Modeling of Joule heating influence on the circulation and ozone concentration in the middle atmosphere

 

Zubov^{a, *},V., E.Rozanov^b,d, A.Shirochkov^c, L.Makarova^c, T.Egorova^b,d, A.Kiselev ^a, Yu.Ozolin ^a, I. Karol^a and W. Schmutz^b

  ^a Main Geophysical Observatory, 7 Karbyshev street, St. Petersburg 194021, Russia,

 ^b Physical-Meteorological Observatory/World Radiation Center, Davos, Switzerland

 ^c Arctic and Antarctic Research Institute, 38 Bering street, St. Petersburg 199397, Russia

^d Institute for Atmospheric and Climate Science, ETH, Zurich, Switzerland

Abstract

A Chemistry Climate model is used to evaluate of the possible influence of Joule heating induced by the solar wind and interplanetary magnetic field (IMF) elements on the ozone concentration and dynamics of the Earth atmosphere. The Joule heating rates in the stratosphere are parameterized on the base of the time series of the solar wind and IMF parameters taken from the NASA  database  (King,1999) for 1996. The results of the 10-year-long model run with the additional Joule source of heat are compared with the output of the unperturbed(control) 10-year-long  model run. Both simulations are performed in equilibrium mode with prescribed boundary conditions and for the minimum of the 11-year solar  cycle. The comparison of the model outputs shows that the simulated atmosphere is rather sensitive to the introduced Joule heating. The most significant changes were found in the lower stratosphere of the Northern Hemisphere (NH). The NH lower-stratospheric temperature increases by 1-3 K almost throughout the whole year with the significance level at 95% or higher. In boreal summer the changes of the ozone concentration are anti-correlated with the temperature as expected from the gas phase photochemical theory. In boreal autumn and spring the variations of the ozone mixing ratio can be affected not only by the local temperature changes but also by the redistribution of the meridional circulation in the stratosphere. In the Southern Hemisphere (SH) the additional Joule heating leads to a significant increase of the stratospheric temperature for the austral winter (~2K). The most substantial SH ozone changes (~10%) are found in the lower stratosphere during the austral spring.

Corresponding author. E-mail address: zubov@main.mgo.rssi.ru (V. Zubov)

1. Introduction

 

Chemistry Climate Models (CCMs) are widely used to evaluate the role of atmospheric chemistry in the formation of the present-day climate as well as to evaluate the future climate system behavior under different emission scenarios (Austin et al., 2003; WMO, 2003). CCMs usually include the detailed 3D description of the dynamics, transport, photochemical processes and their interactions in the atmosphere (e.g. Rozanov et al., 2001). However, the model results still show substantial disagreements with the observational data. For example the majority of the models underestimate the temperature in the lower stratosphere, especially over the poles (Pawson et al. 2000; Austin et al., 2003). Another problem emerges when CCMs are used to simulate the dynamics and chemical response of the atmosphere to the changes of the solar irradiance during the 11-year solar cycle (11SC) ( Shindel at al., 2001; Tourpali et al., 2003, Egorova et al., 2004; Rozanov et al., 2004). There is substantial difference between the amplitude (sometimes even in the sign) of the 11SC signal in the stratospheric fields simulated by the models and the signal obtained from the measurement datasets covering now at least two of the last 11SCs (Hood, 2003; Labitzke et al., 2002).

One way to address the above mentioned problems is to include in a model additional heating sources. According to the recent investigations of Makarova et al. (2004a,b) such kind of heating source can be provided by the solar wind energy input into the global stratosphere. The “solar wind” here stands for the plasma flow of solar origin.

In this paper we evaluate the sensitivity of CCM SOCOL to the frictional or Joule heating rate (JHR) induced by the solar wind (SW) and interplanetary magnetic field (IMF) elements. The JHR are calculated on the basis of the parameterization proposed by Makarova et al. (2004a,b). The parameterization describes the chain of physical processes linking the SW and IMF parameters with the electric currents warming of the stratosphere (JHR). In this study we utilize the SW-IMF parameters for a specific year, namely 1996 (King,1999). However, it should be noted that the SW intensity has a substantial variability from the maximum to minimum of the 11-year solar cycle. Therefore the utilized parameterization can be used also to simulate    the influence of 11-year solar activity on the climate system through the mechanism of the Joule heating.

The paper has the following structure.  A brief description of SOCOL is presented in Section 2. Section 3 describes the design and conditions of the numerical experiments with the model. Section 4 contains the simulation results of the atmospheric response to the additional Joule heating. Conclusions and summary of the study are given in Section 5.

