Latitudinal Movement Research Articles

Tertiary Evolution of the Australian Flora in the Light of Latitudinal Movements of the Continent

Australia has drifted 150 of latitude northwards since breaking away from Antarctica in mid-Eocene times (45 million years BP). Evidence for the climate at that time indicates warm, wet conditions favouring sub-tropical rain forest. Maps are presented of Australia's likely climatic zonation in midEocene, Oligocene and Miocene times, at respectively 45, 30 and 15 million years BP; these show the probable extent of a dry non-seasonal climate in northwest Australia as early as the Eocene. By the Oligocene, desert conditions were established in the north and northwest, with the first Mediterranean climatic zone appearing, also in northwest Australia. By the Miocene, desert extended to almost its present limits, and the Mediterranean zone had moved southward to become more extensive than at present. Accordingly the evolution of desert xerophytes in Australia probably dates back to the Eocene, and of Mediterranean-type xerophytes to the Oligocene.

Dependence of the latitude of the cleft on the interplanetary magnetic field and substorm activity

The latitudinal motion of the cleft (the polar cusp) associated with the southward interplanetary magnetic field (IMF) and substorm activity is examined. The cleft location is identified on the basis of the location of midday auroras and of electron precipitation by the OGO 4 and ISIS 1 satellites. It is found that the IMF and substorm activity control independently the latitude of the cleft and that they can shift the cleft location by 3 or 4 deg under average conditions.

Two barium plasma injections into the northern magnetospheric cleft

Barium plasma was injected into the northern magnetospheric cleft twice during January, 1975. Lofted by rockets launched after local magnetic noon from Cape Parry, NWT, Canada, high‐explosive shaped charges compressed hollow barium cones to generate vapor jets moving upward with initial velocities near 13 km/s parallel to the geomagnetic field. Barium plasma streaks created by solar photoionization of the vapor were convected through the polar magnetosphere and were observed optically from airborne and ground‐based sites until about 40 min after injection. Numerous indicators were monitored to determine the degree of magnetospheric disturbance; ionosondes at Cape Parry and Sachs Harbour, NWT, monitored latitudinal cleft motions preceding rocket launch. Spectrometers in the payloads recorded charged‐particle fluxes during both flights. The first injection occurred poleward in the cleft with subsequent plasma convection antisunward across the polar cap; the second occurred centrally with plasma convection duskward at constant magnetic latitude.

Remarks concerning Ward's ?the latitudinal motion of sunspots and solar meridional circulations?

Investigations based on independent observational materials and carried out by different authors show that sunspot groups display a latitudinal drift curve, the shape of which depends on phase in the solar cycle. Ward has tried to disprove this. His conclusions are based on ignorance of work done previously and on a mathematical misunderstanding.

Electron counts in the neutral sheet and magnetic variations at a geomagnetic longitude associated ground station

A comparison of the variations in the count of electrons E > 36 keV on the satellite Vela 4A, and in the Macquarie Island magnetometer H trace, shows for a time lag of 22-8 min a correlation, r = 0.95, over a 90 min period of the recovery phase of a magnetospheric substorm on 17 August 1968. All-sky camera data suggest that during the correlation period the auroral electrojet showed very little latitudinal movement. Each peak in electron count relates to a current surge in the electrojet as shown by a deepening of the negative bay at Macquarie Island. Using the Fairfield (1968) model of the location of auroral shells in the solar magnetic equatorial plane, and the known location of the satellite, an estimate of the velocity of tail to Earth plasma convection in the plasma sheet of about 0·33 R e/min is obtained for the recovery phase. The relationship is discussed between plasma sheet thinning and subsequent broadening, and the extension of the magnetic field lines into the tail region and their subsequent return. This discussion makes use of the estimated time lags between electron count at the satellite and the time of arrival of auroral particles at the antisolar meridian. From a somewhat speculative explanation, but one largely supported from the literature, of the magnetospheric processes involved in this auroral substorm, a plasma velocity estimate of 0·42 R e/min for the initial phase of the substorm is obtained. These velocities are of the same order as the 0·5 R e/min obtained by Lezniak and Winkler (1970) at 6·6 R e.

Relative and Latitudinal Motion of Atlantic Hot Spots

Although not all hot spots are fixed with respect to one another, the members of small groups of them seem to be fixed internally.

Characteristics of the tropopause over India

A statistical study of the reported height variations of the tropopause over Indian latitudes has been taken up in the present investigation. The analysis show two types of tropopause (1) the tropical tropopause, and (2) the extratropical tropopause. The latitudinal movement of the extratropical tropopause and the height variation of tropical tropopause with seasons are examined. The tropical tropopause near equatorial latitudes shows a lowering of the height during monsoon months (summer months) contrary to the normal expected structure. The characteristics of this equatorial tropopause are examined in relation to meteorological parameters of the troposphere and stratosphere.

Stable Auroral Red arcs observed from Adelaide during 1967–1969

Observations of Stable Auroral Red arcs from Adelaide ( L lat. 45.3°S) on four occasions in the period September, 1967 to October, 1969 are reported. A noted feature was the low intensity of λ6300 Å emission from the arcs, with values ranging from 300 R down to 50 R. On two occasions, small components of A5577 Å emission were detected in the region of the arc and an explanation is offered in terms of the dissociative recombination of O 2 +. Occurrences of oblique ionogram echoes at Christchurch, New Zealand, during optical observation of arcs at Adelaide are also reported. Some evidence for local time control of arc alignment and latitudinal movement is presented. Methods of height determination are discussed.

