Overview of TIMED Extended Mission
The extended TIMED mission along with other NASA HSO and Earth Sciences satellites, NOAA satellites, and foreign assets will shed light on atmospheric coupling processes that underlie solar-terrestrial relationships, atmospheric coupling, natural variability, and ultimately anthropogenic changes to the atmosphere. To accomplish this we must understand the long-term natural variability due to solar cycle effects and stratospheric and tropospheric variability. Variability not explained by these natural processes can then be examined in the context of anthropogenic changes.
The TIMED mission provides a comprehensive view of the flow of energy, originating at the Sun, through Earth's upper and lower atmospheres. This energy takes many forms, including tides, planetary waves, and gravity waves forced by direct and indirect solar-driven processes in the lower atmosphere; Joule and particle heating in the high-latitude ionosphere and thermosphere; solar X-ray, EUV, and UV radiation absorption; global winds, electric fields, and plasma transport; photochemical reactions; and ultimately, radiation of energy to space. Manifestation of these processes in the upper atmosphere and their interrelationships and relative importance are determined by (1) the structure and variability of the solar corona and solar wind and direct coupling with the magnetosphere and plasmasphere, and (2) the structure and variability of the lower atmosphere. The family of HSO spacecraft provides the opportunity to understand the relation between the Sun and the geospace environment as an integrated, coupled system that is continually evolving and subject to nonlinear effects and feedbacks. For example, the response of the MLTI system to solar wind disturbances depends not only on the traditional metric of whether Bz is positive or negative but also on By and the magnitude and timing of solar wind dynamic pressure changes. These parameters determine the nature of particle precipitation into the ionosphere and related heating and conductivity changes, as well as the penetration of electric fields and currents of magnetospheric origin that determine Joule heating rates. In addition, the production of NO, which regulates the thermosphere neutral atmosphere response via radiative cooling, also depends on particle precipitation characteristics and solar X-Ray/EUV fluxes. Variability of the IMF and solar wind speed and density are of course dependent upon the nature and evolution of CMEs as they propagate from Sun to Earth and on the phase of the solar cycle.
The MLTI system is also strongly coupled to the troposphere and stratosphere from below as evidenced, for example, by the response of the mesosphere [Siskind et al., 2005] and ionosphere [Goncharenko and Zhang, 2008]. Emerging "whole atmosphere" models suggest that the MLTI system is coupled to the troposphere, with the influence of El-Niño/Southern Oscillation (ENSO) and QBO effects manifested in recent results [Sassi et al., 2004]. In addition, the release of greenhouse gases in the troposphere due to human activity is predicted to have a dramatic effect on the thermal structure and composition of the MLTI system by direct alteration of its infrared energy balance [Roble and Dickinson, 1989]. The potential for substantial human-induced changes to the MLTI system and the resulting consequences for space operations and MLTI climate remain a frontier of scientific inquiry.
The future will see a new era in our ability to characterize the state of the Sun-Earth system using the HSO, new electronic data handling and data mining technologies, high-performance sun-to-Earth models, new techniques for assimilation of sparse data, and the development of innovative worldwide research tools through integration of ground-based observing sites. The time has come to pull these developing capabilities together into an investigation that seeks to understand aeronomy at a higher level than has previously been possible. TIMED in its extended mission phase will leverage new capabilities in the HSO to focus on global MLTI system behavior and, in addition, it will investigate the large-scale systems-level features that result from elemental processes, like ion-neutral coupling, plasma drifts, and non-LTE radiative cooling.
The TIMED mission is making important contributions in identifying and characterizing the processes that change, evolve, and combine to form the system response. The study of "Systems Aeronomy" must have observational, theoretical, and computational components to succeed. One of the key requirements is the ability to capture global data sets and integrate them into a coherent picture of the MLTI system and its relationship to geospace.
Success requires enhanced coordination between operating satellites throughout the Sun-Earth system, new techniques for creating global maps from networks of ground-based and satellite-based sensors, and a new level of international cooperation leveraging off ILWS, CAWSES, ICESTAR, and other planned worldwide programs and ongoing Earth Science missions.