Understanding the Observed Ozone and Thermal Response To 11-Year Solar Variability

Lon Hood

Lunar and Planetary LaboratoryUniversity of Arizona

Tucson, Arizona

Thanks to: Boris Soukharev, John McCormack, John Austin, Katja Matthes, Bill Randel,K. Shibata

AGU Chapman Conference on: The Role ofthe Stratosphere in Climate and Climate Change Santorini Island, Greece September 28, 2007

MOTIVATION:

1. One potential sun-climate mechanism involves a dynamical responseto stratospheric heating changes associated with increased solar UV radiation and solar-induced changes in stratospheric ozone (e.g., previous talk).

2. In order to simulate accurately the solar UV induced heatingchanges in the stratosphere, it is first necessary to determine and understand solar induced changes in the ozone distribution. It is also necessary to evaluate whether solar induced dynamical heating changes occur in the lower stratosphere (Kodera’s talk yesterday).

Evidence for a solar cycle variation of total ozone in the Version 8 TOMS/SBUV data record calibrated by Frith et al. (2004).

MULTIPLE REGRESSION STATISTICAL MODEL:

O3(t) = ctrendt + cQBOu30mb(t-lagQBO) + cvolcanicAerosol(t) +

csolarMgII(t) + (t)

,

where:

t = time measured in 3-month seasonal increments

O3(t) = deviation of ozone from the seasonal mean,

u30mb(t- lagQBO) = FUB 30 hPa equatorial zonal wind speed (lagged)

Aerosol(t) = Volcanic aerosol index (10 hPa and below only)

MgII(t) = Solar MgII UV index

(t) = residual error term

Ozone solar regression coefficient derived from V. 8 SBUV/SBUV(/2) Data:

Shaded areas are statistically significant at 95% confidence.

Ozone solar regression coefficient derived from SAGE II Data:

Shaded areas are statistically significant at 95% confidence.

Ozone solar regression coefficient derived from UARS HALOE Data:

Shaded areas are statistically significant at 95% confidence.

Summary: Ozone solar cycle regression coefficient derived from three independent satellite data sets :

Shaded areas are statistically significant at 95% confidence.

SBUV

Ozone Solar Regression Coefficient (min to max) at low latitudes derived from SBUV, SAGE II, and UARS HALOE data:

???

?

Ozone Solar Regression Coefficient at low latitudes derived from SBUV datafor three different time periods:

Comparison with Representative 2D and 3D Model Simulations: 25oS to 25oN

Comparison with Representative 2D and 3D Model Simulations: 25oS to 25oN

Austin et al. , ACP, 2007: Coupled Chemistry Climate Model Simulations of the Stratospheric O3 Variation (no QBO):

45-Year Simulations using observed SSTs, observed aerosol extinctions, and solar UV forcing (both 11-year and 27-day).

Matthes et al., in preparation, 2007:

110-Year Simulation relaxing to observed QBO winds, fixed SST’s, solar UV forcing, and particle precipitation forcing at high latitudes.

NCAR WACCM3:

SAGE II:

1. Solar ultraviolet forcing effectively reduces the tropical upwelling rate

near and approaching solar maxima (Kodera and Kuroda, 2002).

Possible Dynamical Mechanisms for Explaining the Unexpected Vertical Structure of the Solar Cycle Ozone Response in the Tropics:

•Light shaded areas are significant at the 2 (95% confidence) level; dark shaded areas are significant at 99% confidence

ERA-40 Seasonal Zonal Wind Solar Regression Coefficient 1979-2001 Crooks and Gray [2005]

Kodera and Kuroda (2002):

Transport-induced ozone increase

Excluding periods following major volcanic eruptions, the decadal variation seen in the TOMS/SBUV column ozone record is also seen in the MSU Channel 4 temperature record at low latitudes.

Courtesy of W. Randel

Temperature solar regression coefficient derived from SSU/MSU4 Data (1979-2005)

(K / 100 Units F10.7 ?)

Temperature solar regression coefficient derived from ERA-40 Data (1979-2001)

Crooks and Gray (2005):

Multiple regression model: Linear trend, QBO (first 2 PC’s of residual of a regression of ERA-40 zonal wind onto 18 other indices), solar cycle, volcanic aerosol, ENSO.

1.75 K

0.5

(Solar Max - Min)

Temperature solar regression coefficient derived from ERA-40 Data (1979-2001)

K. Shibata et al. (2007):

Multiple regression model: Linear trend, QBO (50 and 20 hPa eq. zonal wind time series), solar cycle, Pinatubo aerosol with lag, El Chichon aerosol with lag, ENSO.

1.4

The vertical structure of the temperature solar cycle variation estimated by Shibata et al. from the ERA-40 data is similar to that derived from long-term ozone data sets.

1. Solar ultraviolet forcing effectively reduces the tropical upwelling rate

2. Solar induced circulation anomalies in the upper stratosphere may also perturb the equatorial quasi-biennial wind oscillation, which is the dominant cause of interannual ozone variability in the tropical lower stratosphere.

near and approaching solar maxima (Kodera and Kuroda, 2002).

Possible Dynamical Mechanisms for Explaining the Unexpected Vertical Structure of the Solar Cycle Ozone Response in the Tropics:

Possible Evidence for a Solar Cycle Modulation of the QBO as Proposed Originally by Salby and Callaghan (2000):

R = -0.20 at zero lag; not significant.R = -0.51 at 1-year lag; significant at > 90% confidence.R = -0.64 at 2-year lag; significant at > 95% confidence.

