SH54B-01
Solar-Induced Climate and Production-Change Impacts on Beryllium-10
The link between the production of the cosmogenic isotope Beryllium-10 and changes in the sun's magnetic activity makes 10Be archives important resources for understanding how solar activity may have varied in the past. Thanks to the excellent time resolution that ice core records provide, 10Be observations from Greenland and Antarctica have the potential to offer crucial insights. However since Earth's climate is subject to other types of influences aside from those directly related to solar variability, it is important to understand how to disentangle the confounding effects that heliomagnetic change and climate change can both have on 10Be snow concentration. In particular, prolonged solar minima (like the Maunder Minimum) have the potential to affect climate on larger temporal and spatial scales. Our recent climate simulations using the Goddard Institute for Space Studies ModelE general circulation model focus on calibrating the impacts that irradiance changes and climate changes can have on 10Be during periods such as the Maunder Minimum. The experiments illustrate the effects of a range of climate- and production-change scenarios in an effort to better understand the conditions under which simulated 10Be changes correspond to observed values.
SH54B-02
Calibrating the Sunspot Number Using "the Magnetic Needle"
The 400-year long sunspot series is our primary direct record of Space Climate. Two series exist: the Zurich (now: International) series compiled by Wolf and successors, and the Group series by Hoyt and Schatten. The two series agree well back to ~1875, but before that the Group SSNs are systematically lower than the Wolf SSN. Wolf (and others) noticed that the amplitude, rD, of the daily variation of the Declination of the geomagnetic field varied with the sunspot number, R, and proposed a linear relationship: rD = a + bR. In fact, he used this relationship to calibrate the sunspot number for times before his own observations started (1849). Later researchers were less enthusiastic about this procedure. We re-examine Wolf's relationship using the range of the East component measured in force units [nT], rY, instead. This range is directly related to the intensity of the ionospheric SR currents, which in turn depends on the conductivity of the ionosphere. Solar FUV radiation creates and maintains the ionosphere, therefore the rY range (corrected for the secular decrease of the Earth's main field) is a proxy of the FUV. We show that this proxy reproduces the F10.7 radio flux and the International sunspot number with a correlation coefficient of 0.985, and recalibrate the sunspot number back to 1841 [Geomagnetic data exists that may allow such recalibration back to the 1740s]. The main conclusion is that there does not seem to be any secular increase in solar activity over the last 165 years: cycles 11 and 10 were as active as the most recent cycles 22 and 23.
SH54B-03 INVITED
A Continuous Long-Term Record of Magnetic-Storm Occurrence and Intensity
Hourly magnetometer data have been produced by ground-based magnetic observatories for over a century. These data are used for a wide variety of applications, including many for space physics. In particular, hourly data from a longitudinal necklace of mid-latitude observatories can be used to construct a time series recording the storm-time disturbance index Dst, one of the most useful scalar summaries of magnetic storm intensity which is generally interpreted in terms of an equivalent equatorial magnetospheric ring current. Dst has been routinely calculated in a temporally piece-wise fashion since the IGY using a subset of the available observatories: four or five stations, typically including Honolulu (HON), San Juan (SJG), Kakioka Japan (KAK), Hermanus South Africa (HER), and Alibag India (ABG). In this presentation we discuss a single continuous Dst time series made using a denser and more uniform distribution of observatories than that which is standard: including, additionally, Watheroo Australia (WAT), Apia Samoa (API), and Vassouras Brazil (VSS). Starting first with the data from each individual observatory, we subtract the geomagnetic secular variation, caused primarily by the core dynamo, and the solar-quiet (Sq) variation, caused primarily by the ionospheric dynamo. The latter requires careful spectral analysis, and those intermediate results are, themselves, of scientific interest. Following this, we combine the disturbance residuals from each station to form the continuous Dst time series. Statistics deduced from this model allow us to quantify the likelihood of storm occurrence and intensity, both of which are modulated in time by the solar cycle. This analysis is accomplished using a 50 year Dst time series. The prospects for constructing a longer continuous Dst time series are discussed.
SH54B-04 INVITED
Long-Term Evolution of Solar Magnetic Activity Derived From Stellar Proxies
The variability of the Sun over stellar and planetary evolutionary timescales may have important consequences for planetary atmospheres such as the Earth's, including the forcing of global climate and evolution of life. This solar variability is in part due to the changing magnetism of the Sun, which has origins in the solar dynamo mechanism. A novel approach towards determining solar variability over such long timescales - stretching to billions of years - is to use Sun-like stars in various evolutionary phases as proxies of solar activity. In this talk, I will review efforts to derive this long-term variability of the Sun through theoretical dynamo modelling and observational analysis of stellar magnetic activity. This work is funded by the NASA Living With a Star program through grant NNG05GE47G.