Does tropopause affect how you fly?

[extricate]

Hi,

I guess most of us won't even fly near where the tropopause is but has it been a concern for you when you are planning and preparing for your flight? Care to share?

[sonicbum]

Hi,

well, You can find easily tropopause levels of FL240ish towards the Poles, so we definitely fly quite often above the tropopause, especially in winter time at mid latitudes.
For a quick idea of the impact of the tropopause on aircraft performances You can have a look HERE. (https://www.skybrary.aero/index.php/Tropopause)

[wiggy]

As sonicbum has said it’s very common to end up operating just below, at or above the tropopause….I wouldn’t say I ever had any “concerns” about it TBH, what sort of things were you thinking of?

[Airmann]

All issues regarding tropopause are temperature related. With low tropopause temperatures at altitude are higher, which effects performance. Have to watch out for tropopause dropping and temperature increase while in cruise before planning a climb. Other than that flying in the stratosphere is better due to the fact that there's no weather up there.

[blind pew]

Climbed into it once and lost 80 knots tailwind so went back down and saved some time and money.

[gums]

So true, Air, and Blind.

Flying along the Canadian border from Grand Forks to Montana one day we had almost a 100 knots on the nose at 35K. Called "metro" at Minot anmd asked for winds at 40K - "light and variable"! Sure enough, managed to get the T-33 up there and zoom.

[wiggy]

Still a bit :confused: by the OP.

I thought (obviously incorrectly) that it was common knowledge that in many parts of the world airline ops were performed at or above the trop..

The inflight “concerns” have been mentioned above - possibility of it getting warmer as you get higher above the trop, and the winds, but that’s about it.

I must admit at the pre-flight briefing stage where you might have 15 minutes or less to check out the details of a multi hour flight which has already been run through some fancy computers to optimize levels etc I I recall the tropopause levels along the route were down at 1001 of the things you might take an interest in.

En-route, especially if polar, then maybe the trop became of more interest..

[airseb]

I’d say the only real question I have on that subject is wether said trop is going to mean turbulence. A rapid change in trop altitude is a sure sign of increased shear rate and it usually means CAT. Other than that it’s mostly a detail.

[extricate]

wiggy

Thanks for the replies. Yeah, from where I am in this part of the world, we rarely fly\ to the poles, so rarely we get to fly anywhere near the tropopause. And yes, temperature differences and wind gradients, I'm curious as to how it will affect you, especially if you are in a part of the world where tropopause levels are lower.

Thanks, good reply from Airmann too.

[extricate]

airseb

Yes I'd thought so too and that's where Jetstreams come into play. In fact, I was looking at my flight plan and the part where tropopause levels dropped drastically by about 10,000ft, the wind shear level was moderately so...

[ShyTorque]

As a helicopter pilot, I’m more affected by the male menopause.

[wiggy]

extricate

Ah that explains it thanks…

..:ok:

[Airmann]

wiggy

Let’s get something clear. It doesn’t get warmer when you get above the trop, it just doesn’t get colder (I.e. lapse rate is 0 in the stratosphere). So whatever the temperature at the tropopause, then that’s the temp for the majority of the stratosphere, it does get warmer higher up, but most planes won’t get that high.

As you’re all well aware aircraft performance is calculated with a tropopause at ISA 36,000ft at -56 Celsius (15-[1.98 x 36]). And fundamentally for performance it’s delta ISA that’s important. The issue is that in colder climes where the tropopause can drop to below 30,000ft. and lapse rates are less, the tropopause “starts sooner” and the temperature stops dropping sooner e.g. at -42 degrees. So once you reach the low tropopause your delta ISA keeps increasing until 36,000ft.

In warmer climes where the tropopause can be 55,000ft.+ the temperature keeps dropping as you climb and once you reach 36,000ft. as the trop is still higher your delta ISA will keep decreasing and performance will improve the higher you go. For most modern airliners performance begins to be significantly impacted once delta ISA gets above 10 and you’ll start seeing a signinificant drop in Max Alt.

Sorry if this is obvious information to you guys.

[extricate]

Excellent explanation, thanks for sharing, you hit the nail

[wiggy]

Airmann

Well one of the few things I learnt over the years was “never say never” and in response to your kind comment I’ll offer this by way of reply

Real world, very Northern Russia, winter, tropopause down at very sub FL200, cruising in the mid thirties…climb a couple of thousand feet and the OAT climbed 2 Celsius.

Niche circumstances yes, and I’d agree that most of the time in most other parts of the world climbing when above the tropopause did not lead to warming but I did enough of those very northern routes over 30 ish years to see warming on climb on a few occasions ….it’s not a “given” but in the interests of clarity it can on rare occasions get warmer as you get above the trop, even at airliner cruising levels.

[Uplinker]

You can change the default tropopause value (36,000'), in the Airbus MCDU, and I do so if it is significantly lower or higher on the day, on our route.

This value is used for performance calculations, including OPT and REC MAX cruise altitude, I would have thought?