Mesoscale Model Results Research Articles

On the uncertainty in mesoscale modeling caused by surface parameters

The uncertainty of plant- and soil parameters (albedo, evaporative conductivity, roughness-length, soil volumetric heat capacity, field capacity, capillarity, emissivity), soil-type, subgrid-scale heterogeneity and inhomogeneity on mesoscale model results (e.g., fluxes, variables of state, cloud- and precipitation-formation) is explored. Simulations are performed wherein one parameter at a time is changed for all grid cells of the domain within its natural range of variability. The land-surface scheme employs the frequently operated force-restore-method and a one-dimensional heat-diffusion equation. Transpiration is considered by the often applied “big-leaf/big-stoma”-approach. Except for wind, cloud- and precipitating-particles the uncertainty in the simulated quantities due to soil- or plant-parameters is lower at night and in the early afternoon than at the other time of the day. Therefore, evaluation of meteorological models should be performed at those times when the sensitivity to the choice of plant- and soil-parameters is at a minimum. According to the calculated probability density functions and similarity coefficients, the partitioning of excess water vapor between cloud water and ice can be significantly affected by the choice of field capacity, capillarity, volumetric heat capacity, thermal diffusivity and the emissivity of the earth’s surface. Considering these findings domain-specific and actual parameters should be preferred.

Evaluation of high resolution NWP simulations with radar data

The areal character of radar information is used to validate the simulation results of different mesoscale models (DM, MC2) for a summertime convective precipitation event in the northern Alpine region. Assembling the radar data of different radar sites into a multinational radar composite enables the qualitative comparison with NWP model data on the mesoscale. Moreover wind data of the dopplerized research radar at DLR Oberpfaffenhofen is exploited to evaluate the model dynamics in the vicinity of the radar site. The investigation of the complex structure of a summertime rainfall event (i) highlights the benefit of areal radar data in validating mesoscale model results as well as (ii) exhibits the gain in quality attainable using higher resolution models (Δ ≈ 2 km) with fully explicit (grid-scale) precipitation.

Mechanical behaviour of ±55° filament-wound glass-fibre/epoxy-resin tubes—III. Macromechanical model of the macroscopic behaviour of tubular structures with damage and failure envelope prediction

This series of papers on ±55° filament-wound glass-fibre/epoxy-resin tubes consists of three parts. In the present paper (Part III), the macroscopic mechanical behaviour of the tubular structure is presented. A method for predicting composite tube macroscopic properties from the ply constants is given. A more general analytical method is used for determining ply stresses of a composite tube under a combined load, which will then be compared with 3D finite-element analysis, classical and adjusted laminate theory. Failure envelope prediction is then made according to the micro- and meso-scale model results. The stresses distribution in the tube thickness direction predicted by the present method agrees well with 3D finite-element analyses. Four methods give similar stress distribution results under tensile loading, but different ones under internal pressure loading. For failure envelope prediction, the first-ply-failure theory underestimates the failure load for pressure dominated loading. The effect of possible micro structural damage on the failure load prediction is also discussed and compared with experimental results. In Part I (Bai et al. Compos. Sci. Technol., 1997, 57, 141–153), the microstructure, mechanical behaviour and damage initiation mechanisms were presented. In Part II (Bai et al. Compos. Sci. Technol., 1997, 57, 155–164), micromechanical modelling of the damage initiation was conducted in order to determine the mechanical conditions under which different microcracking mechanisms occur.

The Evolution of the 10–11 June 1985 PRE-STORM Squall Line: Initiation, Development of Rear Inflow, and Dissipation

Abstract Mesoscale analysis of surface observations and mesoscale modeling results show that the 10–11 June squall line, contrary to prior studies, did not form entirely ahead of a cold front. The primary environmental features leading to the initiation and organization of the squall line were a low-level trough in the lee of the Rocky Mountains and a midlevel short-wave trough. Three additional mechanisms were active: a southeastward-moving cold front formed the northern part of the line, convection along the edge of cold air from prior convection over Oklahoma and Kansas formed the central part of the line, and convection forced by convective outflow near the lee trough axis formed the southern portion of the line. Mesoscale model results show that the large-scale environment significantly influenced the mesoscale circulations associated with the squall line. The qualitative distribution of along-line velocities within the squall line is attributed to the larger-scale circulations associated with the le...

