Barotropic Atmosphere

[HailMan06]

I have two questions regarding the atmosphere and its baroclinic/barotropic states.

During the boreal summer how north in the CONUS (particularly the eastern seaboard) can one experience barotropic conditions compared to a baroclinic one further north?

What are the signs of finding out if one is in a barotropic atmosphere or baroclinic atmosphere?

[H2Otown_WX]

I have two questions regarding the atmosphere and its baroclinic/barotropic states.

During the boreal summer how north in the CONUS (particularly the eastern seaboard) can one experience barotropic conditions compared to a baroclinic one further north?

What are the signs of finding out if one is in a barotropic atmosphere or baroclinic atmosphere?

Generally during the summer the expanse of barotropic conditions increases due to greater insolation. The feature driving this is the sub-tropical ridge of high pressure (a barotropic high pressure system) which is on average found around 30 degrees north latitude. I would say during the summer the center of it probably moves to about 35 degrees north and barotropic conditions along the east coast can be found as far north as 40-45 degrees north, depending on how expansive the high is and how much jet stream influence there is across the northern tier.

A good way of determining whether or not you're in barotropic is to look at the vertical structure of major features. Barotropic features are stacked vertically whereas baroclinic features tilt. A barotropic warm-core high pressure will have ridging at all levels (high pressure readings at the surface and high heights on isobaric surfaces above it). A barotropic cold-core high pressure will have ridging only to about 850 mb (roughly 1.5 km) and low heights on isobaric surfaces thereafter. This is the kind of high pressure area you'll find in the upper Midwest or Canada during the winter where the coldest air is found. A baroclinic low will tilt towards cold air (usually to the northwest with height since cold air advection is occurring to the NW of the low). These are the types of lows you will find across the mid-latitudes and they are a product of thermal contrasts (baroclinicity). Baroclinic highs tend to not last very long since subsidence within warms the center, causing it to become barotropic.

[HailMan06]

Generally during the summer the expanse of barotropic conditions increases due to greater insolation. The feature driving this is the sub-tropical ridge of high pressure (a barotropic high pressure system) which is on average found around 30 degrees north latitude. I would say during the summer the center of it probably moves to about 35 degrees north and barotropic conditions along the east coast can be found as far north as 40-45 degrees north, depending on how expansive the high is and how much jet stream influence there is across the northern tier.

A good way of determining whether or not you're in barotropic is to look at the vertical structure of major features. Barotropic features are stacked vertically whereas baroclinic features tilt. A barotropic warm-core high pressure will have ridging at all levels (high pressure readings at the surface and high heights on isobaric surfaces above it). A barotropic cold-core high pressure will have ridging only to about 850 mb (roughly 1.5 km) and low heights on isobaric surfaces thereafter. This is the kind of high pressure area you'll find in the upper Midwest or Canada during the winter where the coldest air is found. A baroclinic low will tilt towards cold air (usually to the northwest with height since cold air advection is occurring to the NW of the low). These are the types of lows you will find across the mid-latitudes and they are a product of thermal contrasts (baroclinicity). Baroclinic highs tend to not last very long since subsidence within warms the center, causing it to become barotropic.

 

Thanks for the explanation it was pretty helpful for me.

[H2Otown_WX]

Thanks for the explanation it was pretty helpful for me.

No problem, if you need anything to be clarified further just let me know.

[Chinook]

 A barotropic cold-core high pressure will have ridging only to about 850 mb (roughly 1.5 km) and low heights on isobaric surfaces thereafter. This is the kind of high pressure area you'll find in the upper Midwest or Canada during the winter where the coldest air is found.

 

This is a good post. Regarding the quoted section, do you mean a barotropic or baroclinic cold high pressure? I would argue this would be called a baroclinic cold high pressure underneath a 500mb low pressure, because it pretty much has to advect cold air away from the center. It has to be part of a tilted system.

[H2Otown_WX]

This is a good post. Regarding the quoted section, do you mean a barotropic or baroclinic cold high pressure? I would argue this would be called a baroclinic cold high pressure underneath a 500mb low pressure, because it pretty much has to advect cold air away from the center. It has to be part of a tilted system.

