Solar Cycle 24 - Predicting Space Weather and Earth Impact
In a recent (2008) interview with W. Dean Pesnell of Goddard Space Flight Center, I posed many questions concerning current solar activity as well as some sensationalized, catastrophic news items as of late. The following are my questions and Dr. Pesnell’s responses.
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Solar Activity: Cycle 24 - questions:
1] Currently, the sun is at the minimum phase (the middle) of its 11 year cycle where things are supposed to be calm and uneventful. Yet, there has been some significant solar activity (flares) in the last year or so, including one “burst” of up to 1 million solar flux units (ten times the normal amount of radio noise) occurring in early December 2006. This seems to call into questions some basic assumptions about the sun’s dynamics. Was this merely an “aberration”?
We are only now entering solar minimum. There is always some large activity during the decline of a solar maximum. The active regions tend to be long-lived and produce large flares. Coronal holes develop during the decline and create large and periodic particle events. The large radio burst of December 2006 was an example of a solar effect we had not truly appreciated in the past. Had such a burst happened before GPS who would have noticed?
Each solar cycle is unique in the phasing of activity. It is early in the study of solar and space weather. We do not yet have sufficiently accurate models to organize the information in a way that illustrates the basic underlying characteristics of the solar cycle.
2] Current solar computer models disagree-offering two opposed conclusions: a weak (sun spot/flare) cycle, and a far more intense one. Has any more data been collected to determine which model is most likely true? What is your opinion on this?
I am an advocate of the weak activity prediction. The polar field remains low and we feel this is a leading indicator of a low amount of solar activity in Cycle 24.
3] You may be aware that the Earth’s Magnetic Field is weakening and will eventually reverse itself (over many thousands of years, according to most estimates). This weakening of the field (potentially a 90% loss of strength) leaves the Earth much less protected from the Solar Wind. Do you see this weakening as a major risk factor’ in the event of any increase (or unusually high increase) in solar activity?
I am not really an expert in this area and cannot evaluate a risk factor. Most of the solar particle and photon radiation is absorbed by the Earth’s atmosphere high above the surface. It would mean the cosmic rays would be less modulated and hence could have a stronger flux toward the equator.
4] Do you think that the current state of Milankovitch cycles (eccentricity, axial tilt, and precession)–specifically, the ellipticity (currently low) and axial tilt (currently high) of the Earth will/would augment any impact from the solar wind?
Any variation of the Earth’s orbit from its current configuration would always make the interaction with the solar wind and magnetic field different. It is hard to say whether a new configuration would cause the interaction to be more or less efficient. An example is the axial tilt (which I would say is medium, Uranus has a high axial tilt.) If this became high the rotation axis of the Earth would point more or less toward the Sun twice per year. The current rotisserie interaction where the solar wind and magnetic field are diverted around the Earth and can’t easily get to the polar regions would twice a year become a target interaction where the particles might be able to come in more easily while the field interaction would become very complicated, while the other part of the year would be almost the same as today.
Changes in the ellipticity would modulate the seasonal effects we already see in Space Weather.
5] The Earth’s gravitational field is also shifting (from bulging at the poles to bulging at the equator) would this have any bearing on the impact/effects of the Solar Wind?
My understanding of the Earth’s gravitational field is that it has a pear shape with bulging at the equator and I have not heard or seen other data.
The gravity changes are referring to redistribution of water around the surface of the Earth and the rebound of the near-surface layers caused by the loss of glacial ice. The changes in shape are quite small but are measurable, changes in the length of day are an example.
The major shape of the Earth remains a pear-shaped bulge at the equator and will remain so for the foreseeable future.
