Met question

[Foz2]

Hi,

Struggling to understand this one, any help would be appreciated.

A parcel of air that is cooling by more than 1 deg/100m is said to be?

A) Conditionally Stable
B)Conditionally unstable
C) Unstable
D)Stable


The answer given is unstable. If a parcel of air is cooling at that rate surely it is stable as it is getting colder quicker than the SALR and the DALR. Should the question not read ' If the ELR is greater than 1deg/100m the environment is said to be?' It is asking about that particular parcel of air - I didnt think the environment was classed as a parcel of air?

Thanks in advance

Foz.

[AndyDRHuddleston]

Hi Foz,

I'm studying met aswell at the moment, but in a much sunnier, Florida!

My initial reaction to the question is that you would need to know the ELR to be able to establish if its stable or unstable. Even if the question assumes the standard 2 degrees / 1000 ft that would make the answer stable, as the equivalent rate of cooling is 3.04 degrees / 1000 ft for your parcel of air.

I'd query that one with your instructor, let me know the answer, because as far as I'm concerned you need to know the true ELR.

Hope that helps you in some way

Andy

[EGBKFLYER]

Not a very clearly worded question I reckon.

1C/100m is the ELR and is just more than 3C/1000', which is the DALR.

The parcel of air, assuming it isn't saturated, will cool at the DALR. At any given height, it will be warmer than its surroundings, and so will continue to rise - giving the answer as 'unstable'

The word 'parcel' generally indicates you should consider heating/ cooling as adiabatic, meaning the parcel is cooling at either of the Dry or Saturated rates and being compared to the environment cooling at the ELR.

In summary - the air is being lifted through an atmosphere cooling at the ELR *BUT* it is cooling itself down at the DALR unless it's saturated, when it cools at the SALR.

To put it another way:

ELR = telling you what temperature it is at what height
DALR = unsaturated parcels always cool at this rate
SALR = saturated parcels always cool at this rate

To get the answer, work out the temp at any height you like using the ELR. Then work out the temp at the same height using the DALR. If the latter is higher, you have a warm parcel(!) which means instability...

[cargodoor]

You probably know this already.

ELR<SALR it is always stable.
SALR<ELR<DALR it is stable unsaturated, unstable saturated.
ELR>DALR it is always unstable.

Hope it helps. Good luck

[OneIn60rule]

Since it's basically 3 degreees per 300 m. (which is darn close to 1000 feet).

As before said, it depends on ELR but usually for such questions you assume that they also assume it to be 2 degrees per 1000 unless they mention a specific ELR.


If it cools at 3 degrees per 1000 feet then it's basically stable. The answer they are looking for though is most likely CONDITIONAL INSTABILITY.
So if at some point this parcel of air becomes saturated then you have it going up at SALR and that my friend will enable it to go up and beyond. (Hence Conditional instability)


So this rules out Unstable as an answer. Stable is a good answer but it's not the most CORRECT one.
Conditionally STABLE I don't think I've heard of that one so I'm ruling that out.

Leaves you with two good answers: Stable OR conditional instability.


Cheers Simon!

[tarbaby]

Cooling rate is 3.04 degrees/1000ft. Air is unstable.

[High Wing Drifter]

Hmmm,

Sounds to me to be conditionally unstable.

The ELR isn't given and neither is the SALR. I assume parcel is dry as it doesn't say otherwise.

If that is the case then the parcel will be cooling at the DALR, which is >3deg/1000'(ish). As no figures then I think assume an ELR of 2deg/1000' and an SALR of 1.8deg/1000. That places the ELR between the DALR and SALR, hence conditionally unstable.