153 research outputs found
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Orographic drag associated with lee waves trapped at an inversion
The drag produced by 2D orographic gravity waves trapped at a temperature inversion and waves propagating in the stably stratified layer existing above are explicitly calculated using linear theory, for a two-layer atmosphere with neutral static stability near the surface, mimicking a well-mixed boundary layer. For realistic values of the flow parameters, trapped lee wave drag, which is given by a closed analytical expression, is comparable to propagating wave drag, especially in moderately to strongly non-hydrostatic conditions. In resonant flow, both drag components substantially exceed the single-layer hydrostatic drag estimate used in most parametrization schemes. Both drag components are optimally amplified for a relatively low-level inversion and Froude numbers Fr ≈ 1. While propagating wave drag is maximized for approximately hydrostatic flow, trapped lee wave drag is maximized for l_2 a = O(1) (where l_2 is the Scorer parameter in the stable layer and a is the mountain width). This roughly happens when the horizontal scale of trapped lee waves matches that of the mountain slope. The drag behavior as a function of Fr for l_2 H = 0.5 (where H is the inversion height) and different values of l2a shows good agreement with numerical simulations. Regions of parameter space with high trapped lee wave drag correlate reasonably well with those where lee wave rotors were found to occur in previous nonlinear numerical simulations including frictional effects. This suggests that trapped lee wave drag, besides giving a relevant contribution to low-level drag exerted on the atmosphere, may also be useful to diagnose lee rotor formation
Recommendation to include hydroxyethyl (meth)acrylate in the British Baseline Patch Test Series
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Impact of non-hydrostatic effects and trapped lee waves on mountain wave drag in directionally sheared flow
The orographic gravity wave drag produced in flow over an axisymmetric mountain when both vertical wind shear and non-hydrostatic effects are important was calculated using a semi-analytical two-layer linear model, including unidirectional or directional constant wind shear in a layer near the surface, above which the wind is constant. The drag behaviour is determined by partial wave reflection at the shear discontinuity, wave absorption at critical levels (both of which exist in hydrostatic flow), and total wave reflection at levels where the waves become evanescent (an intrinsically non-hydrostatic effect), which produces resonant trapped lee wave modes. As a result of constructive or destructive wave interference, the drag oscillates with the thickness of the constant-shear layer and the Richardson number within it (Ri), generally decreasing at low Ri and when the flow is strongly non-hydrostatic. Critical level absorption, which increases with the angle spanned by the wind velocity in the constant-shear layer, shields the surface from reflected waves, keeping the drag closer to its hydrostatic limit. While, for the parameter range considered here, the drag seldom exceeds this limit, a substantial drag fraction may be produced by trapped lee waves, particularly when the flow is strongly non-hydrostatic, the lower layer is thick and Ri is relatively high. In directionally sheared flows with Ri = O(1), the drag may be misaligned with the surface wind in a direction opposite to the shear, a behaviour which is totally due to non-trapped waves. The trapped lee wave drag, whose reaction force on the atmosphere is felt at low levels, may therefore have a distinctly different direction from the drag associated with vertically propagating waves, which acts on the atmosphere at higher levels
Sonorous memory in Jonathan Perel’s El predio (2010) and Los murales (2011)
Throughout his filmic production, Argentine director Jonathan Perel has demonstrated strict adherence to a unique aesthetic programme in which human agents appear to have only a minimal role. Each film contains only diegetic sounds and consists of fixed shots of architectural spaces and objects closely associated with the most recent Argentine military dictatorship (1976–1983) and recent attempts to memorialise the atrocities they committed. Through the close analysis of Perel’s first two films – El predio (2010) and Los murales (2011) – this article focusses on Perel’s highly distinctive use of environmental sound and argues that they are, in fact, uniquely musical works. Drawing on the work of John Cage, Michel Chion, Deleuze and Guattari, and Doreen Massey, the article proposes that Perel manipulates sound in order to situate debates over the memorialisation of recent atrocities in a perpetual present and thus critique contemporary abuses of power in Argentina
Avaliação dos efeitos da ciclofosfamida nos testÃculos escrotal e retido em ratos jovens submetidos à criptorquia unilateral
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