A31A-0037 0800h
Impact of Strong Geomagnetic Storms on the Atmosphere-Ionosphere System: Case Studies
Impact of strong geomagnetic storms on the atmosphere-ionosphere system is in some regions relatively understood, as in the F2 region ionosphere and the lower ionosphere, while in other regions/parameters is known little or controversial. We focus on such parts of that complex process, which have not yet been clarified, with emphasis to European area. The purpose of the paper is to help to fill in gapes in the vertical profile of geomagnetic storm effect. The electron density at F1 region heights, temperature, pressure and wind velocity fields at pressure levels from surface to 100 hPa, and total ozone are studied for six strong geomagnetic storms (Ap>60, Dst<-120 nT) from the 1990s and 2000s. The electron density at F1 region heights was found to decrease during the storms. Effects in total ozone were confirmed to be dependent on the QBO and solar activity. Strengthening of winds in the troposphere and lowermost stratosphere is expected.
A31A-0038 0800h
The Effect of the 2003 Geomagnetic Storm Events on Mesospheric Temperature, Hydroxyl and Ozone
During October and November, 2003, several major geomagnetic storms occurred. Using an array of Michelson interferometers, the effects of these storms on mesospheric hydroxyl and atmospheric temperature could be observed at high latitudes in both the northern and southern hemispheres. Data will be presented from the observatories at Ny Alesund, Spitzbergen; Onsala Sweden; and Rothera, Antarctica showing the effects of these storms on the hydroxyl emission and the atmospheric temperature. The large geomagnetic differences in the stations as well as the seasonal offset allow the effects of the storms to be assessed under a variety of conditions, and conclusions regarding the direct precipitation effects versus longer term heating will be presented.
A31A-0039 0800h
ATMOSPHERIC CHEMISTRY AND CLIMATE RESPONSE TO NOy SOURCE DUE TO ENEGETIC ELECTRON PRECIPITATION
The simulated response of the stratospheric ozone and temperature to the decadal scale solar UV variability is underestimated by virtually all models in comparison with observational data, suggesting that one or more important physical mechanisms are missing. We have introduced an additional NOy source caused by energetic electron precipitation events (EEP) into the fully-coupled UIUC Chemistry-Climate model, extending up into the lower thermosphere, to estimate the potential significance of this process for the chemical composition, temperature and dynamics of the atmosphere. The intensity of the additional NOy source is derived from the satellite measurements of energetic electron precipitation in 1987, a year with relatively low fluxes. Comparison of the 10-year long annually repeating run with EEP switched on against a similar control run without the additional source of NOy reveals statistically significant changes of the atmospheric state. In particular, the annual mean NOy mixing ratio increases by about 3 ppbv in the middle stratosphere and mesosphere over the tropical and middle latitudes. In the upper stratosphere over the polar regions, where the downward transport is generally more intense, the simulated NOy enhancement reaches 10 ppbv. The increase of NOy results in an intensification of the ozone destruction and decrease of the ozone mixing ratio mostly in the middle and lower stratosphere by up to 5% over midlatitudes and up to 20% over southern high-latitudes. Accordingly, the total ozone decrease is the most pronounced over southern high-latitudes (~20%) and northern mid-latitudes (~8%), while in the tropical area the total ozone depletion is about 5% and only marginally statistically significant. The pattern of the temperature response consists of a ~0.5 K cooling in the middle stratosphere over the tropics and up to 2 K over high-latitudes. Some changes in the tropospheric circulations and surface air temperature are also detectable. These results suggest that the magnitude of the ozone and temperature changes due to EEP events can exceed the effects from solar UV fluxes within the present model. They also suggest that the combined effect of the EEP and UV perturbations can be close to the atmospheric response obtained from the observations.