2. Short model description

 

SOCOL is a model tool to study SOlar-Climate-Ozone Links. It is a combination  of the Middle Atmosphere(MA)-ECHAM4 spectral General Circulation Model (GCM) (Manzini and McFarlane, 1998; Manzini et al., 1997) with a modified version of the University of Illinois at Urbana-Champaign atmospheric chemistry-transport model (CTM) described by Rozanov et al. (1999, 2001) and Egorova et al. (2001, 2003). T30 horizontal spectral truncation is used in the MA-ECHAM4. Vertically the model domain is divided into 39 hybrid sigma/pressure layers spanning the atmosphere from the surface to 0.01 hPa. The model time step for dynamics and physics calculations is set to 15 minutes while the radiation heating rates are recalculated every 2 hours. The atmospheric concentrations of 41 chemical species from the oxygen, hydrogen, nitrogen, carbon, chlorine and bromine groups are calculated in the chemical-transport part of the model. The chemical transformations are determined by 118 gas-phase and 33 photolysis reactions and 16 heterogeneous reactions on/in sulfate aerosol (binary and ternary solutions) and polar stratospheric cloud particles (Carslaw et al., 1995). The chemical solver is based on the pure implicit Newton-Raphson numerical scheme. The transport of the species is computed using the numerical advection scheme proposed by Zubov et al. (1999). A look-up-table approach is utilized to estimate the photolysis rates. To study solar-climate links the original photolysis rate parameterization (Rozanov et al., 1999) has been extended by taking into consideration the spectral intervals from 120 to 170 nm (Rozanov et al., 2002).

The GCM and CTM  are (fully interactive.) The winds, temperature and the troposphere humidity are transferred from GCM to CTM to provide the information for chemistry and transport calculations. The CTM returns to GCM 3-D fields of O₃ and stratospheric H₂O mixing ratios, which are used in the GCM radiation code to calculate radiative heating rates.

 

3. Experiment design

 

3.1 Boundary conditions

 

Two simulations have been performed with SOCOL in equilibrium mode representing the 1990s. The first 10-year long simulation takes into account the Joule heating induced by SW-IMF forcing in the stratosphere (perturbed run); the second 20-year long simulation has been performed without the additional JHR (control run). The sea surface temperature and the sea ice distributions are taken from Gates (1992) for the present day conditions. The stratospheric aerosol, greenhouse gas and ozone destroying substances concentrations, and the sources of NO_x, CO are the same as in (Rozanov et al., 1999, 2001). For the photolysis calculations we utilize the solar energy spectrum obtained by the SUSIM instrument onboard of the UARS satellite for the 11SC minimum case. The spectral irradiance used is compiled on the basis of the measurements performed during 1992-1998 (Haberreiter et al., 2002).

 

3.2 Joule heat forcing

 

According to Makarova at al.(2004a,b) the SW-IMF variability and the additional heating of the atmosphere in the 20-40 km altitude range are connected through the following physical processes. The variation of the SW dynamical pressure and vertical component of IMF distorts the shape and size of the Earth magnetopause, resulting to changes in   the strength of the electric field between the charged magnetopause and Earth surfaces. On the other hand there are charged particles in the 20-40 km layer, ionized   by the galactic cosmic rays. Thus, the imposition of electric field on the ionized medium leads to appearance of  electric currents and as a result to the Joule or frictional heating of the stratosphere in the 20-40 km altitude range.

            A parameterization routine has been developed and implemented in SOCOL. The input data are the SW-IMF parameters for 1996 from King (1999) and SOCOL meteorological fields (e.g. the number density of the air). During the SOCOL integration the routine works as a part of the model.  The JHR is calculated every 2 model hours in 10-year perturbed run. The monthly zonal mean values of the calculated JHR are shown in Fig. 1 (January - upper panel, August - lower panel). The January maximum of JHR (~0.18 K/day) is located around 10 hPa over the North Pole. In August the magnitude of the JHR reaches its maximum (~0.16 K/day) over the South Pole. The height-latitudinal distribution of the JHR is almost symmetric relative to the equator, but the winter Hemisphere is slightly warmer. It gets a little bit more amount of heat than summer Hemisphere. The longitudinal  distribution of the monthly mean JHR values (see Fig. 1b of Makarova et al. (2004b)) is rather uniform .

 

 

4. Results

 

The changes in the stratospheric temperature, circulation and ozone concentration resulting from the additional Joule heating are presented below for March, June, September and December. As mentioned above the parameterized heating rates depend mainly on the latitude and height. Seasonal variations of the JHR are not so much pronounced as the JHR changes from the low to high latitudes and from the tropopause to the 10 hPa level. The longitudinal dependence of the monthly mean JHR is almost absent. Such features of the Joule heating distribution in space and time allow us to restrict    the analysis only for the monthly and zonal mean fields in the stratosphere.

