Aaron J. Ridley

Space Weather Modeling Framework: A new tool for the space science community

[1] The Space Weather Modeling Framework (SWMF) provides a high-performance flexible framework for physics-based space weather simulations, as well as for various space physics applications. The SWMF integrates numerical models of the Solar Corona, Eruptive Event Generator, Inner Heliosphere, Solar Energetic Particles, Global Magnetosphere, Inner Magnetosphere, Radiation Belt, Ionosphere Electrodynamics, and Upper Atmosphere into a high-performance coupled model. The components can be represented with alternative physics models, and any physically meaningful subset of the components can be used. The components are coupled to the control module via standardized interfaces, and an efficient parallel coupling toolkit is used for the pairwise coupling of the components. The execution and parallel layout of the components is controlled by the SWMF. Both sequential and concurrent execution models are supported. The SWMF enables simulations that were not possible with the individual physics models. Using reasonably high spatial and temporal resolutions in all of the coupled components, the SWMF runs significantly faster than real time on massively parallel supercomputers. This paper presents the design and implementation of the SWMF and some demonstrative tests. Future papers will describe validation (comparison of model results with measurements) and applications to challenging space weather events. The SWMF is publicly available to the scientific community for doing geophysical research. We also intend to expand the SWMF in collaboration with other model developers.

Mars Global Ionosphere‐Thermosphere Model: Solar cycle, seasonal, and diurnal variations of the Mars upper atmosphere

A new Mars Global Ionosphere-Thermosphere Model (M-GITM) is presented that combines the terrestrial GITM framework with Mars fundamental physical parameters, ion-neutral chemistry, and key radiative processes in order to capture the basic observed features of the thermal, compositional, and dynamical structure of the Mars atmosphere from the ground to the exosphere (0–250 km). Lower, middle, and upper atmosphere processes are included, based in part upon formulations used in previous lower and upper atmosphere Mars GCMs. This enables the M-GITM code to be run for various seasonal, solar cycle, and dust conditions. M-GITM validation studies have focused upon simulations for a range of solar and seasonal conditions. Key upper atmosphere measurements are selected for comparison to corresponding M-GITM neutral temperatures and neutral-ion densities. In addition, simulated lower atmosphere temperatures are compared with observations in order to provide a first-order confirmation of a realistic lower atmosphere. M-GITM captures solar cycle and seasonal trends in the upper atmosphere that are consistent with observations, yielding significant periodic changes in the temperature structure, the species density distributions, and the large-scale global wind system. For instance, mid afternoon temperatures near ∼200 km are predicted to vary from ∼210 to 350 K (equinox) and ∼190 to 390 k (aphelion to perihelion) over the solar cycle. These simulations will serve as a benchmark against which to compare episodic variations (e.g., due to solar flares and dust storms) in future M-GITM studies. Additionally, M-GITM will be used to support MAVEN mission activities (2014–2016).

Computational analysis of the near-Earth magnetospheric current system during two-phase decay storms

Several two-phase decay magnetic storms are examined using a kinetic transport model to find the spatial and temporal distribution of the perpendicular and field-aligned currents in the inner magnetosphere. The global morphology of these currents in the calculational domain (inside of geosynchronous orbit) is discussed as a function of storm epoch, obtaining good comparison between the numerically derived features and observed values of stormtime currents in this region. The model results are also consistent with quiet time plasma observations showing an increasing pressure in to L = 3 or 4, including a pressure maximum near midnight for the generation of region 2 Birkeland currents in the proper direction. A detailed analysis of the characteristic features of these currents is also presented and discussed. It is found that most of the ring current (>90%) during the main phase and early recovery phase is partial rather than symmetric, closing mostly (up to 90%) through field-aligned currents into the ionosphere. Conversely, the quiet time ring current is largely (>60%) symmetric, with most of the asymmetry produced by minor injections of near-Earth plasma sheet material. In general, the peak asymmetric current (which occurs during the main phase) is 2-3 times larger than the peak symmetric current (which occurs during the recovery phase) for any particular two-phase decay event. This is the case for all of the events studied, regardless of storm size, solar wind parameters, or solar cycle. The maximum azimuthal current (integrated over a local time slice) reaches 5 to 20 MA, compared with <2 MA of symmetric current at quiet times.

