Planetary Atmospheres in the Solar Wind: Do Intrinsic Fields Really Shield?
The solar wind continually bombards the planets with a supersonic stream of magnetized plasma, capable of both removing and adding to their atmospheres. Two of the terrestrial planets, Venus and Mars, have no significant intrinsic magnetic field, while the Earth has a strong intrinsic magnetic field that potentially could prevent the addition or removal of atmospheric constituents. We review the solar wind interaction with these three planets and find magnetic shielding present even when the planet does not have an intrinsic magnetic field. Similarly, we find that the presence of a strong intrinsic magnetic field is no guarantee that the atmospheric loss rate will be small. As a result, the loss rates of the three terrestrial planets are remarkably similar at current times. However, the different controlling processes that prevail in these two types of interactions do not necessarily extrapolate back in time in the same ways, leaving the relative historical impacts an open question.
Observed variations of Earth's radiation belt intensities on annual and solar cycle time scales
The Earth's radiation belts show pronounced differences in their characteristics as the Sun's magnetic and solar wind properties change over the 11-year solar cycle. Solar coronal holes can produce regular, recurrent solar wind stream interactions in geospace, often enhancing highly relativistic electrons (HREs) and causing recurrent magnetic storms. These phenomena are characteristic of the approach to solar minimum. This contrasts with major geomagnetic disturbances associated with aperiodic coronal mass ejections that occur most frequently around sunspot maximum. The high-energy trapped electrons can produce deep-dielectric charging in spacecraft systems and subsystems. Rapid discharging during electron irradiation can cause severe (or even fatal) operational anomalies in operating spacecraft. We present observational and modeling results that demonstrate the electron acceleration and loss effects throughout the inner part of geospace during various parts of the solar cycle. We place particular emphasis on long-term, homogeneous data sets from the SAMPEX and POLAR missions. We discuss how present and future missions can contribute to International Living With a Star (ILS) goals and to improved understanding of electron acceleration, loss, and operations impacts.
Coupling the Regions of the Atmosphere by Precipitating Energetic Particles
Through dissociation and ionization, energetic precipitating particles (EPP) of solar and magentospheric origin affect atmospheric composition, creating reactive species such as NO and NO2. Together, NO and NO2 (collectively referred to as NOx), are the primary catalytic destroyers of ozone (O3) in most of the stratosphere. Through its impact on O3, EPP-produced NOx (EPP-NOx) influences the local composition, temperature, and dynamics. Numerous times throughout the solar cycle, EPP-NOx is created directly in the stratosphere by very high energy particles. Additionally, EPP-NOx is created on a routine basis in the mesosphere and lower thermosphere (~80 - 150 km) by lower energy particles. In the polar winter where photodissociation is minimized, EPP-NOx lifetimes are long enough that it can descend to the stratosphere if meteorological conditions are appropriate. Evidence for effects on the stratosphere by EPP-NOx is prevalent. A recent and surprising result is that SECEP is seen not only in years of high geomagnetic activity, but also in years when geomagnetic activity was low and atmospheric descent was strong. This result indicates that the production of NOx through energetic particles is potentially an important element in O3 depletion regardless of the level of geomagnetic activity and that EPP influences can often be enhanced by favorable serendipity between space weather and stratospheric meteorology. Further, it suggests that the atmospheric response to EPP will be modulated by the meteorological response to climate change. In this talk we review the evidence for Sun-Earth coupling through energetic particles and discuss the required observations to determine their full impact on the weather and climate of the entire atmosphere.
All Solar Minima are not Alike: Consequences at Earth
New observations that were collected as part of the IHY Whole Heliosphere Campaign are changing our present understanding of solar quiet intervals and the solar minimum sun-Earth system. These observations indicate that significant differences in coronal hole distribution can occur at the Sun from one solar minimum to the next. The high-speed coronal hole wind is the primary source of space weather disturbances that perturb the Earth's upper atmosphere and create reactive species. The broad low-latitude coronal holes that developed this solar minimum produced strong, long-lived and recurring high-speed streams. This is in contrast to the weaker and more sporadic streams last solar minimum produced by narrow equatorward extensions from polar coronal holes. Since the speed, duration and southward magnetic field component determine the severity of space weather effects, the geospace environment responds quite differently to these two coronal hole distributions. Despite the fact that the present solar minimum is exceptionally quiet with sunspot numbers the lowest in 75 years, solar wind density and IMF strength at the lowest values ever observed and with geomagnetic indices and solar EUV fluxes the lowest in three solar cycles, magnetic activity at Earth is showing new features and has remained surprisingly strong. The details of newly discovered geospace and upper atmospheric effects are described and possible reasons behind them discussed. What these new data sets demonstrate is that the distribution of low-latitude open magnetic flux on the Sun is a key factor in determining how the Earth will respond to a given solar minimum. If the low sunspot conditions of solar minima have analogies to conditions during solar "grand minima" (where sunspots all but disappear for extended periods), then these new results imply that high-speed solar wind streams may introduce complexities to the Earth's response during these times as well.
Decoupling of Lower Troposphere Pressures Observed on Italian Mountains: Consequences of Sun Storms?
Hourly data of atmospheric pressure are normally recorded on Italian active volcanoes (Etna, Stromboli, Vesuvio), as side parameters for environmental and volcanic hazard monitoring purposes. During the 2002-03 Stromboli eruption some wind and air temperature anomalies, directly linked to the volcanic activity, were identified on the top of the volcano. After the eruption, an analysis on the dataset looked for further independent parameters, theoretically influenced by the anomalous air circulation discovered over the top. In particular, attention was focused on the atmospheric pressure, supposing that this parameter could be influenced by circulation of hot air due to volcanic activity. In order to check the anomalies with external control points, data from Stromboli were compared with information from other volcanic and not volcanic areas. What we found were evidences of atmospheric pressure anomalies recorded in all the measuring sites, occurred at least in three different episodes in the periods September-November 2003, July-August and October 2004. The main characteristic of the anomalies was a decoupling of the signal recorded near sea level with respect to that one recorded at higher altitudes (900-1810 m), evidenced by a dramatic decrease in the correlation coefficients calculated, on weekly basis, between the hourly values of atmospheric pressure. No anomalous volcanic activity or atmospheric circulation were signaled during these periods. On the contrary, the anomalies appear to be strongly correlated with the level of solar activity, as determined by the values of the electromagnetic index Kp and of the Wolf number Wf.