FESD, Boulder, CO, July 21, 2014

Middle Atmosphere Conductivity for High H2SO4 Mixing Ratio

Brian A. TinsleyUniversity of Texas at Dallas

tinsley@UTDallas.eduhttp://www.utdallas.edu/physics/faculty/tinsley.html

Stratospheric optical depths, based on extinction measurements, satellite occultation measurements, and other proxy data. (Preliminary data for Pinatubo). From Sato et al., (1993).

From Meyerott et al., p.449 – 460, in Weather and Climate Responses to Solar Variations, Colo. Ass. Univ. Press, 1983

GCR flux (top), 12 km potential from Mühleisen and Fischer (middle), and stratospheric aerosol content (bottom), 1959-1976

Borok (northern Russia) Jz and Ez 1998-2014

In the stable air in winter the boundary layer column resistance is low, Ez is low, and Jz reflects the ionospheric potential. The cosmic ray/solar cycle variation in Jz is consistent with that of Muheleisen and Fischer (Weissenau, Germany, 1968-76), and Olsen (Lake Superior, USA,1966-1982)

REDISTRIBUTION AND PERSISTENCE OF H2SO4 IN STRATOSPHERE

The H2SO4 is formed from volcanic SO2 and is transported throughout the middle atmosphere by the Brewer-Dobson circulation. Ultrafine (nanometer) particles are nucleated and grow to micron size, large enough to sediment and be detected by solar occultation in the visible. Layers appear 5-10 km above the tropopause, and become concentrated in the winter at higher latitudes than ± 60°.

H. J. Fischer and R. Mühleisen, “The ionospheric potential and the solar magnetic sector boundary crossings”, Report Astronomisches Institut der Universität Tübingen, 1980.

Potential from surface to 12 km from balloon soundings from southern Germany, sorted by position in solar wind magnetic sectors. Sector boundaries are at days 0 and 10.

From Reiter, J. Atmos. Terr. Phys., 39, 95-99, 1977.

Superposed epochs for electric field (E) and current density (J) measured at Zugspitze, with key days those of either -/+ or +/- solar wind sector boundary crossings.

Circumstantial evidence of high middle atmosphere column resistance with high H2SO4 mixing ratios

• Jz and Ez reductions correlate with precipitating relativistic electron flux reductions at solar wind speed minima around times of HCS crossings. These reductions are strongest when middle atmosphere H2SO4 mixing ratios are highest, suggesting that the middle atmosphere column resistance is increased by the H2SO4, provided in-situ ionization by particle precipitation (or other sources) is absent.

• There is evidence that cloud microphysical and atmospheric dynamical changes are associated with Jz changes. Changes in surface pressure at high latitudes (the Mansurov effect) are associated with observed changes in polar cap ionospheric potential. This is the simplest and most direct phenomenon demonstrating Jz effects on tropospheric dynamics. (The ionospheric potential changes are due to IMF-By changes. Most of the time there are negligible other space weather inputs that could be responsible for the effects).

• The Mansurov effect, and atmospheric dynamical responses to solar proton events, together with the atmospheric dynamical changes that are associated with relativistic electron reductions and high H2SO4 mixing ratios) make a consistent picture for cloud microphysical responses due to Jz changes affecting atmospheric dynamics. Data on these responses is much more easily obtained and reliable than observations of Jz changes!

• The dynamical responses at relativistic electron minima can be understood as due to the Jz reductions, provided that there is a high middle atmosphere column resistance at that time.

SOLAR WIND ELECTRIC FIELD EFFECTS ON IONOSPHERIC POTENTIAL IN THE MAGNETIC POLAR CAPS

S Polar By+ or N Polar By- S Polar By- or N Polar By+

THE SOLAR WIND ELECTRIC FIELD ENTERING THE ATMOSPHERE VIA THE POLAR IONOSPHERES

The solar wind (VxB) electric field is mapped down magnetic field lines at magnetic latitudes greater than about 60o. The dawn and dusk excursions at 75o magnetic latitude are from Vxx Bz (that gives the east-west solar wind electric field). Superimposed is a variation, maximizing at the magnetic poles, due to Vxx By that gives a north-south solar wind electric field. As By changes from positive to negative, there are 30-50 kV excursions of ionospheric potential maximizing at the magnetic poles. The polar cap potential patterns are superimposed on a ~250 kV potential difference between the ionosphere and the earth’s surface generated by thunderstorms.

MOST RECENT ANALYSIS OF MANSUROV EFFECT

(a): Zonal mean pressure change (hPa) for By+ (red) and By-(blue), 1999-2002 (b) Difference between pressures for By+ and By- (c) Statistical significance.

Spatial dependence and polarity of IMF By dependence of ionospheric potential, from Weimer and Superdarn data.

From Lam, Chisham and Freeman, ERL 8, 045001, 2013

From the analysis of Kirkland et al., , 1996.

Superposed epochs, keyed to days of sector boundary crossings, November-March. Top: Solar wind speed. Middle: MeV electrons from geosynchronous orbit. Bottom: Northern hemisphere Vorticity Area Index.

Variation of the VAI response for high stratospheric volcanic aerosol winters compared with medium-to-low aerosol winters. Key days prior to 1995 are HCS crossings; from

1996 are relativistic electron flux minima.

From Tinsley et al., 2012

EFFECTS OF MIDDLE ATMOSPHERE H2SO4

• Polar H2SO4 molecules collide with and add to size and mass to ions, transforming light air ions to small cluster ions, that can grow to be intermediate and larger cluster ions.

