This is a two-part q., primarily for AMW, but for any of the Teeming Millions who can answer them.
(1) What is the difference between an occluded front and a stationary front? Neither moves very much.
(2) In a prior thread, I asked if at 74 mph a tropical storm develops an eye and if that was the distinguishing feature of a hurricane. AMW was kind enough to furnish a lot of infor, Simpson Scale, etc., and said that No, the eye forms at the tropical depression stage and that is what distinguishes a tropical wave from a tropical depression. I have a problem with that.
If by an eye you mean the center, that’s true. When a wave forms a definite center of circulation, it becomes a depression. However, I’ve seen a lot of radar screens, and anything less than a hurricane has never had an EYE, with an eye wall. By “eye,” I mean a center with eye walls, within which there is little or no wind.
It’s been a few years since I had my college meteorology class, but I’ll take a stab here.
“Front” is merely the word used to describe the boundary line between two different types of air masses - usually one that’s warmer and one that’s colder.
Most (probably all) cyclonic storm systems in our part of the world have two main features: a cold front, which is the leading edge of a mass of cooler air plunging along, generally from a northerly direction, and a warm front, which is a mass of (surprise!) warmer air pushing up from the south ahead of the system. Both of these tend to radiate out from a low-pressure center which drives and energizes the system. Occasionally, the cold front will push ahead more rapidly and “overtake” the warm front, particularly close to the center of the low. When they merge, this creates an occluded front.
A stationary front, on the other hand, is just any kind of front that doesn’t move much - whether it’s a cold, warm, or occluded front.
Well, I don’t recall much specifics about hurricanes from class, but here’s what the Weather Channel’s online glossary has to say:
Thanks for your reply. Note that there is an inconsistency in the definition of an eye. The definition starts out by stating that it is the center of a tropical storm or hurricane, but ends up stating that it usually develops when sustained winds are at 78 mph, which is hurricane force. I guess this discrepancy can be resolved by assuming that it may sometimes form when the sustained winds are less than 74 mph. As a matter of fact, I kinda recall that happened recently, when the sustained winds were 70 mph.
Going back to definitions, a storm is called a “tropical depression” once it has shown a circular motion, after which point it might grow up to be a tropical storm and later a hurricane.
No circular motion, no tropical depression.
Based on that definition, a tropical depression must have an eye.
This is a matter of terminology again. You are equating “eye” with “center” and the words are synonymous, but by “eye” I mean a center of circulation that has an eye wall. In fact, your initial line: a storm is called a tropical depression…grow up to be a tropical storm" is obvious self-contradictory. How can a “storm” which is a “tropical depression” grow up to be a “tropical storm” when it began as a storm? All low pressure areas have a circular motion (counter-clockwise in the northern hemisphere). You meant of course that a SYSTEM is called a tropical depression once it has shown a circular motion. This, in itself, is not accurate. It must be a tropical system and have, I guess, some of the tropical characteristics that AMW listed in my prior post. I am now satisfied, thanks to the first response to my OP, that 74 mph has been arbitrarily assigned as the definition of a hurricane since at 78 mph an eye wall forms, but at times it may form at slightly slower speeds. In addition, wind speeds are give only at 5 mile intervals.
I could not find schief 2’s website on weather.com, but I found an interesting site on hurricanes. It states as follows.
Like mid-latitude storms (low pressure systems with cold fronts, warm fronts and/or occludd ftonts), a hurricane is a low pressure system, but hurricanes are “warm core” systems – the air at their ceenter is warmer than the surrounding air, while mid-latitude storms are “cold core” systems, with the lowest temperatures at or near the center. Cold core systems gain their energy largely from spatial temperture variations within the atmosphere, while a tropical cyclone’s main fuel is the heat released by showers and thunderstorms, the strongest of which occur near the eye. The eye, however, is relatively calm because the air within the eye is sinking and clouds require rising air to form. The sinking air also causes an increase in temperature and a decrease in pressure within the eye. That warming associated with the sinking causes very rapid pressure falls and that’s why once an eye forms, the hurricane usually intensifies quickly.
Not all hurricanes have a discernible eye. Some have low level cloud cover, indicating that the air is not sinking all the way to the bottom. The part of the cyclone called the eyewall immediately surrounds the eye with rising air and deep rain clouds. It houses the most pooerful elements of the hurricane.