What is the best model tool

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Abstract

The Sun is the primary source of energy for Earth's atmosphere. One possible natural cause of climatic change is a variation in the Sun's luminosity. The Sun emits its radiative energy in a broad spectral rank. One major and well-known mechanism of the Sun's influence on climate is the variability at short wave lengths that affect upper atmospheric ozone. The task on hand is to understand how the Earth's climate system responds to variations of the Sun. The research undertaken within the present dissertation is centered on the influence of the solar radiation on the middle atmosphere and on the down ward propagation of the resulting signal. Therefore, this work investigates the effect of variations of the solar irradiance, in particular of the spectral variability with emphasis on the UV radiation, on ozoneand other trace gases, and evaluates their influence on the temperature and dynamics of the entire atmosphere, from the mesopause to the Earth's surface. To fulfill this goal a new Chemistry Climate Model (CCM) with interactive photochemistry on the basis of MA-ECHAM4 has been developed. The middle-atmosphere general circulation model (GCM) MA-ECHAM4 is made available through collaboration with the Max-Planck Institute for Meteorology in Hamburg. MA-ECHAM4 has been coupled to the photochemistry-transport model MEZON. The resulting CCM has been called SOCOL (modeling tool for studies of SOlarClimate OzoneLinks, Russian "Falcon"). To validate how well SOCOL reproduces a present-day climatology, a 40-year long control run for present day conditions has been carried out and compared with observational and reanalysis data. The model performance is shown to be very satisfactory applying an overall inspection of the simulated physical and chemical fields as well as using a rigorous statistical analysis. At the same time a number of weaknesses have been identified in the model that need to be addressed for future model improvement. In particular, the analysis of the simulated zonal wind and temperature deviations shows that for an improvement it will be necessary to pay special attention to the tropopause region in the tropics and at high latitudes as well as to the description of the processes in the upper stratosphere and mesosphere , where statistically significant cold biases have been found in the model during boreal summer. Despite of these model deficiencies, the overall performance of the CCM SOCOL as a modeling tool is reasonable and many features of the real atmosphere are simulated rather well. The CCM SOCOL has been ported on regular PCs and was show not to attain good wallclock performance. Thus many research groups can use it for studies of chemistry-climate problems even without access to large super-computer facilities. With the CCM SOCOL several 20-year-long steady-state model simulations have been performed with detailed, realistic spectral energy distributions at maximum and minimum of the solar irradiance to determine their potential effects on the entire atmosphere and Earth's climate. The original MA-ECHAM4 radiation code has not been designed for solar variability studies: it has only one interval in the UV and visible parts of the solar spectrum and does not account at all for the solar flux at wave lengths shorter than 250 nm. Therefore , heating rates due to absorption in the UV by ozone and oxygen have been parameterized in the Lyman-oc line, Schumann-Rungeband and Hartley band, which are important in the stratosphere and mesosphere. First, the annual mean zonal mean solar signal in ozone, temperature, zonal wind and surface air temperature has been analyzed. Annual mean zonal mean values ​​of ozone, temperature and zonal wind have been compared with various results of observation analysis. An analysis for annual mean solar-induced changes for several species has been performed. Second, the annual mean analysis has been extended to seasonal and geographical patterns. The simulated response of ozone to the imposed changes in solar ultraviolet flux shows a positive correlation in the tropical stratosphere and a negative correlation in the tropical mesosphere, in agreement with theoreticalexpectation. The model suggests an acceleration of the polar night jets in both hemispheres and a dipole structure in the temperature changes at high latitudes. The model results also show an alteration of the tropospheric circulation and of the surface air temperature resulting in a statistically significant warming of 1 K in the annual mean over North America and Siberia. This supports the idea of ​​a solar-climate connection, which propagates down ward into