• With sufficient H2SO4 the growing cluster ions can reach a critical size (~ 1 nm radius) where they are stable as neutrals and continue to grow to become nucleated aerosol particles.

• Aerosol particles serve as sites for attachment and recombination of air ions and cluster ions. Aerosol particles can be formed by nucleation on ions, or by classical homogenous nucleation, or nucleation on meteoric smoke particles, or on cosmic dust particles. Then attachment and recombination reduce the ion concentration and the conductivity.

• The clustering of polar molecules increases ion radius and mass, and reduces ion mobility and conductivity.

The initial mesospheric mixing ratio was 243 ppbm of H2SO4

NUCLEATION ON IONS JUST ABOVE THE WINTER STRATOPAUSE

The winter mesopause is not as cold and does not have the upward Brewer-Dobson flow of the summer mesopause.

Sulfate particles nucleated on ions or meteoric smoke particles do not grow as large, and are transported by the Brewer-Dobson flow towards the stratopause.

Just above the stratopause the high temperature liberates the H2SO4 from the neutral particles.

EFFECTS OF THE TEMPERATURE STRUCTURE OF THE MIDDLE ATMOSPHERE

• The stratosphere at 40 km was considered as a site for H2SO4/H2O aerosol production by Tinsley and Zhou, 2006. The mesosphere is are another potential region for conductivity reductions, although the mobility of the ions is higher. A greater mesospheric conductivity reduction is needed to create a middle atmosphere column resistance comparable to the tropospheric column resistance, for affecting the current density Jz.

• For condensation occurring near the temperature minimum of the mesopause, condensation may continue until the particles are large enough to fall towards the temperature maximum of the stratopause and evaporate.

• This was modeled by Mills et al. (2005) who found a mesospheric sulfate layer of aerosol particles, that in the summer polar region acts as nuclei for formation of polar mesospheric clouds, and polar mesospheric summer echoes, even in quiescent volcanic periods.

• As the temperature increases going towards the stratopause the particles will evaporate, and near and above the stratopause the H2SO4 and H2O molecules evaporate off the sedimenting particles, and then will preferentially attach to sub-critical ions.

Yu and Turco (2001) modeled ion mediated nucleation and the growth of the molecular clusters to nanoparticles at 288K. Kazil and Lovejoy (2004) found similar results for the middle and upper troposphere.

Kirkby et al., (2011) made laboratory measurements, with results consistent with the theoretical models.

292K

278K

248K

KIRKBY ET AL., 2011

ESTIMATES OF COLUMN RESISTANCE WITH H2SO4

Cosmic ray ionization rate, (q), e.g, from Tinsley and Zhou, (2006)Ion-ion recombination rate (α) from Bates (1982)Attachment rates (βi) from Hoppel (1985)_

Mobility of light (non clustered) air ions (µ) scaled with pressure and temperature from ‘reduced mobility’ (Gringel, 1985)Mesospheric H2SO4.H2O mixing ratio 60 ppbm. This is from (visible) solar occultation of lower stratospheric (20-25 km) particles for 18 months (30-60 ppbm) following Pinatubo (Deshler et al. 1993). Note that Mills et al (2005) estimated 243 ppbm initially in the mesosphere following Pinatubo. The Agung eruption(1963) injected more H2SO4 than Pinatubo.

Size distribution of molecular clusters and aerosol particles (Si) (from ion-mediated nucleation) from Yu and Turco (2001), for 1 hour after start of simulation.Considering only attachment of light (not clustered) air ions to particles. using

dn/dt = 0 = q - αn2 - ΣiβiSin

where n is light ion concentration, get resistivity (ρ), in Ωm 1.6x1012 at 65 km, 3.0x1012 at 60 km, 5.2 x1012 at 55 km, 1.0 x1013 at 50 km.Integration gives column resistance above 50 km of 7 x1016 Ωm2.Compare with clean air column resistance above 50 km of about 2 x1014 Ωm2.Compare with ionosphere-earth column resistance of about 1017 Ωm2 over oceans.

CONCLUSIONS.

• Ultrafine aerosol particles (diameter ~ 10 nm) are transparent to visible radiation, and thus cannot be observed by satellite or ground based measurements of solar occultation or scattered visible light. The presence of increased amounts of ultrafine aerosols would be only in a few years after major volcanic eruptions, and then effects on the global circuit for only for a few days at sub-auroral latitudes when the relativistic electron flux was at a deep minimum, such as at HCS crossings. Only at these times do observations of tropospheric potential gradient and current density show signatures of their presence.

• In the presence of relativistic electron precipitation and Bremsstrahlung radiation with energy exceeding the dissociation energy of clusters (~ 5 ev or 300 nm, Gupta, 2000) the ultrafine particles would be dissociated. In addition the relativistic electron precipitation creates large amounts of new ionization, and the high conductivity is restored.

• At deep solar minima, as in the Maunder Minimum, the relativistic electron precipitation is likely to be minimal, and large effects on the global circuit (and climate!) are to be expected.

• There have been large volcanic eruptions in addition to Pinatubo, e. g., Aging in 1963, and El Chicon in 1982, and much larger ones such as Krakatoa, Tambora, Taupo and Santorini in previous centuries. Large ones will again occur in the future. The effects on the global circuit of these would be worth modelling, using the approaches of Yu and Turco, Kazil and Lovejoy, and Mills et al.