Yuriy Kuleshov

Seasonal Forecasting in the Pacific Using the Coupled Model POAMA-2

AbstractThe development of a dynamical model seasonal prediction service for island nations in the tropical South Pacific is described. The forecast model is the Australian Bureau of Meteorologys Predictive Ocean–Atmosphere Model for Australia (POAMA), a dynamical seasonal forecast system. Using a hindcast set for the period 1982–2006, POAMA is shown to provide skillful forecasts of El Nino and La Nina many months in advance and, because the model faithfully simulates the spatial and temporal variability of rainfall associated with displacements of the southern Pacific convergence zone (SPCZ) and ITCZ during La Nina and El Nino, it also provides good predictions of rainfall throughout the tropical Pacific region. The availability of seasonal forecasts from POAMA should be beneficial to Pacific island countries for the production of regional climate outlooks across the region.

Spatial Distribution and Frequency of Thunderstorms and Lightning in Australia

A review of thunderstorm and lightning observations in Australia, with emphasis on studies of their spatial distribution and frequency over the Australian continent, is presented. Long-term thunderday records, lightning data obtained by ground-based lightning detection instruments CIGRE-500 and CGR3 and by NASA satellite-based instruments OTD and LIS have been analyzed to develop maps of total lightning flash density, Nt, (i.e. cloud-to-ground and intracloud) and of ground flash density, Ng. The peak lightning occurrence is in the north-western part of the Australian continent with Nt values up to about 35 km-2yr-1. Ground flash density (Ng) values vary from over 6 km-2yr-1 in the northern parts of Australia to about 1 km-2 yr-1 and below in the southern parts. There are significant seasonal and yearly variations in the frequency of thunderdays. Some aspects of the hazards from thunderstorms and lightning appear to be special to Australia, including lightning initiated wildfires, lightning injuries to telephone users and faults on power lines caused by high wind gust speeds.

An analysis of tropical cyclone occurrence in the Southern Hemisphere derived from a new satellite-era data set

Satellite remote sensing is vital to accurately estimate tropical cyclone (TC) parameters such as position and intensity. A TC archive for the Southern Hemisphere (SH) has been prepared for the ‘satellite era’, and it now consists of best track data, covering name (and/or unique identification number), position and intensity (in terms of central pressure). Based on these best track data, TC climatologies for the South Indian Ocean (SIO) and South Pacific Ocean (SPO) are investigated. Variability in TC activity is examined depending on different phases of the El Niño-Southern Oscillation (ENSO). The outcomes demonstrate prospects for improving the regional seasonal prediction of TC activity. The growth in the availability of satellite data is found to have a significant influence on the quantity and quality of available TC data, particularly in relation to the intensity of TCs. To provide a means of accessing detailed information and data on historical TCs in the SH, a specialized website for disseminating results and data was developed using the OpenLayers platform. This allows dynamic map navigation of detailed information for user-selected regions.

Precipitable Water Vapor Estimates in the Australian Region from Ground-Based GPS Observations

We present a comparison of atmospheric precipitable water vapor (PWV) derived from ground-based global positioning system (GPS) receiver with traditional radiosonde measurement and very long baseline interferometry (VLBI) technique for a five-year period (2008–2012) using Australian GPS stations. These stations were selectively chosen to provide a representative regional distribution of sites while ensuring conventional meteorological observations were available. Good agreement of PWV estimates was found between GPS and VLBI comparison with a mean difference of less than 1 mm and standard deviation of 3.5 mm and a mean difference and standard deviation of 0.1 mm and 4.0 mm, respectively, between GPS and radiosonde measurements. Systematic errors have also been discovered during the course of this study, which highlights the benefit of using GPS as a supplementary atmospheric PWV sensor and calibration system. The selected eight GPS sites sample different climates across Australia covering an area of approximately 30° NS/EW. It has also shown that the magnitude and variation of PWV estimates depend on the amount of moisture in the atmosphere, which is a function of season, topography, and other regional climate conditions.

Improving the Operational Methodology of Tropical Cyclone Seasonal Prediction in the Australian and the South Pacific Ocean Regions

Tropical cyclones (TCs) can have a major impact on the coastal communities of Australia and Pacific Island countries. Preparedness is one of the key factors to limit TC impacts and the Australian Bureau of Meteorology issues an outlook of TC seasonal activity ahead of TC season for the Australian Region (AR; 5°S to 40°S, 90°E to 160°E) and the South Pacific Ocean (SPO; 5°S to 40°S, 142.5°E to 120°W). This paper investigates the use of support vector regression models and new explanatory variables to improve the accuracy of seasonal TC predictions. Correlation analysis and subsequent cross-validation of the generated models showed that the Dipole Mode Index (DMI) performs well as an explanatory variable for TC prediction in both AR and SPO, Nino4 SST anomalies—in AR and Nino1

