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C. B. Emmanuel, B. R. Bean, L. G. McAllister, and J. R. Pollard

Abstract

Acoustic probing of the lower atmosphere (<150 m) reveals structures that appear similar to those of instability waves produced by wind shear at the stable interface of a temperature inversion. The acoustic sounder was located in the vicinity of a meteorological tower 152 m in height. Profiles of wind velocity and temperature were taken during the acoustic sounder operation. Regions of enhanced thermal stability and wind shear produce strong echoes which the acoustic sounder maps on a height vs time facsimile record. In this paper we limit our discussion of those echo returns that have the characteristic appearance of Helmholtz waves. Richardson numbers calculated from the tower measurements over the layer thickness as determined from the acoustic sounder returns appear to he of the order of ½, while sub-strata embedded within the layer thickness exist where the Richardson number drops near the theoretically predicted critical value of ¼. In addition, measurements of the wavelengths associated with the “breaking” phenomenon conform to the theoretically predicted range of values.

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B. R. Bean, C. B. Emmanuel, R. O. Gilmer, and R. E. Megavin

Abstract

During the 1972 IFYGL “alert” periods, the NOAA/RFF/DC-6 gust probe instrumented aircraft was used to record time series of wind, temperature and water vapor at heights ranging from 18 to 300 m above the surface of Lake Ontario. The time series records show great variability. This is especially the case for evaporation when, in the fall, polar continental outbreaks move across the lake. In particular, such an outbreak of cold dry air moved across the lake at 12–15 m s−1 on 9 October 1972. This resulted in a drop of the air temperature at 30 m above the take from 12 to 6°C while the evaporation rate increased to more than 1 cm day−1. This may be compared to the 0.5 cm day−1 typical evaporation rate observed in the tropics during BOMEX. Furthermore, IR lake surface temperatures show cold regions (∼5°C) along the north shore, presumably due to strong upwelling, while the center and south shore regions of the lake were of the order of 12–15°C. The turbulent flux quantities of momentum, heat and water vapor were obtained by the eddy correlation technique and their spectra were determined at severed locations over the lake surface for 3 min sampling lengths. At the aircraft speed of 92 m s−1 this represents a flight path of about 17 km. The spectra demonstrate the tendency for the peak value to march to longer wavelengths with increasing height.

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C. Vera, J. Baez, M. Douglas, C. B. Emmanuel, J. Marengo, J. Meitin, M. Nicolini, J. Nogues-Paegle, J. Paegle, O. Penalba, P. Salio, C. Saulo, M. A. Silva Dias, P. Silva Dias, and E. Zipser

Moisture is transported in South America westward from the tropical Atlantic Ocean to the Amazon basin, and then southward toward the extratropics. A regional intensification of this circulation to the east of the Andes Mountains is called the South American low-level jet (SALLJ), with the strongest winds found over eastern Bolivia. SALLJ is present all year and channels moisture to the La Plata basin, which is analogous to the better-known Amazon basin in terms of its biological and habitat diversity, and far exceeds the latter in its economic importance to southern and central South America in terms of hydroelectricity and food production. The relatively small SALLJ spatial scale (compared with the density of the available sounding network) has a limited understanding of and modeling capability for any variations in the SALLJ intensity and structure as well as its possible relationship to downstream rainfall.

The SALLJ Experiment (SALLJEX), aimed at describing many aspects of SALLJ, was carried out between 15 November 2002 and 15 February 2003 in Bolivia, Paraguay, central and northern Argentina, western Brazil, and Peru. Scientists, collaborators, students, National Meteorological Service personnel, and local volunteers from South American countries and the United States participated in SALLJEX activities in an unprecedented way, because SALLJEX was the most extensive meteorological field activity to date in subtropical South America, and was the first World Climate Research Program/Climate Variability and Prediction Program international campaign in South America.

This paper describes the motivation for the field activity in the region, the special SALLJEX observations, and SALLJEX modeling and outreach activities. We also describe some preliminary scientific conclusions and discuss some of the remaining questions

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Douglas J Parker, Alan M Blyth, Steven J. Woolnough, Andrew J. Dougill, Caroline L. Bain, Estelle de Coning, Mariane Diop-Kane, Andre Kamga Foamouhoue, Benjamin Lamptey, Ousmane Ndiaye, Paolo Ruti, Elijah A. Adefisan, Leonard K Amekudzi, Philip Antwi-Agyei, Cathryn E. Birch, Carlo Cafaro, Hamish Carr, Benard Chanzu, Samantha J. Clarke, Helen Coskeran, Sylvester K. Danuor, Felipe M. de Andrade, Kone Diakaria, Cheikh Dione, Cheikh Abdoulahat Diop, Jennifer K. Fletcher, Amadou T Gaye, James L. Groves, Masilin Gudoshava, Andrew J. Hartley, Linda C. Hirons, Ishiyaku Ibrahim, Tamora D. James, Kamoru A. Lawal, John H Marsham, J N Mutemi, Emmanuel Chilekwu Okogbue, Eniola Olaniyan, J. B. Omotosho, Joseph Portuphy, Alexander J. Roberts, Juliane Schwendike, Zewdu T. Segele, Thorwald H.M. Stein, Andrea L Taylor, Christopher M Taylor, Tanya A. Warnaars, Stuart Webster, Beth J. Woodhams, and Lorraine Youds

Abstract

Africa is poised for a revolution in the quality and relevance of weather predictions, with potential for great benefits in terms of human and economic security. This revolution will be driven by recent international progress in nowcasting, numerical weather prediction, theoretical tropical dynamics and forecast communication, but will depend on suitable scientific investment being made. The commercial sector has recognized this opportunity and new forecast products are being made available to African stakeholders. At this time, it is vital that robust scientific methods are used to develop and evaluate the new generation of forecasts. The GCRF African SWIFT project represents an international effort to advance scientific solutions across the fields of nowcasting, synoptic and short-range severe weather prediction, subseasonal-to-seasonal (S2S) prediction, user engagement and forecast evaluation. This paper describes the opportunities facing African meteorology and the ways in which SWIFT is meeting those opportunities and identifying priority next steps.

Delivery and maintenance of weather forecasting systems exploiting these new solutions requires a trained body of scientists with skills in research and training; modelling and operational prediction; communications and leadership. By supporting partnerships between academia and operational agencies in four African partner countries, the SWIFT project is helping to build capacity and capability in African forecasting science. A highlight of SWIFT is the coordination of three weather-forecasting “Testbeds” – the first of their kind in Africa – which have been used to bring new evaluation tools, research insights, user perspectives and communications pathways into a semi-operational forecasting environment.

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