A31A-0040 0800h
Interannual and Solar-Cycle Terms in Middle Atmospheric Temperature Time Series from HALOE
Temperature versus pressure or T(p) time series from the Halogen Occultation Experiment (HALOE) have been generated and analyzed for the period of 1991-2004 and for the mesosphere and upper stratosphere at latitude zones from 40N to 40S. Multiple linear regression (MLR) techniques were used for the analysis of the seasonal and the significant interannual, 11-yr solar cycle, and/or decadal-scale dynamical terms. Both sub-biennial (688-dy) and QBO-like (800-dy) terms are resolved for the upper stratosphere along with a 13.5-yr term due to their predicted modulation. A solar cycle (SC) term emerges for the tropical stratopause region, but its amplitude is only about half that predicted from most models. The SC terms for the middle to upper mesosphere have amplitudes that agree will with model predictions. At northern hemisphere middle latitudes there is some lag for the apparent SC response in the mid mesosphere, possibly due to interference from the effects of wintertime wave activity. SC amplitudes from the MLR models are somewhat weaker but in-phase for the southern hemisphere latitudes, and may be more representative of the true solar cycle forcing effects.
A31A-0041 0800h
Polar NOx in the Middle and Upper Stratosphere Observed by MIPAS on ENVISAT
The Michelson Interferometer for Passive Atmosphere Sounding (MIPAS) on board of the polar orbiter ENVISAT, launched on March 1st, 2002, detects non-LTE emissions of NO (5.3 $\mu$m) and NO$_2$ (6.2 $\mu$m) with high spectral resolution. The simultaneous detection of both NO$_x$ species along with the pole-to-pole coverage of MIPAS data offers an unique opportunity to study the descent of mesospheric/thermospheric NO$_x$ into polar winter stratosphere. Vertical profiles of both NO$_x$ species have been retrieved from a large set of MIPAS observations with the scientific non-LTE data processor developed at IMK and IAA. Derived data show a clear NO$_x$ enhancement in the upper stratosphere due to NO$_x$ descent during polar night which disappears in the sunlit spring stratosphere.
A31A-0042 0800h
Chemical Effects in 11-Year Solar Cycle Simulations With the Freie Universit\"at Berlin Climate Middle Atmosphere Model With Interactive Chemistry (FUB-CMAM-CHEM)
Parameterisation of NOx transport from the mesosphere to the stratosphere may be important when simulating the 11-year solar cycle influence upon stratospheric ozone in climate- chemistry models (CCMs). The downward NOx transport occurs primarily in the wintertime polar night jet (PNJ) hence may lead to a characteristic positive dipole ozone signal (higher ozone at solar maximum) in the annual mean. Such a dipole, peaking at 40-45 km near 60°N and 60°S, has been noted in some satellite observations. In this talk we present results of 11-year solar cycle simulations of the Freie Universit\"at Berlin Middle Atmosphere Model with interactive chemistry (FUB-CMAM-CHEM). Variations in NOx transport from the mesosphere were parameterised by including an idealised NOx source at high latitudes above 70 km. The NOx source represents the effect of high-energy electron precipitation associated with intense solar wind streams which lead to decreased NOx (hence increased ozone) near solar maximum. Other NOx sources, associated with low and medium energy electrons arising in the aurora tend to have the opposite effect (increased NOx at solar maximum) and are not included in this study . The model calculates the observed dipole ozone signal which is however stronger than that observed, probably due to the neglect of the compensating effects of low and medium energy electrons. The model further calculates a negative ozone signal in the lower stratosphere (~20 km) near the equator which is also suggested by some satellite observations but occurs a little higher up (25-30 km). Our results imply that the negative ozone signal in the model arises at least partly via a chemical effect in which ozone-destroying chemicals are released from their reservoirs via enhanced insolation at solar maximum. In the mesosphere a decrease in ozone is calculated at solar maximum associated with the classical HOx cycle enhanced via Lyman-alpha photolysis of water vapour.
A31A-0043 0800h
The 27-day solar rotational cycle in the Freie Universitaet Berlin Climate Middle Atmosphere Model with interactive chemistry (FUB CMAM CHEM)
We simulated twenty, perpetual Januaries each under solar minimum and maximum conditions using the Freie Universitaet Berlin Climate Middle Atmosphere Model with interactive chemistry (FUB CMAM CHEM) and including the 27-day solar rotational cycle. Cross-correlation functions (r) of tropical ozone and ultra-violet suggested peak values of +0.5 to +0.6 (with % changes in ozone of 0.4 to 0.6%) in the middle atmosphere and (-0.6 to -0.8) in the mesosphere (with % changes of up to 1%) , in line with other modelling and satellite studies. Peak correlations were generally 5-10% stronger for the solar maximum, compared with the solar minimum run. They also differed in altitude and in phase lag between solar minimum and maximum. This suggests it is important to separate data into solar minimum and maximum periods for such analyses. Modelled ozone-UV correlations peak at generally higher altitudes (0.2-1hP) compared with satellite studies which peak near 4hPa. Ozone sensitivity varied between 0.2 to 0.3% per % change in UV throughout the stratosphere. In addition to ozone, we examined chlorine monoxide (ClO) and hydroxyl (OH), as well as transformed Eulerian mean quantities such as the vertical velocity component. These quantities were also found to exhibit a clear cross-correlation response with UV over the 27-day cycle. In the troposphere at solar maximum we calculated a strong, positive correlation between temperature and the phase of the 27-day cycle which peaked at the surface (r=+0.99) with a peak-to-peak amplitude of +0.3 to +0.4K; this feature was not present for the solar minimum run.
