Statistics of Turbulence in the Stable Boundary Layer Affected by Gravity Waves

In order to investigate effects of interactions between turbulence and gravity waves in the stable boundary layer on similarity theory relationships, we re-examined a dataset, collected during three April nights in 1978 and in 1980 on the 300-m tower of the Boulder Atmospheric Observatory (BAO). The BAO site, located in Erie, Colorado, USA, 30 km east of the foothills of the Rocky Mountains, has been known for the frequent detection of wave activities. The considered profiles of turbulent fluxes and variances were normalized by two local, gradient-based scaling systems, and subsequently compared with similarity functions of the Richardson number, obtained based on data with no influence of gravity currents and topographical factors. The first scaling system was based on local values of the vertical velocity variance $\sigma _\mathrm{w}$ and the Brunt–Väisäla frequency $ N,$ while the second one was based on the temperature variance $\sigma _{\theta }$ and $N.$ Analysis showed some departures from the similarity functions (obtained for data with virtually no influence of mesoscale motions); nonetheless the overall dependency of dimensionless moments on the Richardson number was maintained.     

Summer Floods in Central Europe – Climate Change Track?

In Central Europe, river flooding has been recently recognized as a major hazard, in particular after the 1997 Odra /Oder flood, the 2001 Vistula flood, and the most destructive 2002 deluge on the Labe/Elbe. Major recent floods in central Europe are put in perspective and their common elements are identified. Having observed that flood risk and vulnerability are likely to have grown in many areas, one is curious to understand the reasons for growth. These can be sought in socio-economic domain (humans encroaching into floodplain areas), terrestrial systems (land-cover changes – urbanization, deforestation, reduction of wetlands, river regulation), and climate system. The atmospheric capacity to absorb moisture, its potential water content, and thus potential for intense precipitation, are likely to increase in a warmer climate. The changes in intense precipitation and high flows are examined, based on observations and projections. Study of projected changes in intense precipitation, using climate models, for several areas of central Europe, and in particular, for drainage basins of the upper Labe/Elbe, Odra/Oder, and Vistula is reported. Significant changes have been identified between future projections and the reference period, of relevance to flood hazard in areas, which have experienced severe recent floodings.     

Fuzzy logic circulation types based on the Osuchowska-Klein classification system created for Poland

Fuzzy logic was applied as a methodology to create an objective calendar of daily atmospheric circulation based on an existing atmospheric circulation classification system for Poland called the Osuchowska-Klein method, which includes 13 circulation patterns. In this study, circulation patterns given by Osuchowska-Klein were expressed as normalized values of sea level pressure in a regular 5°?×?5° grid over the area of interest. Cases of daily atmospheric circulation (i.e., normalized values for the same domain) observed from January 1948 to December 2007 were defined in the same manner. The pattern-matching procedure employed in the study was made objective with the application of fuzzy logic sets in a few steps as follows: (1) discrimination and grouping of grid points as well as their classification in order to clearly define each Osuchowska-Klein circulation pattern, (2) calculation of the similarity between observed normalized pressure and that of the pattern at each selected grid point using a membership function, (3) determination of the degree of fulfillment for every class of grid points, (4) determination of the degree of a case and pattern, (5) selection of the circulation type for a particular day based on the degree of fulfillment for each pattern. The largest value of the degree of fulfillment indicates the type of circulation pattern on any given day. Finally, a validation of the obtained results is discussed. This was accomplished using the chi-square test and a comparison of consistency between the traditional and objective approach types. The results do show some differences between the subjective and objective methods, however, they are not major differences, especially when taking into account the fact that the two methods are quite different, as well as the complex nature of pressure systems.     

Unified structural approach to linear flood routing

The structural theory of linear systems, which allows the non-homogeneous initial and boundary conditions to be expressed as part of a generalised system input, is applied to the problem of linear flood routing. The standardising functions needed to accomplish this are derived for three methods of lumped hydrologic flood routing (lag and route, Muskingum and Kalinin-Milyukov) and to three methods of distributed hydraulic flood routing (kinematic wave and two simplified forms of the linear St. Venant model). The appropriate Green's functions needed to complete the solution for these six cases are also presented.