Event characteristics of intra-seasonal climate circulations

An analysis of rainfall characteristics over the summer rainfall areas of South Africa is done in order to find links between rainfall variability and the general circulation. Seasonal rainfall totals are clearly linked to significant rain days, indicating the importance of evaluating synoptic-scale event characteristics. Rank ordered rainfall characteristics reveal that normal rainfall may be considered as the middle three quintiles, with the outer quintiles representing wet and dry conditions. The general circulation in tenns of atmospheric state (humidity and temperature), moisture and heat transport, and energy exchange - with attention to tropical-extratropical cloud-bands, are central to wet seasons in South Africa. These are generally associated with deep convection that is driven by vertical instability. Transport of moisture into South Africa generally takes place from the east with the Indian Ocean being a major source of water vapour. Although important, fluctuations in moisture transport are not clearly associated with rainfall. This is because moisture is a necessary but not a sufficient condition for rainfall. Atmospheric dynamics producing rainfall are a combination of disturbances of mid-latitude and tropical origin. These disturbances often initiate the tropical-temperate cloud-band where eddy available potential energy, generated through surface heating over land, is converted to eddy kinetic energy. It is generally mid-latitude disturbances with stronger vertical shear that are associated with rainfall events. Increased baroclinic activity in the Southern Ocean south of South Africa, as such, is generally associated with dry seasons. During these seasons there is usually a greater amount of available potential energy which strengthens the southern branch of the Hadley Cell. The effect of this is to increase the strength of the subtropical jet through enhanced poleward flux of angular momentum. The resulting increase in baroclinicity in the South Atlantic Ocean then disrupts rainfall over South Africa through the advection of dry air from the west by the vertical-mean wind component. General circulation models are shown to capture inter-annual variability such that forecasts of regional rainfall, of useful skill at a seasonal scale, may be made. However, the skill level with regard to daily circulation, restricts their use to the large-scale circulation. Nonetheless, the analysis of rainfall and the links to large-scale circulation, discussed in the thesis, provide information to produce more skilful seasonal forecasts without having to model small-scale features directly. Such forecasts may also include additional information on rainfall characteristics, such as number of rain-days and length of dry spells

Retroactive skill of multi-tiered forecasts of summer rainfall over southern Africa

Sea‐surface temperature (SST) variations of the oceans surrounding southern Africa are associated with seasonal rainfall variability, especially during austral summer when the tropical atmospheric circulation is dominant over the region. Because of instabilities in the linear association between summer rainfall over southern Africa and SSTs of the tropical Indian Ocean, the skilful prediction of seasonal rainfall may best be achieved using physically based models. A two‐tiered retro‐active forecast procedure for the December–February (DJF) season is employed over a 10‐year period starting from 1987/1988. Rainfall forecasts are produced for a number of homogeneous regions over part of southern Africa. Categorized (below‐normal, near‐normal and above‐normal) statistical DJF rainfall predictions are made for the region to form the baseline skill level that has to be outscored by more elaborate methods involving general circulation models (GCMs). The GCM used here is the Centre for Ocean–Land–Atmosphere Studies (COLA) T30, with predicted global SST fields as boundary forcing and initial conditions derived from the National Centres for Environmental Prediction (NCEP) reanalysis data. Bias‐corrected GCM simulations of circulation and moisture at certain standard pressure levels are downscaled to produce rainfall forecasts at the regional level using the perfect prognosis approach. In the two‐tiered forecasting system, SST predictions for the global oceans are made first. SST anomalies of the equatorial Pacific (NIÑO3.4) and Indian oceans are predicted skilfully at 1‐ and 3‐month lead‐times using a statistical model. These retro‐active SST forecasts are accurate for pre‐1990 conditions, but predictability seems to have weakened during the 1990s. Skilful multi‐tiered rainfall forecasts are obtained when the amplitudes of large events in the global oceans (such as El Niño and La Niña episodes) are described adequately by the predicted SST fields. GCM simulations using persisted August SST anomalies instead of forecast SSTs produce skill levels similar to those of the baseline for longer lead‐times. Given high‐skill SST forecasts, the scheme has the potential to provide climate forecasts that outscore the baseline skill level substantially

Climate drivers of plague epidemiology in British India, 1898–1949

Plague, caused by Yersinia pestis infection, continues to threaten low- and middle-income countries throughout the world. The complex interactions between rodents and fleas with their respective environments challenge our understanding of human plague epidemiology. Historical long-term datasets of reported plague cases offer a unique opportunity to elucidate the effects of climate on plague outbreaks in detail. Here, we analyse monthly plague deaths and climate data from 25 provinces in British India from 1898 to 1949 to generate insights into the influence of temperature, rainfall and humidity on the occurrence, severity and timing of plague outbreaks. We find that moderate relative humidity levels of between 60% and 80% were strongly associated with outbreaks. Using wavelet analysis, we determine that the nationwide spread of plague was driven by changes in humidity, where, on average, a one-month delay in the onset of rising humidity translated into a one-month delay in the timing of plague outbreaks. This work can inform modern spatio-temporal predictive models for the disease and aid in the development of early-warning strategies for the deployment of prophylactic treatments and other control measures

