SA23A-1122
Effect of atmospheric neutral density on the Earth's trapped-belt proton flux
We have developed two models invoking a polynomial regression technique, adopted from theoretical nuclear physics, to determine the functional relationship between charged particle fluxes at minimum and maximum solar activity in the Earth's inner trapped-radiation belts. Based upon this model the charged particle flux (particularly at low energy below 350 MeV) is clearly shown to depend on solar modulation. For a given altitude the models produce two sets of curves, one for solar minimum and one for solar maximum cycles. The task at hand is to illustrate the functionality of these models. For that we are employing solar cycle 20 as base-lined in this analysis. In the case of that cycle the epoch of 1964 is used for F10.7 maximum activity and the epoch of 1970 is used for F10.7 minimum activity. We will show that charged-particle flux (protons in this case) versus energy in the range of 30 MeV to 350 MeV is a function of density for altitudes in the range of 350 km to 600 km. The effect of neutral atmospheric density is to spread the charged-particle (proton) flux over a bi-variant surface. The models provide the potential for evaluating charged particle (proton) intensity as a function of time through the density's dependence on the solar-cycle 10.7 cm radiation.
SA23A-1123
Backscattered fraction of precipitating ionospheric photoelectrons
The FAST electron spectrometer offers a serendipitous opportunity to determine for the first time the fraction of precipitating photoelectrons that are backscattered. Ionospheric photoelectrons produced by solar EUV radiation can escape into the plasmasphere and travel along magnetic field lines to the opposite hemisphere. In 2002 the FAST satellite orbit sliced through the plasmasphere above 3000 km altitude where it detected photoelectrons coming from both hemispheres with energies in the range 10 to 800 eV. When one hemisphere is sunlit and the other is in darkness, the photoelectrons arriving at the satellite from the dark hemisphere are photoelectrons that are backscattered from the dark thermosphere after traveling from the sunlit hemisphere. This paper compares the measured and modeled backscattered fraction of photoelectrons. The backscatter ratio of precipitating electrons is important in relation to auroral energy deposition rate, which depends on the amount of backscattered energy flux. Direct experimental determination of auroral electron backscatter is not possible because the precipitating auroral flux is too variable in space and time.
SA23A-1124
Parameterization of a cross polar cap potential decrease during a hard solar energetic particle event using the Hill saturation model
The 20 January 2005 solar energetic particle (SEP) event was one of the hardest on record with the largest ground level (neutron monitor) event since 1956. On this day, the MINIS balloon campaign had one payload with electric field instrumentation aloft in the stratosphere above Antarctica at 71° S, 10° W geographic. When the SEPs arrived at earth, the horizontal electric field measured in the stratosphere by the MINIS balloon payload, which is characteristic of overhead large-scale ionospheric electric fields, rapidly (less than 3 minutes) decreased from 15 mV/m to near 0 mV/m as both pole-ward and east-ward components essentially vanished. The balloon payload measured a coincident 20-fold increase in electrical conductivity. As SEP flux declined, both the horizontal electric field and conductivity approached pre-SEP values until bulk coronal mass ejection plasma arrived the following day. In order to understand what physical mechanisms caused the horizontal electric field to vanish at SEP arrival, we examine the 20 January 2005 event using the Hill model which defines a saturation potential that limits the cross polar cap potential. Northward IMF and tenuous solar wind density ( less than 0.5 cm-3) combine to form a circumstance where the cross polar cap potential is low (less than 50 kV). According to the Hill model, the saturation potential is a function of the height-integrated ionospheric Pedersen conductivity. A rapid SEP-induced ionospheric conductivity enhancement creates a situation where saturation is meaningful. By using ion density output from the Sodankylä Ion Chemistry model, we investigate how the rapid ionospheric conductivity enhancement on 20 January 2005 can decrease the saturation potential, thus limiting the cross polar cap potential, and we compare the results to the MINIS balloon electric field measurements.
