Letter to the Editor

The solar wind disappearance event of 11 May 1999: source region evolution^*

¹ Physical Research Laboratory, Astronomy & Astrophysics Division, Navrangpura, Ahmedabad 380 009, India e-mail: jerry@prl.res.in
² Department of Applied Maths and Theoretical Physics, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, UK e-mail: [D.Tripathi;H.E.Mason]@damtp.cam.ac.uk

Received: 28 February 2008
Accepted: 27 June 2008

Abstract

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 effects at 1 AU, arising from non-explosive solar events.