Horizontal path temperature fluctuation measurements were made on board a KC-135 aircraft, at altitudes ranging from 30,000 to 48,000 feet, such that the altitudes below, in, and above the tropopause were sampled. In general, we find that there is a low background level ofturbulence, and there appears to be superimposed on this background higher level turbulent "patches' . These patches are a few kilometers in extent, and the boundaries of these patches are abrupt with the transition to background taking place in distances ofapproximately 50meters. These abrupt boundaries are consistent with the optical measurements taken at the same thne. The measured structure functions are ofthe form D(r) r" with 0.2 n 2 down to scale sizes of 20 cm, which was the limiting resolution ofthe instrumentation. Each ifight segment was conducted under constant conditions (i.e., speed, temperature, altitude). Contrary to expectations, the log slopes of either the power spectral densities or ofthe structure functions are often non-Kolmogorov, as characterized by a k5"3 power spectral density, or by a structure function ofthe form This statement must be tempered, however, by uncertainties in the frequency response ofthe temperature sensor. In addition, the data show regions in which the expected functional relationship (rP +.> k-(P1)) between the structure function and power spectral density does not hold. These characteristics of high altitude turbulence suggest that past measurement techniques used to measure c2 may be inapplicable in the high altitude regime, and c2 as a sole descriptor ofturbulence may be incomplete.

Electron density profiles and isodensity contours derived from Jicamarca incoherent scatter radar observations in Peru for October 1–2, 1970, are compared in detail with results from the Phillips Laboratory global theoretical ionospheric model. This model solves the ion continuity equation for O+ concentration through production, loss, and transport of ionization. The primary factor controlling the peak plasma density at Jicamarca is the vertical E×B drift, which drives the ionization upward during the day and downward at night. When we use the measured drift in the model, we achieve excellent results with the measured electron density profiles. We illustrate the sensitivity of the low‐latitude plasma density calculations to changes in the vertical E×B drift and changes in the neutral winds. We also compare the calculated profiles and peak parameters with an empirical model, the International Reference Ionosphere (IRI). We illustrate several limitations associated with the IRI that contribute to its limited capability at the magnetic equator.

Abstract. At low latitudes under moderate to high solar conditions, a number of comparisons between the international reference ionosphere (IRI-90) model of F region electron density profiles and observed profiles measured by the Jicamarca incoherent scatter radar indicate that during the daytime the observed profile shape can be much broader in altitude than that specified by IRI-90, while at night, just after sunset, observed F2 peak altitudes are significantly higher than what is specified by IRI-90. Theoretically derived ionospheric parameters such as F2 peak density (NmF2), F2 peak altitude (hmF2), and profile shape, which are contained in the parameterized ionospheric model (PIM), have been shown in some cases to be in better agreement with Jicamarca observations. This paper describes a new low-latitude option for IRI-90 that uses five ionospheric parameters derived from PIM: the bottomside profile half thickness, NmF2, hmF2, and two parameters of a topside Chapman profile. The generation of electron density profiles using these five parameters is presented, as well as a description of how these parameters can be implemented into the IRI-90 model.

A joint radar/aircraft optical turbulence measurement is discussed. The joint measurement was made over White Sands, New Mexico with a KC135E aircraft equipped with fiber film temperature probes and a ground-based atmospheric profiler. General meteorological conditions were such that the turbulence on the day of the experiment was fairly weak. Emphasis was placed on the 36,000ft to 42,000ft altitude regime. Results showed good agreement between the atmospheric profiler and the aircraft-based measurements.