Low‐frequency waves in the magnetosphere

In the magnetosphere are found low‐frequency (100–100,000 Hz) electromagnetic waves generated externally by lightning and ground‐based transmitters and internally by energetic charged particles. Dispersion and anisotropy characterize the medium, and both ducted and nonducted paths of propagation are found. Lightning‐generated ducted ‘whistlers,’ observed on the ground, give information on the distribution of electrons and the latitudinal drift motions of ducts in the magnetosphere. Nonducted whistlers observed in satellites give information on electron and ion concentrations, the earth's magnetic field, and wave damping by energetic particles.Noise generated in the magnetosphere (or ionosphere) includes steady noise, or hiss, and the structured forms known as discrete emissions. In the auroral zone, hiss is seen in close association with the aurora and over a frequency range of at least 4 kHz to several hundred kHz. It has been attributed tentatively to incoherent Cerenkov radiation from the incoming auroral particles. At middle latitudes, noise from the magnetosphere is mostly of the discrete type with associated hiss and appears to be limited to frequencies below the minimum gyrofrequency on the path of propagation. A related type of noise, called ‘polar chorus,’ appears at high latitudes below about 1500 Hz. Discrete emissions may occur spontaneously or be triggered by whistlers or man‐made signals from the ground. The upper cutoff frequency is controlled by the minimum gyrofrequency on the path of propagation, indicating that the region of generation lies in the equatorial plane. Discrete emissions have been attributed to cyclotron resonance between whistler‐mode waves and electrons. Emissions offer new possibilities for studying wave‐particle interactions in the earth's magnetosphere and in other plasmas, both natural and man‐made.

Seasonal variations in the ionospheric drifts over the magnetic equator

The present article deals with the diurnal and seasonal variations of the N-S and E-W components of drift speeds over the magnetic equator at Thumbe during 1964 for E- and F-regions. It has been found that during Equinox the drift is predominantly westward; whereas during summer considerable southward component is present in both the regions, during winter a slight northward component is indicated. These deviations from westward direction of the drift are suggested to be due to latitudinal movements of the equatorial electrojet.

Auroral motions observed with riometers: latitudinal movements and a median global pattern

Riometers at L-values of 4, 7 and 14 are used to elucidate the latitudinal movement of auroral absorption events, and the pattern so derived is combined with the results of a previous study on longitudinal movements. The resulting picture shows that in a median case the auroral disturbance begins near L = 7 at the midnight meridian, and spreads out with velocities of about 0.4 R e /min in the equatorial plane. It appears possible that the factor governing the time sequence of auroral precipitation is a hydromagnetic disturbance.

The Post-glacial history of vegetation and climate at Ennadai Lake, Keewatin, and Lynn Lake, Manitoba (Canada)

Abstract. Peat from Keewatin and Manitoba contained macrofossil and palynological evidence of former latitudinal movements of the forest — tundra boundary probably in response to the changing location of the mean summer position of the Arctic front. There was very rapid melting of the large late-Wisconsin icesheet between 8000 and 6000 years B. P., and swift immigration of Picea, with no evidence of tundra vegetation after deglaciation. From 6000 to 3500 years B. P. the Boreal forest extended far north of its present limit, with a short-lived cooler phase about 5000 years ago. This generally warm period was followed by cooler and variable climatic episodes after 3500 B. P. and by a climatic deterioration about 2600 years ago. There was an amelioration between 1500 and 600 B. P., followed by a prolonged cold episode which terminated peat growth in the tundra. The approximate mean summer temperatures at Ennadai Lake have been estimated from the changing location of the northern limit of forest. The radiocarbon dates for these climatic events coincide with a number of changes recorded in the climatic history of northwest Europe.

Central Canadian palynology and its relevance to northwestern Europe in the late quaternary period

Analyses of fossil pollen grains and macroscopic plant remains have been made of peat from Keewatin and Manitoba in central Canada, at sites in the tundra and at the northern edge of the Boreal forest. Organic accumulation began immediately after very rapid deglaciation of the region between 8,000 and 6,500 years ago, when Picea forest swiftly colonised the bare ground. There is no evidence for establishment of tundra vegetation after the ice retreat. There is evidence from pollen analysis, plant macrofossils and fossil soils that the forest extended north of its present range by about 300 km from 6,000 to 3,500 years B.P. Movements of the forest limit have been interpreted as reflecting climatic change, and in particular the latitudinal movement of the Arctic airmass in summer (which is considered to determine the northern limit of tree growth in central Canada). Several radiocarbon determinations which have been made of the age of significant horizons in the pollen diagrams show that the inferred climatic changes were synchronous with those experienced by northwestern Europe during the last 6,000 years. The changes in this area also seem to have paralleled those of northern Europe, and this is explained by analogy with the modern pattern of Northern Hemispheric general circulation. Because of the global nature of circulation patterns it is to be expected that the timing of climatic changes should be the same throughout the world, but not that the change should be in the same direction in all regions. The synchroneity and parallelism mentioned above make it worthwhile to employ palynological evidence from central Canada (relatively undisturbed by human activity) to investigate climatic changes in northern Europe, where the fossil-pollen record for the past 5,000 years has been affected by anthropogenic factors.

Pollen Diagrams from Sub-Arctic Central Canada

Peat from Keewatin and Manitoba contained macrofossil and palynological evidence of former latitudinal movements of the forest-tundra boundary in response to the changing location of the mean summer position of the Arctic front. Radiocarbon dating demonstrates the synchroneity of these climatic changes with those registered in northwest Europe during the past 6000 years.

On mean latitudinal movements of sunspots

An analysis of the motions of sunspots in latitude indicates that (1) between about − 16° and + 16° heliographic latitude the spots are drifting towards the equator, while beyond these parallels they are moving towards the poles, and that (2) this larger system of meridional “vortices” seems to be super-imposed by another system which divides the Sun into zones about 10° wide from South to North.