SA23A-1125
Synoptical Auroral Ovals: A Comparison study with TIMED/GUVI Observations
Whether the aurora Australis is a mirror image of its northern hemispheric counterpart is a question that auroral physicists have been wanting to answer. Owing to geophysical constraints, especially the large offset between the location of the southern magnetic and southern geographic poles, there is a paucity of information about the aurora Australis. Comparisons of some instantansous global-scale northern and southern auroras acquired conjugately by Polar and IMAGE spacecraft recently have shown mixed results. In this study, we present data from a different source to provide insight into the global morphology and behavior of the auroral oval. Approximately 20,000 Earth's disk FUV images acquired from the Global Ultraviolet Imager (GUVI) on-board NASA's Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) satellite between February 2002 and February 2006 are processed and analyzed. Synoptic auroral distributions for the northern and southern ovals are derived. Our study result reveals that the statistical oval is nearly hemispherically symmetric (within ±80%). Several known features in the morphology of the aurora Borealis are also observed in the Southern Hemisphere: For instance, the auroral midday gap and the premidnight maximum. The hemispherical symmetry of the auroras deteriorates as the partition of solar illumination in the two hemisphere polar region becomes asymmetric. It is estimated that the solar illumination effect accounts for up to ~50% of the hemispheric asymmetry. We found evidence that suggests that the aurora is suppressed under sunlit conditions in the South just as it is in the North. We also found that the auroral energy flux increases monotonically with the increase of the solar zenith angle. These results suggest that ionospheric conductivity plays an active role in regulating magnetospheric energy deposition in the auroral zone.
SA23A-1126
Contribution of the Overtone Vibration-Rotation Emissions From Chemiluminescent NO to Storm-time Thermospheric Energy Budget
Recent work [Mlynczak et al.; 2005, 2007] has pointed out that about 50% of the energy input into the atmosphere during a solar storm is radiated away as 5.3 μm fundamental vibration-rotation band (Δv=-1) emission from NO. The energy radiated away as 15 ƒÝm emission from CO2, on the other hand, is only about 2.3% of the 5.3 μm NO emission. We calculate the contribution to the energy budget by the overtone emission from chemiluminescent NO. Based on the model of spectrally resolved 5.3 μm emission from NO observed by CIRRIS-1A from an aurorally dosed high-altitude atmosphere [Duff et al., 2005] we show that the energy radiated away by chemiluminescent NO in the first overtone (Δv=-2) near 2.7 μm is about 20% of the 5.3 μm emission, about an order of magnitude larger than that radiated away as 15 μm emission from CO2. We plan to parameterize this contribution to the energy budget as function of input storm energy and altitude so that it can be included in the atmospheric models.
SA23A-1127
Contribution of the N2(A)+O Reaction to Thermospheric Nitric Oxide
A time-dependent photochemical model of thermospheric nitric oxide (NO) including the N2(A3Σu+,v) + O(3P)→NO(X2Π) + N(2D) reaction (\ital{Thomas and Kaufman,J.Phys.Chem.,1996)} is compared with Student Nitric Oxide Explorer (SNOE) data over an altitude range of 90-170 km for a period of ± 45 days surrounding the 1999 vernal equinox. While including this reaction affects the modeled NO production rate primarily at altitudes > 130 km, as a result of diffusive coupling the modeled NO density is also enhanced at lower altitudes. The altitudes may be classified into three zones depending on the type of diffusion predominating within each: 90-100 km, 110-170km, and 100-110 km where the vertical transport is respectively controlled by eddy diffusion, molecular diffusion, and a mixture of the two. Correspondingly, it is found that inclusion of the title reaction in the existing model increases the equatorial NO density at 11 AM LST by an average of 13%, 44% and 28% in these regions. Comparison with the zonally-averaged SNOE data reveals that over the full range of altitudes the averaged daily error between model and data is 18% upon inclusion of the title reaction. More specifically, in the 90-100 km, 100-110 km and 110-170 km regions it is 23%, 29% and 15%, respectively. In addition, the differences between model and data comparisons are evaluated using more recently published reaction and diffusion rate coefficients, but it is found that the overall agreement between model and data is best when the only adjustment to the model is the title reaction itself.
SA23A-1128
Observing Nitric Oxide in the Polar Night by Stellar Occultation
It is now understood that NO plays a key role in the coupling of the stratosphere, mesosphere and lower thermosphere (SMLT) via energetic particle precipitation. A significant body of evidence suggests that NO created by energetic particles is transported to the lower atmosphere during polar night, where it participates in catalytic ozone destruction. To date, measurements of the highly variable NO abundance have only been made during sunlit conditions and the lack of nighttime NO measurements is a significant impediment to developing a quantitative understanding of the role played by this crucial species. We describe a space-based experiment designed to make the first measurements of NO concentration in the polar night, using the method of stellar occultation. Our approach will utilize a moderately high resolution (~90 mA) spectral measurement of NO absorption in either the δ-band at ~193 nm or the γ-band at ~215 nm. These two band features are compared to optimize tradeoffs between measurement signal-to-noise, the NO absorption strength and contamination due to competing absorption sources. The latter is primarily caused by O2 absorption in either the Schumann-Runge bands (193 nm) or the Hertzberg continuum (215 nm). We quantify the measurement capabilities required to obtain vertical profiles of NO between 70 and 150 km in the polar night, and show that an instrument with appropriate light gathering capability can be made with mass and dimensions appropriate for sounding rockets and small satellites. The expected horizontal sampling density provided by the available target stars is sufficient to characterize the polar night region. We will also describe both laboratory measurements and a planned rocket experiment which will demonstrate the viability of the stellar occultation technique.
