Eiscat Radar School , Kiruna, Sweden Aurora and Auroral Studies with IS radars Kari Kaila University of Oulu Department of Physical Sciences

Eiscat Radar School , Kiruna, Sweden Introduction

Eiscat Radar School , Kiruna, Sweden Aurorae: Where the name comes? Aurora is latin and means dawn. It looks like dawn is approaching after dark night In many languages it means Northern light Aurora borealis is Northern dawn and Aurora Australis Southern Dawn In Finnish language it is Revontulet and means Fox fires

Eiscat Radar School , Kiruna, Sweden Aurorae: What they are? Aurorae are luminous phenomenon which are seen during dark nights They were mysterious phenomena, which have been observed couple of thousands of years Mostly they are calm and quiet Sometimes they are very vivid

Eiscat Radar School , Kiruna, Sweden

Aurorae: How do they look like? Most often they can be seen east-west directed arcs low in the north They are pale or gray surfaces in the sky In the pre midnight sector they move typically very slowly southward When getting brighter, the greenish colour becomes clear visible

Eiscat Radar School , Kiruna, Sweden Aurorae: How do they look like? Most common forms are quiet arcs and luminous diffuse light in the north Sometimes the quiet arc starts to disturb. It becomes a folded band. Vertical rays may appear in the arc or band and clear motion can be seen in the form. All the forms move southward

Eiscat Radar School , Kiruna, Sweden Aurorae: How do they look like? Suddendly the southernmost arc stops, fades and the a beautiful display starts: auroral breakup or auroral substorm The southernmost arc becomes brighter and long rays appear on it. Soon new bright arcs and bands appear and different colours are visible and within minutes the sky is full of different bright auroral forms.

Eiscat Radar School , Kiruna, Sweden

Aurorae: Where they are? They can be seen close to the poles, in north and in south At the poles they are rather rare They are most commonly observable about 2000 km from the magnetic poles When passing the maximum region, they became again rare closer to the Equator

Eiscat Radar School , Kiruna, Sweden

Aurorae: Connection to the Sun? The appearance of aurorae follows the periodes of the Sun Aurorae appear more often when the sun is active. The Sun has 11 years cycle and so do the aurorae have. The Sun rotates around its axis in about 27 days. If bright auroral display may repeat again after 27 days.

Eiscat Radar School , Kiruna, Sweden

Instruments: satellites, photometers, cameras

Eiscat Radar School , Kiruna, Sweden

DMSP-F13 F ols.tir.gif

Eiscat Radar School , Kiruna, Sweden

Polar images This image has been acquired with the Earth Camera that is one of three cameras in the Visible Imaging System (VIS). The design and assembly of the VIS was performed by the VIS team at The University of Iowa. The VIS is one of twelve instruments on the Polar satellite of the NASA Goddard Space Flight Center. The Principal Investigator is Dr. L. A. Frank and the Instrument Scientist and Manager is Dr. John B. Sigwarth.