Motion in the Night-time Es Region at Brisbane

Abstract

SummaryAn analysis is made of night-time motion in the Es region, as determined from a study of radio echoes at 2 -28 Mc/s. Night-time Es usually consists of moving clouds of ionization of lateral extent ~ 1 0 km; these clouds may be either isolated or closepacked to" form layers of ionization. There is evidence that the clouds are sometimes elongated in a direction different from their direction of travel.Good correlation is found between velocities of Es movement as determined by fading analysis (Mitra 1949) and direction-finding techniques. Speeds of movement are grouped about 70 m/sec, and the winds are predominantly towards the north. GENERALIt has been shown in previous papers (Thomas and Svenson 1955;Thomas 1956a) that the two types of Es at Brisbane (" sequential" type (Ess), and " constant-height" type (Esc))' show considerable vertical motion of a tidal nature. It is logical to expect large horizontal motions to accompany the vertical movements in the ionosphere. Measurements of horizontal drift velocities of " patches" of Es ionization have been reported from many parts of the world. In Australia, Harvey (1955) has measured the drift velocities of large patches of (mainly) sequential Es as it occurs near Sydney.An examination of theP'frecords at Brisbane shows that there are frequently Esc traces which, over a period of time, gradually decrease and/or increase their range. Examples are shown in Figures 1 and 2. These changes are quite distinct from the large decrease of range associated with Ess formation. Since the changes of range are the same at all frequencies up to fE s , measurements made at anyone frequency will be characteristic of measurements at all other frequencies; use is therefore made of the various fixed frequency records which have been made at Brisbane by the techniques described by Thomas and McNicol (1955) and by McNicol, Webster, and Bowman (1956).The various types of records available are outlined below:

Azimuth‐dependent Es layer instability: A missing link found

“…Measurements have indicated that E s layers contain tilts as much as 25° [e.g., Webster , 1958; From and Whitehead , 1978; Paul , 1990]. Spurs [ Thomas and Burke , 1956] are intriguing because they appear to resemble the results presented in Figures 3 through 5. An example from Thomas and Burke [1956] is presented in Figure 12.…”

“…Spurs [ Thomas and Burke , 1956] are intriguing because they appear to resemble the results presented in Figures 3 through 5. An example from Thomas and Burke [1956] is presented in Figure 12. Shown plotted are ionospheric reflections obtained as a function of group delay and local time at a fixed frequency of 2.28 MHz.…”

A review of some recent work on mid-latitude spread-F occurrence as detected by ionosondes.

“…The movements in general were in directions in the north-west quadrant. In addition, sporadic-E-cloud movements and ES layer drifts are consistent in speed and direction in the north-west quadrant (THOMAS and BURKE, 1956; BOWMAN,…”

Measurements of Changes in the Phase Path of Radio Waves Reflected from the Ionosphere at Normal Incidence

“…Occasionally the leading and trailing edges of such cloud echoes extend to ranges beyond that of the main echo, giving rise to converging and diverging traces on group-path records and decreasing and increasing phase paths on P,t records as discussed by Thomas and Burke (1956).…”

“…(iii) Distinction between Sequential and Constant-height Es Regions.-It can be stated generally that the type of sporadic-E echo classified as " sequential Es " is consistently more phase coherent and stable than the type designated as " constant-height Es" (McNicol and Gipps 1951). This feature has been used as an aid in distinguishing between these two types of Es (Thomas 1956). …”