Preparing for the Living With a Star Ionosphere-Thermosphere Storm Probe II Mission II
Presiding: J M Grebowsky, NASA Goddard Space Flight Center; J ( Yee, Applied Physics Laboratory, Johns Hopkins University
SA14A-01 15:30h
Direct and Indirect Thermospheric Heating Sources
Solar variability is often cast in terms of radiative emission and the associated long-term climate response; however, growing societal reliance on technology is creating more interest in day-to-day solar variability. This variability is associated with both solar radiative and solar wind emissions. In this paper we explore the combined effects of radiative and solar wind fluctuations at Earth. The fluctuations in radiative and geomagnetic power create an extended interval of solar maximum for the upper atmosphere. We use a trio of empirical models to estimate, over the last three solar cycles, the relative contributions of solar extreme ultraviolet (UV) power, Joule power, and particle kinetic power to the Earth's upper atmosphere energy budget. Daily power values are derived from three source models. The SOLAR2000 solar irradiance specification model provides estimates of the daily extreme and far UV solar power input. Geomagnetic power is derived from a combination of satellite-estimated particle precipitation power and an empirical model of Joule power from hemispherically-integrated estimates of high-latitude energy deposition. During the interval 1975 to 2004, the average daily contributions were: particles--36 GW, Joule--95 GW and solar--464 GW for a total of 595 GW. Solar wind-driven geomagnetic power provided 22% of the total global upper atmospheric energy. In the top 15 power events, geomagnetic power contributed two-thirds of the total power budget. In each of these events, Joule power alone exceeded solar power. With rising activity, Joule power becomes the most variable element of solar-upper- atmosphere interactions. This variability has significant implications for satellite drag, pointing accuracy and collision avoidance.
SA14A-02 15:45h
Solar EUV and Geomagnetic Storm Control Of The Ionosphere-Thermosphere System
Recent studies using ionospheric total electron (TEC) content data from ground and space-borne GPS receivers suggest a prompt daytime TEC increase at low and middle latitudes during the early main phase of intense geomagnetic storms. GPS and other data, such as DMSP electric fields and ground-based magnetometers, suggest the presence of zonal electric fields near the magnetic equator contributing to vertical plasma uplift and dramatic changes in low and mid-latitude ionospheric structure. Recent analysis of several events over the past few years suggests this early positive daytime ionospheric response is a common feature, but the degree of response and its relation to interplanetary parameters is not well characterized. We will present GPS data from these same intense events, focusing on the first three hours after interplanetary coronal mass ejections (ICMEs) reach the magnetosphere, as determined from ACE data. Using the broad local time coverage of the global network of GPS ground receivers, and the continuous latitude sampling of space-borne GPS receivers, we will elucidate the relationship between the low and mid-latitude TEC response and parameters describing the ICME interplanetary parameters, such as the z-component of the interplanetary magnetic field (Bz). Thermospheric feedback mechanisms, for example changes to winds and neutral composition on the dayside, will be considered in the analysis.
SA14A-03 16:00h
Global Thermosphere-Ionosphere Response To Storms
The period of post-solar maximum geomagnetic storms in October and November 2003 were some of the largest storms ever recorded. The thermospheric and ionospheric responses have been simulated using the NCAR TIMEGCM. The model shows large areas of O/N2 depletion spreading from high latitudes, and corresponding reductions in the ionospheric electron density. The model is used as a framework to interpret some of the compositional effects observed by the GUVI instrument on the TIMED satellite, and corresponding ionospheric total electron content. We explore how the I-T system responds to the development and subsidence of geomagnetic storms, and we describe some of the important physical processes that will affect planning for the utilization of measurements from the Geospace investigations in NASA's Living With a Star Program. The study also illustrates the value of measuring both the neutral and ionized gases, of obtaining quasi-global views from imaging instruments, and the synergy between satellite data, ground-based measurements, and models.
SA14A-04 16:15h
Large decreases in ionospheric total electron content as a result of thermospheric composition changes during geomagnetic storms.
