diffusion plays a strong role in the enhancement of radiation belt electrons yet leaves a significant portion of the variance unaccounted for. We have also tuned parameters to model the electron fluxes during four individual geomagnetic storms during 1998 and found that the parameter values must differ from those of the long term and from each other to achieve the best PE. This suggests that the different solar wind drivers have varying degrees of influence on the MeV electron variations during different magnetic storms. This model can be used to forecast the MeV electron variations inside geosynchronous orbit with a reasonably good PE on the basis of real-time solar wind measurements only. Copyright 2005 by the American Geophysical Union.	[HTML] [PDF]

Use of lognormal distributions in Dst variations for space weather forecast Yago K., Y. Kamide, Use of lognormal distributions in Dst variations for space weather forecast, Space Weather, 1 (1), 1004, doi:10.1029/2003SW000013, 2003. 2003-10-28 Abstract: An attempt is made to approximate Dst variations during geomagnetic storms in terms of lognormal distributions. Dst variations for the entire duration of a geomagnetic storm are found to be fitted by a lognormal distribution reasonably well, indicating that by using Dst variations during the main phase, how Dst recovers during the recovery phase can be predicted. This is very useful for space weather predictions. On the other hand, there are quite a few geomagnetic storms that cannot satisfactorily be fitted by lognormal forms because of a long duration of the recovery phase. During the recovery phase of these “abnormal” storms, highly fluctuated interplanetary magnetic fields are seen, such that these events must represent HILDCAAs. Copyright 2003 by the American Geophysical Union.	[HTML] [PDF]

A radiation belt-ring current forecasting model Zheng Y., M.-C. Fok, G. V. Khazanov, A radiation belt‐ring current forecasting model, Space Weather, 1 (12), 1013, doi:10.1029/2003SW000007, 2003. 2003-12-10 Abstract: A radiation belt‐ring current (RB‐RC) forecasting model is presented. This model solves the convection‐diffusion equation of plasma distribution in the 10 keV to a few MeV range. There are four major auxiliary components to the RB‐RC model: a global magnetic field model, an electric field model, a plasma sheet model (plasma source), and a radial diffusion model. All four components are driven by solar wind and interplanetary magnetic field conditions. In this paper, a brief description of the model and input parameters is given. This model has been used to simulate several geomagnetic storms. In particular, the effects of the inductive electric field on the evolution of the radiation belt electron fluxes are investigated in detail via a case study of the 12 August 2000 storm. It is found that, in general, the inductive electric field arising from the time‐varying magnetic field can enhance the flux level around geosynchronous orbit during the recovery phase of the storms. The model is validated through comparing the simulation results with the Los Alamos National Laboratory satellite measurements. Further refinement and improvement of the model is also discussed. Copyright 2003 by the American Geophysical Union.	[HTML] [PDF]

Precursor analysis and prediction of large-amplitude relativistic electron fluxes Weigel R. S., A. J. Klimas, D. Vassiliadis, Precursor analysis and prediction of large‐amplitude relativistic electron fluxes, Space Weather, 1 (12), 1014, doi:10.1029/2003SW000023, 2003. 2003-12-12 Abstract: An analysis of large‐amplitude relativistic electron fluxes, J e, is given using models that predict their appearance based on solar wind precursors. It has been noted that relativistic electron flux bursts in the magnetosphere are associated with high‐speed solar wind streams. This observation is used to motivate several models that quantify the association in terms of 2 × 2 contingency tables. For each model, the minimal cost structure for which the model would be useful is computed as a function of large threshold values of J e. The first model is based on the observation that a threshold crossing in the daily averaged solar wind velocity, V SW, tends to precede large relativistic electron fluxes. The optimal ratio of correct to false alarms forecasts found using this algorithm is 18:4 for a threshold corresponding to amplitudes of J e at L = 4.4 above J c = 10 3 particles/str?cm 2 ?s (corresponding to 110 total events). The second model allows for jumps in the solar wind to be an event indicator and yields slight improvements in the forecast ratio for larger values of J c. The dependence of the optimal forecast ratio on L shell is also considered. It is shown that there are L values for which a threshold crossing of the daily average of V SW from below to above 600 km/sec is a sufficient condition for the appearance of large‐amplitude relativistic electron fluxes on one of the following three days. It is also shown that the condition of a threshold crossing of V SW above 600 km/s is not a necessary condition, because ≃80% of events were not preceded by this condition. Copyright 2003 by the American Geophysical Union.	[HTML] [PDF]

