weather pressure help

[Dave2292]

hello again, what would high pressure be in millibars? as in what would be better for imaging planets as I hear higher pressure is better for a stable atmosphere. have read a little online but its definitely easier to come here.

thanks in advance for any help.

[Paul M]

Atmospheric pressure is measured in measured in hecto pascals which are equal to millibars, the unit we used to use.

A typical Low preassure might be 990 hPa while a High might be 2020 (the record is 2055 or some such)

It's not the absolute pressure that matters but what the column of air above is doing. In H's the air is generally descending, making it stable but not necessarily transparent due to inversion layers.

Low pressures signify ascending air, often associated with convection, the major cause of turbulence and poor seeing.

I hear talk of jet streams causing poor seeing. It's a new concept to me. Jest streams are a laminar flow, low turbulence, not  convective in itself though they do suck the air out of the top of low pressure systems so magnifying them.

[Dave2292]

2 hours ago, Paul M said:

Atmospheric pressure is measured in measured in hecto pascals which are equal to millibars, the unit we used to use.

A typical Low preassure might be 990 hPa while a High might be 2020 (the record is 2055 or some such)

It's not the absolute pressure that matters but what the column of air above is doing. In H's the air is generally descending, making it stable but not necessarily transparent due to inversion layers.

Low pressures signify ascending air, often associated with convection, the major cause of turbulence and poor seeing.

I hear talk of jet streams causing poor seeing. It's a new concept to me. Jest streams are a laminar flow, low turbulence, not  convective in itself though they do suck the air out of the top of low pressure systems so magnifying them.

I shall try and get my head around this haha thanks 

[Budgie1]

4 hours ago, Paul M said:

A typical Low preassure might be 990 hPa while a High might be 2020 (the record is 2055 or some such)

I think that's 1020 hPa and the record is 1053 hPa.

When I lived on the Isle of Lewis my weather station recorded a low of 936.7 hPa on Christmas Eve 2013. Seeing was definitely not good when you look at the wind speed in the screenshot I took at the time!  

High and Low pressure systems also rotate in different directions, in the Northern Hemisphere a Low rotates anti-clockwise and High clockwise. Not that it makes much difference to seeing, but it does to the direction the of the air being pulled in. It could be dry cold air from Russia or the Artic, damp moist air from the Atlantic or dry warm from North Africa.  

[Paul M]

3 hours ago, Budgie1 said:

8 hours ago, Paul M said:

A typical Low preassure might be 990 hPa while a High might be 2020 (the record is 2055 or some such)

I think that's 1020 hPa and the record is 1053 hPa.

Indeed, as I was typing that I realised I was already 5 minutes late setting off to work. No time to proof read!

I think that's the UK record you quote. The world record for sea level pressure is considerably higher.

My favorite stargazing airmass is maritime polar. That tends to give good clarity but poor seeing. A few showers to dodge too.

High pressure in winter seems to be getting more rare. Better seeing but trouble with dew and mist.