The geomagnetic storms of April 17-21, 2002 and May 29-30, 2003 caused large decreases in the O/N2 column density ratio in the thermosphere. For these storms, O/N2 column density decreases of > 50% were observed to extend to mid-to-low latitudes with the FUV sensitive Earth Camera of the Visible Imaging System (VIS) on the Polar spacecraft. Simultaneously in these same regions, the ground-based GPS network observed ~80% reductions in the Total Electron Content (TEC) of the ionosphere. The reduction in the O/N2 column density ratio is due mainly to increases in the molecular species that have welled-up into the thermosphere from the lower levels of the atmosphere due to auroral heating. The geomagnetic-storm driven increase in molecular densities at typical ionospheric heights rapidly charge exchange with the ambient ionized atoms and subsequently dissociatively recombine with the ionospheric electrons leading to a reduction in the total charge density. The transition boundaries between high and low regions of O/N2 as well as TEC can be tracked in the images and the thermospheric winds can be determined from the motion of the boundaries. The motion of these boundaries during the development of the geomagnetic storm will be discussed.
SA14A-05 16:30h
Challenges to Understanding the Storm-Time Electrodynamics of the Ionosphere at low and Middle Latitudes.
In this report we describe the horizontal and vertical motions observed by the DMSP satellites for different storm periods. Short and long lived vertical drifts at the equator have lifetimes that are dependent on local time and the persistence of zonal ion drifts across the equatorial region is a function of local time, storm time, and longitude. The effects of potentials applied at high latitudes via the magnetosphere, and of wind dynamo electric fields modified by high latitude auroral processes must be considered in describing the behavior of these ion drifts. The expansion of the auroral zone complicates the interpretation of ion drifts that appear at what is usually a midlatitude location equatorward of the auroral zone. In addition to illustrating the common features of the ionospheric electrodynamics we also indicate unique features that may be dependent on the initial state of the ionosphere at the time of the storm onset. The measurements required to resolve questions about the sources for the electrodynamic signatures will be discussed in the light of the expected capabilities of the LWS IT storm probes mission
SA14A-06 16:45h
Longitudinal Variability of Plasma Structuring in the Equatorial and Middle Latitudes During Magnetically Quiet and Disturbed Times - A Global M-I-T Coupling Issue
The synoptic global views of the equatorial anomaly provided by the GUVI instrument on TIMED has shed new light on the longitudinal variability of equatorial plasma structure first studied with the OGO - 6 satellite almost 30 years ago (Basu et al., Radio Sci., 1976). The eastward electric field at the magnetic equator during the post-sunset hours drives the equatorial ionosphere unstable, generates plasma bubbles and causes scintillations. This eastward electric field also causes a resurgence of the equatorial ionization anomaly providing a large scale ionization distribution as a function of latitude. The GUVI images of 135.6 nm emissions are able to image the variability of the anomaly peaks as a function of longitude while chains of GPS ground stations have provided information regarding the variability of both the total electron content and scintillations. A marked longitudinal variability of the anomaly peaks even on magnetically quiet days probably indicates the influence of other poorly known "drivers", such as complex neutral dynamics. The relationship between the large scale plasma density gradients, small-scale structuring and the requirement for a seeding mechanism for plasma instabilities is far from resolved. During magnetic storms, penetration of electric fields of magnetospheric origin provides another degree of complexity, facilitating the growth of instabilities in certain longitude sectors and inhibiting them in others, depending on the interplay of storm time and local time effects. In addition, during severe magnetic storms plumes of greatly enhanced density and associated small-scale irregularities are seen at middle latitudes, primarily over the continental US (Basu et al., GRL, 2005). Such plasma structuring, seen at middle and equatorial latitudes under high solar flux conditions, cause severe disruption of satellite communication and GPS navigation systems. A comprehensive I/T Storm Probe Mission, augmented by sensors to define magnetospheric inputs, is necessary for an understanding of these phenomena so that predictive space weather models can be developed to minimize societal impacts.