Wind speed

This module is aimed at measuring the solar wind speed near the Sun.

The input data are sequences of visible-light coronagraphic images — for the first test presented here we are employing data acquired by the SOHO/LASCO-C2 coronagraph.

All the total-brightness images (orange filter) acquired over a period of 3 days are downloaded, calibrated with the standard SolarSoft routines, converted to polar coordintes, and packed in a single datacube. The temporal evolution of the brightness observed in each pixel is de-trended to remove variations related with large-scale coronal features and to identify small scale features, such as plasma blobs or density inhomogeneities. At each latitude, the radial intensity profiles observed over the selected time interval are analyzed with a cross-correlation algorithm, providing an average value of the wind speed. The resulting latitudinal distributions of the wind speed are shown in a polar plot superposed over one of the LASCO-C2 images, normalized with a radial filter.

The subroutine works with the latest available LASCO images in quasi real-time, providing a measurement of the actual wind speed on the plane of the sky every 6 hours daily.