Exploring the Global Response of the Sun-Heliosphere-Magnetosphere-Ionosphere-Atmosphere System II
Presiding: C C Goodrich, Center for Integrated Space Weather Modeling, Boston University; C E DeForest, Southwest Research Institute
SA12A-01 INVITED 10:30h
Dynamics of Magnetosphere-Ionosphere Coupling at Low Latitudes: How Well do we Understand it?
Based on theoretical considerations and an array of numerical simulations, we review the physics of the electrodynamic link via field-aligned region-2 currents between the inner magnetosphere and the ionosphere of Earth. In the canonical picture, high-latitude convection is a source electric field for the ionosphere. Region-2 field-aligned currents related to plasma pressure gradients in the near-Earth plasma sheet and ring current create an electric field that opposes and partially cancels the convection electric field at latitudes equatorward of the diffuse aurora. Region-2 currents can be thought of as a time-dependent gate that allows a fraction of the convection electric field to penetrate to the subauroral and low-latitude ionosphere. The characteristic lifetimes of this penetration are determined by the time history of the source electric field, the bulk properties of the plasma sheet and plasma distribution, the magnetic field configuration, and by the distribution of auroral/subauroral conductivites. The fraction of the penetrating electric potential drop is controlled by these and by the strength of the source. Ionospheric electric fields at latitudes away from the auroral oval are dependent, in a self-consistent manner, on ionospheric plasma density distributions. The specific focus of this paper is on how the density and temperature of the plasma sheet and the magnetospheric magnetic field configuration control the shielding capability of region-2 currents. We conclude by discussing how this relatively simple picture is affected by uncertainty about how plasma is transported in the plasma sheet, particularly when the solar-wind driver is changing in time.
SA12A-02 INVITED 10:50h
Does the Mid-Latitude Ionosphere Exist During Superstorms?
The mid-latitude ionosphere naively lies in a latitude belt between the high latitude and equatorial ionosphere. These three regions are distinguished by their F-region electrodynamic convection processes. The equatorial latitudes are dominated by the "eastward" electric fields that causes the Appleton equatorial anomalies. At mid-latitude the plasma corotates with the ground-based observer. The high latitudes are dominated by variants of the "two-cell" convection pattern with auroral weather superimposed. Present day modeling of the Earths ionosphere-thermosphere almost rigidly follows these guidelines. A host of observable boundaries exist to demark the regions: the mid-latitude trough, the equatorward edge of the auroral boundary, the plasmapause, the poleward shoulder of the equatorial anomaly, region II current in the afternoon-evening sector, etc. The first clue that all is not well understood during a superstorm is that these boundaries move deep into the mid-latitudes. Auroral displays are seen in the southern states of the USA, magnetometers even further equatorward register auroral electrojets, the F-layer moves up in altitude, a sure sign of a non-corotational electric field, the equatorial anomalies move poleward, and persistent highly coherent structures form in the F-region plasma on the dayside. All lead to the conclusion that our understanding and, hence, modeling of mid-latitude processes are lacking. Concepts such as the mid-latitudes that are shielded from high latitude electric fields by the ring currents became less than satisfactory when the ring currents themselves are located at the equatorward edge of the quiet time mid-latitude domain! The idea that mid-latitude storm effects via the thermosphere are propagated from high latitudes to mid-latitudes becomes less than useful when the "high latitudes" energy disposition is occurring at low latitudes within the mid-latitudes! Most physics based models of the ionosphere require empirical representations of the drivers, i.e., the electric fields, the auroral precipitation, the low latitude electric field and some even need the thermosphere and neutral winds. These empirical representations almost never contain representations for superstorm conditions! Hence, how are superstorms to be introduced into these models? The cutting edge modeling uses data assimilation techniques to get around this issue, but what can reasonably be expected from this technique during a superstorm? Recent observations and simulations during superstorms will be discussed to address these questions in the context of does the mid-latitude ionosphere exist during superstorms?
SA12A-03 11:10h
Relative Importance of Storm-Time Mechanisms in the Observed TEC Response to the March 31, 2001 Geomagnetic Storm
The interpretation of the global state of TEC storm effects requires knowledge of electric fields, neutral winds, temperature and composition changes. Observational data, such as GPS TEC measurements, combined with a data assimilation model are ideal to reveal ionospheric structures. However, identifying, understanding and quantifying each mechanism's role in TEC variations during magnetically disturbed periods are quite difficult when only observational measurements are used. In order to understand all these physical processes, the global, three-dimensional, time-dependent, non-linear coupled model of the thermosphere, ionosphere, plasmasphere and electrodynamics (CTIPe) can be used to investigate and understand the dynamic and electrodynamic response of the global ionosphere during magnetic storms. CTIPe is a self-consistent model and solves the momentum, energy, and composition equations for the neutral and ionized atmosphere. It requires a few external drives, such as solar UV and EUV, Weimer electric field, TIROS/NOAA auroral precipitation, tidal forcing from the lower atmosphere, and penetration electric fields from the Rice Convection Model (RCM). Model results are compared to observational data to identify the relative importance of each mechanism in the ionosphere response to the March 31, 2001 geomagnetic storm.
SA12A-04 INVITED 11:25h
Recent impacts of energetic particle precipitation on the Earth's middle atmosphere
The extraordinary solar storms of October-November 2003 have now received much attention in the literature, and it is well-known that the associated energetic particles caused immediate production of HOx and NOx in the upper stratosphere and mesosphere that led to significant ozone depletion. Less obvious is whether unprecedented enhancements in stratospheric NOx and concurrent reductions in ozone several months following the storms were a direct result of the storms themselves, or of energetic particle precipitation later in the winter. Complicating the picture is the fact that the late winter upper stratospheric polar vortex in 2004 was stronger than previously observed since records began (1979). Insight to this dilemma can be gained by comparison of atmospheric effects after other periods of high geomagnetic activity, and in both hemispheres. Using satellite data and modeling, this presentation will compare and contrast the response of the middle atmosphere after several different periods of high geomagnetic activity in recent years. Emphasis will be placed on understanding the effects after the late 2003 storms in the context of storms that occurred at similar times of year relative to the northern and southern hemispheres; this will include, for instance, the solar proton events of October 1989 and November 2000 and 2001, and the solar storms of April 2002.
SA12A-05 11:45h
Tracing solar energy through the upper atmosphere: SNOE and TIMED observations of nitric oxide
As solar particle and photon energy is deposited into the upper atmosphere, the immediate ionization, dissociation, and excitation of atoms and molecules leads to important modifications of the composition and temperature there. A key product of these energetic processes is nitric oxide. Though always a minor species, NO plays a strong role in the thermospheric energy balance because unlike the major species O, O2, and N2, it emits efficiently in the infrared. Radiance from NO is then a key process by which the atmosphere cools in response to solar energy deposition. The presence of NO has other important impacts on the chemistry and ion composition in the atmosphere. Recent observations of NO have revealed dramatic global increases of NO in response to solar energetic particle precipitation and soft X-ray irradiance. The morphology of these responses has been particularly interesting in that winter hemisphere NO appears to be primarily controlled by high latitude energetic particle precipitation, while energetic particles appear to have little or no impact in the summer hemisphere. Thus the nature of the coupling between the Sun and Earth's upper atmosphere is highly variable in time and space. This complex coupling is well demonstrated by observations of the response to large solar eruptive events such as occurred in April of 2002 and October of 2003. In this talk we will focus on these and other large events to show the morphology of NO in response to solar storms and to elucidate the processes governing that response. Observations of NO abundance from the Student Nitric Oxide Explorer (SNOE) and of NO radiance from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics missions will be utilized.