Weather question?

Question

On the local new when weather is given, areas of low pressure systems quite often are regions of poor flying weather,and high pressure areas are favorable flying weather.

When air is cold the altimeter reads higher and when air is warmer the altimeter reads lower.

As warm air rises it expands and pressure decreases about 1" per thousand ft. warm temperatures determine low pressure and cold temperatures high pressure.

The weather man on TV said. As a rule of thumb low pressure-bad weather high pressure good weather.

The equator is an area of low pressure . The poles are areas of high pressure.This seems to be the opposite of what the weather man says.

What don't I understand ?

Answer 1

At the thermal equator the low pressure causes rising air and cloudiness.  

At the poles the descending air is warming, so there is less cloud formation.  

Both are areas of good weather.

Answer 2

Although your question is kind of vague, what I think you don't get is that atmospheric pressure is relative.  High pressure is just a comparison to what it's replacing.  For example, if you open your refrigerator on a hot day, it's cooler (and more dense) than the surrounding air.  If, however, the house was minus 5 degrees, the temp is actually higher in the fridge, and less dense.  It's all relative.

Answer 3

I understand your question, Michael. It is very simple: you associate warm weather with nice weather with high pressure. That is true ... unless:

A high pressure means sinking air and as pressure increases, it gets adiabatically warmed up (as behind your fridge). That is what you will observe if you looke e.g. at the charts called geopotential heights and temperature at 500 hPa. At that altitude (around 5 km up in the atmosphere) a low pressure is colder than a high pressure.

But at ground level, the picture is entirely different because here, the sun heat can be stored or dissipated depending on how high the sun is over the horizon at noon. For example, I live in Norway at latitude 60 nord. Here, if a high pressure happens between about the autumn equinoxe and spring equinoxe, for each day, the temperature will sink. In the other half year, it will increase.

Yes, the equator is a hot place and a region of low pressures. That's why you have the so-called rain forest belt along those latitudes. Yes, the north and south poles are regions of high pressures. That's why it doesn't rain/snow so much there.

If the earth was standing still, the air would then move from the poles to the equator on the surface, and from the equator to the poles at altitude.

But the earth spins and that creates the so-called Coriolis effect that bend air masses (and sea currents!) clockwise on the northern hemisphere.

That's why the rising air from the equator cannot reach the poles and falls back in a clockwise motion to build two belts of high pressure at about latitude 30 north and south. Those are the great deserts on earth.

Likewise, the cold and dry air from the poles never get a chance to reach the equator as it meets milder air and creates a front at about the latitudes 60 north and south. Those are the temperate regions with many low pressures moving eastward as the are taken by the jet streams at the top of the tropopause.

I hope it helps.

Answer 4

Do you not think bad weather happens at the equator or what? The most violent hurricanes and cyclones begin near the equator. The tallest thunderstorms can exceed 70,000 feet at the equator. You'll never see a thunderstorm at the poles. I can't tell you what it is you don't understand. You realize that hot doesn't mean good weather and cold doesn't mean bad weather don't you?