Robert J. Watson

The Convective Storm Initiation Project

The Convective Storm Initiation Project (CSIP) is an international project to understand precisely where, when, and how convective clouds form and develop into showers in the mainly maritime environment of southern England. A major aim of CSIP is to compare the results of the very high resolution Met Office weather forecasting model with detailed observations of the early stages of convective clouds and to use the newly gained understanding to improve the predictions of the model. A large array of ground-based instruments plus two instrumented aircraft, from the U.K. National Centre for Atmospheric Science (NCAS) and the German Institute for Meteorology and Climate Research (IMK), Karlsruhe, were deployed in southern England, over an area centered on the meteorological radars at Chilbolton, during the summers of 2004 and 2005. In addition to a variety ofground-based remote-sensing instruments, numerous rawinsondes were released at one- to two-hourly intervals from six closely spaced sites. The Met Office weather radar network and Meteosat satellite imagery were used to provide context for the observations made by the instruments deployed during CSIP. This article presents an overview of the CSIP field campaign and examples from CSIP of the types of convective initiation phenomena that are typical in the United Kingdom. It shows the way in which certain kinds of observational data are able to reveal these phenomena and gives an explanation of how the analyses of data from the field campaign will be used in the development of an improved very high resolution NWP model for operational use.

GPS scintillation in the high arctic associated with an auroral arc

A rapid signal-fading event produced by diffractive scintillations was observed around 0123 UT on 8 November 2004 by three closely sited (less than 250 m apart) GPS scintillation receivers in northern Norway. The entire duration of the event was about 10 s and was recorded by all three receivers. Intense, short duration events such as these are not clearly observable in the 1-min scintillation index (S4) because they do not necessarily last for the entire minute. In spite of their short duration they can cause a receiver to lose lock because of their intensity. The geomagnetic conditions were disturbed at this time with the interplanetary magnetic field southward for a period of several hours. Magnetometers from the IMAGE network in Scandinavia showed evidence of a 2000 nT substorm. The GPS measurements are compared with all-sky camera (ASC) data to show that the signal fades can be attributed to the GPS ray paths crossing electron density structures associated with the aurora. The ASC images reveal moving auroral structures at the same time as the GPS signals show movement of the ionospheric regions causing fading. The results indicate that at high latitudes low-elevation GPS signals can suffer sudden fading due to E-region auroral events. This is the first time that a direct connection has been established between the loss of lock on a GPS receiver and diffractive fading caused by auroral precipitation.

The exbD gene of Photorhabdus temperata is required for full virulence in insects and symbiosis with the nematode Heterorhabditis

Photorhabdus are bacteria found colonizing the gut of a specialized stage of the nematode Heterorhabditis, called the infective juvenile (IJ). The IJ is a free‐living stage of the nematode that seeks out and infects insect larvae. Once inside the insect the IJ release Photorhabdus into the haemolymph where the bacteria rapidly proliferate, killing the insect within 48–72 h. The nematodes grow and reproduce in the insect cadaver by feeding on the Photorhabdus biomass. In this study we use Photorhabdus temperata K122 to show that genes involved in iron acquisition play a key role during the course of the tripartite bacteria–nematode–insect interaction. We show that a strain carrying a mutation in a gene with homology to exbD, encoding a component of the TonB complex, is unable to grow well in conditions where iron is not freely available. In addition, this mutant, BMM417, requires a longer time to kill the insect larvae than the wild‐type bacteria and this defect in pathogenicity is complemented by the co‐injection of iron. Moreover, the increase in LT50 observed with BMM417 is correlated with a significantly slower in vivo growth rate suggesting that iron is limiting in the insect. We also show that BMM417 is unable to support the growth and development of the Heterorhabditis nematode. Addition of exogenous iron to the growth media restores nematode growth and development on BMM417, suggesting that aspects of iron metaboism in Photorhabdus are important during the symbiosis with the nematode.

The role of iron uptake in pathogenicity and symbiosis in Photorhabdus luminescens TT01.

BackgroundPhotorhabdus are Gram negative bacteria that are pathogenic to insect larvae whilst also having a mutualistic interaction with nematodes from the family Heterorhabditis. Iron is an essential nutrient and bacteria have different mechanisms for obtaining both the ferrous (Fe2+) and ferric (Fe3+) forms of this metal from their environments. In this study we were interested in analyzing the role of Fe3+ and Fe2+ iron uptake systems in the ability of Photorhabdus to interact with its invertebrate hosts.ResultsWe constructed targeted deletion mutants of exbD, feoABC and yfeABCD in P. luminescens TT01. The exbD mutant was predicted to be crippled in its ability to obtain Fe3+ and we show that this mutant does not grow well in iron-limited media. We also show that this mutant was avirulent to the insect but was unaffected in its symbiotic interaction with Heterorhabditis. Furthermore we show that a mutation in feoABC (encoding a predicted Fe2+ permease) was unaffected in both virulence and symbiosis whilst the divalent cation transporter encoded by yfeABCD is required for virulence in the Tobacco Hornworm, Manduca sexta (Lepidoptera) but not in the Greater Wax Moth, Galleria mellonella (Lepidoptera). Moreover the Yfe transporter also appears to have a role during colonization of the IJ stage of the nematode.ConclusionIn this study we show that iron uptake (via the TonB complex and the Yfe transporter) is important for the virulence of P. luminescens to insect larvae. Moreover this study also reveals that the Yfe transporter appears to be involved in Mn2+-uptake during growth in the gut lumen of the IJ nematode. Therefore, the Yfe transporter in P. luminescens TT01 is important during colonization of both the insect and nematode and, moreover, the metal ion transported by this pathway is host-dependent.

