Level Topography

[Hedvige Ransonet]

Im having trouble getting the house level to work with the topography. The topography was created with absolute elevation points. The house levels were adjusted by relocating the project relative to Survey point. However the topography is way off, no matter how I try to adjust the survey point or the Base project point.

I personaly don't think you need to seperate the topo and the house model, when you will want to add pads and other landscape elements it will be in a dif revit file and that is not the best working method.

I'm not sure what do you mean by "way off" but read this short article (link below) it may help you to bring your topo and house together. BTW i'm not sure what happaned but it seems like something with your coordination working process was wrong and it may couse coordination issues later.

Here is a way to get out of this. Select the project base point, unclip it, right click and "move to startup location", clip it again. Then, create a level which will have the same elevation as the project base point. Then, make sure that the survey point is clipped. Go to Manage/Project Location/Specify Coordinates at Point. Select the level that you created and write 0 elevation. Now you can delete that level.

When I try to adjust or modify the topography, the 97' elevation (which show up correctly as 97' with spot elevation call-outs) is now at 563.77' when I highlight a point in edit mode. I guess when I start the grading the topography would just have to be put into another file for proper editing and imported back into the house file. Am I correct to think this way?

It is recommended to have the topo in a separate file but it is not a must. You can still see the topo points with the absolute elevation value (as when you start placing them) when moving the project base point and survey point to where your project requires. Keep in mind that the only thing absolute in a Revit model is the Origin Point, not Project base Point, not Survey Point. Everything else is relative to the Origin Point or to one another.

Regional model sensitivity simulations in which the height of elevated terrain was reduced to explore simulated changes in features of the low-level jet (LLJ) are presented. Such an approach has not been reported, and it provides complementary insight to the previous LLJ studies. The simulations were carried out for a 45-day period during the 1993 summer flood in the central United States, when strong LLJs were frequent. The simulations illustrate directly the significance of topographical blocking, leeside cyclogenesis, and terrain thermal effects exerted by the Rocky Mountains in support of LLJ formation. In particular, it is shown that in the absence of topography the ridging from the Bermuda high extended considerably westward with weaker southerly flow over the High Plains, thus diminishing the potential for LLJ development. The slope-induced nocturnal horizontal thermal gradient was indicated to have a significant role in the formation of the LLJ.

As implied by the aforementioned studies, the present consensus is that the most important forcing mechanisms for the LLJ are the response to diurnal boundary layer evolution over slopes and elevated terrain and the dynamical relationship to upper-level flow. It has to be emphasized that these two types of processes must not be viewed as competing or mutually exclusive explanations for the LLJ. Rather, the characteristics of the LLJ are established by their combined influences. General discussions of the combined forcing mechanisms have been given by Mitchell et al. (1995) and Zhong et al. (1996), among others.

Although both theory and observation have extensively documented the Rocky Mountain slope effects on the LLJ [see Strensrud (1996) for a review], direct quantification of the contribution of the elevated terrain to the LLJ forcing, through elimination or modification of the topography in regional model simulations, has not been reported to our knowledge. A hypothetical modification of the topography in the continental United States in a model simulation will affect the characteristics of the LLJ that are topographically forced. Adopting such an approach would provide complementary insight into the knowledge obtained in previous LLJ studies. In particular, it would outline a reference meteorological state absent of the topographical forced processes. Alteration of the topography in a model simulation is likely to modify the following LLJ forcing mechanisms: (i) the background southerly flow in the south-central United States that prevails during summer as a result of modification of the summer meteorological systems over the region, (ii) leeside cyclogenesis in the eastern slopes of the Rocky Mountains, and (iii) the along-slope induced nocturnal thermal gradient and the related mesoscale ageostrophic flow component that contributes to LLJ formation.

The flood of 1993 occurred at the maturity of an El Nio event with moderate SST anomalies over the equatorial Pacific. The above-normal convective heating in the intertropical convergence zone (ITCZ) shifted toward the equator (Trenberth and Guillemot 1996). This positive phase of the North Pacific teleconnection pattern persisted over the Pacific for 4 months prior to the flood. Then the ridge that prevailed over the western United States diminished and thus the zonal flow in the western Pacific was intensified. This zonal flow provided a channel for cyclones propagating directly to the central United States.

Synoptic patterns over the United States during the flood were characterized by a weaker Bermuda high, deeper leeside troughs east of the Rocky Mountains, and more frequent occurrence and stronger intensity of the LLJ (Mo et al. 1995; Arritt et al. 1997). The stronger upper-level jet streams and associated storm tracks pushed southward while the subtropical high retreated along the ITCZ.

Global model simulations. Global predictability vanishes after a couple of weeks, so such an approach is not well suited to the study of the details of seasonal regional processes relevant to a given anomalous large-scale environment such as the one that prevailed during the summer of 1993.

Regional climate model forced continuously in time by observed meteorological lateral boundary conditions, so as to maintain the large-scale atmospheric conditions of 1993 in the modified topography simulations. In sensitivity simulations we found that if lateral boundaries are not too close or too far from the center of the domain this approach would provide a reasonable compromise for the modeling evaluation. Specifically, we carried out simulations while extending the domain farther to the east, south, west, and north to evaluate the final placement of the lateral boundaries.

In locations where topography was reduced, the initial conditions and lateral boundary conditions in the resulting void were extrapolated as follows: standard atmosphere lapse rate for the temperature and constant (same as at the surface) for wind and relative humidity. In the present simulations the lateral boundaries were located far away from the area of interest (the LLJ region east of the Rocky Mountains), minimizing spurious effects of altered terrain. Most parts of the lateral boundaries are at sea level or associated with very shallow topography; only small portions of the lateral boundaries are over high terrain (in Central America, and northwest Canada). Thus, overall the prescribing of lateral boundary conditions when topography is removed is likely to have only secondary spurious effects.

In this subsection we present simulated lower-atmosphere patterns implying potential LLJ characteristics. It would be difficult to present the average flow during LLJ events for the simulated period, because of the spatial and temporal variation of the LLJ from one case to another. Therefore we present the simulated 45-day averaged geopotential and flow, which imply the potential for LLJ development.

Relatively strong daytime southerly flow is a prerequisite for the development of a pronounced nocturnal LLJ. At 1800 UTC (around local noon), the difference in the flow field east of the Rocky Mountains between CTRL (Fig. 2c) and FLAT (Fig. 2d) is noticeable. This result illustrates that the effects of elevated topography on the intensification of the daytime flow potentially are strongly conducive to nocturnal LLJ formation.

The 45-day average difference in wind velocity (CTRL minus FLAT) at σ = 0.91 at 0600 UTC showed a pronounced cyclonic flow perturbation over the western United States (Fig. 3). At its eastern side, this perturbation is forced by the combined effects of topographical flow blocking and leeside cyclogenesis. The flow perturbation is further supported by thermally induced pressure perturbation over the elevated terrain in the control simulation [see observational evaluation in Reiter and Tang (1984) and Tucker (1999)]. The southerly flow component difference was enhanced east of the Rocky Mountains in the area where the LLJ was simulated (see Fig. 5 later). The presented relative vorticity at 850 hPa (smoothed) corresponding to the velocity difference between the CTRL and FLAT simulations provides another perspective on the characteristics of the cyclonic perturbation.

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