C.-I. Meng

The polar electrojet.

Abstract It is shown that the polar electrojet which causes intense ‘negative bays’ or polar magnetic substorms in the high latitudes, flows usually westward in all longitudes along a closed oval curve. This substorm oval is also the site along which at the instant the active aurora is situated. Further, it appears to be the line of intersection of the outer boundary of the outer radiation belt with the ionosphere. The center of the oval is appreciably displaced from the earths magnetic axis pole, along the midnight meridian. The oval coincides approximately with the statistically determined auroral zone only in the midnight sector. The strength of the polar electrojet is not uniform along the substorm oval; some of the excess current in the most intense part of the electrojet (near the midnight meridian) returns across the polar cap, encircling a focus in this cap; the remainder departs from the afternoon sector and crosses the midnight meridian to complete its circuit by rejoining the main westward flow in the morning sector, with its focus in the midnight sector not far outside the oval. This latter flow produces positive bays everywhere south of the focus; these bays can be particularly intense in the afternoon sector along the auroral zone, and were formerly interpreted as indicating the existence of an eastward polar electrojet. The changing geometry of the polar eleetrojet is brought into relation with the dynamical morphology of the simultaneous auroral substorm, which has lately been determined by study of simultaneous all-sky camera records from the entire polar region.

The dynamics of the aurora—II Westward traveling surges

Abstract During an auroral substorm, a violent expanding motion of an auroral system located around the midnight sector generates rapid wavy motions of auroral arcs or bands that lie in the evening sector. This particular type of motion is called the westward traveling surge . In this paper, various characteristics of the surges are described in detail and their geomagnetic and ionospheric effects are examined.

DYNAMICS OF THE AURORA. IV. POLAR MAGNETIC SUBSTORMS AND WESTWARD TRAVELING SURGES

Abstract Polar magnetic substorms associated with the westward traveling surge are examined in detail, using an extensive all-sky and magnetic networks in Canada-Alaska-Siberia. Since the surge is accompanied by an intense negative bay and since it advances into the polar cap along the auroral oval during the auroral substorm, the region in which a negative bay is observed expands along the path of the surge. Thus, as Akasofu , Chapman and Meng (1965) have recently suggested, the so-called westward electrojet extends into the polar cap, rather than being terminated in the midnight sector of the auroral zone.

DYNAMICS OF THE AURORA. V. POLEWARD MOTIONS

Abstract The poleward motion of auroral bands in the midnight sector during the early phase of the auroral substorm is described. Several examples are presented and discussed in detail. The polar magnetic substorm associated with the poleward motion is also examined. Since the poleward motion initiates all the other aspects of the auroral substorm (such as the westward traveling surges and the formation of patches), it is essential to understand this phenomenon in order to explore the cause of the planetary-scale auroral displays. It is shown that the auroral substorm is initiated in the auroral oval itself and that before or during the substorm there is no equatorward auroral motions across the dipole pole from the dayside to the nightside along the noon-midnight meridian.

Low latitude negative bays

Abstract It is shown that the eastward current flowing along the auroral zone in the afternoon sector does not generate the westward return current in the middle and low latitudes, but spreads to the equator. It is shown also that the so-called ‘negative bay’ which had been thought to be due to the westward return current is caused by the simultaneous growth of the asymmetric storm-time radiation belt (the ring current). The present study suggests a very close relationship among the auroral substorm, the polar magnetic substorm and the formation of the storm-time radiation belt (the ring current).

DYNAMICS OF THE AURORA. VI. FORMATION OF PATCHES AND THEIR EASTWARD MOTION

Abstract The formation of patches in the morning sector occurs about 10 ~30 min after the onset of the auroral substorm in the midnight sector. This phenomenon is examined in detail by using the IGY Alaska-Canada all-sky and magnetic records. Patches drift eastwards and their drift speed is obtained for a number of cases.

Dynamics of the aurora—VII Equatorward motions and the multiplicity of auroral arcs

Abstract Equatorward motions of auroras are described in detail as follows: 1. The equatorward shift associated with the earths rotation; 2. The equatorward motion during the recovery phase of the auroral substorm; and 3. The equatorward spread of irregular bands during the substorm. The multiplicity of arcs associated with the equatorward motion is also described.

Polar magnetic substorm in the evening sector.

Abstract The morphology of the disturbance field of the polar magnetic substorm in the evening sector is studied by using a chain of four Alaskan north-south stations distributed between dp lat 61° and 70°. It is shown that in the evening sector a typical auroral zone station is situated in a transition belt between the region of an intense negative bay on the poleward side and the region of a weak positive bay on the equatorward side and thus experiences a great variety of types of the disturbance field. In this paper, the most common types of the disturbances are classified, and a typical latitudinal change of the disturbance between 70° and 60° is obtained.

Intense negative bays inside the auroral zone—II: Indented positive bay

Abstract During the polar magnetic substorm, there occurs an intense negative bay superposed on a gradual positive change both in the region well inside the auroral oval and in the region a little equatorward side of it. It is suggested that this phenomenon is an indication of large-scale change of the polar electrojet system during the substorm and that it can be understood on the basis of the simultaneous auroral motions (the auroral substorm).

Intense negative bays inside the auroral zone—I The evening sector

Abstract Intense negative bays which occur well inside the auroral zone in the early evening hours are examined. As suggested by Akasofu , Chapman and Meng (1965), they can be explained by the westward extension of the polar electrojet which follows the traveling auroral surge along the auroral oval. It is shown that the polar electrojet flowing westward along the auroral oval is in accord with the results of two different kinds of analyses of polar geomagnetic disturbance, namely the ‘SD analysis’ and the ‘spiral analysis’.