Stergios Misios

Mechanisms involved in the amplification of the 11-year solar cycle signal in the tropical Pacific Ocean

AbstractIt is debated whether the response of the tropical Pacific Ocean to the 11-yr solar cycle forcing resembles a La Nina– or El Nino–like signal. To address this issue, ensemble simulations employing an atmospheric general circulation model with and without ocean coupling are conducted. The coupled simulations show no evidence for a La Nina–like cooling in solar maxima. Instead, the tropical sea surface temperature rises almost in phase with the 11-yr solar cycle. A basinwide warming of about 0.1 K is simulated in the tropical Pacific, whereas the warming in the tropical Indian and Atlantic Oceans is weaker. In the western Pacific, the region of deep convection shifts to the east, thus reducing the surface easterlies. This shift is independent of the ocean coupling because deep convection moves to the east in the uncoupled simulations too. The reduced surface easterlies cool the subsurface but warm the surface due to the reduction of heat transport divergence. The latter mechanism operates together w...

Projected changes in solar UV radiation in the Arctic and sub-Arctic Oceans: Effects from changes in reflectivity, ice transmittance, clouds, and ozone

Ultraviolet-B (UV-B), UV-A, and erythemal solar irradiance over ocean-covered areas north of 55°N are simulated for the past (1950–1960), present (2005–2015), and future (2090–2100) using a radiative transfer model. The simulations focus mainly on the effects of changes in ocean surface reflectivity, cloudiness, and stratospheric ozone. Based on projected changes in sea ice cover and thickness, changes in irradiance transmitted into the ocean are also derived. The input parameters of the radiative transfer model were obtained from four Coupled Model Intercomparison Project phase 5 Earth System Models driven by the emission scenarios Representative Concentration Pathway (RCP) 4.5 and RCP 8.5. Over a large fraction of the area under study, the overall effect from the projected changes in the factors considered is a reduction in the ultraviolet solar irradiance by the end of the 21st century relative to the levels in the 1950s. Increases were projected only for all skies during August for locations below 65°N due to the projected decrease in cloudiness. The reduction in clear-sky UV-A irradiance (on average 4–7% depending on scenario and season) is entirely driven by the reduction in surface reflectivity, while the projected ozone recovery is responsible for a great portion of the reduction in clear-sky UV-B irradiance (10–18% on average). Under all skies, the changes in the monthly mean noontime erythemal irradiance range from +15% to −38%, depending on the location and season. Compared to the 1950s, up to 10 times higher levels of UV-B irradiance are projected to enter large parts of the Arctic Ocean by 2100, mainly because of the partial disappearance of sea ice.

A new observational solar irradiance composite

Variations in the solar spectral irradiance (SSI) are an important driver of the chemistry, temperature, and dynamics of the Earths atmosphere and ultimately the Earths climate. To investigate the detailed response of the Earths atmosphere to SSI variations, a reliable SSI data set is needed. We present an observational SSI composite data set that is based on 20 instruments and has been built by using probabilistic approach that takes into account the scale‐dependent uncertainty of each available SSI observation. We compare the variability of this new composite with available SSI reconstructions and discuss the respective modeled responses in the Earths atmosphere. As the composite is based on purely statistical means, we consider it as a valuable independent data set.

The atmospheric response to solar variability: simulations with a general circulation chemistry model for the entire atmosphere

The coupled general circulation and chemistry model HAMMONIA and the MPI-ESM, consisting of the MAECHAM5 atmospheric GCM and the ocean model MPIOM, have been applied in a multitude of setups to study the response of the earth system to the variable forcing from the sun. This paper motivates the use of complex entire atmosphere models for the study of solar-terrestrial relations, and presents numerical results concerning solar rotational forcing, the response of the atmosphere-ocean system up to the lower thermosphere to 11-year forcing, and the response to particle precipitation. An issue analyzed in more detail is the so-called “secondary” response maximum in equatorial lower stratospheric ozone and temperature. Comparing numerical experiments with a variety of simulation setups it is argued that solar signals in this atmospheric region are easily obscured by variability stemming in particular from ENSO. However, simulations with solar variability as the only variable forcing suggest that indeed, the secondary maximum is of solar origin.

Solar influences on climate over the Atlantic / European sector

There is growing evidence that variability associated with the 11-year solar cycle has an impact at the Earth’s surface and influences its weather and climate. Although the direct response to the Sun’s variability is extremely small, a number of different mechanisms have been suggested that could amplify the signal, resulting in regional signals that are much larger than expected. In this paper the observed solar cycle signal at the Earth’s surface is described, together with proposed mechanisms that involve modulation via the total incoming solar irradiance and via modulation of the ultra-violet part of the solar spectrum that influences ozone production in the stratosphere.

Stratospheric Responses to the 11-year Solar Cycle in MAECHAM5 with and without Ocean Coupling

The current generation of general circulation models (GCMs) faces major difficulties in reproducing, both qualitatively and quantitatively, the observed stratospheric response to the 11-year solar cycle. Because the majority of the previous studies used atmosphere-only GCMs without ocean coupling, it has been suggested that the inclusion of ocean dynamics may improve the simulated solar cycle signals. Our ensemble simulations with a coupled atmosphere-ocean GCM shows no indication that the ocean coupling alters significantly the solar cycle signals in the stratosphere. Although a measurable warming in the tropical oceans during solar maxima is detected in the coupled ensemble, its amplitude is too weak to affect the stratosphere. As such, the simulated temperature and zonal-mean zonal wind changes in the stratosphere are qualitatively similar both in the coupled and uncoupled ensembles. The simulated tropospheric response to the solar cycle forcing, however, differs significantly between the ensemble with and without ocean coupling.

Pathways, Impacts, and Policies on Severe Aerosol Injections into the Atmosphere: 2011 Severe Atmospheric Aerosols Events Conference

WHat: Geologists, meteorologists, physicists, and numerous scientists from other disciplines met to discuss climatic and environmental changes as a result of various kinds of huge injections of aerosols into the atmosphere and the possible consequences for the world population. WHen: 11–12 August 2011 WHere: Hamburg, Germany H uge amounts of aerosols can be generated by volcanic eruptions, forest fires, and asteroid impacts. They would also occur as a result of nuclear weapon explosions and subsequent fire storms. Climate engineering might make use of the strong effects of large amounts of aerosols with the goal of reducing the solar radiation that warms the atmosphere. These events were topic of an international conference1 of the Research Group Climate Change and Security (CLISEC) of KlimaCampus at the University of Hamburg and the King Abdullah University of Science and Technology, Saudi Arabia (KAUST). It was at the KlimaCampus of the University of Hamburg that, for the first time, one meeting included discussions of all kinds of aerosol sources in all aspects, from pathways and impacts to policies. The conference was divided into four sessions, each dealing with different aspects of large aerosol injections, and included a lecture by O. B. Toon about severe atmospheric aerosol events along the geologic time scale. The following summarizes the sessions. LI F E CYC LE O F L A RG E A E RO SO L INJECTIONS. The first session dealt with the life cycle of large aerosol injections from particle generation, injection into the atmosphere, vertical transport mechanisms, and transfer into the stratosphere, as well as various kinds of removal processes. H.-F. Graf reported on a simulation of volcanic and biomass-burning plumes with a very high resolving numerical model. D. Kunkel talked about the risk