Observations of neutral winds from visible trails of gun‐launched vehicles and radio soundings of the ionospheric sporadic E layers are described and compared. It is shown that the wind structure accounts for many features of the sporadic E layer variation on two nights of observation, through the vertical ion convergence mechanism described most recently by MacLeod [1966]. Except for some transient disagreements, the sporadic E is found to accompany the height variation of certain levels of zero ion velocity induced by the neutral wind. The peak electron number density of the layers diminishes when the wind structure leads to ion divergence at the sporadic E height, and the density is observed to increase when the ion velocity permits the descent of ‘new’ ionization from above. New layers ‘arrive’ at night in accord with the observed development and descent of new nodes of ion convergence. The daytime evolution of a principal sporadic E layer is described and related to its subsequent nighttime association with the wind structure. Together with other published evidence that similar layers consist of long‐lived monatomic ions ultimately from meteoric influx, it is concluded that the neutral wind serves as a scavenger of this material that would otherwise accumulate to a far higher ionic concentration in the upper atmosphere.

The newly installed 420‐mm smoothbore gun at Yuma Proving Ground, Arizona, is described with its associated ground instrumentation. With an improved ignition system, this gun has placed an 84‐kg projectile at an altitude of 180 km. Twenty‐four of these projectiles carrying liquid trimethyl aluminum have been used to measure ionospheric winds through the creation of luminous trails. Analysis of these trails shows the presence of quite large easterlies at 110 km and a general descent of the wind patterns through the night. Harmonic analysis of the wind components at fixed altitude shows periodic components that are 2–5 times larger than the mean components and predominate periods of 10–12 hours. Seventy‐five per cent of the trails showed a characteristic clockwise rotation of the velocity vector. The absence of these phenomena at Barbados and the observation of counterclockwise rotation of trails over Argentina show the need for a theory to explain this behavior and its dependence on latitude and the earth's rotation.

Project HARP (High Altitude Research Project) is using gun‐launched projectiles to probe the upper atmosphere. Under this program, 130‐mm projectiles have reached 70 km, and 420‐mm projectiles have been placed 143 km over Barbados. The first experimental program for the 420‐mm gun has been the production of luminous TMA trails for the measurement of winds above 90 km. This smoothbore extended gun is 36 meters long, weights 180 metric tons, and has flown vehicles that generate TMA trails from 90 km to 138 km. In the time period July 1964 to February 1966, forty‐nine such nighttime trails have been photographed and twenty‐nine of these analyzed. During twenty‐two of these flights, concurrent ionosonde records have been taken, and the locations of sporadic‐E layers have been determined for comparison with the wind profiles. The wind data analyzed showed little evidence for the Rosenberg suggestion that the wind vector rotates with increasing altitude. Nine direction reversals occurring in less than 3 km were observed, and fourteen layers of constant direction flow with thicknesses greater than 8 km were observed. A maximum wind speed of 147 m/sec was measured. The six trails of the night of September 20–21, 1965, showed a rapid variation of meridional component of wind at fixed altitude with peak‐to‐peak amplitude of over 200 m/sec. Sine waves were fitted to wind components at fixed altitude with fair‐to‐good standard deviations.

The usual powder charge in the 16-inch HARP gun can be as long as 12 feet in an even longer chamber. If the charge length is more than "I feet shorter than the available chamber, the pressure time curve can be significantly improved by dividing this interval into 2 to 4 sub-intervals by use of wooden spacers. An even more dramatic improvement can be achieved by igniting this column of powder at several points. Recently, five point ignition with two squibs in each location has been used in the 119-foct long 16-inch gun at Yuma Proving Ground, Arizona with very good results. ýA' The service charge for a 16-inch gun is 660 pounds of standard 16-inch gun propellant. This charge will launch a 3000-pound projectile at 2800 feet per second, but is too slow burning to launch the standard HARP projectile plus sabot weight of 410 pounds at this velocity. With multiple point ignition, 1275 pounds of this propellant accelerated the HARP projectile to 5900 feet per second and an apogee of 414,000 feet was #pUhve4. Even better performance can be achieved with multiple point ignition. A WM/M propellant with 0.220 web (920 pounds) allows the HARP projectile to reach 6800 feet per second and an altitude of 540,000 feet Swhilp a n2?25 M8M propellant yields a muzzle velocity of 7000 feet per seronfd and a 590,000-foot apogee.

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