11 00 Open Sun

The Open Sun in 2007/8 : 

The Open Sun in 2007/8 Barbara Bromage University of Central Lancashire

Where will we be in the solar cycle during IHY (2007/8)?: 

Where will we be in the solar cycle during IHY (2007/8)? Here are cycles 20 to 23 (diamond symbols), with the 11-year mean cycle superimposed (solid lines) on each, scaled to match the height of the observed peak. Cycle 21 was 11 years; 22 was less; 20 and 23 are longer. Skylab was 1973; SOHO began operations 1996. IGY, in 1957, was at solar maximum (the largest ever!).

The Current Cycle (23): 

The Current Cycle (23) The crosses indicate a current prediction of minimum, which may be a little early. Cycle 23 falls increasingly behind the mean cycle, suggesting that minimum might not occur until 2008.

The Solar Corona near Times of Solar Minimum & Solar Maximum: 

The Solar Corona near Times of Solar Minimum & Solar Maximum

What is it like near solar minimum?: 

What is it like near solar minimum? Large active regions (few) close to equator. Large coronal holes covering each pole. Trans-equatorial extensions to the polar coronal holes, seen in the 2-3 years up to solar minimum. Prominence channel alongside the coronal hole. New cycle active regions appear at high latitude. Lots of quiet Sun in between – generally low activity. Global magnetic field weak, leads to high cosmic ray flux. Heliospheric current sheet at low “tilt angle” – few magnetic field sectors.

Trans-equatorial Coronal Holes – Skylab (1973) and Soho (1996): 

Trans-equatorial Coronal Holes – Skylab (1973) and Soho (1996) In the approach to solar minimum, coronal holes such as these are long-lived, rotating quasi-rigidly at the equatorial rotation rate. We can predict when they will cross the meridian (and become geo-effective). Fast solar wind streams from the coronal hole compress the magnetopause and can initiate geomagnetic substorms.

The Open SunThe Interplanetary Magnetic Field (IMF), carried in the solar wind, connects the geomagnetic field to the Heliosphere.: 

Earth’s Rotation Axis Auroral oval Solar wind plasma Solar wind The Open Sun The Interplanetary Magnetic Field (IMF), carried in the solar wind, connects the geomagnetic field to the Heliosphere.

Sun-Earth Connection : 

Sun-Earth Connection CDS observations in the last week of June, together with EISCAT observations of the ionosphere 1-2 July. From CDS, we get spectroscopic data from upper chromosphere to the corona.

EISCAT UHF radar pointing to magnetic north: 

EISCAT UHF radar pointing to magnetic north

The Cosmic Ray Cycle: 

The Cosmic Ray Cycle Cosmic rays are modulated by the Sun’s magnetic field and so have a 22-year cycle, anti-correlated with the sunspot cycle (approximately). This half-cycle is expected to have a ‘triangular peak’. It is clearly rising towards a peak now and should be near maximum by 2007.

So, what events can be studied in the approach to Solar Minimum?: 

So, what events can be studied in the approach to Solar Minimum? Trans-equatorial coronal holes, leading to geomagnetic substorms and aurora which can be predicted to within a few hours (public outreach possibilities). Large isolated sunspot regions near the equator; these may produce occasional large flares, proton events and CMEs. CMEs from prominences around the polar holes (particularly post-minimum). The first new-cycle flux/active regions emerging at mid-latitudes. High cosmic ray fluxes, with possible Forbush decrease events in response to proton flares. The signatures could be followed in the stratosphere and upper troposphere.