Correlation between speeds of coronal mass ejections and the intensity of geomagnetic storms Yurchyshyn V., H. Wang, V. Abramenko (2004), Correlation between speeds of coronal mass ejections and the intensity of geomagnetic storms, Space Weather, 2, S02001, doi:10.1029/2003SW000020. 2004-02-06 Abstract: We studied the relationship between the projected speed of coronal mass ejections (CMEs), determined from a sequence of Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph Experiment (SOHO/LASCO) images, and the hourly averaged magnitude of the B z component of the magnetic field in an interplanetary ejecta, as measured by the Advanced Composition Explorer (ACE) magnetometer in the Geocentric Solar Magnetospheric Coordinate System (GSM). For CMEs that originate at the central part of the solar disk we found that the intensity of B z is correlated with the projected speed of the CME, V p. The relationship is more pronounced for very fast ejecta (V p > 1200 km/s), while slower events display larger scatter. We also present data which support earlier conclusions about the correlation of B z and the Dst index of geomagnetic activity. A possible application of the results to space weather forecasting is discussed. Copyright 2003 by the American Geophysical Union.	[HTML] [PDF]

Adaptive linear prediction of radiation belt electrons using the Kalman filter Rigler E. J., D. N. Baker, R. S. Weigel, D. Vassiliadis, A. J. Klimas (2004), Adaptive linear prediction of radiation belt electrons using the Kalman filter, Space Weather, 2, S03003, doi:10.1029/2003SW000036. 2004-03-12 Abstract: Prior studies have examined the time‐stationary (and quasi‐stationary) dynamic response of relativistic electrons in the Earth's outer radiation belt to changes in solar wind bulk speed using linear prediction filters [Baker et al., 1990 ; Vassiliadis et al., 2002]. For this study, we have implemented an adaptive system identification scheme, based on the Kalman filter with process noise, to determine optimal time‐dependent electron response functions. The nonlinear dynamic response of the radiation belts can then be tracked in time by recursively updating the optimal linear filter coefficients as new observations become available. We demonstrate a significant improvement in zero‐time‐lag electron log‐flux “predictions” relative to models that are based on time‐stationary linear prediction filters, while incurring only a slight increase in computational complexity. We conclude by discussing modifications necessary for an operational specification and forecast model, including the assimilation of real‐time data, more sophisticated model structures, and a more practical gridded description of the radiation belt state. Copyright 2004 by the American Geophysical Union.	[HTML] [PDF]

Variations of 0.7–6.0 MeV electrons at geosynchronous orbit as a function of solar wind Li X. (2004), Variations of 0.7–6.0 MeV electrons at geosynchronous orbit as a function of solar wind, Space Weather, 2, S03006, doi:10.1029/2003SW000017. 2004-03-24 Abstract: The variations of MeV electron flux at geosynchronous orbit are predictable based on solar wind measurements. Using a model based on the standard radial diffusion equation applied for the years 1995–1999, a prediction efficiency of 64.4% and a linear correlation of 0.81 were achieved for the logarithm of average daily flux of 0.7–1.8 MeV electrons. The same model with different parameters gave a prediction efficiency of 70.2% and 72.4% and a linear correlation of 0.84 and 0.85, respectively, for 1.8–3.5 MeV and 3.5–6.0 MeV electrons during the same time period. The radial diffusion coefficient in the model is a function of location, solar wind velocity, interplanetary magnetic field, season, and solar cycle. The average lifetime of the electrons is a function of the radial distance and solar cycle. The radial diffusion equation is solved with given boundary conditions. These results suggest that MeV electrons at geosynchronous orbit, extending over a wide energy range, have a systematic response to the solar wind variations. This model has been updated and is making real‐time forecasts of daily averaged >2 MeV electron fluxes at geosynchronous orbit. Copyright 2004 by the American Geophysical Union.	[HTML] [PDF]