 

I meant barotropic, my understanding of a barotropic cold high is it occurs with high density, low thickness air. In other words, you've got high surface pressure that rapidly decreases as you ascend leading to lower heights aloft (e.g. 500 mb). This would be true in a stacked system making it barotrpic, no? I'm not quite sure what you mean by "advect cold air away from the center." Are you talking about at the surface where there's high pressure?

[Mallow]

I meant barotropic, my understanding of a barotropic cold high is it occurs with high density, low thickness air. In other words, you've got high surface pressure that rapidly decreases as you ascend leading to lower heights aloft (e.g. 500 mb). This would be true in a stacked system making it barotrpic, no? I'm not quite sure what you mean by "advect cold air away from the center." Are you talking about at the surface where there's high pressure?

 

 

I think he's saying that since there's a temperature gradient in these systems, they're baroclinic systems. A temperature gradient means vertical wind shear (as does the stacking of a low above a high), and vertical (geostrophic) wind shear necessarily implies that pressure and density surfaces are not coincident. So, by definition, not barotropic.

 

EDIT: Specifically, a temperature gradient on a constant pressure surface means it's not barotropic.

[H2Otown_WX]

I think he's saying that since there's a temperature gradient in these systems, they're baroclinic systems. A temperature gradient means vertical wind shear (as does the stacking of a low above a high), and vertical (geostrophic) wind shear necessarily implies that pressure and density surfaces are not coincident. So, by definition, not barotropic.

Hmm, I see what you're saying. I guess I don't know what a barotropic cold high is then, is there such a thing?

[Chinook]

Here's the way I see it:

 

Barotropic
 

a) high pressure at 500mb with warm temperatures co-located (high pressure at surface, warm, very weak temperature advection)

 

b.) low pressure at 500mb with cold temperatures co-located (low at the surface with generally cold)

 

c) special condition: hurricane or tropical storm. Low pressure with warm temperatures co-located.

 

Baroclinic

 

Some temperature advection is occurring, which will lead to some wind shear. Generally a surface low has cold temperatures to the west, warm temperatures to the east. Vice versa for a surface high. Cold high pressure areas are nearly guaranteed to be related to a baroclinic system. Cold highs are usually on the west side of a 500mb trough, with some warm and cold advection occurring near the high pressure.

 

Interesting situation

What if very weak temperature advection is occurring with a noticeable temperature gradient (i.e. front), and this is near a jet stream? It's a typical mid-latitude situation. It's not very baroclinic but not very "tropic" ish.

[Mallow]

Easiest way to determine baroclinic vs barotropic is to just look for (significant) temperature gradients. If they exist, it's not barotropic. Any other "definition" is essentially derivative of this basic concept.

 

EDIT: I should specify that the above is only true on a constant pressure surface. Looking at a surface map, this can get confusing.

[HailMan06]

Ok so I have been looking up how to identify whether a high/low pressure system is baroclinic or barotropic. Someone correct me if I'm wrong but one can find out by looking at the isobaric and compare those with isotherms of the same altitude.. If they generally align with each other then that system is barotropic.. But if they don't align then the system is baroclinic since cold/warm air advection takes place.

[HailMan06]

Bump for clarification.

[Mallow]

Ok so I have been looking up how to identify whether a high/low pressure system is baroclinic or barotropic. Someone correct me if I'm wrong but one can find out by looking at the [isobars] and compare those with isotherms of the same altitude.. If they generally align with each other then that system is barotropic.. But if they don't align then the system is baroclinic asince cold/warm air advection takes place.

 

Yes, if an atmosphere is barotropic, then isobars and isotherms will be aligned. Or, to turn it around, if you're looking at a map of constant pressure, and there is a temperature gradient at that level, then it is not a barotropic atmosphere.

[HailMan06]

Yes, if an atmosphere is barotropic, then isobars and isotherms will be aligned. Or, to turn it around, if you're looking at a map of constant pressure, and there is a temperature gradient at that level, then it is not a barotropic atmosphere.

Ok Mallow thanks for that, you helped me a lot with understanding this.