During the east phase of the QBO (at 40 hPa), the vertical wind shear near 10 hPa is westerly. This produces transport-induced increases in NOx which cause photochemical ozone decreases. These decreases appear to be deeper and longer near solar maxima.

E

East Phase Winds, ERA-40 Composite:

From Pascoe et al., 2005

E

McCormack et al. , in press, 2007: 2D Model Simulations of the Effect on Ozone of a Solar-Modulated QBO:

Exp 1: Solar UV Forcing Only (no QBO)Exp 2: Solar UV + Solar-Modulated QBOExp 3: Solar UV + QBO + Imposed 11-Year Planetary Wave Forcing

1. A solar cycle variation of ozone and temperature occurs

CONCLUSIONS

2. No statistically significant solar cycle ozone response occurs in the tropicalmiddle stratosphere (~ 10 hPa). It is suggested that this may be caused, at least in part, by a solar modulated QBO, which effectively enhances the odd nitrogen response to the easterly QBO phase under solar maximum conditions.

in the lower stratosphere. This may be caused by solar UV-induced changes in the subtropical winter upper stratosphere, which effectively reduces the tropical upwelling rate near solar maxima (Kodera and Kuroda, 2002).

3. Several recent studies using CCCM’s have been able to simulate, at least qualitatively, the observed double-peaked structure of the tropical ozone response. However, to do so, it has so far been necessary to force the models using either observed SST’s or observed QBO winds. No fully self-consistent simulation has yet been performed.

During the east phase of the QBO (at 40 hPa), the vertical wind shear near 10 hPa is westerly. This produces transport-induced increases in NOx which cause photochemical ozone decreases. These decreases appear to be deeper and longer near solar maxima.

E

East Phase Winds, ERA-40 Composite:

From Pascoe et al., 2005

E

Evidence for a solar cycle variation of total ozone in the Version 8 TOMS/SBUV data record calibrated by Frith et al. (2004).

The UARS HALOE data set (e.g., Remsberg et al., JGR, 2001) provides relatively accurate measurements of the ozone profile in the lower stratosphere.

HALOE

Correlation coefficient between TOMS/SBUV total ozone and HALOE ozone profile data averaged between 35S and 35N.

R = 0.58

Excluding periods following major volcanic eruptions, the decadal variation seen in the TOMS/SBUV column ozone record is also seen in the MSU Channel 4 temperature record at low latitudes.

2. Pascoe et al., 2005: The transition from the QBO west phase to the

1. McCormack, 2003; McCormack et al., 2007: Solar-induced heating

QBO east phase is inhibited when the tropical ascending branch of the Brewer-Dobson circulation is strong (Kinnersley and Pawson, JAS, 1996). The tropical ascending branch of the Brewer-Dobson circulation is strongest under solar minimum conditions (Kodera and Kuroda, 2002). Therefore, the duration of the westerly QBO phase tends to be longer under solar minimum conditions.

Two Possible Ways in Which the QBO may be Perturbed by the Solar Cycle:

changes modify the residual meridional circulation in the tropical stratosphere, producing vertical velocity anomalies causing the westerly QBO phase to descend more rapidly near solar maxima than near solar minima. This results in a longer westerly phase duration near solar minima.

In the SAGE II data, there also appear to be deeper, longer ozone minima during the QBO east phase near the two solar maxima (excluding the Pinatubo period):

EE

E

Vertical structure of the ozone QBO:

Vertical structure of the NOx QBO:

Randel and Wu, JAS, 1996

Randel and Wu, JAS, 1996

1. The rate of descent of the easterly QBO shear zone is slower and more variable than that of the westerly shear zone.

Paper by Pascoe et al., JGR, 2005 (see also Baldwin et al., Rev. Geophys., 2001):

2. Kinnersley and Pawson (JAS, 1996) argue that changes in the descent rate of the QBO easterlies are influenced by the annual variation of the strength of the Brewer-Dobson upwelling at the equator, which is weakest during May, June, and July.

From Baldwin et al., 2001Easterlies Westerlies

From Pascoe et al., 2005

Frequency of transitions from west to east phase at 44 hPa:

Paper by Pascoe et al., JGR, 2005:

3. Under solar maximum conditions, the rate of descent of easterlies is faster than otherwise. This causes the duration of the westerly phase to be longer under solar minimum conditions (cf. Salby and Callaghan, 2000).

If the Kinnersley and Pawson interpretation is correct, this suggests a weaker B-D ascent branch under solar maximum conditions. The latter would be consistent with higher total ozone in the tropical lower stratosphere near solar maximum.

Easterly Descent Rate West Phase Duration at 44 hPa

Evidence for a solar cycle variation of total ozone in ground-based Dobson spectrophotometer data (after WMO, 2006).

Dobson Data

(Anthropogenic Chlorine)

Comparison of five long-term total ozone data sets with the solar 10.7 cm radio flux, a proxy for solar UV variations (from WMO, 2006).

F10.7

Indirect evidence for a statistically significant response of tropical lower stratospheric ozone to 27-day solar UV variations.

The observed column ozone response amplitude (about 0.9 DU / 0.01 Mg II units) is about 1.5 times larger than expected based on the observed upper and middle stratospheric ozone response.

Evidence for a statistically significant response of tropical lower

stratospheric temperature to 27-day solar UV variations:

From Hood, GRL, 2003

NCEP Temperature, 20oS to 20oN:

First, consider a region where the solar signal is relatively strong and significant: 4 hPa, 20S - 40S