Radar cells from the GATE experiment, from Spain and from the Montreal area were followed and measurements of their total rain flux and area were extracted. The values of the flux and area, for each one of the cells, for initial time increments T(,0) were used to evaluate various extrapolation schemes for forecasting purposes. The extrapolation procedure that gave the smallest error in forecasting the changes in flux and area, was found to be the linear one and the optimum increment T(,0) was about 30 min. However, even though these techniques have the advantage of establishing a trend in the behavior of the flux and area with time, a comparison of the forecast errors from the linear extrapolation scheme with those from the assumption of no change in cell area and rain flux shows insignificant improvements. A technique including both cell motion and internal changes in flux and area of the rain cells was developed to evaluate the accuracy of rain accumulation forecasts. Again, it was found that the errors were similar with those generated by the assumption of no change in rain flux and area from the moving cell. / The preceding results were used as a possible input into the design and evaluation of cloud seeding experiments. Based on this, a method is developed which gives the necessary number of experiments (i.e., seeded cases) in order for a seeding factor to be statistically significant at specified confidence levels. As a conclusion, it can be stated that the use of short term rain predictions (which are translated as differences of the rain flux in time) is very promising. In comparison to other techniques described in the literature this method appears to be superior, in the sense that fewer experiments are needed to detect seeding factors at specified confidence levels.

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Low phosphate fertilizer efficiency in high pH soils is primarily due to the retardation of P movement in the soil-P fertilizer reaction zone. The objective of this study was to obtain fundamental information on the influence of multi-ionic interactions on the solubility and diffusion of P in columns containing a model soil system and two soil types. The study also aimed to identify the salt combinations and factors that have the potential to enhance the solubility and movement of P in calcareous soil condition. The results showed that the interaction of NH4+ and SO42- was consistent at enhancing the water solubility and movement of P under a high soil pH condition. This effect was attributed to the combination of various mechanistic factors associated with (NH4)2SO4 compound including significant pH reduction, cation exchange reaction of NH4+ with the exchangeable Ca2+, and anionic competition of SO42- with P for precipitation with Ca2+.

Incoherent scatter radars are powerful ground based instruments for ionospheric measurements. By analysis of the Doppler shifted backscatter spectrum, containing the signature of electrostatic plasma waves, plasma bulk properties are estimated. At high latitudes the backscattered radar power is occasionally enhanced several orders of magnitude above the thermal backscatter level. These enhancements occur during geomagnetic disturbed conditions and are referred to as naturally enhanced ion acoustic echoes (NEIALs). NEIALs are linked to auroral activity with optical auroral emission observed in the vicinity of the radar measurement volume simultaneously to NEIALs. The backscatter enhancements are thought to be caused by wave activity above thermal level due to instability. A number of theories have been put forward including streaming instabilities and Langmuir turbulence to explain NEIAL observations. NEIALs occur in two classes distinct by their Doppler features. Observations of the first type, which has been studied more extensively, are generally modelled well by the Langmuir turbulence model. The difficulty in trying to understand the driving mechanism of the instability is the limited spatial resolution of the radar measurements. Observations of the second type, reported on more recently, have been interpreted as evidence for naturally occurring strong Langmuir turbulence by means of their Doppler features. Aperture synthesis is a technique to increase the spatial resolution of the radar measurements to below beam width of the single receiver antennas. The technique is employed to investigate the structure of NEIALs in the plane perpendicular to the magnetic field at sub-degree scale corresponding to hundreds of meters to a few kilometres at ionospheric altitudes. Calibration of the radar interferometer is necessary and a calibration technique is presented in paper I. Interferometry observations of a NEIAL event with receivers deployed at the EISCAT incoherent scatter radar on Svalbard are presented in paper II. The size of the enhanced backscatter region is found to be limited to 900 x 500m in the plane perpendicular to the geomagnetic field. These observations constitute the first unambiguous measurements giving evidence for the limited size of the enhanced backscatter region. In paper III observations of strong Langmuir turbulence signatures are presented. The apparent turbulent region in these observations is limited to two narrow altitude regions, 2km extent, and electron density irregularities caused by the turbulence are thought to reach down to decimeter scale length. The turbulence observations were obtained during energetic electron precipitation thereby differing from other observations during which a low energy component in the electron precipitation is reported. In paper IV a statistical study of strong Langmuir turbulence radar signatures is presented. The study reveals differing local time distributions for these signatures from type I NEIALs indicating di_ering driving conditions for the two types of NEIALs. It is found that strong Langmuir turbulence signatures are predominantly observed in the pre-midnight sector where auroral break-up aurora prevails. / <p>QC 20150303</p>

Low phosphate fertilizer efficiency in high pH soils is primarily due to the retardation of P movement in the soil-P fertilizer reaction zone. The objective of this study was to obtain fundamental information on the influence of multi-ionic interactions on the solubility and diffusion of P in columns containing a model soil system and two soil types. The study also aimed to identify the salt combinations and factors that have the potential to enhance the solubility and movement of P in calcareous soil condition. The results showed that the interaction of NH4+ and SO42- was consistent at enhancing the water solubility and movement of P under a high soil pH condition. This effect was attributed to the combination of various mechanistic factors associated with (NH4)2SO4 compound including significant pH reduction, cation exchange reaction of NH4+ with the exchangeable Ca2+, and anionic competition of SO42- with P for precipitation with Ca2+.

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This PhD thesis investigates the relative importance of oceanic and atmospheric influences on extremes, long-term trends, and seasonal to interannual variability of precipitation for different regions in the Southern Hemisphere in observations, reanalysis data, and output from general circulation models (GCM). Examination of interannual rainfall extremes over southwest Western Australia (SWWA) reveals a characteristic dipole pattern of Indian Ocean sea surface temperature anomalies (SSTA). This coincides with a large-scale reorganization of the wind field over the tropical/subtropical Indian Ocean changing SSTA, via anomalous Ekman transport in the tropical Indian Ocean and via anomalous air-sea heat fluxes in the subtropics, and altering moisture advection onto SWWA. The potential impact of these Indian Ocean SSTA in driving modulations of mid-latitude precipitation across southern and western regions of Australia is assessed in atmospheric GCM simulations. The SSTA give rise to changes in the thermal properties of the atmosphere, meridional thickness gradient, subtropical jet, thermal wind, and baroclinicity over southern regions of Australia, thus modulating precipitation. In addition, links between anomalous wet conditions over East Africa and these characteristic Indian Ocean SSTA are explored during the "short rain" season in October-November. Interannual extremes m New Zealand rainfall and their modulation by modes of Southern Hemisphere climate variability, namely the Southern Annular Mode (SAM) and El Nino-Southern Oscillation (ENSO), are investigated. Late twentieth Century trends in New Zealand precipitation are examined for the period 19792006 to quantify the relative impact of recent changes in the large-scale atmospheric circulation related to the SAM and ENSO. Increasingly drier conditions over much of New Zealand can be partially explained by the SAM and ENSO. Cool season rainfall variability in southeastern Australia is investigated via a classification and characterization of the predominant types of synoptic systems occurring in the region, focusing on frontal and cutoff low systems. Two definitions of the autumn break developed for northwestern Victoria are employed to produce a synoptic climatology of the break phenomenon. Trends in characteristics of the autumn break indicate that the most recent drought in southeastern Australia is comparable in severity with the two major droughts in the twentieth Century.