What is the ensemble Kalman filter and how well does it work

In this paper we described the ensemble Kalman filter algorithm. This approach to nonlinear Kalman filtering is a Monte Carlo procedure, which has been widely used in weather forecasting applications. Our goal was to apply the ensemble Kalman filter to representative examples to quantify the tradeoff between estimation accuracy and ensemble size. For all of the linear and nonlinear examples that we considered, the ensemble Kalman filter worked successfully once a threshold ensemble size was reached. In future work we will investigate the factors that determine this threshold value

Estimations of the uncertainty in timing the relationship between magnetospheric and solar wind processes

Abstract We present here a statistical study quantifying the errors associated with the most commonly used methods for propagating discontinuities in the interplanetary magnetic field (IMF) from an upstream monitor to the magnetosphere by the magnetospheric and ionospheric communities. The purpose of this paper is to show the quantified errors in the different techniques. Step changes in the IMF orientation were first identified at the WIND satellite. A total of 363 events were identified. Ninety percent of the events measured at WIND (330) were clearly observed in the IMP 8 data. Of those events, the time delay between the satellites could be determined to within 2 min in 288 events. Four propagation methods were used to estimate the time delay between WIND and IMP 8: (1) using only the X distance between the satellites; (2) assuming that the propagation front plane is in the plane of the Parker spiral; (3) using the IMF in the X–Y plane to estimate the propagation front plane; and (4) using the total IMF to determine the Z component of the propagation front plane. The average (Ē) and maximum (Emax) propagation error (in minutes) as a function of Y–Z distance (in Re) were determined for each method. It is concluded that the average uncertainty in propagation is 7.5–8.5 min for off-axis distances of 30 Re (which is the average WIND off-axis distance, and approximately the largest off-axis distance of IMP 8). For off-axis distances of 100 Re (the largest off-axis distance of WIND), the uncertainties are 17.5–25 min, depending on the propagation method.

Global MHD simulations of Saturn's magnetosphere at the time of Cassini approach

We present the results of a 3D global magnetohydrodynamic simulation of the magnetosphere of Saturn for the period of Cassinis initial approach and entry into the magnetosphere. We compare calculated bow shock and magnetopause locations with the Cassini measurements. In order to match the measured locations we use a substantial mass source due to the icy satellites (∼1 x 10 28 s -1 of water product ions). We find that the location of bow shock and magnetopause crossings are consistent with previous spacecraft measurements, although Cassini encountered the surfaces further from Saturn than the previously determined average location. In addition, we find that the shape of the model bow shock and magnetopause have smaller flaring angles than previous models and are asymmetric dawn-to-dusk. Finally, we find that tilt of Saturns dipole and rotation axes results in asymmetries in the bow shock and magnetopause and in the magnetotail being hinged near Titans orbit (∼20 R S ).

Using steady state MHD results to predict the global state of the magnetosphere-ionosphere system

Using magnetospheric MHD codes for space weather prediction has many advantages over other techniques including the specification of the entire magnetospheric state instead of some subsection, such as the ionospheric electric potential pattern. Time-dependent MHD simulations are computationally expensive and therefore nonfeasible to continuously run in real time. This study focuses on determining whether a quasi steady state magnetospheric configuration, determined by an MHD code, can be used as a prediction for the true state of the magnetosphere during relatively steady interplanetary magnetic field (IMF) intervals. To determine the feasibility of this, the University of Michigan MHD code was run to a nearly steady solution using the average IMF By and Bx and solar wind conditions observed on March 19–20, 1999. The IMF Bz was set to nearly the minimum observed during this period. Ground-based magnetograms were simulated using the model output, which were then compared with the actual magnetograms for the given stations, using the root-mean-square (RMS) difference to determine the error. The RMS differences were compared to the RMS variation of the data. Different ionospheric conductance models were used to investigate possible sources of error. The model results within the polar cap and at lower latitudes showed that the model was reproducing the global structure of the region 1 currents accurately. It is further noted that the RMS differences leave room for significant improvement in the specification.

