Coastal Meteorology A Review of the State of the Science (1992) / Chapter Skim
Currently Skimming:
4. The Influence of Orography
4. The Influence of Orography
Pages 31-44
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 31... ...
For typical atmospheric stratification of N_ 10-i to 10-2, an elevation of only 100 m is often sufficient to cause "blocking" of the onshore flow at low levels. Such blocking occurs along the west and east coasts of the United States; along the east coast, it is often referred to as cold air damming.
|
From page 32... ...
Here one expects the coastal mountains to represent a wall, and the momentum balance in the along-shore direction near the wall is not expected to be geostrophic. The smoothed topographies in current-generation numerical weather prediction (NWP)
|
From page 33... ...
While theoretical considerations define the scales and processes important to the coastal zone, they are less successful in fully explaining particular case studies (Walter and Overland, 1982; Mass end Ferber, 1990~. LOW FROUDE NUMBER FLOW: TRAPPED PHENOMENA Isolated Response: Kelvin Wave and Gravity Current Along subtropical mountainous coastlines such as California and Australia, subsidence in the subtropical high pressure often develops a strong marine inversion structure below the height of the coastal topography.
|
From page 34... ...
GOES visible image 1800 GMT, May 27, 1983; (b) observed wind and subjective sea-level pressure analysis for the same time based on satellite images and available surface synoptic data.
|
From page 35... ...
There is also a need to understand all factors that contribute to the depth and spatial variability of coastal marine stratus and fog as a result of interactions among wave dynamics, radiation, and cloud processes. Damming The case of damming refers to blocked winds on the windward side of a mountain for uniform onshore flow or modification of a frontal feature by coastal orography.
|
From page 36... ...
COASTAL METEOROLOGY // ~ 14 1 6 /N ~ ~ - , - N ~ ~ (A — ~JJ>~. / j~18 15/ JO \ 16 ~; / :17 ~,~: ,: 18 directly considered; however, it is clear from their analyses that the cold air damming region extended to coastal weather stations.
|
From page 37... ...
Numbers, Coastal Mountain Half-Width Im, Inversion Thickness hi, and Reduced Gravity g' for Coastally Trapped Disturbances in Southern Africa, Southeastern Australia, California, and the Alps (noncoastal) 37 Southern Southeastern Africa Australia California Alps Rm 0.1 0.8 1.3 2.0 Fr 0~33 0.18 0.21 0.4 RmlFr 0.30 4.44 6.19 5 Im (km)
|
From page 38... ...
Similar to the Puget Sound case, the induced mesoscale low creates an along-shore pressure gradient that can initiate northward propagation of trapped phenomena from the south (Dorman, 1987) and modify the position and magnitude of the lee eddy.
|
From page 39... ...
Such lee-eddy features should be amenable to numerical modeling given sufficient vertical and horizontal resolution; models can include simplified cloud processes. KATABATIC AND OTHER LOCAL WINDS So far we have discussed phenomena with spatial scales of the order of the Rossby radius (50 to 150 km)
|
From page 40... ...
with a local wind maximum on the scale of 30 km, such as those south of Point Arena (Samuelsen, 1992; Winant et al., 1988~. The katabatic wind is a drainage wind current caused by the gravitational flow of cold air off high ground, whose direction is controlled almost entirely by orographical features.
|
From page 41... ...
found that katabatic winds inland of Terra Nova Bay, Antarctica, are present some 25 km beyond the end of the main slope; this is also seen for southeastern Alaska in Figure 4.6. The physical processes important in the development of katabatic winds are radiative cooling, development of a sloped pressure gradient force, adiabatic warming of downward moving air, fnction, and entrainment (Gutman, 1983; Manins and Sawford, 1979; Nappo and Rao, 1987; Pansh, 1984; Pansh and Waight, 1987~.
|
From page 42... ...
Persistent katabatic flow requires replenishment of cold air either by convergence of drainage currents upwind or by continued localized intense cooling. As katabatic winds develop, the mixing processes become enhanced, and the turbulent heat flux to the surface increases.
|
From page 43... ...
· Studies should be conducted to determine the predictability of smallscale hydrodynamic features, such as hydraulic jumps, eddies, wind maxima, and katabatic flows. · Long-term measurement programs should be supported to determine the low-frequency climatology of winds in the coastal zone.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.