A sharp gust of solar wind hit Earth’s magnetic field

A sharp gust of solar wind hit Earth's magnetic field at approximately 20:30 UTC on June 4, 2011. High-latitude sky watchers in both hemispheres should be alert for auroras.

Solar wind
speed: 495.9 km/sec
density: 2.6 protons/cm³

Planetary K-index
Now: Kp= 5 storm
24-hr max: Kp= 5 storm

Interplanetary Mag. Field
B_total: 22.3 nT
B_z: 16.2 nT north

The ACE spacecraft did detect a sudden increase in solar wind speed Saturday afternoon and the Bz is now tilting sharply south at times. This could trigger minor geomagnetic storming at high latitudes.

Sunspot 1226 is starting to shrink in size, but may still produce C-Class flares. None of the currently visible sunspot groups are magnetically complex and the chances for strong solar flares are very low.

The geomagnetic field was quiet to active over the past 24 hours. The ACE spacecraft detected an interplanetary shock passage at 04/1958Z. Solar winds jumped from around 325 km/s to 455 km/s, density increased, and the IMF Bt went from 5nT to 20 nT. A geomagnetic sudden impulse was observed at 04/2045Z (54 nT) on the Boulder USGS magnetometer. This signature is consistent with the arrival of a CME. The greater than 2 MeV electron flux at geosynchronous orbit was at high levels throughout the period.

The geomagnetic field is expected to be mostly active with isolated minor storm conditions, and isolated major storming at high-latitudes, for day one (05 June). The source for the activity is a combination of continued CME effects, and the arrival of a geoeffective coronal hole high-speed stream. For day two (06 June) the geomagnetic field is expected to be quiet to unsettled with isolated active conditions. By day three (07 June) mostly quiet to unsettled levels are expected as the activity subsides.