Assessment of the non-hydrostatic effect on the upper atmosphere using a general circulation model (GCM)

[1] Under hydrostatic equilibrium, a typical assumption used in global thermosphere ionosphere models, the pressure gradient in the vertical direction is exactly balanced by the gravity force. Using the non-hydrostatic Global Ionosphere Thermosphere Model (GITM), which solves the complete vertical momentum equation, the primary characteristics of non-hydrostatic effects on the upper atmosphere are investigated. Our results show that after a sudden intense enhancement of high-latitude Joule heating, the vertical pressure gradient force can locally be 25% larger than the gravity force, resulting in a significant disturbance away from hydrostatic equilibrium. This disturbance is transported from the lower altitude source region to high altitudes through an acoustic wave, which has beensimulated inaglobal circulation model forthefirst time. Due to the conservation of perturbation energy, the magnitude of the vertical wind perturbation increases with altitude andreaches 150(250) m/sat300(430) kmduringthe disturbance. The upward neutral wind lifts the atmosphere and raises the neutral density at high altitudes by more than 100%. These large vertical winds are not typically reproduced by hydrostatic models of the thermosphere and ionosphere. Our results give an explanation of the cause of such strong vertical winds reported in many observations. Citation: Deng, Y., A. D. Richmond, A. J. Ridley, and H.-L. Liu (2008), Assessment of the non-hydrostatic effect on the upper atmosphere using a general circulation model (GCM), Geophys. Res. Lett., 35, L01104, doi:10.1029/2007GL032182.

A large-scale traveling ionospheric disturbance during the magnetic storm of 15 September 1999

enhancement of GPS total electron content (� 1.0 � 10 16 m � 2 ). Multipoint and imaging observations of these parameters show that the LSTID moved equatorward over Japan with a velocity of � 400–450 m/s. From a comparison with the Sheffield University Plasmasphere-Ionosphere Model (SUPIM) we conclude that an enhancement (250–300 m/s) of poleward neutral wind (that is propagating equatorward) caused these observational features of the LSTID at midlatitudes. To investigate generation of the LSTID by auroral energy input, we have used auroral images obtained by the Polar UVI instrument, magnetic field variations obtained at multipoint ground stations, and the empirical Joule heating rate calculated by the assimilative mapping of ionospheric electrodynamics (AMIE) technique. Intense auroral energy input was observed at 0800–1100 UT (4–6 hours before the LSTID), probably causing equatorward neutral wind at lower latitudes. It is likely that the poleward wind pulse that caused the observed LSTID was generated associated with the cessation of this equatorward wind. The effect of Lorentz force is also discussed. INDEX TERMS: 0310 Atmospheric Composition and Structure: Airglow and aurora; 2427 Ionosphere: Ionosphere/atmosphere interactions (0335); 2435 Ionosphere: Ionospheric disturbances; 2437 Ionosphere: Ionospheric dynamics; 2788 Magnetospheric Physics: Storms and substorms; KEYWORDS: large-scale traveling ionospheric disturbance, thermosphere–ionosphere coupling, magnetic storm, airglow imaging, GPS network, ionosonde

Understanding storm‐time ring current development through data‐model comparisons of a moderate storm

[1] With three components, global magnetosphere (GM), inner magnetosphere (IM), and ionospheric electrodynamics (IE), in the Space Weather Modeling Framework (SWMF), the moderate storm on 19 May 2002 is globally simulated over a 24-hour period that includes the sudden storm commencement (SSC), initial phase, and main phase of the storm. Simulation results are validated by comparison with in situ observations from Geotail, GOES 8, GOES 10, Polar, LANL MPA, and the Sym-H and Dst indices. It is shown that the SWMF is reaching a sophistication level for allowing quantitative comparison with the observations. Major storm characteristics at the SSC, in the initial phase, and in the main phase are successfully reproduced. The simulated plasma parameters exhibit obvious dawn-dusk asymmetries or symmetries in the ring current region: higher density near the dawn and higher temperature in the afternoon and premidnight sectors; the pressure is highest on the nightside and exhibits a near dawn-dusk symmetry. In addition, it is found in this global modeling that the upstream solar wind/ IMF conditions control the storm activity and an important plasma source of the ring current is in the solar wind. However, the ionospheric outflow can also affect the ring current development, especially in the main phase. Activity in the high-latitude ionosphere is also produced reasonably well. However, the modeled cross polar cap potential drop (CPCP) in the Southern Hemisphere is almost always significantly larger than that in the Northern Hemisphere during the May storm.