A31A-0044 0800h
Stratospheric Ozone Variation Induced by the 11-Year Solar Cycle: Recent 40-Year Simulation Using 3-D Chemical Transport Model with Reanalysis Data
The chemical and dynamical impacts of the 11-year solar cycle are investigated with the focus on stratospheric ozone variation and its correlations with meteorological variations, e.g. temperature and zonal wind, using a three dimensional chemical transport model (CTM) of the Meteorological Research Institute (MRI). When we investigate the influence of the solar activity on climate, an abundance of meteorological observations, including objective analyses, are usable. In contrast, there are few datasets of spatially and temporally wide-raging observations of atmospheric chemical constituents. Models have been then used for investigation for correlations between the chemical and dynamical impacts of the 11-year solar cycle. However, the meteorological and chemical fields generated by these models are hypothetical cases in virtual worlds; they balance each other physically in the models, but it is not known exactly that these cases occur in the actual atmosphere. We have then compared meteorological fields of re-analyses with the ozone distributions simulated by a CTM using the same meteorological fields and variable solar flux, without ozone-temperature feedback processes. The meteorological fields of re-analyses are supposed to include the ozone-feedback effect as well as the QBO and volcanic effects occurred in the actual atmosphere. Photodissociation coefficients generated in the CTM are derived from the actual solar flux which varies quasi-decadally. The simulated ozone, therefore, includes the actual solar cycle variation which synchronizes with the meteorological variations. Consequently, solar cycle components of the simulated ozone are supposed to be physically consistent with those of the meteorological fields of re-analyses; this case must have occurred in the actual atmosphere. [Model description] The chemical module includes 122 chemical reactions with 49 chemical species. The chemical species are transported with semi-Lagrangian scheme. The dynamical module is based on a general circulation model, which has been developed by MRI. The vertical resolution is set to 45 layers (surface to 0.01 hPa), while the horizontal resolution is set to 64 by 32 in longitude and latitude (5.6 by 5.6 degrees). Meteorological fields in the dynamical module are data-assimilated into ECMWF re-analysis (ERA-40). ERA-40 covers the years 1957-2002 and the altitude range from the surface to 1 hPa. The solar flux used in the chemical module was compiled by Lean et al.; the flux dataset contains time series of ultraviolet spectrum (120-735 nm) based on solar observations. A 40-year simulation (1960-2000) was made under the condition of the ERA-40 meteorological fields and the transient solar flux. In order to extract solar cycle components from the model result, a multiple linear regression analysis was adopted using F10.7 observations as an explanatory variable. The distribution of the amount of the solar cycle component of ozone varies not only altitudinally and latitudinally but also longitudinally. Peak differences of ozone concentration between solar maximum and minimum are calculated as approximately 4% in the stratosphere. Solar cycle changes of temperature also show altitudinal, latitudinal, and longitudinal variations from -1.0K to +0.8K in the stratosphere. There is a high correlation (~0.8) between the two horizontal distributions in the lower stratosphere and a strong but negative correlation (~-0.7) in the upper stratosphere.
