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HomeSolarSolar ConditionsSolar Wind Speed Saturday, Nov 01 2014 06:31 UT
Solar Conditions

Solar Wind Speed

Updates: every 10 minutes

(last updated 01 Nov 2014 06:23 UT)

Solar Wind Parameters Used: Date: 01 11 2014 0620 UT Velocity: 432 km/sec Bz: 5.0 nT Density = 1.0 p/cc Calculated Information from Solar wind parameters: Magnetopause Stand Off Distance = 15.2Re Solar Wind Dynamic Pressure Dp = 0.16nPa

Solar Wind Speed diagramSolar Wind Speed diagramSolar Wind Speed diagram

These diagrams indicate the i) solar wind speed and ii) strength of the interplanetary magnetic field (IMF) in a north/south direction. Higher solar wind speeds and strong south pointing (negative) IMF are associated with geomagnetic storms on earth. The red area on the image indicates an approximate region in which disturbed conditions might be expected.

The plots on this page were produced from data supplied by the NOAA Space Weather Prediction Center (SWPC). This Real Time Solar Wind (RTSW) data set originates from NASA's Advanced Composition Explorer (ACE) satellite (centre) and the STEREO A (ahead) and STEREO B (behind) satellite. The above centre image shows with a black square the value of the solar wind speed (horizontal) axis and the strength of the interplanetary magnetic field in a north/south direction (Bz - vertical axis). Higher solar wind speeds and strong south pointing (negative) interplanetary magnetic field are associated with geomagnetic disturbances on earth. The red area on the image indicates an approximate region in which disturbed conditions might be expected. The coloured dot within the black square, is an indicator of solar wind density, and is yellow when density exceeds 5 particles per cubic cm, red when density exceeds 10 particles per cubic cm, otherwise green.

The ACE spacecraft is positioned at the L1 point between the Earth and the sun and gives approximately one hour advance notice of conditions on Earth.

The STEREO A and B satellites are respectively, ahead of and behind the Earth in its orbit around the Sun. Due to the archimedean spiral of the solar wind's magnetic field, the STEREO B (behind) satellite has a number of days preview of "long lived" structures in the solar wind (also known as co-rotating structures). These structures extend into space and rotate with the Sun. You can see the spiral shape in the solar wind model output link at the bottom of this page. Coronal hole high speed solar wind streams are an example of a co-rotating structure. The average rotation speed of the Sun is about 13.3 degrees per day, you can use the angular separation divided by this value, to roughly estimate the delay time in days before they are seen by the ACE spacecraft, and the Earth. Note this simple day delay can not really be used for coronal mass ejections (also known as solar wind shocks) as they are not co-rotating structures, and would probably arrive at the Earth more quickly. Note that the STEREO spacecraft move away from the Earth at approximately 22 degrees per year, and will eventually pass around behind the Sun. For a more sophisticated estimate of STEREO B lead time please see the SWPC STEREO B 7 day plot.

The solar wind magnetic field, can be measured in three compoenents, Bz, Bx, and By. Bx lies along the Sun-Earth line, with Bz and By defining a vertical plane (the clock "face"). The solar wind clock angle is the angle produced from the vector sum of By and Bz.

The image below shows recent trends in solar wind speed and interplanetary magnetic field north/south direction.

Solar Wind Trend diagram

Solar Wind Model Driven by ACE data

IPS is running an ACE data driven model of the solar wind each day in the Australian Space Forecast Centre. The model output displays a complete solar rotation of several solar wind parameters, over the last 27 days.

Using 27 day persistance, which is the average solar roatation period, IPS forecasters can use this information to anticipate the arrival of the coronal hole high speed stream, and warn its customers of the expected disturbance.

Reference

Florens, "M. S. L., Cairns, S. A. Knock, and P. A. Robinson (2007), Data-driven solar wind model and prediction of type II bursts, Geophys. Res. Lett., 34, L04104, doi:10.1029/2006GL028522".

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