the low levels of the troposphere. The influence of variations of UV and visible radiation on the atmosphere has been investigated separately because the atmosphere absorbs very differently. Two additional 20-year long runs have been carried out, one only with perturbations in UV radiation and another one only with changes in visible radiation. The results show that UV radiation variations may quite substantially alter stratospheric jet in contrast to visible radiation. The analysis shows that the changes in UV radiation do play a significant role in determining the surface air temperature distribution, similar to changes in visible, but due to a lag in the response with different strengths during different seasons. The study of the 27-day solar rotation cycle is also suitable for the model validation, because the observational data cover more then 100 such cycles, while only two 11-year cycles oecurred during the satellite era. Nine 1-year long runs have been performed applying daily spectral solar irradiance. The correlation of zonal mean hydroxyl radical, ozone and temperature averaged over the tropics with solar irradiance time series have been analyzed. The correlation of the hydroxyl with the solar irradiance changes is positive in the upper stratosphere and mesosphereand is in a good agreement with previous estimations, which confirms the model's treatment of chemical processes in the middle atmosphere. The response of the ozone to the increase of the solar irradiance is negative in the mesosphere for zero phase lags, reflecting the enhancement of the hydroxyl radical destroying the ozone. The simulated ozone sensitivity is in a reasonable agreement with observations. The temperature correlations with solar irradiance are not robust, because its variability strongly depends on non-linear dynamics and transport in the atmosphere. Finally, the possible ways of model improvement and future activity aimed to study solar-climate links are discussed. Further investigation of the identified solar-climate link is required, including overcoming the steady-state assumption made here, i.e. implying perpetual solar maximum or / and solar minimum conditions. The work has been supported by the Poly-Project "Variability of the Sun and Global Climate" of ETHZ and partly by PMOD / WRC, Davos. The sun is the primary energy source of the earth's atmosphere. One possible natural reason for climate change is variations in the sun's luminosity. The sun emits its radiation energy in a broad spectrum. A major, well-known mechanism of the sun's influence on climate is the short-wavelength variability that affects ozone in the higher atmosphere. The present task is to understand how the earth's climate system responds to variations in the sun. The research undertaken with this dissertation focuses on the influence of solar radiation on the middle atmosphere and on the downward propagation of the resulting signal. Therefore, this work examines the influence of variations in solar radiation intensity, in particular the spectral variability with a focus on UV radiation, ozone and other trace gases. It evaluates the influence on the temperature and dynamics of the entire atmosphere, from the mesopause to the surface of the earth. To achieve this goal, a new chemistry-climate model (CCM) with interactive photochemistry was developed on the basis of MA-ECHAM4. As part of a collaboration, the general circulation model (GCM) of the middle atmosphere MA-ECHAM4 was made available by the Max Planck Institute for Meteorology in Hamburg. MA-ECHAM4 was coupled to the MEZON photochemistry transport model. The resulting CCM is called SOCOL (model for studies of solar climate-ozone coupling, Russian "falcon"). To determine how well SOCOL reproduces current climatology, a 40-year control run was carried out for today's conditions and with observations and reanalysis data The performance of the model is very satisfactory based on a general assessment of the simulated physical and chemical fields and rigorous statistical analysis. At the same time, a number of weaknesses have been identified that need to be addressed for future model improvements Temperatures shows that special attention must be paid to improving the tropical and polar tropopause region, as well as an improved description of the processes in the upper stratosphere and mesosphere, where statistically significant systematic deviations mi t exist too low temperatures during the northern hemisphere summer. Despite these weaknesses, the functions of the CCM SOCOL as a model tool are adequate and many properties of the real atmosphere are well described. The CCM SOCOL was ported to regular PCs, whereupon good CPU runtimes can