Gap Winds in a Fjord. Part II: Hydraulic Analog

Abstract A simple shallow-water model of gap wind in a channel that is based upon hydraulic theory is presented and compared with observations and output from a 3D mesoscale numerical model. The model is found to be successful in simulating gap winds. The speed and depth of gap wind flow is strongly controlled by topography. Horizontal or vertical channel contractions can act to force strong, shallow supercritical flow downwind and light, deep subcritical flow upwind. Force-balance analysis of the hydraulic model output confirms mesoscale model results and indicates that the prime force balance in gap wind is between external pressure gradient and friction for supercritical flow and between external pressure gradient and height pressure gradient for subcritical flow. This force balance changes near channel controls when the balance is between advection and height pressure gradient. Sensitivity analyses show positive sensitivity of gap wind speed to changes in discharge and external pressure gradient, nega...

Numerical Simulations of the Evolution of a Cold Front and Its Precipitation

Short-range (36-h) simulations of a surface cold front that occurred over the Great Plains of the United States during the SESAME-AYE III period are made using a significantly modified version of a hydrostatic, sigma-coordinate, quasi-Lagrangian, primitive-equation gridpoint model. The necessity of using blended data from FGGE Level IIIb and IIb for input is demonstrated. The evolution of the environment associated with the cold front was well predicted by the model when compared with analyses and observations of the cold front location, horizontal temperature gradient, wind field, dry line, temperature inversion, and precipitation. The current model results caught several observed features that were not present in the other mesoscale model results. Also, comparisons between moist and dry versions of the current model showed a stronger frontal upward motion and a faster moving front showed in the moist version of the model experiment than in the dry version, as expected. The evolution of several local maxima of frontal intensity, defined in terms of temperature gradient, were related to the combination of local maxima of convergence and deformation effects in different locations along the cold front. The genesis of negative relative vorticity along the inverted cold front over the lee of the United States Rockies was found to be related to the effect of solenoidal forcing. The negative solenoidal forcing here was formed by the orographic pressure gradient perpendicular to the strong temperature gradient. The movement of the local maximum of mesoseale lower-level convergence along the cold front moving from the southern portion of the front to north drove the major frontal intensity from south to north in terms of frontogenesis and cyclogenesis. The model precipitation agreed well with observation in terms of timing and location. The evolution of maximum precipitation followed the evolution of the maximum low-level convergence ahead of the cold front, where ample moisture combined with potential instability. The generation of the temperature inversion in the vicinity of the frontal surface over the southern portion of the cold front prohibited convection there, and localized the frontal precipitation along the northern portion of cold front and east of southern temperature inversion. The temperature inversion was generated by differential temperature advection through the frontal circulation within the PBL, and modified by the vertical stretching effect that stabilized the lower layer behind the cold front and destabilized ahead of the cold front.

The inland boundary layer at low latitudes: II Sea-breeze influences

Two-dimensional mesoscale model results support the claim of evening sea-breeze activity at Daly Waters, 280 km inland from the coast in northern Australia, the site of the Koorin boundary-layer experiment. The sea breeze occurs in conditions of strong onshore and alongshore geostrophic winds, not normally associated with such activity. It manifests itself at Daly Waters and in the model as a cooling in a layer 500–1000 m deep, as an associated surface pressure jump, as strong backing of the wind and, when an offshore low-level wind is present, as a collapse in the inland nocturnal jet.

Numerical Experiments on the Influence of the Mesoscale Circulation on the Cumulus Scale

Abstract The EML mesoscale model developed by Pielke (1974) was used to simulate the sea breeze circulation over South Florida with its modification of the thermal and moisture structure of the synoptic air mass over South Florida. The numerical experiment was performed for a case study day (16 May 1968) during which extensive cloud observations were performed. To examine the response of the cumulus scale, the one-dimensional time-dependent cumulus model developed by Cotton (1975) was initiated with the theoretical soundings predicted by the mesoscale model, along with cloud scales and cloud areal coverage observed on the case study day. The mesoscale model results demonstrated that the sea breeze over South Florida alters the synoptic environment by 1) substantially perturbing the vertical thermodynamic profile, 2) increasing the depth of the planetary boundary layer, 3) inducing larger surface fluxes of momentum, heat, and moisture, 4) changing the vertical shear of the horizontal wind in lower levels o...