Solar rotation in the subphotospheric layers

The solar rotation rate at latitudes 0 degrees, 15 degrees and 30 degrees h as been inferred by averaging the results of 120 regions of 15 degrees x15 degrees, which have been studied over a total area of about 75 degrees in l atitude and 360 degrees in longitude. A local helioseismology technique, th e ring diagram analysis method, has been used to analyse the horizontal vel ocity vectors from about 0.95 R. up to the surface. Our results are in very good agreement with those of other authors over most of the depth range. H owever, near the surface we find sharp local features which are not reporte d in other studies. The independent measurements of the rotation rate in th e north and south hemispheres show asymmetries below 0.975 R(<)circle dot>. The data used are full-disc dopplergrams taken by Solar Oscillation Invest igation/Michelson Doppler Imager (SOI/MDI) on board of the SOlar and Helios pheric Observatory (SOHO) during its first Dynamic Program, between 1996 Ma y and June.