U11A-01 INVITED 08:00h
Solar Variability and Climate Change
One of the most exciting and important challenges in science today is to understand climate variability and to make reliable predictions. The Earth's climate is a complex system driven by external and internal forces. Climate can vary over a large range of time scales as a consequence of natural variability or anthropogenic influence, or both. Observations of steadily increasing concentrations of greenhouse gases --primarily man-made-- in the Earth's atmosphere have led to an expectation of global warming during the coming decades. However, the greenhouse effect competes with other climate forcing mechanisms, such as solar variability, cosmic ray flux changes, desertification, deforestation, and changes in natural and man-made atmospheric aerosols. Indeed, the climate is always changing, and has forever been so, including periods before the industrial era began. Since the dominant driving force of the climate system is the Sun, the accurate knowledge of the solar radiation received by Earth at various wavelengths and from energetic particles with varying intensities, as well as a better knowledge of the solar-terrestrial interactions and their temporal and spatial variability are crucial to quantify the solar influence on climate and to distinguish between natural and anthropogenic influences. In this paper we give an overview on the recent results of solar irradiance measurements over the last three decades and the possible effects of solar variability on climate.
U11A-02 INVITED 09:00h
Space Weather From Explosive Events at the Sun
Space Weather is a broad new field of research that seeks to understand short-term disturbances in the Earth-Sun system that can directly affect life and society. The importance of Space Weather has grown in direct proportion to our society's increasing use of advanced technological systems that can be affected by transient conditions in the Earth-Sun system. Communications systems, satellite and Space Station operations, astronauts, and airline passengers have all been impacted by Space Weather events. Although Space Weather events have many causes, the most extreme are associated with explosions in the solar corona. The explosions occur when large magnetic loop structures become unstable and release much of their energy in a matter of minutes. This unleashes a sequence of events, including rapid heating of the Earth's atmosphere from UV radiation and filling the inner solar system with high energy ionizing radiation. Finally, if the explosion occurs close to the middle of the solar disc, a shock wave from the explosion will impact and energize the Earth's magnetosphere one or two days later. Understanding these events involves solving a large group of scientific questions, such as why the magnetic loops go unstable; how they lose their energy; how the shock is formed and how it interacts with material along its path to energize ions to a significant fraction of the speed of light. The reaction of the Earth's magnetosphere and radiation belts to the impact of such a shock, and the eventual effects on the Earth's atmosphere are further broad areas of inquiry that seek to understand the final stages of the event. Over half of the SH sessions at this AGU meeting deal with aspects of such problems, and a new NASA program (Living With a Star) is dedicated to understanding this system with an eventual goal that will enable U.S. forecasting. A broad new set of observations along with extensive development of theories and numerical models will be needed to achieve this goal. This tutorial will introduce the topic, focusing on scientific investigations involving the shocks and high speed ions (Solar Energetic Particles) associated with these events. The generation of high speed ions, like many aspects of Space Weather, is of broad interest since it occurs at many sites through the solar system and universe.