WX0603 · Wind & Terrain
24 questions · 24 multiple choice · 0 written · ASA 109 Marine Weather — Wind & Terrain
💡 Show hint
This is a general class of winds. Specific examples of prominent katabatic winds often have individual names.
See katabatic wind. A katabatic wind flows downhill, driven by gravity acting on air cooled by the surface (e.g. glaciers, mountain slopes at night).
AI answer
The Tehuantepecer is a violent northerly wind that funnels through the Isthmus of Tehuantepec gap from the Gulf of Mexico to the Pacific. The Papagayo is farther south near Costa Rica.
AI answer
💡 Show hint
This effect can be dramatic in some cases, although we must make an effort to remember how to predict what corners it applies to. See textbook Figure 6.1-13. Think of a Buys-Ballot analogy.
Using the Buys-Ballot law analogy: with wind at your back, low pressure is to your left (NH). The corner effect enhances wind on the left side of the waterway, which is the same as looking downwind on the left side.
AI answer
💡 Show hint
We assume we are sailing along in unstable weather with gusty wind, but are not near cliffs or hills that are influencing the mean (average) wind flow.
When wind gusts bring faster air from aloft down to the surface, that air retains its direction from above where friction is less and wind is veered relative to surface wind. See gust and ART 4 on wind and terrain.
AI answer
💡 Show hint
Put another way, if the wind on the beach is northeast, what direction would you expect it to be some distance out into the water?
The key is friction which slows down the wind; land has a lot of friction, water has much less. As wind moves from high-friction land to low-friction water, it speeds up and veers. The factor of 2 in the amount is not hard to remember, and the veer is on the order of 10 to 20 degrees.
AI answer
💡 Show hint
Have you ever pulled in from sailing in a stiff breeze, tied up the boat and while walking to the car noticed that the wind had finally settled down, just after you decided to come in?
You can count on stronger winds on the water. The factor of 2 is a rough guideline. See ART 4 on wind and terrain; G248 shows how wind increases as friction decreases.
AI answer
💡 Show hint
This is the source of sea breezes, which are fundamental to coastal weather.
All are true, plus more. Because it is generally darker, land absorbs more heat than water. Water is transparent so energy spreads over great depth. And the specific heat capacity of water is much higher than land. All contribute to the land-water heating difference that drives sea breezes.
AI answer
💡 Show hint
The effect of terrain on wind depends on the strength and direction of the wind, the driving force of the wind, the shape, size, height, texture, and temperature of the land, as well as the time of day and the season of the year!
Read over the answers along with the right one. The message is All There. For more see ART 4 on wind and terrain.
AI answer
💡 Show hint
Do the mountains make a difference? Does the direction of motion of the front make a difference? In this question, “ahead of,” “behind” etc means time-wise.
In a waterway with mountains, the channeling effect matters. The wind change at the front (strong to weak or vice versa) depends on the alignment of the frontal winds with the channel. In this case, weak winds ahead, strong behind.
AI answer
💡 Show hint
Remember we are considering winds near lands, not gale conditions, just seasonal winds. Think of key issues with wind and terrain.
The problem to look out for is wind enhanced by the land shape. There are numerous cases of islands where a light breeze to the windward side gets dramatically accelerated around or over the island. In these cases, a harbor with a breakwater on the windward side could be much more peaceful than one on the supposedly calm leeward side.
AI answer
💡 Show hint
What aspect of a wind affects our safety?
Sea breezes are the most common land effect on coastal wind, but in itself it is rarely a safety concern. Channeled gap winds make the strongest and most dangerous winds most often.
AI answer
💡 Show hint
This effect can be dramatic in some cases, although we must make an effort to remember how to predict what corner it applies to.
Compare the answers with the question. See corner effect and ART 4 on wind and terrain.
AI answer
💡 Show hint
We refer here to the Northern Hemisphere, and to the general case with a more or less pure sea breeze.
Sea breezes are more generally the resultant of a developing thermal wind and an existing gradient wind. The thermal component veers throughout the day (due to Coriolis), and the sea breeze builds as heating increases. Hence it veers and builds. Also, the wind is descending in the sky from a region with less friction and hence a natural shift.
AI answer
💡 Show hint
We are presumably talking about wind at night.
See sea breeze and land breeze. See also mistral. “Coastal breeze” is not a defined term.
AI answer
💡 Show hint
Which is the usual case in clear skies throughout the world during late afternoon.
When land is warmer than water, air rises over land and cooler air flows in from the sea = sea breeze. See sea breeze and ART 4 on wind and terrain.
AI answer
💡 Show hint
This is the most prevalent of the various types of local winds, found throughout the world. It can be a gentle breeze or up to 20 knots in some cases.
See sea breeze and ART 4 on wind and terrain.
AI answer
💡 Show hint
Note that there are other sources of this same type of breeze. Remember how winds are named.
When land is cooler, air over the warmer water rises and air flows from land to sea = land breeze. Winds are named for where they come from.
AI answer
💡 Show hint
The source of heat referred to is latent heat, which is obtained from warm moist air, the fuel of all storms.
A tropical cyclone (hurricane) never becomes a high. It can weaken to a tropical storm but that’s going the wrong way in this context. Once it leaves the tropics and loses its warm water fuel, it transitions into an “extratropical” cyclone. It is not a frontal structure; it is more of a rough structure.
AI answer
Sea breezes, of the answers given, channeled winds make the strongest and could be most righteous effect. Friction effects certainly occur whenever there is wind, but these do not really make for strong winds. Channeled winds (gap winds) are the most dangerous.
AI answer
💡 Show hint
We are not looking for something that is just there all the time, but something that actually dominates the speed and direction of the wind.
Sea breezes dominate coastal wind patterns worldwide. Local weather patterns completely dominate the wind flow near most coastal waters.
AI answer
💡 Show hint
We have to consider cases where there is little influence on the wind from local weather patterns, and we have to consider an average of all types of coasts.
On average, the sea breeze influence extends roughly 1 to 3 miles offshore, but it could be 5 to 10 mi or more in prominent sea breeze areas. It is also difficult to separate a pure sea breeze from thermal enhancements.
AI answer
💡 Show hint
This is for Northern Hemisphere and yes, it does matter.
In the NH, sea breezes veer (clockwise) throughout the day due to the Coriolis effect. An easterly breeze in mid morning veers to more from the south-southeast by mid afternoon. The NW wind backs to the W, then as it transitions extends somewhat out over the water. Thus the NW wind backs to the W as it transitions from land to sea influence.
AI answer
💡 Show hint
Does it matter what hemisphere we are in? Does the terrain of the shoreline matter? Does it matter what is causing the wind?
As you approach shore, friction increases and the wind backs (shifts counterclockwise in the NH). A NW wind would back somewhat to the west. The results depend on the shape of the object and the wind speed.
AI answer
A rough working rule: wind disturbance extends about 10 to 12 times the object's height downwind. Stay farther than 12 times its height to be clear of the dirty air. Though the results depend on the shape of the object and wind speed.