SA23A-1129
Interannual variability in the effects of energetic particle precipitation (EPP) on the stratosphere
Odd nitrogen produced routinely in the mesosphere or lower thermosphere (MLT) by low- or medium-energy particles, or sporadically in the stratosphere by very high energy electrons or solar protons, can affect stratospheric ozone distributions. This talk focuses on the magnitude and variability of the contribution of EPP- NOx (odd nitrogen produced by EPP) to the stratosphere during the last two decades. New results from meteorological analyses, satellite-based observations, and 3D model simulations will be presented. We will show that interannual variations in the amount of EPP-NOx in the southern hemisphere stratosphere depend primarily on variability in energetic particle precipitation. In the northern hemisphere, however, meteorological variability appears to be more significant. Observations suggest that EPP contributes up to about 40 percent (10 percent) of the polar (hemispheric) NOx source in the stratosphere. We will highlight some of the gaps in our understanding of the pathways by which coupling between the stratosphere and MLT is affected by EPP, and the need for observations of NOx throughout the MLT in the polar winter.
SA23A-1130
Simulations of Medium Energy Electron Precipitation in WACCM
The NOx catalytic cycle is the primary O3 destruction mechanism throughout most of the stratosphere. Oxidation of nitrous oxide (N2O), emitted at the ground and transported to the stratosphere, is thought to be the largest source of stratospheric NOx. However, observations during the last two decades have shown that NOx produced by energetic particle precipitation (EPP-NOx) in the mesosphere and lower thermosphere (MLT) can descend to the stratosphere during the polar night. Estimates based on satellite measurements of NOx suggest that up to 40% of the NOx in the stratospheric polar region might be derived from EPP on an annual basis. Understanding stratospheric O3 distributions thus requires quantification of the contribution of EPP-NOx to the stratosphere. This presentation describes recent work to investigate the descent of EPP-NOx to the stratosphere using the Whole Atmosphere Community Climate Model (WACCM) from the National Center for Atmospheric Research (NCAR). WACCM is a coupled chemistry climate model extending in altitude from the Earth's surface up to 140 km. It includes comprehensive, interactive chemistry of the middle atmosphere, and is thus well-suited for these studies. In this presentation, we describe a new parameterization of medium energy (~30-300 keV) electron precipitation in WACCM, which produces EPP-NOx in the mesosphere. We will describe the calculation of ionization rates, including spatial distributions, and subsequent production of NOx. The importance of medium energy electron precipitation in producing NOx and modifying stratospheric ozone and temperature will be assessed, and compared to the effects of EPP-NOx produced by auroral electrons.
SA23A-1131
The Middle Atmosphere and Energetic Particle Precipitation - response in the Canadian Middle Atmosphere Model
Abstract: Penetration of ionizing particles from space can substantially modify the composition of the middle atmosphere, its temperature distribution and dynamics. Persistent auroral precipitation affects primarily the upper polar mesosphere but under the right transport conditions it can influence the stratosphere. Galactic cosmic rays and strong but sporadic solar protons can penetrate deeper into the stratosphere. The effect of ionizing particle precipitation varies in response to changes in solar activity and the terrestrial magnetic field. To investigate the response of the middle atmosphere to the energetic particles precipitating from the space and build a hierarchy of different forcing mechanisms, the Canadian Middle Atmosphere Model (CMAM) has been used in several multi-year experiments. Observed daily electron and proton fluxes from 1979 to 2006 and parameterized galactic cosmic rays have been introduced in the model to obtain production rates of NOx, Ox and HOx. It has been found that auroral precipitation has a non-negligible impact on the NOy budget in the polar stratosphere with the largest impact in the southern hemisphere where the annual mean ozone loss is increased by between 5% and 15%. Sporadic solar proton events have a small long-term impact which is greatest during the solar cycle maximum. Due to their persistence, galactic cosmic rays may have a larger long-term temperature effect than solar proton events.