Principle of Locality and Analysis of Radio Occultation Data

A fundamental principle of local interaction of radio waves with a refractive spherical medium is formulated and illustrated using the radio occultation (RO) method of remote sensing of the atmosphere and the ionosphere of the Earth and the planets. In accordance with this principle, the main contribution to variations of the amplitude and the phase of radio waves propagating through a medium makes a neighborhood of a tangential point, where the gradient of the refractive index is perpendicular to the radio wave trajectory. A necessary and sufficient condition (a criterion) is established to detect the displacement of the tangential point from the radio ray perigee using analysis of the RO experimental data. This criterion is applied to the identification and the location of layers in the atmosphere and the ionosphere by the use of Global Positioning System RO data. RO data from the CHAllenge Minisatellite Payload (CHAMP) are used to validate the criterion introduced when significant variations of the amplitude and the phase of the RO signals are observed at the RO ray perigee altitudes below 80 km. The detected criterion opens a new avenue in terms of measuring the altitude and the slope of the atmospheric and ionospheric layers. This is important for the location determination of the wind shear and the direction of internal wave propagation in the lower ionosphere and possibly in the atmosphere. The new criterion provides an improved estimation of the altitude and the location of the ionospheric plasma layers compared with the backpropagation radio-holographic method previously used.

Seasonal prediction of the South Pacific Convergence Zone in the austral wet season

The position and orientation of the South Pacific Convergence Zone (SPCZ), modulated by the El Nino-Southern Oscillation (ENSO), determine many of the potentially predictable interannual variations in rainfall in the South Pacific region. In this study, the predictability of the SPCZ in austral summer is assessed using two coupled (ocean-atmosphere) global circulation model (CGCM)-based seasonal prediction systems: the Japan Meteorological Agencys Meteorological Research Institute Coupled Ocean-Atmosphere General Circulation Model (JMA/MRI-CGCM) and the Australian Bureau of Meteorologys Predictive Ocean-Atmosphere Model for Australia (POAMA-M24). Forecasts of austral summer rainfall, initialized in November are assessed over the period 1980–2010. The climatology of CGCM precipitation in the SPCZ region compares favorably to rainfall analyses over subsets of years characterizing different phases of ENSO. While the CGCMs display biases in the mean SPCZ latitudes, they reproduce interannual variability in austral summer SPCZ position indices for forecasts out to 4 months, with temporal correlations greater than 0.6. The summer latitude of the western branch of the SPCZ is predictable with correlations of the order of 0.6 for forecasts initialized as early as September, while the correlation for the eastern branch only exceeds 0.6 for forecasts initialized in November. Encouragingly, the models are able to simulate the large displacement of the SPCZ during zonal SPCZ years 1982–1983, 1991–1992, and 1997–1998.

Seasonal Prediction of Climate Extremes for the Pacific: Tropical Cyclones and Extreme Ocean Temperatures

Climate change and climate extremes have a major impact on Australia and Pacific Island countries. Of particular concern are tropical cyclones and extreme ocean temperatures. As a practical response to climate change, through the Pacific Australia Climate Change Science and Adaptation planning Program (PACCSAP), enhanced web-based information tools to provide seasonal forecasts for climatic extremes in the Western Pacific have been developed. Using the dynamical seasonal prediction model POAMA (Predictive Ocean Atmosphere Model for Australia), we aim to improve accuracy of seasonal forecasts of tropical cyclone activity and extreme sea surface temperatures for the Western Pacific. Since the PACCSAP has commenced, encouraging scientific and technological results have been obtained, particularly in the development of web-based information tools to provide climatic extremes forecasts in the Pacific and the Australian regions. Improvements to a statistical model for seasonal tropical cyclone prediction in the Australian region have been made. Additional functionality was added to the Pacific Tropical Cyclone Data Portal, such as enhanced flexibility of spatial and temporal selection. New web-based information tool for sea surface temperature seasonal prediction is also currently under development. Improved knowledge of extreme climatic events, together with the assistance of tailored forecast tools, will help enhance the resilience and adaptive capacity of Australia and Pacific Island Countries under climate change.

A study on the relationship between ionospheric correction and data control for GPS radio occultation in Australia

GPS radio occultation, (RO) is an emerging and robust space-based earth observation system, with the potential for atmospheric profiling and meteorological applications. GPS RO requires GPS receivers onboard Low Earth Orbit (LEO) satellites to measure the radio signals from GPS satellites so that the atmospheric profiles of parameters such as temperature, pressure and water vapour can be obtained via a complicated atmospheric retrieval process. This research focuses on the ionospheric correction using the Radio Occultation Processing Package (ROPP) to investigate the effect from ionosphere for GPS radio occultation in the Australia region. The MSISE-90 model with the statistical optimization method produced the best results for altitudes greater than 40 km. The influence from the ionosphere can be removed using the generic Lc method which produced the best results for altitudes less than 40 km.

Climate Change and Southern Hemisphere Tropical Cyclones International Initiative – Progress since the First International Conference on Indian Ocean Tropical Cyclones and Climate Change

Tropical cyclones (TCs) are the most dangerous and damaging weather phenomena to regularly affect countries in the South Indian and the South Pacific Oceans. The year-to-year impact varies, and historical records demonstrate significant interannual variability in TC frequency and spatial distribution of cyclone tracks. Additionally, the climate is changing on a global scale and it is important to understand how a warmer climate may affect TC activity. Since 1999 national meteorological services from the regions of the Southern Hemisphere (SH) combined their efforts in improving our understanding of changes in regional TC activity due to climate change. As the first step of the “Climate change and Southern Hemisphere tropical cyclones” International Initiative, high-quality TC archive for the SH has been created.