Computation of the vertical velocity on the synoptic scale

Several sets of equations which can be used to find the vertical velocity are examined. A distinction is made between assumptions that are based on physical considerations and those based on computational necessity. Since the equations are solved as boundary value problems it is necessary to impose boundary conditions. These are discussed. Investigations are made into the use of the overrelaxation method for solving partial differential equations with either Dirichlet or Neumann boundary conditions. Emphasis is placed upon the determination of the optimum overrelaxation factor. A simple method of calculating this factor for the ω-equation is tested. The derivation, meaning and solution of the balance equation is discussed. New methods of solving this equation are introduced and are compared with existing methods. The boundary conditions for the linear balance equation are investigated and this leads to the derivation of a new boundary condition for the balance equation. The geostrophic ω-equation is examined and the elliptic condition is derived. Appropriate boundary conditions for ω are discussed and the effects of the form of the static stability on ω and ϴt are investigated. Simple models of the atmosphere are used from which several inferences are drawn. These are tested with case studies. The inconsistency of the usual boundary conditions for ω and ϴt, is also examined

Study of a quasi-optic oscillator

This thesis is concerned with an experimental study of a novel microwave oscillator which is based on quasi-optic principles rather than more conventional closed cavity techniques. A quasi-optic open cavity resonator is used in order to combine and stabilize the frequency of many solid state source modules. At mm wavelengths, the small physical size of the open resonator, (127 mm diameter mirrors at Q-band) enables the fabrication of medium power oscillators with dimensions suitable for integration within a practical system. A self-oscillating microstrip patch antenna, mounted conformally with the resonator mirror surface, is developed as the basic source module. A suitable method of coupling many of these modules efficiently to a beam mode supported by the open resonator is discussed, together with the dependence of the preferred active cavity mode upon the array geometry. Initial experimental investigations have been undertaken at J-Band (12-18 GHz) yielding techniques that have been successfully applied at Q-Band (26 - 40 GHz).<p

Increased light, moderate, and severe clear-air turbulence in response to climate change

Anthropogenic climate change is expected to strengthen the vertical wind shears at aircraft cruising altitudes within the atmospheric jet streams. Such a strengthening would increase the prevalence of shear instabilities, which generate clear-air turbulence. Climate modelling studies have indicated that the amount of moderate-or-greater clear-air turbulence on transatlantic flight routes in winter will increase significantly in future as the climate changes. However, the individual responses of light, moderate, and severe clear-air turbulence have not previously been studied, despite their importance for aircraft operations. Here we use climate model simulations to analyse the transatlantic wintertime clear-air turbulence response to climate change in five aviation-relevant turbulence strength categories. We find that the probability distributions for an ensemble of 21 clear-air turbulence diagnostics generally gain probability in their right-hand tails when the atmospheric carbon dioxide concentration is doubled. By converting the diagnostics into equivalent eddy dissipation rates, we find that the ensemble-average airspace volume containing light clear-air turbulence increases by 59% (with an intra-ensemble range of 43–68%), light-to-moderate by 75% (39–96%), moderate by 94% (37–118%), moderate-to-severe by 127% (30–170%), and severe by 149% (36–188%). These results suggest that the prevalence of transatlantic wintertime clear-air turbulence will increase significantly in all aviation-relevant strength categories as the climate changes