Recent Changes in the Climate At the Dead Sea – a Preliminary Study

In the last decade pan evaporation measured at the Southern Dead Sea has significantly increased. Wind, temperature and humidity measurements at the Dead Sea starting in the 1930s as well as 3-D model simulations all seem to indicate a statistically significant change in the local climate of the Dead Sea region. The potential contribution to this climatic change through the weakening of the local land-sea breeze circulation caused by the reduction in the Dead Sea surface area in 1979–1981, is examined. It is suggested that since the breeze tempers the Dead Sea climate, its weakening has caused the air temperature to increase, the relative humidity to decrease and thus increased the pan evaporation. The climatic changes as implied by the MM4 Mesoscale PSU/NCAR model simulations, seem to fit the observed changes and to suggest a local tendency to the more arid climate that now prevails to the south of the study region.     

Responses of interrill runoff and erosion rates to vegetation change in southern Arizona

Vegetation change, fi-om grassland to shrubland, has occurred over much of the Sonoran and Chihuahuan Deserts during the past century. The effect of this vegetation change on interrill runoff and erosion was examined by conducting rainfall-simulation experiments on large runoff plots on contemporary grassland and shrubland hillslopes. These experiments show that, compared to the grassland, the interrill portions of shrubland hillslopes (1) have higher runoff rates, (2) experience equilibrium runoff conditions much more frequently, (3) exhibit higher overland flow velocities, and (4) are subject to greater rates of erosion. The environmental change that has led to the vegetation change has been relatively minor, but its geomorphic impact has been substantial.     

A new, instantaneous aeolian sand trap design for field use

A new aeolian sediment trap is described which can give up to 1 Hz measurement frequency in field conditions. The trap adopts a circular, horizontal trap design with a load cell connection to give continuous, unobtrusive trap measurement of sediment flux. Simultaneous velocity recording is carried out using an anemometer. Trap construction costs are approximately £200. Initial results in field conditions using a direct comparison of wind velocity data, sampled at an equivalent frequency, have given a first-order relationship between sediment flux and velocity. The trap enables simultaneous sampling of wind velocity and sediment flux at a sufficiently short interval to enable investigation of sediment transport dynamics under a variety of field conditions.     

Doppler radar spectral width broadening due to beamwidth and wind shear

The spectral width observed by Doppler radars can be due to several effects including the atmospheric turbulence within the radar sample volume plus effects associated with the background flow and the radar geometry and configuration. This study re-examines simple models for the effects due to finite beam-width and vertical shear of the horizontal wind. Analytic solutions of 1- and 2-dimensional models are presented. Comparisons of the simple 2-dimensional model with numerical integrations of a 3-dimensional model with a symmetrical Gaussian beam show that the 2-dimensional model is usually adequate. The solution of the 2-dimensional model gives a formula that can be applied easily to large data sets. Analysis of the analytic solutions of the 2-dimensional model for off-vertical beams reveals a term that has not been included in mathematical formulas for spectral broadening in the past. This term arises from the simultaneous effects of the changing geometry due to curvature within a finite beamwidth and the vertical wind shear. The magnitude of this effect can be comparable to that of the well-known effects of beam-broadening and wind shear, and since it can have either algebraic sign, it can significantly reduce (or increase) the expected spectral broadening, although under typical conditions it is smaller than the beam-broadening effect. The predictions of this simple model are found to be consistent with observations from the VHP radar at White Sands Missile Range, NM.