Airplane radiation dose decrease during a strong Forbush decrease SpurnÝ F., K. Kudela, T. Dachev (2004), Airplane radiation dose decrease during a strong Forbush decrease, Space Weather, 2, S05001, doi:10.1029/2004SW000074. 2004-05-13 Abstract: An important decrease of onboard air crew exposure level was registered at the Forbush decrease observed during the period of disturbed solar conditions at the end of October 2003. The onboard dosimetry and geophysical data are presented and compared. Comparable decrease is observed for onboard measurements and geographically nearby cosmic ray neutron monitor's data. It seems that both quantitative and qualitative changes of cosmic rays fields accompany such type of events. Some previous data on similar results obtained during 2001 year both on solar cosmic ray events and Forbush decreases are also referred to and compared with new ones. Copyright 2004 by the American Geophysical Union.	[HTML] [PDF]

Prediction performance of space weather forecast centers following the extreme events of October and November 2003 Oler C. (2004), Prediction performance of space weather forecast centers following the extreme events of October and November 2003, Space Weather, 2, S08001, doi:10.1029/2004SW000076. 2004-08-05 Abstract: A review and analysis of the five strongest interplanetary coronal mass ejection (ICME) events of late October and early November 2003 (the strongest events of the “Halloween” epoch) are studied with respect to the prediction performance of five space weather forecast centers. Accurate time-of-arrival predictions and rapid responses to the upstream detection of strong ICMEs are of paramount importance to critical infrastructures such as power companies. Prediction and performance analysis results indicate that (1) the average time-of-arrival error for all forecast centers was 9.26 hours, which is consistent with the guidance errors associated with the leading shock propagation prediction models; (2) time-of-arrival predictions from Solar Terrestrial Dispatch (STD) surpassed all others in accuracy, with an average time-of-arrival prediction error of 1.22 hours; (3) overall, the strongest ICME impact events of 29 and 30 October were the most poorly predicted; (4) the most accurate shock propagation prediction model operated by the Geophysical Institute of the University of Alaska Fairbanks was the HAFv.2 model; and (5) STD provided the most rapid notification to the Northeast Power Coordinating Council concerning the detection and imminent arrival of most of the ICMEs. A better method of conveying time-of-arrival prediction information is presented that may be more easily digested by consumers of space weather services. Copyright 2004 by the American Geophysical Union.	[HTML] [PDF]

Real-time shock arrival predictions during the “Halloween 2003 epoch” Dryer M., Z. Smith, C. D. Fry, W. Sun, C. S. Deehr, S.-I. Akasofu (2004), Real-time shock arrival predictions during the “Halloween 2003 epoch”, Space Weather, 2, S09001, doi:10.1029/2004SW000087. 2004-09-01 Abstract: The “Halloween” epoch from 19 October to 20 November 2003 was marked by 19 major solar flares that were accompanied by metric type II radio bursts. Several of these flares were followed by major geomagnetic storms. The radio bursts were used in real time because they imply coronal and interplanetary transport. Most of these events were also associated with halo (or partial halo) coronal mass ejections (CMEs). A continuing, widely distributed, real-time research project called “fearless forecasts,” using an ensemble of four physics-based models, has been made of the ensuing shock arrival times since 1997 at the L1 libration point. Model inputs include consideration of the type II shock speed estimates above the flare sites as well as preliminary CME leading edge speeds in the plane of sky. Thus the model ensemble used inputs that were guided by both speed estimates. The rationale for using CME speeds includes the assumption that their high speeds represented the shocks themselves in addition to an assumption concerning their quasi-sphericity as they left the Sun. We compare the shock arrival predictions to those observed by the solar wind and magnetic field monitors on the Advanced Composition Explorer (ACE) and the solar wind monitor on the Solar and Heliospheric Observatory (SOHO) satellite. Success rates of the models are provided as a metric for this kind of active epoch. These success rates are 79% for one of the considered models using a “hit” window of ±24 hours and 74% when ±15 hours was used. This model demonstrates the importance of simulating both nonhomogeneous background environments and complex shock interactions. Copyright 2004 by the American Geophysical Union.	[HTML] [PDF]