SA23A-1132
N2O production during high energy auroral precipitation
The ACE instrument on SCISAT-I observed very high values of NOx in the lower polar mesosphere in February of 2004. It also measured unusually high mesospheric values of N2O as adduced by both absolute amount and by comparison with simultaneously measured CH4 data. GOMOS data for the same period have revealed high polar NO2 values. Anomalous N2O values in the mesosphere have also been seen by ACE in other years. We suggest that the excess N2O is produced by the reaction of N with NO2. Atomic N is critical to the production and questions arise as to whether N produced by solar radiation of NO is adequate to drive the process is there are high mixing ratios of NO. Thus we have used the CMAM chemistry climate model to examine whether the N2O production is driven by NOx transport from above and photolysis or by in-situ production of N and NO by high energy electron ionization. Our results suggest that N produced by auroral ionization is essential for the production of N2O and, given the short lifetime of N, that N2O is produced locally where NO2 is present below around 80 km. The ionization rate is inferred from observations of electron fluxes and energies by the MEPED instruments on NOAA polar orbiting environmental satellites.
SA23A-1133
NOx Enhancements in the Middle Atmosphere: The Relative Significance of Solar Proton Events and the Aurora as a Source
In this study we combine odd nitrogen (NOx) observations from the satellite instruments with a radio wave ionisation index to provide a detailed description of the generation and descent of polar NOx into the upper stratosphere during the Northern Hemisphere winter of 2003-2004. The measurements are used to study the relative contributions of ionization due to solar proton events, energetic electron precipitation, and auroral precipitation on NOx production, and its subsequent downward transport to the upper stratosphere. We show that NOx generated from the large solar proton storm in October/November 2003 was transported into the upper stratosphere in agreement with model calculations, but that aurorally generated NOx also descended later in the winter. Both periods were highly significant and produced large long-lived decreases in stratospheric ozone. The observations made by GOMOS/Envisat deep into the nighttime polar vortex prove critical in differentiating between the stratospheric effects of these two events.
SA23A-1134
Measurements of Solar Proton Event Generated HO2 and OH
The Aura MLS instrument measures rotational emission of HO2 and OH in both day and night. For the first time, Aura measured these two radicals during solar proton events. Data using the new v2.2 version of the retrieval will be shown for several solar proton events. The observed concentration dependence on altitude is different for the two radicals. The observed morphology, but not the absolute values of concentration, agree with the TIME-GCM model.
SA23A-1135
Ion-Induced Nucleation Under Atmospheric Conditions
Experimental studies of aerosol nucleation in air, containing trace amounts of ozone, sulphur dioxide, and water vapor at concentrations relevant for the Earths atmosphere are reported. The production of new aerosol particles is found to be proportional to the negative ion density. These results suggest that ions are important for nucleation processes in the atmosphere and cloud cover -- and may thus link cosmic rays to Earth's climate. The production of aerosols in the Earth's atmosphere is an unresolved and challenging problem. Atmospheric and experimental observations have shown that the nucleation of aerosol particles can occur under conditions that cannot be explained by classical nucleation theory. Several ideas have been put forward to solve the nucleation problem, e.g., Ion-induced Nucleation and Ternary Nucleation. However, experimental investigations exploring the role of ions in particle production are scarce, and often at conditions far removed from those relevant for the lower part of the atmosphere. In our laboratory we have performed1 an experimental investigation of nucleation that confirms the importance of ions under conditions that do prevail in the lower atmosphere. The measurements were performed in a 7 m3 reaction chamber, which was continuously flushed with dry purified air. Variable concentrations of water vapor (H2O), ozone (O3), and sulphur dioxide (SO2) could be added to the chamber, where the pressure was held a few Pa above atmospheric pressure, and the temperature fixed at 296 K. UV-lamps (253.7 nm) were used to initiate a photochemical reaction that transforms (H2O), ozone (O3), and sulphur dioxide (SO2) to sulphuric acid (H2SO4). Ions were produced in the chamber by galactic cosmic radiation. This natural production of ions could be enhanced with gamma sources, mounted outside of the chamber. A Gerdien tube was used to measure the ion current, and aerosols generated in the chamber were measured with a TSI Ultra Fine Condensation Particle Counter (3--150 nm). The experimental data indicate that particle production rates scale with the negative ion density and the results thus suggest that ions play a fundamental role in the production of new aerosol particles in the Earths atmosphere and cloud cover. (1) H. Svensmark et al., Proc.~Roy.~Soc.~London A, 463, 385--396 (2006), DOI: 10.1098/rspa.2006.1773.