To account for the interannual variability of model results we tested the difference between our multiyear calculations (perturbed against control run) by the two sided statistical Student’s test of mean (von Storch and Zwiers, 2001). It allows us to clarify the JHR signal in the abovementioned stratospheric fields with a priori specified level of statistical significance (80% and 95% levels in this study).

 

4.1 March

 

Fig. 2 shows the monthly zonal mean temperature, zonal wind and ozone mixing ratio changes from the control to perturbed run in March. The temperature decreases more than 3 K over the high northern latitudes in the stratosphere (Fig. 2a). On the contrary the tropical lower stratosphere becomes significantly warmer (~2 K). The westerly flow is accelerated by about 5-8 m/s in the middle latitudes of the Northern Hemisphere (NH) according to the thermal wind balance (Fig. 2b). Such kind of changes can not be explained by the local impact of Joule heating. In the tropical low stratosphere the JHR is too small to provide up to 1.5 K warming. In the high and middle northern latitudes the JHR has even opposite sign in comparison with the simulated changes of the temperature. Probably these changes are due to the correspondent changes of the stratosphere circulation in the NH. As a result of the changes the polar jet in the NH becomes more intensive, resulting in weakening the intensity of the Brewer–Dobson circulation (upwelling fluxes in tropics and downward flow in the high-middle latitudes). The relevant changes of the ozone mixing ratio (Fig. 2c) provide additional evidence of the earlier mentioned changes of the meridional circulation. In the tropics the ozone concentration increases by 2% in the lower stratosphere. It can be connected to  the deceleration of the upwelling flow. The region of elevated ozone coincides reasonably well with the region of warming. In the polar region of the NH the ozone mixing ratio is significantly reduced (up to 10%). This depletion of the polar ozone concentration could be explained by the weakening of the downward movements and decrease of the horizontal ozone transport from the middle latitudes due to accelerated polar night jet. The changes of the temperature and zonal wind in the middle and high latitudes of the Southern Hemisphere (SH) are rather small and non-significant.

 

4.2 June

 

The response of the monthly zonal mean temperature, zonal wind and ozone mixing ratio to the additional Joule heating in June are presented in Fig. 3. The northern stratosphere over the high-middle latitudes becomes substantially warmer below 5 hPa (Fig. 3a). The warming reaches 3 K over the pole in the 20-50 hPa layer, while the temperature of the upper polar stratosphere decreases about 1 K. The NH response of the ozone mixing ratio anti-correlates with the temperature changes. The ozone concentration is reduced by about 2-5% in the lower stratosphere of the extra-tropical latitudes (Fig. 3c). This ozone-temperature relationship can be understood using the theory of the local photochemical processes. The rates of the gas phase photochemical reactions are sensitive to the ambient air temperature. Therefore, the stratospheric warming enhances the ozone destruction by the catalytic photochemical cycles (e.g. Brasseur and Solomon, 1984).

The easterly flow velocity increases slightly (about 2 m/s) almost throughout all the stratosphere of the extra-tropical latitudes (Fig. 3b). The local temperature effect on ozone is clearly visible under the conditions of the low interannual variability in the summer stratosphere. The significance level of the mentioned above changes is at 95% or better.

            In the high and middle latitudes of the SH stratosphere the temperature increases significantly up to 2K due to the additional Joule heating (Fig. 3a). These temperature changes are seen through the entire austral winter. They can be important for the formation of polar stratospheric clouds and chlorine activation during the polar night. As it will be shown below this  warming can substantially affect the ozone concentration inside the “ozone hole” area in the SH spring.

 

 

4.3 September and December

 

In September the response of the NH stratosphere to the additional Joule heating is close to its response in June (Fig. 4). The area of the ozone reduction (about 2-5%) coincides reasonably well with the region of warming (~3K) in the high and middle latitudes (Fig. 4c and Fig. 4a). The ozone increase in the upper polar stratosphere is believed to be due to not only the relevant cooling but also due to some weakening of the westerly zonal flow in the middle latitude of the upper stratosphere (Fig. 4c and Fig. 4b).

In December the local effect of the temperature changes on the ozone is not very large in the NH. The temperature increase (~1K) is accompanied by the ozone depletion by up to 2% in the lower stratosphere of the NH middle latitudes (Fig. 5a and Fig. 5c). However, the ozone changes are much more pronounced in the NH polar stratosphere. The ozone concentration increases by 7-10% over the North Pole (Fig. 5c). It can be explained by the weakening of the westerly jet in the stratosphere of the NH middle latitudes (Fig. 5b). The simulated changes of the zonal wind velocities in the NH are in line with the significant changes of the temperature according to the thermal wind balance (Fig. 5a). The polar jet becomes more unstable and that reduces the polar region isolation from the middle latitudes. This rearranging of the stratospheric circulation provides in turn the increase of the ozone transport from the middle latitudes to the polar area.