Modelling seasonality of Lassa fever incidences and vector dynamics in Nigeria

Lassa fever (Lf) is a viral haemorrhagic disease endemic to West Africa and is caused by the Lassa mammarenavirus. The rodent Mastomys natalensis serves as the primary reservoir and its ecology and behaviour have been linked to the distinct spatial and temporal patterns in the incidence of Lf. Nigeria has experienced an unprecedented epidemic that lasted from January until April of 2018, which has been followed by subsequent epidemics of Lf in the same period every year since. While previous research has modelled the case seasonality within Nigeria, this did not capture the seasonal variation in the reproduction of the zoonotic reservoir and its effect on case numbers. To this end, we introduce an approximate Bayesian computation scheme to fit our model to the case data from 2018–2020 supplied by the NCDC. In this study we used a periodically forced seasonal nonautonomous system of ordinary differential equations as a vector model to demonstrate that the population dynamics of the rodent reservoir may be responsible for the spikes in the number of observed cases in humans. The results show that in December through to March, spillover from the zoonotic reservoir drastically increases and spreads the virus to the people of Nigeria. Therefore to effectively combat Lf, attention and efforts should be concentrated during this period

Modeling the Chandra Space Environment

ABSTRACT This paper describes the development of CRMFLX, an ion model for the outer magnetosphere developed for scheduling periods when the Advanced CCD Imaging Spectrometer (ACIS) instrument onboard the Chandra X-ray Observatory can be safely moved into the focal plane position required for science observations. Because exposure to protons with energies of approximately 100 keV to 200 keV has been shown to produce an increase in the charge transfer inefficiency (CTI) of the ACIS instrument, a tool for predicting encounters with magnetospheric regions rich in these particles is required. The model is based on data from the EPIC/ICS instrument onboard the Geotail satellite and provides the user with flux values for 100 kev to 200 keV protons as a function of satellite position and the geomagnetic activity Kp index

Six Years of Chandra Observations of Supernova Remnants

We present a review of the first six years of Chandra X-ray Observatory observations of supernova remnants. From the official "first-light" observation of Cassiopeia A that revealed for the first time the compact remnant of the explosion, to the recent million-second spectrally-resolved observation that revealed new details of the stellar composition and dynamics of the original explosion, Chandra observations have provided new insights into the supernova phenomenon. We present an admittedly biased overview of six years of these observations, highlighting new discoveries made possible by Chandra's unique capabilities.Comment: 82 pages, 28 figures, for the book Astrophysics Update

Modelling the persistence and control of Rift Valley fever virus in a spatially heterogeneous landscape

The persistence mechanisms of Rift Valley fever (RVF), a zoonotic arboviral haemorrhagic fever, at both local and broader geographical scales have yet to be fully understood and rigorously quantified. We developed a mathematical metapopulation model describing RVF virus transmission in livestock across the four islands of the Comoros archipelago, accounting for island-specific environments and inter-island animal movements. By fitting our model in a Bayesian framework to 2004–2015 surveillance data, we estimated the importance of environmental drivers and animal movements on disease persistence, and tested the impact of different control scenarios on reducing disease burden throughout the archipelago. Here we report that (i) the archipelago network was able to sustain viral transmission in the absence of explicit disease introduction events after early 2007, (ii) repeated outbreaks during 2004–2020 may have gone under-detected by local surveillance, and (iii) co-ordinated within-island control measures are more effective than between-island animal movement restrictions

The Met Office Unified Model Global Atmosphere 6.0/6.1 and JULES Global Land 6.0/6.1 configurations

We describe Global Atmosphere 6.0 and Global Land 6.0: the latest science configurations of the Met Office Unified Model and JULES land surface model developed for use across all timescales. Global Atmosphere 6.0 includes the ENDGame dynamical core, which significantly increases mid-latitude variability improving a known model bias. Alongside developments of the model’s physical parametrisations, ENDGame also increases variability in the tropics, which leads to an improved representation of tropical cyclones and other tropical phenomena. Further developments of the atmospheric and land surface parametrisations improve other aspects of model performance, including the forecasting of surface weather phenomena. We also describe Global Atmosphere 6.1 and Global Land 6.1, which include a small number of long-standing differences from our main trunk configurations that we continue to require for operational global weather prediction. Since July 2014, GA6.1/GL6.1 has been used by the Met Office for operational global NWP, whilst GA6.0/GL6.0 was implemented in its remaining global prediction systems over the following year

AIDS survey methodology with black Americans

Unique substantive and methodological issues are involved in conducting survey research on sexual and HIV risk related behaviors among Americans of African descent. Problem conceptualization, sampling, design of instruments, mode of data collection, interviewer/respondent characteristics, community resistance, and data analysis and interpretation are discussed. The lack of survey research on sensitive health issues is noted. Possible methods for addressing these issues are drawn from the experiences of the authors in conducting national research on the general and at risk Black community populations. It is concluded that attention to these issues can substantially improve the quality of research on AIDS related behaviors in Black communities. Finally, it is suggested that behavioral theories and sophisticated methodological and analytic approaches, sensitive to the special cultural dimensions of racial/ethnic life in the United States, would contribute substantially to the scientific armamentarium needed to successfully meet the challenge of the AIDS epidemic.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29527/1/0000614.pd