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The Solar Wind Disappearance Event of 11 May 1999: Source Region Evolution.  

Janardhan Padmanabhan   Submitted: 2008-07-17 00:44

Context. A recent, detailed study of the well-known solar wind disappearance event of 11 May 1999 traced its origin to a coronal hole (CH) lying adjacent to a large active region (AR), AR8525 in Carrington rotation 1949. The AR was located at central meridian on 05 May 1999 when the flows responsible for this event began. We examine the evolution of the AR-CH complex during 5-6 May 1999 to study the changes that apparently played a key role in causing this disappearance event. Aims. To study the evolution of the solar source region of the disappearance event of 11 May 1999. Methods. Using images from the Soft X-ray Telescope (SXT), the Extreme-ultraviolet Imaging Telescope (EIT) and the Michelson Doppler Imager (MDI) to examine the evolution of the CH and AR complex at the source region of the disappearance event. Results. We find a dynamic evolution taking place in the CH-AR boundary at the source region of the disappearance event of 11 May 1999. This evolution, which is found to reduce the area of the CH, is accompanied by the formation of new loops in EUV images that are spatially and temporally correlated with emerging flux regions as seen in MDI data. Conclusions. In the period leading up to the disappearance event of 11 May 1999, our observations, during quiet solar conditions and in the absence of CMEs, provide the first clear evidence for Sun-Earth connection originating from an evolving AR-CH region located at central meridian. With the exception of corotating interacting regions (CIR), these observations provide the first link between the Sun and space weather e ects at 1 AU, arising from non-explosive solar events.

Authors: P. Janardhan, D. Tripathi, and H.E. Mason
Projects: None

Publication Status: Accepted for publication in A&A Letters
Last Modified: 2008-09-23 20:56
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Janardhan Padmanabhan   Submitted: 2007-12-10 12:08

During the period 1999-2002 there have been three instances, in May 1999, March 2002 and May 2002 respectively, when the solar wind densities at 1 AU dropped to abnormally low values (< 0.1 cm{-3}) for extended periods of time (12-24 hours). These long lasting low-density anomalies observed at 1AU are referred to as ``{it{solar wind disappearance events}}'' and in this paper, we locate the solar sources of the two disappearance events in March and May 2002, show that like the well studied disappearance event of 11 May 1999, these events too originate in active region complexes located at central meridian and are characterized by highly non-radial solar wind outflows. We also show that during disappearance events, the interplanetary magnetic field is stable and unipolar and the associated solar wind outflows have extended Alfvén radii. Using the fact that solar wind flows from active regions have higher ratios of O{7+}/O{6+}, than wind from coronal holes we try to pinpoint the solar sources of these very unusual and rare events and show that they represent the dynamic evolution of either active region open fields or small coronal hole boundaries embedded in or near large active region complexes located at or close to central meridian.

Authors: Janardhan, P., Fujiki, K., Sawant, H.S., Kojima, M., Hakamada, K and Krishnan, R.
Projects: None

Publication Status: To appear in Journal of Geophysical Research - 2008
Last Modified: 2007-12-11 10:42
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