[1] A sequence of nine weather balloons were launched recently over the island of Hawaii during the nights of 12, 13, and 17 December, 2002, providing measurements of ascent rate, horizontal wind speed and direction, temperature, and other quantities. The measurements show short intervals of altitude with a large increase in ascent rate, occurring only near the tropopause, indicating regions of strong upward air velocity at this location. The large ascent rates correlate well to the strength of a jet stream, and with the presence of a local critical level, indicating mountain waves as the primary cause. No corresponding decreases in ascent rate were measured, suggesting strong threedimensional effects.
Equations are developed for the effect of velocity uctuations on a moving temperature sensor. The impact of these uctuations on perceived uctuations of the index of refraction is computed. The magnitude of this effect is estimated using known ranges of uctuations in atmospheric temperature and velocity. By the use of a method to estimate velocity uctuations from temperature uctuations and concurrently measured atmospheric data, balloon derived uctuation data are used to estimate the perceived uctuations of a faster moving sensor. We conclude that normally observed velocity uctuations, if uncorrected, can have a signi cant impact on the perceived optical properties in the troposphere for higher velocity temperature sensors. Nomenclature a = constant or coef cient B r .x/ = spatial covariance (units of r 2 ) b = constant or coef cient C p = speci c heat at constant pressure, J/kg/K C 2 x = structure constant of the quantity x (units of x 2 =m 2=3 ) D x .r / = structure function of quantity x (units of x 2 ) d = distance, m g = acceleration of gravity, m/s 2 i; j; k = unit vectors (with caret) k = spatial wave number, m ¡1 n = nondimensional index of refraction P = pressure or partial pressure when subscripted, Pa r = nondimensional recovery factor; see Eq.(2) S x .k/ = one-sided, one-dimensional spatial power spectrum of x T = temperature, K U = true air speed vector, m/s u; v; w = components of wind velocity, W to E, S to N, and upward, respectively, m/s V = velocity vector, m/s x = distance, m Z = altitude in plots, km z = distance in vertical direction, m°= ratio of speci c heat at constant pressure to speci c heat at constant volume " = turbulent kinetic energy dissipation rate, W kg ¡1 or m 2 s ¡3 µ = potential temperature, K; see Eq. (21) = wavelength of refracted radiation, m  = dissipation rate of temperature variance, K 2 s ¡1 Subscripts d = dry air gs = ground speed n = index of refraction r = recovery T = temperature U or u = velocity Presented as Paper 98-2830at the AIAA w = wind wv = water vapor 1; 2 = location 1 or 2 Superscripts = time-averaged or mean component 0 = uctuating component Introduction O PTICAL turbulence in the atmosphere is de ned as uctu-ations of the index of refraction, both in space and time. Whereas it is most obviously manifested by the twinkling of stars, it also is a major source of performance degradation for optical systems. For instance, in the presenceof optical turbulence,a projected beam appears to wander, broaden, and scintillate, thereby reducing image quality and effectively reducing the average power that arrives at a spot. Optical turbulence is caused by the presence of adjacent parcels of air, at slightly differentindex of refraction, moving about in the path of propagating electromagnetic waves.The index of refraction, n, in the atmosphere can be written as 1where P is the partial pressure of either the dry air d or the water vapor wv and the a coef cients are the wavelength-dependent coef cients for either the dry air or the water vapor. Fluctuations in the index...
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