Heliospheric Weather Expert Service Centre STEREO-A HI J-Map (Science Mode)

The STA/JMAP product presents a time - elongation plot (also known as a J-map) of the differenced Heliospheric Imager (HI) visible light observations along the position angle corresponding to the ecliptic. This product is based upon the science mode data; it provides observations acquired over the current month and is updated with the latest available observations each day (but depending on the download schedule data may only be available up to 3 or 4 days after acquisition). See also the similar near-real-time product which is generated from the beacon mode data STA/JMAP-RT ) .

The HI instrument is a wide angle visible light imager that is able to detect the Thompson scattering of sunlight off solar wind structures as they propagate out through the heliosphere. The scattered light, which is from the line of sight integration, is typically three or more orders of magnitude dimmer than the background from the F-corona. However, this F-corona background varies much more slowly than the propagating solar wind features that we are trying to detect and therefore by subtracting a background level determined over a period of a day or more enables the removal of this. The differenced images that are used in movies and the generation of J-maps involve a further step where the background subtracted images are aligned with the star field and then consecutive images subtracted in order to highlight temporal variations over timescales of 40 minutes to several hours (depending on the camera and telemetry mode cadence).

Solar wind features that are radially propagating, such as CMEs, will appear on the map as a curved locus starting at 4 degrees elongation (bottom of the plot). The shape of the locus depends on the characteristics and geometry of the transient and its propagation. Near-horizontal traces where the elongation only changes slowly over the duration of the plot are due to other solar system objects (in particular planets). Vertical lines are the result of instrumental artefacts (such as jitter). The HI instrument consists of two cameras and a slight discontinuity may be observed at the cross-over between field of views at an elongation of about 17.5 degrees. Data gaps appear as uniform grey areas.

The elongation is the angular separation between the Sun and a point in the plane of the sky as observed from the STEREO-A spacecraft.

This web page forms part of the European Space Agency's network of space weather services and service development activities, and is supported under ESA contract number 4000134036/21/D/MRP. For further product related information or enquiries contact the helpdesk. E-mail: helpdesk.swe@esa.int All publications and presentations using data obtained from this site should acknowledge RAL Space and The ESA Space Safety Programme. For further information about space weather in the ESA Space Safety Programme see: https://www.esa.int/spaceweather Access the ESA SWE Portal here: https://swe.ssa.esa.int.