The spatial scale of correlation of the day-to-day variability of Sq

A study of the variability of the amplitude of Sq at a fixed hour from one day to the next at nine stations from the dip equator to about 22° north of it has produced interesting results. The amplitude and sign of the variability change virtually randomly, making the mean practically zero. The variability occurs at all hours of the day. Its magnitudes in the components D, H and Z have the same diurnal variation, which peaks in the noon period like Sq(H) in low latitudes, and a weak seasonal variation that peaks at the June solstice (local summer). It is demonstrated that changes in the current intensities of the equatorial electrojet (EEJ) and the worldwide part of the Sq (W Sq) current layers have contrasting phases and can sometimes be in antiphase. Indeed, the changes are mostly independent. Inclusion of the magnetic element D revealed that the EEJ current system has not only an east–west but also a north–south component. The study shows that the meridional component of the EEJ current intensity evidenced at the Kodaikanal and Annamalainagar stations is an integral part of the zonal component at Trivandrum. This confirms the results of Rastogi (1996) and validates those of Onwumechili (1997). The results suggest that ionospheric conductivity mainly controls the magnitude, while the electric field and ultimately winds mainly control the phase and randomness of the day‐to‐day variability of the hourly amplitudes of Sq. The random component is attributed to local and/or regional atmospheric winds, probably of gravity wave origin.

Section: Introductionmentioning

confidence: 99%

Day-to-day variability of geomagnetic hourly amplitudes at low latitudes

Okeke

Onwumechili

Rabiu

1998

“…If the foregoing interpretation is correct, the reason for the differing conclusions of Schlapp & Mann (1983) and Hibberd (1981) become clear. In his original investigation Hibberd selected for examination quiet periods in which there was a large day to day variability, since it is easier to study an effect that is large and recognizable rather than one that is small compared with other effects that may be present.…”

Section: Discussion a N D Conclusionmentioning

confidence: 99%

“…In what follows, the daily ranges of AH, and AH, are denoted by RN and R,, respectively. This conclusion has been challenged by Schlapp & Mann (1983). Using data for all days in 1964 and 1965 they found that the correlations between RN and R , were not significantly different for different degrees of quietness.…”

Section: Introductionmentioning

confidence: 99%

Global scale of the day-to-day variability of Sq

Hibberd

Davidson

1988

This paper examines whether the day-to-day variability of the daily range of Sq(H) is a local phenomenon with a coherence range of 1000-2000 km or is a large-scale phenomenon with similar variability occurring in all low and middle latitudes. Daily ranges of H a r e obtained for four stations on the same meridian in the northern and southern hemispheres, for all quiet days in 1962-71, and the differencing procedure described by Hibberd (1981) is used to help reduce the effects of disturbance. When the day-to-day changes in the daily range of H are small it is impossible to distinguish unambiguously between changes that represent true variability in Sq and changes resulting from residual disturbances of non-Sq origin. When the day-to-day changes in the daily ranges are large, the difference between the daily ranges for the northern hemisphere pair of stations and that for the southern hemisphere pair vary from day to day in a similar manner in the two hemispheres. It is concluded that the day-to-day variability of Sq occurs on a global scale.

“…The day-to-day variability of S, is a well-known phenomenon which has been studied in some detail. Previous work (Schlapp 1968;Greener & Schlapp 1979) has shown that the spatial scale of the correlation of Sq-ranges between different stations is of the order of 2000 km, and is thus regional rather than world-wide. One of the problems in studying the variability of S, is that, even on the quietest days, there may be some residual disturbance.…”

Section: Introductionmentioning

confidence: 98%

“…Hibberd (1981) has proposed a method o f eliminating much disturbance, based on taking the difference in S, range between stations at different latitudes. Using this method, he claimed that on very quiet days, the day-to-day variations in S, range were more globally correlated than on other quiet days, but Schlapp & Mann (1983) have shown that, when a larger body of data is analysed, no such tendency can be found. Butcher & Brown (1981) have studied the variability in the horizontal component of the S, variation, S,(H), and have found that there are many quiet days when the daily variation is perturbed by the presence of minor disturbances such as negative bays.…”

Section: Introductionmentioning

confidence: 99%

The effect of disturbance on the day-to-day variability of Sq

Mann

Schlapp

1985

Self Cite

Other workers have recently shown that the apparent day-to-day variability of S, is appreciably reduced when days with bay-like disturbances are removed from the analysis.In this paper, it is shown that when these days are removed, there is only a small effect on the scale o f the spatial coherence of Sq-ranges and therefore the regional scale of the correlation must be a real feature of S, range variability rather than an effect due to disturbance.