In  the Southern Hemisphere the ozone and temperature changes have the statistical significance (80% and higher) only in the austral spring (Fig. 4). The temperature of the upper and middle polar stratosphere decreases up to 3 K (Fig. 4a). It provides the stronger meridional gradient of temperature accompanied by the acceleration of the westerly polar winds (Fig. 4b). The stabilization of the polar flow prevents the penetration of the ozone rich air masses from the middle latitude to the polar region. As a result the ozone concentration decreases about 2% in the upper stratosphere of the high latitudes. However, below 10 hPa the ozone mixing ratio significantly increases. This increase reaches 15% at 50 hPa in the SH polar region (Fig. 4c). This could be explained by the expected decrease of polar stratospheric clouds of the type II (PSCII), consisting of H₂O ice in the polar lower stratosphere, because of their dependence on the thermal threshold. The warming during the austral polar night (see Fig. 3a) can reduce dramatically the PSCII amount to the beginning of the austral spring and as a result the photochemical release of the active chlorine and bromine radicals from the unstable Cl, Br–compounds formed by the heterogeneous reactions on PSCII particles. It reduces in turn the ozone depletion by these radicals in the catalytic cycles of the ozone destruction.

 

5. Conclusions

 

In this study the Chemistry Climate model SOCOL has been used to investigate the potential impact of the Joule heating in the stratosphere on the temperature, circulation and ozone concentration. The model has been integrated for 10 years in the two steady-state numerical experiments: with and without the additional Joule heating.

            Comparison of the results obtained from the model runs shows that  a well pronounced response of the stratosphere to the additional Joule heating was found in the NH. From May to September the NH temperature increases about 2-4 K in the lower-middle stratosphere and decreases about 1-2 K in the upper stratosphere. The simulated changes of the NH ozone concentration are anti-correlated with the temperature variations according to the photochemistry of the gas phase processes. The zonal wind changes are rather small. From May to September the simulated stratosphere in NH is characterized by a low interannual variability. Therefore, the obtained signals have a high level of statistical significance (at or more than 95%).

The reaction of the NH stratosphere from November to January is similar to the abovementioned stratospheric response. However, the statistical significance of the NH stratospheric signal is lower than for the period from May to September, possible due to higher interannual variability of the winter stratosphere. In October the changes of the temperature in the NH are similar to those obtained from May to September, but the zonal wind response in the middle latitudes is much more pronounced and provide the substantial increase of the ozone concentration (up to 10%) in the high latitudes of the NH upper stratosphere.

            The response of the NH stratosphere to the Joule heating has some special features for the transition time (February, March). In this period the stratospheric temperature decreases more than 3 K over the North Pole. The relevant increase of the westerly zonal flow (~10 m/s) leads to the additional isolation of the polar region and subsequent weakening of the Brewer-Dobson circulation. The ozone layer is depleted in the middle and high northern latitudes (by about 7-10%) due to these changes of the stratospheric dynamics.

In the Southern Hemisphere the heterogeneous chemistry plays an important role in  the stratospheric response to the SW-IMF forcing. The additional Joule heating leads to the significant increase of the temperature (about 1-2 K) in the SH stratosphere during the austral winter. Apparently this warming prevents the PSC-II formation in the polar night stratosphere of the SH. As result the largest  SH ozone changes (~10%) were found in the polar lower stratosphere during the austral spring.

We can conclude from the model results that the stratospheric circulation and ozone amount are rather sensitive to the Joule heating induced by the SW-IFM energy input into the stratosphere. The lower stratosphere becomes significantly warmer from the additional heating almost throughout the entire year in the NH and tropics.. Probably it will allow us to correct the cold bias problem of CCM SOCOL in the lower stratosphere at least partially.

 

Acknowledgments. This work has been supported by the INTAS project under grant INTAS-01-0432. The work of I.K., A.K., Y.O., and V.Z. was partially funded by RFFI (Russian Fund of Fundamental Researches, grant 02-05-65399). The work of E.R. and T.E. was supported by the Swiss Federal Institute of Technology, Zürich and Physical-Meteorological Observatory/World Radiation Center, Davos

 

 

Figure captions

 

Figure 1. Monthly zonal mean values of the parameterized Joule heating rate (K/day), (a) for January, (b) for August.

Figure 2. Simulated changes of the monthly zonal mean (a) temperature, in K, (b) zonal wind, in m/s, and (c) ozone mixing ratio in %, due to Joule heat forcing for March. The shading indicates the level of the statistical significance (light – at or better than 80%; heavy – at or better than 95%).

Figure 3. Same as at Fig. 2, but for June.

Figure 4. Same as at Fig. 2, but for September.

Figure 5. Same as at Fig. 2, but for December.

 

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