Polar Northern Hemisphere Middle Atmospheric Influence due to Energetic Particle Precipitation in January 2005

Solar eruptions and geomagnetic activity led to energetic particle precipitation in early 2005, primarily during the January 16-21 period. Production of OH and destruction of ozone have been documented due to the enhanced energetic solar proton flux in January 2005 [e.g., Verronen et al., Geophys. Res. Lett.,33,L24811,doi:10.1029/2006GL028115, 2006; Seppala et al., Geophys. Res. Lett.,33,L07804, doi:10.1029/2005GL025571,2006]. These solar protons as well as precipitating electrons also led to the production of NO(x) (NO, NO2). Our simulations with the Whole Atmosphere Community Climate Model (WACCM) show that NO(x) is enhanced by 20-50 ppbv in the polar Northern Hemisphere middle mesosphere (approx.60-70 km) by January 18. Both the SCISAT-1 Atmospheric Chemistry Experiment (ACE) NO(x) measurements and Envisat Michelson Interferometer for Passive Atmospheric Sounding (MIP AS) nighttime NO2 observations show large increases during this period, in reasonable agreement with WACCM predictions. Such enhancements are considerable for the mesosphere and led to simulated increases in polar Northern Hemisphere upper stratospheric odd nitrogen (NO(y)) of2-5 ppbv into February 2005. The largest ground level enhancement (GLE) of solar cycle 23 occurred on January 20, 2005 with a neutron monitor increase of about 270 percent [Gopalswamy et al., 29th International Cosmic Ray Conference, Pune,00,101-104,2005]. We found that protons of energies 300 to 20,000 MeV, not normally included in our computations, led to enhanced stratospheric NO(y) of less than 1 percent as a result of this GLE. The atmospheric impact of precipitating middle energy electrons (30-2,500 keV) during the January 16-21, 2005 period is also of interest, and an effort is ongoing to include these in WACCM computations. This presentation will show both short- and longer-term changes due to the January 2005 energetic particle precipitation

Heliospheric interstellar H temperature from SOHO/SWAN H cell data

International audienceWe show a first comparison between selected SOHO/SWAN H cell data recorded in 1996-1997 and a simple classical "hot model" of the interstellar (IS) H flow in the inner heliosphere. Our goal is to obtain some constraints on the interplanetary background Ly-[FORMULA] profiles, for the first time without any assumption on the H cell characteristics. For this purpose the H cell optical thickness and its temperature are free parameters of the study, but we assume that the direction of the flow and the allowed range for the upwind line-of-sight apparent Doppler shift are known from previous studies.We derive apparent temperatures (or line-of-sight (LOS) temperatures) between 11,000 and 20,000 K according to the direction. This implies a significant broadening with respect to the linewidths expected for a flow at the same temperature as the interstellar helium flow (6,000 [FORMULA] 1000 K) in the optically thin approximation. Radiative transfer is probably responsible for a fraction of this effect, and heating at the heliospheric interface for the remaining. The best solutions are found for an upwind velocity of 26 km s-1, in excellent agreement with an independent study by Quémerais et al. (1999), and for very similar H cell absorption width and temporal decrease. The deceleration of interstellar H at heliopause crossing is found to be between 2.5 and 4.5 km s-1.We also use one particular H cell absorption map to derive directly from the data how the LOS temperature (or linewidth) varies with the angle with the wind direction. Interestingly, we measure a temperature minimum between the upwind and crosswind directions, while classical models predict a monotonic increase of the LOS temperature from upwind to downwind. We believe that this behavior is the first evidence for the existence of two distinct populations at different velocities (primary and secondary IS atoms), as predicted by heliosphere-interstellar gas interface models. If confirmed, this should be an extremely good diagnostic of the interface

Monitoring solar activity on the far side of the Sun from sky reflected Lyman α radiation

International audienceSolar active regions are known to be brighter in Lyman α radiation than the quiet sun. Accordingly, they illuminate more H atoms in interplanetary space through resonance scattering. As we show here, this excess of illumination related to active regions is clearly seen in full-sky Lyman α maps recorded by the SWAN instrument on board SOHO, including those excesses resulting from active regions which are on the far side of the Sun. Since solar activity is most often connected to solar active regions, this technique could be used in the future to improve the quality of Space Weather forecast, by earlier detection of the birth of a new active region on the far side of the sun, before it comes into Earth's view at the East limb

Arctic and Antarctic polar winter NOx and energetic particle precipitation in 2002-2006

We report GOMOS nighttime observations of middle atmosphere NO2 and O-3 profiles during eight recent polar winters in the Arctic and Antarctic. The NO2 measurements are used to study the effects of energetic particle precipitation and further downward transport of polar NOx. During seven of the eight observed winters NOx enhancements occur in good correlation with levels of enhanced high-energy particle precipitation and/or geomagnetic activity as indicated by the Ap index. We find a nearly linear relationship between the average winter time Ap index and upper stratospheric polar winter NO2 column density in both hemispheres. In the Arctic winter 2005 - 2006 the NOx enhancement is higher than expected from the geomagnetic conditions, indicating the importance of changing meteorological conditions

Interplanetary hydrogen absolute ionization rates: Retrieving the solar wind mass flux latitude and cycle dependence with SWAN/SOHO maps

We present results of the total hydrogen ionization rate obtained from the inversion of almost 10 years of full-sky maps of the interplanetary Lyman α background measured by the SWAN instrument on SOHO. Thanks to a new estimate of the absolute calibration of the SWAN instrument and its variation during the 10 years of operation of SOHO, we are able to derive absolute values of the ionization rate as well as its latitudinal dependence. We show how the anisotropy of the ionization rate changes from solar minimum to solar maximum. At solar maximum, the so-called ionization groove has completely disappeared and the ionizing fluxes are the same at all heliographic latitudes. We find that the hydrogen ionization cavity which surrounds the Sun increases in size with solar activity. This is evidenced by the low IP Lyman α intensities measured during and after the solar maximum. Our model calculation also shows that the increased radiation pressure is not sufficient to explain the larger cavity observed at solar maximum. We find also that ionization rates derived from in situ solar wind measurements do agree with the SWAN results at solar minimum but are significantly smaller at solar maximum. Derived in situ ionization rates do not show the solar cycle dependence we see from the SWAN data. In conclusion, we discuss possible explanations for this discrepancy