A31A-0045 0800h
The Response of the QBO to Zonal-Mean Ozone Perturbations Consistent with the 11-Year Solar Cycle
The response of the quasi-biennial oscillation (QBO) to zonal-mean ozone perturbations consistent with the 11-year solar cycle is examined using a two-dimensional model of the tropical stratosphere. Driven by prescribed Kelvin and Rossby-gravity waves at the lower (100 hPa) boundary, the model accounts for wave driven changes in the zonal-mean circulation and thus can simulate the zonal wind, temperature, and ozone QBOs in the tropical stratosphere. We find that 11-year solar cycle-like perturbations to the zonal-mean ozone field alter both the wave-ozone and zonal-mean ozone feedbacks, which combine to affect the structure and period of the QBO. In particular, under conditions representative of solar max, the diabatic heating resulting from ozone feedbacks drives a slightly stronger QBO circulation and produces a shorter QBO period, in agreement with observations of quasi-decadal variability of the QBO. The implications of these results on quasi-decadal variability of the global circulation will also be discussed.
A31A-0046 0800h
Plausible Solar Influences on Wave Activities in the Middle and Lower Atmosphere
Recent satellite observations show that solar ultraviolet (UV) flux changes by 6-8% near 200 nm between extremes in the 11-year solar cycle, although the total insolation change is negligibly small. Such UV flux changes would bring about ozone changes in the middle atmosphere, which might directly influence tidal wave activity there. On the other hand, the ozone changes are considered to bring about changes of temperature and wind fields in the middle atmosphere. Hence, meridional planetary wave propagation could be influenced according to the change of resultant refractive properties of the atmosphere. In addition, some investigators have suggested the existence of an 11-year component in the Hadley circulation in the troposphere, which might influence planetary wave activity through convective activity changes. However, little convincing evidence supporting the speculation has been obtained and whether some presented relations to the 11-year solar cycle are true or accidental has not been clarified. In this paper, we will discuss plausible solar influences on activities of waves in the middle and lower atmosphere in detail.
A31A-0047 0800h
Solar Variability and Stratosphere-Troposphere Coupling
Observations suggest that the atmosphere is approximately twice as sensitive to solar variability as would be expected from radiative calculations. This suggests that processes amplify an atmospheric solar signal, which is seen in the stratosphere, to affect surface climate. However, the mechanism is not well understood. During the winter season, zonal wind anomalies in the stratosphere tend to progress northward and downward through the stratosphere on a timescale of a few weeks. The process of wave, mean-flow interaction in effect amplifies the anomalies as the progress downward from ~1 hPa to the troposphere. This creates a plausible pathway for solar effects on climate during winter. This process cannot be the complete explanation because solar-climate effects are seen year-round. A plausible year-round mechanism involves the modulation of the wave guide for planetary scale waves, even in summer. I will provide an overview of the winter mechanism for solar effects on climate, with examples from observations and simulations. I will also discuss the effects of lower stratospheric circulation anomalies on planetary-scale waves in the summer, and argue that this mechanism could communicate stratospheric variability downward even in summer.
A31A-0048 0800h
Solar cycle modulation of the Southern Annular mode
Effect of the 11-year solar cycle on the activity of the October/November Southern Annular Mode (SAM) is examined by the analysis of the ERA40 reanalysis data from 1968 to 2001. It is found that year-to-year variability of October-November mean SAM signal significantly differ according to the solar activity: In the high solar years, signal of the SAM extends up to the upper stratosphere during October to December and the activity below lower stratosphere lasts until following early winter. Whereas in the low solar years, signal of the SAM is confined only inside the troposphere from October to December and it breaks off in January. These situations are parallel to that observed in the winter mean North Atlantic Oscillation found by previous studies [Kodera 2002, 2003; Ogi et al., 2003]. The origin of the difference is discussed based on both the observed data and model simulation.
A31A-0049 0800h
The Evolution of Stratospheric Dynamics and Thermal Structure in the Presence of a Weak Surface Temperature Gradient
The dynamic response of the stratosphere to a weak pole-to-equator surface temperature gradient is examined in order to assess the ease with which polar stratospheric clouds might have formed during warm climates in the geologic record. This study uses a general circulation model with a resolved middle atmosphere to analyze the changes in the general circulation during warm climates and their effects on the residual mean circulation in the winter stratosphere. While the eddy kinetic and potential energies of the entire atmosphere decrease markedly when the surface temperature gradient is weakened, the eddy energy in the stratosphere remains largely unchanged. This is partially attributable to the relative stability of the amount of energy in the largest stationary eddies, but the dynamic response of the lower stratosphere also contributes by altering the refractive index for vertically propagating waves. The pole-to-equator gradient in the height of the tropopause lessens as the surface temperature gradient decreases, limiting the depth to which the polar stratospheric vortex penetrates. The resulting adjustment of the lower stratospheric meridional temperature gradient produces winds in thermal wind balance that are considerably lighter in the lower stratosphere than in present observations. This allows energy in some shorter stationary eddies to propagate vertically into the stratosphere, ensuring that the residual mean circulation of the winter stratosphere remains strong. The convergence of the Eliassen-Palm Flux in the stratosphere is larger in the simulations with a weak surface temperature gradient than in those with a contemporary one. Temperatures during the polar night remain as far from radiative equilibrium values in simulations using the weak surface temperature gradient as in simulations using a present one.
