MAGNETIC RECONNECTION IN THE SOLAR WIND AT CURRENT SHEETS ASSOCIATED WITH EXTREMELY SMALL FIELD SHEAR ANGLES

Using Wind 3 s plasma and magnetic field data, we have identified nine reconnection exhausts within a solar wind disturbance on 1998 October 18-20 driven by a moderately fast interplanetary coronal mass ejection (ICME). Three of the exhausts within the ICME were associated with current sheets having local field shear angles, theta, ranging from 4 degrees to 9 degrees, the smallest reported values of theta yet associated with reconnection exhausts in a space plasma. They were observed in plasma characterized by extremely low (0.02-0.04) plasma beta, and very high (281-383 km s(-1)) Alfven speed, V-A. Low beta allows reconnection to occur at small theta and high V-A leads to exhaust jets that are fast enough relative to the surrounding solar wind to be readily identified. Very small-theta current sheets are common in the solar wind at 1 AU, but typically are not associated with particularly low plasma beta or high V-A. On the other hand, small-theta current sheets should be common in the lower solar corona, a plasma regime of extremely low beta and extremely high V-A. Our observations lend credence to models that predict that reconnection at small-theta current sheets is primarily responsible for coronal heating.