be achieved. Therefore, the model can be used for studies of the chemistry-climate problem by many research groups even without access to large supercomputers. With the CCM SOCOL, several stationary model simulations were carried out over 20 years each with detailed, realistic spectral energy distributions of the solar radiation intensity under conditions of the solar maximum and minimum in order to determine the potential effects on the entire atmosphere and the earth's climate. The original of the radiation code from MA-ECHAM4 is for investigations of solar variability: there is only one interval in the UV and in the visible parts of the solar spectrum and does not take into account the radiation flux at wavelengths shorter than 250 nm. Absorption by ozone and oxygen in the area of ​​the solar Lyman-Ct-Line, the Schumann-Runge-Band and the Hartley-Band can be parameterized, which are important in the stratosphere and mesosphere. For the model validation, first annual mean values ​​of the zonal mean of the solar signal in ozone, the temperature, the zonal wind and the soil air temperature were analyzed. Annual mean values ​​of ozone, temperature and zonal wind were compared with various analyzes derived from observations. Furthermore, an analysis of the annual mean values ​​of sun-induced changes in different species was carried out. Second, the analysis of the annual mean values ​​was expanded to include seasonal and geographical patterns. The modeled response of ozone to solar forcing shows a positive correlation in the tropical stratosphere and negative correlation in the tropical mesosphere, in agreement with the theoretical expectation. The model assumes an acceleration of the polar beam currents and a dipole structure of the temperature changes at great latitude. The model also shows a change in tropospheric circulation and surface temperature, which lead to a statistically significant warming of 1 K on an annual average over North America and Siberia. This supports the idea of ​​a sun-climate connection that spreads down into the lower layers of the troposphere. The atmospheric influence of the variations in the UV and visible spectral ranges was investigated separately because the atmosphere absorbs very differently in both ranges. Two additional 20 year long runs were performed, one with only the changes in UV, the other with only changes in visible irradiance. The results show that the changes in UV as opposed to changes in the visible - can substantially affect the beam current. The analysis shows that changes in UV radiation play a significant role in adjusting the surface temperature, similar to changes in the visible spectral range, but due to a time lag at different times of the year. Studying the 27-day cycle of the solar rotation offers another opportunity for model validation because the observations cover more than 100 such cycles, whereas only two 11-year cycles fall into the satellite era. Nine annual runs were carried out using daily, spectrally resolved power densities. The correlation between the zonally averaged concentration of hydroxyl radical, ozone and temperature over the tropics was determined. The correlation between OH and solar power density is positive in the upper strarosphere and mesosphere and is in good agreement with previous estimates, confirming the treatment of chemical processes in the middle atmosphere in SOCOL. The correlation of ozone is negative in the mesosphere due to ozone destruction from the additional OH and in agreement with observations. The temperature correlation is not robust because its variability depends heavily on nonlinear dynamics and transport. The possible avenues for model improvement and future activities related to the sun-earth connection are discussed. Additional investigations are necessary, including overcoming the stationarity assumption made here, which assumes a continuous solar maximum or minimum. The work was made possible by the Poly-Project "Variability of the Sun and Global Climate" of the ETHZ and partly by PMOD / WRC, Davos.Show more

Permanent link

https://doi.org/10.3929/ethz-a-005011563

Publication status

published

Contributors

Examiner: Ohmura, Atsumu
Examiner: Peter, Thomas

Subject

SOLAR RADIATION ABSORPTION, EMISSION AND DISPERSION (METEOROLOGY); SUNSHINE (METEOROLOGY); OZONE LAYER, ATMOSPHERE (METEOROLOGY); CLIMATIC FLUCTUATIONS (CLIMATOLOGY); CLIMATE MODELS + PROXY DATA (CLIMATOLOGY); CLIMATE FLUCTUATION (CLIMATOLOGY); METEOROLOGICAL MODELS; METEOROLOGICAL MODELS; SUNSHINE (METEOROLOGY); SOLAR RADIATION ABSORPTION (METEOROLOGY); CLIMATE MODELS + PROXY DATA (CLIMATOLOGY); OZONE LAYER (METEOROLOGY)

Organizational unit

03517 - Peter, Thomas / Peter, Thomas