The use of GPS measurements for water vapor determination

Abstract A workshop on the use of Global Positioning System (GPS) measurements in weather and climate with emphasis on water vapor determination, was organized by the National Environmental Research Councils (NERC) Environmental Systems Science Centre (ESSC), at the University of Reading, Reading, United Kingdom, and took place there 29–31 August 2001. This paper gives a broad overview and general background of the use of GPS data for weather and climate. It outlines the objectives of the workshop and presents ongoing national, regional, and international activities both for ground-based and satellite-based systems. This includes work in the United States, China, and Japan, and different European efforts, including activities under European Community programs. Data assimilation of GPS data for weather prediction and climate is discussed as are ways in which to develop GPS-based systems to become an integrated part of the World Weather Watch. This includes ways of systematically using GPS data from the in...

An attenuation time series model for propagation forecasting

A key problem in the efficient use of higher (Ka- and V-band) frequencies lies in the mitigation of propagation impairments caused by meteorological phenomena. The traditional approach to this problem is based upon a relatively simplistic statistical model in the form of a fade margin. At higher frequencies this traditional approach becomes inefficient due to the large margin required. This inefficiency has lead to the introduction of dynamic fade mitigation techniques (FMTs). We present a method of generating attenuation time series that can be used for the development and evaluation of FMTs. The method we propose is based on the use of proven numerical weather prediction models in conjunction with a propagation model. This approach has two unique aspects. First, the spatial correlation and dynamic behavior of the attenuation fields are inherited from the meteorological environment. Second, the model can provide forecasts of attenuation. It is foreseen that this a priori knowledge of the occurrence of fades, their likely depth and likely duration can be exploited to manage the resource control of entire networks. This paper presents a description of the method and demonstrates the ability to generate attenuation time series. Conclusions are drawn regarding its use in real-time for network resource management.

Map of low-frequency electromagnetic noise in the sky

The Earths natural electromagnetic environment is disturbed by anthropogenic electromagnetic noise. Here we report the first results from an electromagnetic noise survey of the sky. The locations of electromagnetic noise sources are mapped on the hemisphere above a distributed array of wideband receivers that operate in a small aperture configuration. It is found that the noise sources can be localized at elevation angles up to ∼60° in the sky, well above the horizon. The sky also exhibits zones with little or no noise that are found toward the local zenith and the southwest of the array. These results are obtained by a rigorous analysis of the residuals from the classic dispersion relation for electromagnetic waves using an array analysis of electric field measurements in the frequency range from ∼20 to 250 kHz. The observed locations of the noise sources enable detailed observations of ionospheric modification, for example, caused by particle precipitation and lightning discharges, while the observed exclusion zones enable the detection of weak natural electromagnetic emissions, for example, from streamers in transient luminous events above thunderclouds.

Array analysis of electromagnetic radiation from radio transmitters for submarine communication

The array analyses used for seismic and infrasound research are adapted and applied here to the electromagnetic radiation from radio transmitters for submarine communication. It is found that the array analysis enables a determination of the slowness and the arrival azimuth of the wave number vectors associated with the electromagnetic radiation. The array analysis is applied to measurements of ∼20–24 kHz radio waves from transmitters for submarine communication with an array of 10 radio receivers distributed over an area of ∼1 km ×1 km. The observed slowness of the observed wave number vectors range from ∼2.7 ns/m to ∼4.1 ns/m, and the deviations between the expected arrival azimuths and the observed arrival azimuths range from ∼−9.7° to ∼14.5°. The experimental results suggest that it is possible to determine the locations of radio sources from transient luminous events above thunderclouds with an array of radio receivers toward detailed investigations of the electromagnetic radiation from sprites.

Diversity improvement estimation from rain Radar databases using maximum likelihood estimation

This research examines route diversity as a fade mitigation technique in the presence of rain, for terrestrial microwave links. The improvement in availability due to diversity depends upon the complex spatio-temporal properties of rainfall. To produce a general model to predict the advantage due to route diversity it is necessary to be able to predict the correlation of rain attenuation on arbitrary pairs of microwave links. This is achieved by examination of a database of radar derived rain rate fields. Given a representative sample of rain field images, the joint rain attenuation statistics of arbitrary configurations of terrestrial links can be estimated. Existing rain field databases often yield very small numbers of high joint attenuation events. Consequently, estimates of the probability of joint high attenuation events derived from ratios of the number of occurrences can be highly inaccurate. This paper assumes that pairs of terrestrial microwave links have joint rain attenuation distributions that are bi-lognormally distributed. Four of the five distribution parameters can be estimated from ITU-R models. A maximum likelihood estimation (MLE) method is used to estimate the fifth parameter, i.e., the covariance or correlation. The predicted diversity statistics vary smoothly and yield plausible extrapolations into low probability situations.

A Portable Wideband Impulsive Noise Location System

Many power-system-related effects and sources of man-made noise cause impulsive interference. Due to its wideband nature, this type of interference is difficult to remove by filtering. This paper presents a system that is capable of locating and characterizing sources of impulsive interference. It is based on three separate asynchronous receiving units. The operating principle of the location system is outlined, and a prototype practical implementation is described. The location accuracies achieved both in the laboratory and in practical field trials are reported.