SA34A-01 INVITED
The Big Picture: Synoptic Views of Auroral Particle Precipitation
Global images and composite views of auroral energy deposition into the ionosphere come from UV imagers (such as on Polar) and from low-altitude polar orbiting satellites, such as the DMSP series. The advantages and disadvantages of each technique are briefly reviewed. Then a series of contrasts in the behavior of particle precipitation are drawn. These are (1) Ion versus electron precipitation; (2) Diffuse auroral precipitation versus discrete auroral precipitation; (3) Dayside versus nightside precipitation; (4) Sunlit versus darkness; and (5) Geomagnetically active times versus quiet times. For example, ion precipitation is supplies approximately 20 percent of the precipitating energy to the ionosphere, declining during times of increasing geomagnetic activity. The relative importance of diffuse versus discrete aurora is still not adequately investigated, but (despite occasional guesses to the contrary) the two appear to be roughly comparable in precipitating energy input to the atmosphere.
SA34A-02
Global inventory of precipitating populations during the 15-30 January 2005 long-duration flares and magnetic storms: Relative efficacy at ozone destruction
Because of long nitric oxide lifetimes and the importance of transport in understanding local observations, production (and thus particle precipitation) must be known on a global scale. Observations of particle precipitation are being or have been collected from space-based imagers and in-situ particle detectors (i.e., on IMAGE, TIMED, DMSP, NOAA POES, FAST) and by recently expanded and enhanced ground-based sensor networks in celebration of the International Polar Year (i.e., AARDDVARK, GLORIA, etc.). These resources and upcoming new missions allow a robust, and flexible assessment of global precipitation from auroral to radiation belt energies, from the polar to the equatorial regions by developing assimilation techniques, which do not depend on any one data source. To explore the requirements and the potential of this type of assimilative effort in advancing our understanding of system behavior and coupling between the upper and middle atmospheric regions, this presentation draws together observations of precipitating populations from a variety of data sources during the 15-30 Jan 2005 long duration flare events and magnetic activity including several solar particle events, auroral, radiation belt, ring current and mid-low latitude ion-atom precipitation as well as high energy intense polar rain. A preliminary evaluation of the relative potential of each population for disrupting stratospheric ozone will be undertaken.
SA34A-03 INVITED
Modeling the Chemical and Dynamical Response of the Whole Atmosphere to Energetic Particle Precipitation
Investigations into the role of the middle and upper atmosphere on climate have led to development of coupled chemistry climate models that extend in altitude to the mesosphere and lower thermosphere. These models are now being used to investigate the importance of variable solar and geomagnetic forcing on composition and dynamics throughout the whole atmosphere.This study reviews investigations into the influence of energetic particle precipitation (EPP) on stratospheric composition and dynamics, and presents analysis of simulations using NCAR's Whole Atmosphere Community Climate Model (WACCM). We find ionization from EPP in the polar regions during the declining phase of solar cycle 23 lead to significant increases in the concentration of hydrogen and nitrogen species. This period was remarkable in that it included a series of large solar proton events (SPEs). Analysis of an ensemble of WACCM simulations indicates that SPEs affect ozone chemistry either directly via increased catalytic loss from the enhanced hydrogen and nitrogen species, or indirectly from perturbations to active chlorine and bromine partitioning. In the stratosphere, ozone and temperatures changes can persist for months following an SPE and are not restricted to the region where SPE ionization occurred.
SA34A-04
Impact of Solar Energy Protons and Magnetospheric Energetic Particles on the Upper Atmosphere
In addition to solar irradiance, solar and magnetospheric energetic particles are important sources of ionization of nuetral gases in the upper atmosphere. Energetic particles have a significant impact on thermospheric chemistry, energetics, and dynamics, as well as ionospheric electrodynamics. However, due to the difference in their characteristic energies, there are some distinctive differences among solar energetic protons, the ring current energetic protons and electrons, and auroral precipitating electrons in terms of their relative effects on the ionosphere and thermosphere. This paper will demonstrate the atmospehric effects associated with the various sources of energetic particles based on numeric simulations from the NCAR general circulation models, with an emphesis on the intercomparison amongst the different source particles.
SA34A-05 INVITED
Energetic Particle Precipitation Effects on the Polar Winter Stratosphere as Observed by MIPAS/Envisat
Energetic particle precipitation (EPP) in the polar atmosphere has important implications on stratospheric ozone chemistry. Solar protons or highly energetic electrons generated during solar storms cause sporadicly in situ production of stratospheric NOx and HOx radicals involved in catalytic ozone destruction. Further, NO produced continuously in the mesosphere and lower thermosphere by medium energy electron precipitation descends to the stratosphere during the polar winter, where it represents an additional, though variable source of NOx. The capability of MIPAS to measure all important NOy species, as well as ClO and HOCl with global coverage including the polar night regions make this instrument an ideal candidate to study EPP effects on stratospheric chemistry. We present a quantitative assessment of EPP-induced stratospheric composition changes as observed by MIPAS during 2002-2004, including the unusually strong solar proton event in October/November 2003. Enhanced levels of NOx in the upper stratosphere and lower mesosphere have been found for several winters within polar vortices. NOx was subsequently transformed to other NOy species, leading, for example, to a secondary upper stratospheric HNO3 maximum. The impact of upper stratospheric enhanced NOx levels, the mechanisms of their transformation to other NOy species, and their effect on the stratospheric ozone budget has been studied with chemical models. The stratospheric ozone loss in the polar regions reached 20 DU and lasted over months to years.
