Saturday, October 27, 2007

Magnetic connection and convection

The Sun influences Earth in many ways. On one hand it provides the light and heat that sustains life on our planet. On the other hand it bathes the Earth in ultraviolet light, showers it with x-rays, gamma-rays, electrons, and atomic nuclei, and wraps the Earth in the folds of its own magnetic field.

By mapping convection cells in Earth's magnetic field for the first time, scientists have shown that the behavior of the cells is linked to solar activity. The activity of our Sun has profound implications for the habitability of Earth.

Scientists have fully mapped convection cells in Earth's magnetic field for the first time using Cluster data. Results show that the behavior of the cells is heavily linked to solar activity. The activity of our Sun is closely connected to the habitability of planet Earth. The Sun provides much of the energy that allows life to survive. Additionally, solar activity has profound effects on our climate as well as the safety of satellites and astronauts in orbit. Recently, scientists discovered links between solar activity and heavy rains in eastern Africa and today we continue to find unique ways in which Sun is tied to our global climate. Studying the links between the Sun and the habitability of Earth can provide important clues for astrobiologists trying to determine the conditions necessary to produce habitable planets beyond our Solar System.

Convection cells, made of plasma, an ionized and highly variable gas, are found at altitudes of hundreds kilometers over the polar caps. Their behavior pattern is intimately linked to the response of the Earth's magnetic environment to solar activity. Although Earth is largely protected from the hazards of interplanetary space by the magnetosphere and atmosphere, they don't form an isolated bubble.

The solar wind, a stream of particles continuously blowing from the Sun, compresses Earth's magnetosphere on the dayside and stretches it into a long tail on the nightside. Most solar wind is deflected by the magnetosphere but some material manages to enter. Understanding how this works is of crucial importance to space-borne infrastructure (GPS, telecommunication satellites) and for the safety of astronauts.

One way to monitor this interaction is to study the convection cells. In the region, called the high-latitude ionosphere where they are located, the behaviour of the plasma cells strongly depends on the response of the magnetosphere to the orientation of the interplanetary magnetic field (IMF, an extension of the solar magnetic field, carried by the solar wind). This means that the behaviour of polar cap convection cells is a good tracer of the Sun-Earth connection.

As Tinsley 2007 in The role of the global electric circuit in solar and internal forcing of clouds and climate shows the change in the ionospheric coupling from the solar wind that induces changes of the global electrical circuit produced from polar cap ionospheric convection potential changes.

Reports of a variety of short-term meteorological responses to changes in the global electric circuit associated with a set of disparate inputs are analyzed. The meteorological responses consist of changes in cloud cover, atmospheric temperature, pressure, or dynamics. All of these are found to be responding to changes in a key linking agent, that of the downward current density, Jz, that flows from the ionosphere through the troposphere to the surface (ocean and land). As it flows through layer clouds, Jz generates space charge in conductivity gradients at the upper and lower boundaries, and this electrical charge is capable of affecting the microphysical interactions between droplets and both ice-forming nuclei and condensation nuclei.

Four short-term inputs to the global circuit are due to solar activity and consist of (1) Forbush decreases of the galactic cosmic ray flux; (2) solar energetic particle events; (3) relativistic electron precipitation changes; and (4) polar cap ionospheric convection potential changes. One input that is internal to the global circuit consists of (5) global ionospheric potential changes due to changes in the current output of the highly electrified clouds (mainly deep convective clouds at low latitudes) that act as generators for the circuit.

The observed short-term meteorological responses to these five inputs are of small amplitude but high statistical significance for repeated Jz changes of order 5% for low latitudes increasing to 25–30% at high latitudes. On the timescales of multidecadal solar minima, such as the Maunder minimum, changes in tropospheric dynamics and climate related to Jz are also larger at high latitudes, and correlate with the lower energy component ( 1 GeV) of the cosmic ray flux increasing by as much as a factor of two relative to present values. Also, there are comparable cosmic ray flux changes and climate responses on millennial timescales. The persistence of the longer-term Jz changes for many decades to many centuries would produce an integrated effect on climate that could dominate over short-term weather and climate variations, and explain the observed correlations.

Thus, we propose that mechanisms responding to Jz are a candidate for explanations of sun–weather–climate correlations on multidecadal to millenial timescales, as well as on the day-to-day timescales analyzed here.

We also see this in Troshichev et al with troposphere coupling

The detail analysis of the aerological data from Vostok station (Antarctica) for 1978–1992 made it possible to find the dramatic changes of the troposphere temperature influenced by strong fluctuations of the interplanetary electric field ESW. The warming is observed at ground level and cooling at h>10 km if the electric field of dawn–dusk direction is enhanced (when interplanetary magnetic field ΔBZ<0).>10 km) is observed if the dawn–dusk electric field decreases (when ΔBZ>0). There is a linear relationship between the value of ΔESW and ground temperature at Vostok station: the larger is leap in the ESW the stronger is temperature deviation. The effect reaches maximum within one day and is damped equally quickly. The temperature deviations occur not only while passing the front of the interplanetary shocks but while crossing the layers of interaction between the quasi-stationary slow and fast solar wind fluxes those are not accompanied by the cosmic ray variations at all. The appropriate response to the ESW changes is observed in tropospheric pressure and wind as well. It is suggested that the interplanetary electric field influences the katabatic system of atmospheric circulation, typical of the ice dome in winter Antarctic.


Blogger egp said...

Is there a link to the THEMIS project?

3:39 PM  

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