Search Results

You are looking at 1 - 6 of 6 items for :

  • Author or Editor: R. Wood x
  • Journal of Atmospheric and Oceanic Technology x
  • All content x
Clear All Modify Search
P. R. Field, R. Wood, P. R. A. Brown, P. H. Kaye, E. Hirst, R. Greenaway, and J. A. Smith

Abstract

Ice particle interarrival times have been measured with a fast forward scattering spectrometer probe (FSSP). The distribution of interarrival times is bimodal instead of the exponential distribution expected for a Poisson process. The interarrival time modes are located at ∼10−2 and ∼10−4 s. This equates to horizontal spacings on both the centimeter and meter scales. The characteristics of the interarrival times are well modeled by a Markov chain process that couples together two independent Poisson processes operating at different scales. The possibility that ice crystals shattering on the probe tip causes the bimodal interarrival times is explored and cannot be ruled out. If the observations are indicating real spacings of particles in clouds, then the observations show very localized (centimeter scale) concentrations of ∼100 s cm−3 embedded within an average concentration of typically ∼1 cm−3. If the localized high concentrations are produced by the ice crystals shattering, then the concentration measured by the FSSP is overcounted by a factor of 5 in the worst case measured here, but more typically by a factor of 2. This uncertainty in concentration will adversely affect the predicted radiative influence of these clouds.

Full access
R. Wood, I. M. Stromberg, P. R. Jonas, and C. S. Mill

Abstract

A system has been developed for use on a light aircraft for the measurement of the turbulent wind vector components that does not rely on the use of either an inertial navigation system (INS) or Doppler radar. The system described here uses a five-hole probe to measure the wind vector relative to the aircraft. A GPS system, a vertical gyroscope for aircraft pitch and roll angles, a gyrocompass system, and a strap-down three-axis accelerometer system are used to obtain aircraft motion. Flight tests and results of an intercomparison with the United Kingdom Meteorological Office C-130 are presented. Under conditions of straight and level flight, the estimated rms errors are 0.3 m s−1 for the vertical wind component and 2 m s−1 for the horizontal components.

Full access
Barry A. Bodhaine, Norman B. Wood, Ellsworth G. Dutton, and James R. Slusser

Abstract

Many different techniques are used for the calculation of Rayleigh optical depth in the atmosphere. In some cases differences among these techniques can be important, especially in the UV region of the spectrum and under clean atmospheric conditions. The authors recommend that the calculation of Rayleigh optical depth be approached by going back to the first principles of Rayleigh scattering theory rather than the variety of curve-fitting techniques currently in use. A survey of the literature was conducted in order to determine the latest values of the physical constants necessary and to review the methods available for the calculation of Rayleigh optical depth. The recommended approach requires the accurate calculation of the refractive index of air based on the latest published measurements. Calculations estimating Rayleigh optical depth should be done as accurately as possible because the inaccuracies that arise can equal or even exceed other quantities being estimated, such as aerosol optical depth, particularly in the UV region of the spectrum. All of the calculations are simple enough to be done easily in a spreadsheet.

Full access
C. R. Wood, R. D. Kouznetsov, R. Gierens, A. Nordbo, L. Järvi, M. A. Kallistratova, and J. Kukkonen

Abstract

Two commercial large-aperture scintillometers, Scintec BLS900, were tested on pathlengths of 1840 and 4200 m at about 45–65 m above ground in Helsinki, Finland. From July 2011 through June 2012, large variability in diurnal and annual cycles of both the temperature structure parameter and sensible heat flux were observed. Scintillometer data were compared with data from two eddy-covariance stations. A robust method was developed for the calculation of from raw sonic-anemometer data. In contrast to many earlier studies that solely present the values of , the main focus here is on comparisons of itself. This has advantages, because optical-wavelength scintillometers measure with few assumptions, while the determination of implies the applicability of the Monin–Obukhov similarity theory, which has several inherent limitations. The histograms of compare well between sonic and scintillometer. In-depth analysis is focused on one of the scintillometer paths: both and comparisons gave similar and surprisingly high correlation coefficients (0.85 for and 0.84–0.95 for in unstable conditions), given the differences between the two measurement techniques, substantial sensor separation, and different source areas.

Full access
H.H. Jonsson, J.C. Wilson, C.A. Brock, R.G. Knollenberg, T.R. Newton, J.E. Dye, D. Baumgardner, S. Borrmann, G.V. Ferry, R. Pueschel, Dave C. Woods, and Mike C. Pitts

Abstract

A focused cavity aerosol spectrometer aboard a NASA ER-2 high-altitude aircraft provided high-resolution measurements of the size of the stratospheric particles in the 0.06–2.0-µm-diameter range in flights following the eruption of Mount Pinatubo in 1991. Effects of anisokinetic sampling and evaporation in the sampling system were accounted for by means adapted and specifically developed for this instrument. Calibrations with monodisperse aerosol particles provided the instrument's response matrix, which upon inversion during data reduction yielded the particle size distributions. The resultant dataset is internally consistent and generally shows agreement to within a factor of 2 with comparable measurements simultaneously obtained by a condensation nuclei counter, a forward-scattering spectrometer probe, and aerosol particle impactors, as well as with nearby extinction profiles obtained by satellite measurements and with lidar measurements of backscatter.

Full access
Robert Atlas, Ross N. Hoffman, Zaizhong Ma, G. David Emmitt, Sidney A. Wood Jr., Steven Greco, Sara Tucker, Lisa Bucci, Bachir Annane, R. Michael Hardesty, and Shirley Murillo

Abstract

The potential impact of Doppler wind lidar (DWL) observations from a proposed optical autocovariance wind lidar (OAWL) instrument is quantified in observing system simulation experiments (OSSEs). The OAWL design would provide profiles of useful wind vectors along a ground track to the left of the International Space Station (ISS), which is in a 51.6° inclination low-Earth orbit (LEO). These observations are simulated realistically, accounting for cloud and aerosol distributions inferred from the OSSE nature runs (NRs), and measurement and sampling error sources. The impact of the simulated observations is determined in both global and regional OSSE frameworks. The global OSSE uses the ECMWF T511 NR and the NCEP operational Global Data Assimilation System at T382 resolution. The regional OSSE uses an embedded hurricane NR and the NCEP operational HWRF data assimilation system with outer and inner domains of 9- and 3-km resolution, respectively.

The global OSSE results show improved analyses and forecasts of tropical winds and extratropical geopotential heights. The tropical wind RMSEs are significantly reduced in the analyses and in short-term forecasts. The tropical wind improvement decays as the forecasts lengthen. The regional OSSEs are limited but show some improvements in hurricane track and intensity forecasts.

Full access