October–November 2003's space weather and operations lessons learned Barbieri L. P., R. E. Mahmot (2004), October–November 2003's space weather and operations lessons learned, Space Weather, 2, S09002, doi:10.1029/2004SW000064. 2004-09-10 Abstract: The Sun-Earth space weather related to sunspots NOAA 484, 486, and 488 affected a number of NASA spacecraft and instruments between mid-October and early November 2003. Information available from Earth and space science missions indicate that about 59% of the spacecraft and about 18% of the instrument groups experienced some effect from the solar activity. This paper summarizes the impacts on spacecraft, instruments, and science data. The database that the paper is based on describes spacecraft and instrument effects observed as well as mission operators' preventive actions from 34 reporting missions. The database is Appendix A and provides additional material that could be of interest and that could be useful to satellite developers, operators, instrument managers, and scientists. The types of environmental effects observed were electronic upsets, housekeeping and science noise, proton degradation to solar arrays, upper atmosphere–induced changes to orbit dynamics, high levels of accumulated radiation, and proton heating. The paper develops best practices that are intended to foster continued and expanded feedback on the space environment in all mission phases, to promote designing to the mission's observing mode so that planning is appropriate to mission science goals, to distribute operational experience and lessons learned widely among both developing and operating missions, and to uniformly apply the developed knowledge base among NASA's missions. Copyright 2004 by the American Geophysical Union.	[HTML] [PDF]

Understanding midlatitude space weather: Storm impacts observed at Bear Lake Observatory on 31 March 2001 Sojka J. J., D. Rice, J. V. Eccles, F. T. Berkey, P. Kintner, W. Denig (2004), Understanding midlatitude space weather: Storm impacts observed at Bear Lake Observatory on 31 March 2001, Space Weather, 2, S10006, doi:10.1029/2004SW000086. 2004-10-26 Abstract: On 30 March 2001 in the late evening an auroral display was observed over the United States of America. The Bear Lake Observatory (BLO) magnetometer in Utah measured changes of 550 nT in less than 30 min. During the same period, BLO ionosonde measurements showed deep high-frequency radio wave absorption up to 7 MHz. BLO's GPS single-frequency receiver experienced geolocation errors of 20 m for over 3 hours. These storm signatures were also accompanied by L -band scintillation effects which approached an S4 value of 0.2, which is large for midlatitudes. Although such measurements have been have been made at midlatitude locations for many decades, our knowledge of the processes and couplings involved in such events remains incomplete and, at best, qualitative. The interpretation of key ionospheric parameters' storm response is discussed in the context of present-day auroral and geospace electrodynamics understanding. We find that at BLO (L = 2.38) the available data raise more questions and can provide almost no answers without observational inputs from other locations. One solution to this impasse is to field a ground-based sensor network to resolve the spatial scales of the geospace electrodynamics. On the basis of the instrument complement at BLO, we argue for a contiguous U.S. deployment of modest magnetic/optical/RF observatories to observe the next solar maximum period's geomagnetic storms and to use these data to explore the physical processes and couplings on space weather effective scales in assimilative models in conjunction with space-based observations. Copyright 2004 by the American Geophysical Union.	[HTML] [PDF]

An ensemble-type Kalman filter for neutral thermospheric composition during geomagnetic storms Codrescu M. V., T. J. Fuller-Rowell, C. F. Minter (2004), An ensemble-type Kalman filter for neutral thermospheric composition during geomagnetic storms, Space Weather, 2, S11003, doi:10.1029/2004SW000088. 2004-11-11 Abstract: Global circulation models (GCMs) for the thermosphere ionosphere system have been in use for more than 20 years. In the beginning the GCMs were run on supercomputers, were expensive to run, and were used mainly to provide insight into the physics of the region and to interpret measurements. Advances in computer technology have made it possible to run GCMs on desktops and to compare their results with real-time or near-real-time measurements. Today's models are capable of reproducing generic geomagnetic storm effects, but modeling specific storms is still a challenge because accurate descriptions of the energy input during storms are not easy to obtain. One way to compensate for the uncertainty in model inputs for a given period is to assimilate measurements into the model results. In this way, meteorologists have been improving their ability to model tropospheric weather for the last few decades. Data assimilation algorithms have seen an explosive growth in the last few years, and the time has come to apply such techniques to the thermospheric storm effects problem. We present results from an ensemble Kalman filter scheme that determines the best estimate of the global height-integrated O/N 2 ratio by combining GCM results and uncertainties with measurements and their errors. We describe the differences that result from the application of an ensemble Kalman filter to an externally forced system (neutral chemical composition) versus a system dominated by the initial condition and internal dynamics (tropospheric weather and ocean models). The results demonstrate that an ensemble of 10 members is able to characterize the state covariance matrix with sufficient fidelity to enable the Kalman filter to operate in a stable mode. Some information about the external forcing was extracted from the estimate of the state. The general trend of the forcing was followed by the filter, but departures were present over some periods. Copyright 2004 by the American Geophysical Union.	[HTML] [PDF]