A31A-0050 0800h
Solar Influence on Troposphere Through the Polar and the Equatorial Stratosphere
A possible mechanism of the solar influence on climate through dynamical processes is discussed. Variation of the solar ultra violet (UV) heating rate resulting from changes in the solar irradiance and ozone concentration produces small anomalous zonal wind in the subtropical stratopause region. This initial solar effects in the stratopause region is amplified through interaction with planetary waves propagating from the winter troposphere. There are two possible mechanisms for the downward penetration of the solar effect. One is the that the zonal wind anomalies produced in the subtropical stratopause region shifts poleward and downward in the westerly jet in the winter hemisphere similar to the polar night jet oscillation. When zonal wind anomaly reaches in the lower stratosphere, it induces changes in meridional propagation of tropospheric waves. Tropospheric wave change creates a circulation change similar to the Arctic or Antarctic Oscillation. Another possibility is that the modification of the wave mean-flow interaction in the upper stratosphere induces also change in meridional or the Brewer Dobson (BD) circulation. The BD circulation further modulates the Hadley circulation in the equatorial troposphere. This process may be responsible for the solar influence on the summer monsoon and the El Nino/ Southern Oscillation (ENSO).
A31A-0051 0800h
Footprint for the Dynamical Solar Impact from the Stratosphere: A Coupled Ocean-Atmosphere Model Study
Recent studies show a possible solar influence on climate through changes in stratospheric circulation. This mechanism was mainly discussed on the 11-year solar cycle using atmospheric general circulation models. To understand a longer variation, the use of a coupled ocean-atmosphere model is necessary. Unfortunately, however, usually the coupled ocean-atmosphere models neither extend sufficiently high nor treat active ozone to realistically simulate the solar influence in the stratosphere. The solar impact in the stratosphere can be characterized as change in the wave mean-flow interaction in the winter stratosphere. So that for a mimic of solar forcing, a zonal symmetric momentum forcing was imposed in the upper stratosphere to study the dynamical response in the troposphere and to compare with the observed solar cycle responses. The model was integrated one hundred years for each east- and westward forcing experiment. The result shows that the AO or AAO type circulation anomalies appear in the high latitude of the troposphere during the winter and change mid-latitudes ocean temperature. The anomalous sea surface temperatures (SSTs) persist until summer by interacting atmosphere in baroclinic zone and modulate midlatitudes rainfall. Circulation anomalies also produce change in the mean SST in the equatorial central Pacific region similar to the La Nina condition. In the equatorial region, changes in Brewer Dobson circulation in the stratosphere modulate Hadley circulation which affects the summer monsoon activities. Stronger polar vortex condition, comparable to high solar activity, suppresses rainfall in the equatorial Africa but reinforce Indian monsoon.
A31A-0052 0800h
Low cloud amount and cosmic ray induced ionization: Correlated latitudinal variations
A highly significant correlation between the annual flux of cosmic rays at the Earth's orbit and the amount of low clouds has recently been found for the past 20 years. However, a comprehensive physical explanation still remains elusive. We have calculated the tropospheric ionization caused by a cosmic ray induced nucleonic-electromagnetic cascade in order to study the relation between the cosmic ray induced ionization and the global distribution of the observed low cloud amount. We find that the time evolution of the low cloud amount can be decomposed into a long-term trend and inter-annual variations, the latter depicting a clear 11-year cycle with very strong correlation (r=0.84) with cosmic ray induced ionization. We also find that the relative inter-annual variability in low cloud amount increases polewards from the equator and exhibits a highly significant one-to-one relation with inter-annual variations in the ionization over a large latitude range. This latitudinal dependence gives strong support for the hypothesis that cosmic ray induced ionization modulates cloud properties.