SA34A-06
Solar Induced Variations of Odd Nitrogen and Ozone in the Stratosphere and Lower Mesosphere: Analysis of UARS HALOE Data
Several sensitivity studies using 3D chemistry climate models have suggested that solar-induced changes in odd nitrogen are important for solar cycle ozone variations. This is possible since odd nitrogen is the leading source of ozone catalytic losses at most altitudes in the stratosphere. Here, we investigate solar-induced variations of odd nitrogen and associated ozone variations using UARS HALOE data over the 1991-2003 period. Specifically, a multiple regression statistical model is applied to 3-month averages of these data at and above 10 hPa where measurements of odd nitrogen are sufficiently numerous. As a measure of solar forcing, we consider separately both the MgII solar UV index and the auroral Ap index. The former is a measure of solar UV forcing of ozone and also correlates well with the occurrence frequency of major solar proton events. The latter is a good proxy for magnetospheric energetic electron precipitation that influences the production rate of odd nitrogen in the thermosphere and mesosphere. Consistent with earlier studies, evidence is obtained for a decadal odd nitrogen variation at the highest available latitudes (50-70 degrees) that projects positively onto the solar cycle. At these latitudes, annual averages of HALOE odd nitrogen correlate best with the Ap index and solar wind plasma speed indicating a dominant source in the form of energetic electron precipitation followed by downward transport during the polar night. At the same high latitudes in the upper stratosphere (1 hPa), interannual variations of odd nitrogen correlate negatively with simultaneous HALOE ozone measurements. Thus, at high latitudes, particle precipitation induced odd nitrogen variations can significantly impact stratospheric ozone concentrations on interannual time scales. At latitudes lower than 50 degrees, statistically significant solar induced odd nitrogen variations occur only near and above the stratopause in the tropics. This low-latitude response is apparently caused primarily by increased photolysis of NO under solar maximum conditions. Throughout most of the rest of the stratosphere, no statistically significant response is obtained. This implies that decadal variations of odd nitrogen, regardless of their source, played no major role in the solar cycle variation of ozone at middle and low latitudes during the 1991-2003 period.
SA34A-07 INVITED
Interannual Variability in Mesospheric Wintertime Descent: Implications for Thermosphere-Stratosphere Coupling
Observations from the Sounding of the Atmosphere with Broadband Emission Radiometry (SABER) experiment on the NASA/Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite show an unusual vertical displacement of the winter stratopause in 2006 with zonal mean temperatures at 0.01 hPa (80 km) exceeding 250 K. By contrast, at the conventional stratopause location near 50 km, temperatures were unusually cold. Simulations with the NOGAPS-ALPHA model suggest that these are coupled to an unusually warm and disturbed lower stratosphere that filtered out many of the gravity waves that normally break at and above 50 km. The model also shows that downward transport in the 2006 Arctic vortex at mesospheric altitudes was enhanced relative to 2005. These results might explain observations of enhanced upper atmospheric NO descending to the upper stratosphere in 2006. They highlight the importance of gravity waves and their filtering by winds in the stratosphere in modulating the coupling of the upper atmosphere with the stratosphere. The implications of this are that solar-terrestrial coupling studies must consider meteorological variability forced from the lower atmosphere in addition to the more familiar solar/geomagnetic variations.
SA34A-08
The Mesospheric Polar Vortices in GEOS, WACCM, SABER, and EOS-MLS
Satellite data analysis is combined with global modeling to characterize the 3-D structure and day-to-day variability of the polar vortex in the mesosphere. We use satellite temperature and geopotential height data from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument and temperature, carbon monoxide, and methane data from the Microwave Limb Sounder (MLS) instrument to characterize the structure of the upper stratospheric and mesospheric polar vortex in each hemisphere on a daily basis. The mesospheric vortex, as seen by these satellite instruments, is then compared to the representation of the mesospheric vortex in the GEOS-4 and GEOS-5 data assimilation systems as well as in the Whole Atmosphere Community Climate Model (WACCM). We will show the 3-D structure of the mesospheric vortex at times when the stratospheric vortex is strong as well as how this structure is modified during stratospheric warming events. This work will conduct model/observation intercomparisons of the mesospheric vortex to further understanding of its role in the descent of EPP-NOx.