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chrisbell-nottheweatherman

What counts as a surface chart?

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Just a quick query regarding classification of different types of model outputs.  In the current (10th January onwards) Model Output Discussion thread (http://forum.netweather.tv/topic/79043-model-output-discussion-10th-jan-onwards/page-76 ), Vorticity0123, in post number 1502, shows a chart showing the 500hPa geopotential heights from GFS, referring to it as an upper-level chart, which seems obvious and understandable to me.  However, he then posts a GFS 6z output of 500hPa heights, along with Temperatures and pressures.  This causes me to pose two questions:

 

1.  Are the pressures on the second chart at the surface?

 

2.  Given the temperatures on the second chart (500hPa output referred-to by Vorticity0123 as a surface chart) appear to be those from aloft, and that it shows 500hPa heights, does it really count as a surface chart?

 

Thanks.

Edited by chrisbell-nottheforecaster

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Just a quick query regarding classification of different types of model outputs.  In the current (10th January onwards) Model Output Discussion thread (http://forum.netweather.tv/topic/79043-model-output-discussion-10th-jan-onwards/page-76 ), Vorticity0123, in post number 1502, shows a chart showing the 500hPa geopotential heights from GFS, referring to it as an upper-level chart, which seems obvious and understandable to me.  However, he then posts a GFS 6z output of 500hPa heights, along with Temperatures and pressures.  This causes me to pose two questions:

 

1.  Are the pressures on the second chart at the surface?

 

2.  Given the temperatures on the second chart (500hPa output referred-to by Vorticity0123 as a surface chart) appear to be those from aloft, and that it shows 500hPa heights, does it really count as a surface chart?

 

Thanks.

They are surface pressures, the 500hpa is thickness, so the layer between surface (ish) 1000hPa up to 500hPa , I think with temp at 500hPa, as they are ruddy cold. I don't have any German but thickness is often seen with surface pressure charts

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They are surface pressures, the 500hpa is thickness, so the layer between surface (ish) 1000hPa up to 500hPa , I think with temp at 500hPa, as they are ruddy cold. I don't have any German but thickness is often seen with surface pressure charts

 

Thanks Jo.  Is there any practical difference between heights and thickness?  I ask as  I thought that 850hPa, 700hPa, 500hPa and 300hPa were heights, and 1000-500hPa was a measure of thickness.

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Thanks Jo.  Is there any practical difference between heights and thickness?  I ask as  I thought that 850hPa, 700hPa, 500hPa and 300hPa were heights, and 1000-500hPa was a measure of thickness.

 

Thickness is indeed the distance (in altitude) between two pressure levels. On the contrary, a chart of geopotential heights at 500 hPa., for example, gives lines of equal height (isohypses) at which the pressure is equal to 500 hPa.

 

 

 

2.  Given the temperatures on the second chart (500hPa output referred-to by Vorticity0123 as a surface chart) appear to be those from aloft, and that it shows 500hPa heights, does it really count as a surface chart?

 

A good question it is. For the post itself, I used the surface pressure for the analysis, though I did, perhaps incorrect, interpret the troughing also with the geopotential heights (given in color). Searching for answers on the internet has given some contradicting results:

 

From MetMonkey: 

 

 

COLOUR SHADING: Geopential Mean Temperature Height in Dekametres known as [DAM] Orange/Red gradients represent high values and Blue/Indigo represent low values.

 

From weatherfaqs.co.uk:

 

 

Colour shading500hPa height, colour coded as at scale by diagram. (units = dekametres [dam] / interval = 4 dam). Orange/Red high values - blue/indigo etc., low values.

 

The best information I have found came from a Netweather thread itself:

 

http://forum.netweather.tv/topic/46373-understanding-500-hpa-charts/ 

 

I hope this helps a little. I'm sorry to have caused some confusion in my post. I'll try to be more clear in the future.

 

Sources:

http://forum.netweather.tv/topic/46373-understanding-500-hpa-charts/

http://weatherfaqs.org.uk/node/189

http://www.null.co.uk/

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Thickness is indeed the distance (in altitude) between two pressure levels. On the contrary, a chart of geopotential heights at 500 hPa., for example, gives lines of equal height (isohypses) at which the pressure is equal to 500 hPa.

 

 

 

A good question it is. For the post itself, I used the surface pressure for the analysis, though I did, perhaps incorrect, interpret the troughing also with the geopotential heights (given in color). Searching for answers on the internet has given some contradicting results:

 

From MetMonkey: 

 

From weatherfaqs.co.uk:

 

The best information I have found came from a Netweather thread itself:

 

http://forum.netweather.tv/topic/46373-understanding-500-hpa-charts/ 

 

I hope this helps a little. I'm sorry to have caused some confusion in my post. I'll try to be more clear in the future.

 

Sources:

http://forum.netweather.tv/topic/46373-understanding-500-hpa-charts/

http://weatherfaqs.org.uk/node/189

http://www.null.co.uk/

 

 

No problem - I understood that you were mainly referring to surface-level pressure and therefore it made sense for you to describe that output as a surface chart - it just got me wondering what the definition of surface vs. upper.Posted Image

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No problem - I understood that you were mainly referring to surface-level pressure and therefore it made sense for you to describe that output as a surface chart - it just got me wondering what the definition of surface vs. upper.Posted Image

 

No firm definition. We often call 500hPa upper air, but mid levels would be perhaps more accurate. It also depends on the seasons. The troposphere is deeper in summer.

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No firm definition. We often call 500hPa upper air, but mid levels would be perhaps more accurate. It also depends on the seasons. The troposphere is deeper in summer.

 

Thanks - I was thinking more towards the idea of whether one defines a chart as "surface" or "upper" if it contains elements of both.

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a simple approach is a surface chart is just that isobars on a surface chart although even that is not that simple. The isobars are the lines joining places of equal pressure but indicate the direction of the wind above the friction layer, generally defined as being 2,000ft above the surface they flow over!

Normally the direction of the wind on the actual surface is 'backed', that is moved anti clockwise from the direction the isobars show. This is due to the friction, greater over land and much less over the sea.

The GFS charts are, I think, a mix of these isobars with surface centres along with the temperatures indicated by their colour at 500mb. If you look on Extra you can see how this temperature at 500mb with the 552dm height shown as the black line can and often does differ from the 1000-500mb thickness chart, again shown on Extra by colours with the surface isobars.

All very confusing I am sure but it may be an idea to read up on thickness charts and 500mb charts, below is a link to a good site, started by an ex senior forecaster with UK Met

http://weatherfaqs.org.uk/

don't be afraid to pm me if you are still puzzled and I will do my best to help

Edited by johnholmes

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Thanks John - I think I'm up to speed with the basics of the 500, 300 and 850hPa heights vs. the 500-1000hPa thickness charts - really, I was idly wondering whether a model output chart showing features of both surface (for example, the isobar pressure charts you described above as being based on the lower section of free atmosphere) and upper (for example, 500hPa temperature or anomalies) ought to be categorised as a surface or upper-level output.  More a matter of semantics than practical meteorology I suppose.

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