ATC requests cloud tops at night

[JammedStab]

Happened the other night while in cruise on a fairly dark night at FL340. No buildups around but there appeared to be significant cloud below. Captain played with the radar and gave a pirep with a specific altitude.

Is there some kind of technique used to determine this or was he really just guessing.

[compressor stall]

Did you ask him?

[shaftsburn]

Assuming stabilisation is available and switched on:

Relative height(ft) = (Radar Tilt - Half of beam width) x 100 x Range(nm)

I've never used it and never needed to use it, so don't know how if it works in practice.

[BOAC]

Probably a reasoned guess/(?BS?) - there is no way you can determine cloud tops with radar.

[deefer dog]

When studying for my exams I was led to believe it was possible, and even got a question on the subject. In practice I have never managed to get it to work, even with the amazing kit we have nowadays. Me thinks BS also.

[Nemrytter]

Probably a reasoned guess/(?BS?) - there is no way you can determine cloud tops with radar.News to me. Radar systems are routinely used for monitoring cloud top height - usually from satellites but it also works from aircraft (with a bit of extra mathematics).

[SloppyJoe]

Do cloud tops (no buildups) even produce a return?

[deefer dog]

From Airbus:

The radar does not detect clouds, fog or wind (droplets are too small, or no precipitation at all). How therefore can wx radar carried in aircraft detect the cloud tops?

[despegue]

No, they do not.
It is BS to be able to determine non cumuli cloudtops using the inflight weather radar.

[wiggy]

+1 (actually +lots)

A standard aircraft weather radar cannot be used determine the altitude of the tops of non-convective cloud.....if it did it would be somewhat limited a detecting embedded Cb.

[Nemrytter]

How therefore can wx radar carried in aircraft detect the cloud tops?Depends on the clouds. Some non-convective clouds can also be detected.

[zerozero]

Incredible someone's ego is so HUGE he cannot simply admit, "I do not know the cloud tops."

Really. Who cares?

ATC should have asked some poor turboprop pilot slugging it out in the high teens, low 20s.

[Wageslave]

Depends on the clouds. Some non-convective clouds can also be detected.

NO!

How many times does it need to be said? Wx radar cannot detect clouds. Period.

It seems astonishing that something so fundamental is being discussed on a "Professional" pilots' forum!

Leaving aside ground and aircraft returns (before some smartarse chimes in) Wx radar can only detect precipitation - and doesn't do too well if it is frozen precip, so unless the cloud has water (rain) droplets or perhaps ice (hail) inside it you won't get a return. Ice as in hail gives a poor return, snow virtually none.

AS there won't be a significant amount of liquid water in cloud at FL300 radar often isn't very helpful up there, and in any case the only (likely weak) return you might get is from the places where hail is present, and that almost certainly won't be at the tops of clouds as hail usually don't go that far up inem, see?

That's why the call it "weather" radar. Because it sees weather
not clouds...

[Nemrytter]

so unless the cloud has water (rain) droplets ... inside it you won't get a return.You have oversimplified. A cloud is composed of water droplets, the difference is the size of the droplets. The boundary between a droplet being 'cloud' or 'rain' is not absolute and it is possible for a weather radar to detect cloud droplets - particularly in convective systems and over mountainous terrain. These will usually give only weak returns, however.

Yes it's a pedantic point but it is important: Saying that weather radar 'cannot' detect clouds is incorrect. Plain and simple.

[zerozero]

Pedantic and impractical.

For all PRACTICAL intents and purposes, wx radar as typically installed is not useful in determining cloud tops as originally queried by ATC.

I would have giggled watching someone adjust their wx radar in order to answer this question. I like to tell kids we watch cartoons on those screens when we're bored. Much better chance of THAT!

:8

[glendalegoon]

of all the statements so far, compressor stall has the answer.

you should have asked him. why didn't you?

isn't it possible that he was using the radar to make a quick search for buildups before giving the answer based upon climbout visual observation?


and yes, its true that hail doesn't show up that well on radar, how often have you seen radomes blasted apart by hail.

Its time to acknowledge that if you ask a question and someone calls you ''stupid'' for asking the question, then don't deal with that person anymore (after landing).


I was flying with a copilot back in the 80's in a regional turboprop. It was my habit to have 121.5mhz tuned up to listen for ELTs as we were over very mountainous terrain. We picked up an ELT and reported it to atc.

ATC asked us to take a bearing on it. (get this folks) And my F/O said he would do that. I looked at him and asked him what he intended to use to take a bearing on the signal. And he actually pointed to the ADF.

(oh, for you magenta line kids, that stands for automatic direction finder and it only works in the KHZ range, and low/medium at that)

I calmly picked up the MIC and told him that none of our planes were equipped with VHF DF.

I didn't make the F/O feel bad but I did take the time to explain things.

So, ASK. You might learn something.

Asking on PPRUNE instead of getting it from the horses mouth would be like Buzz Aldrin asking on PPRUNE the thinking process of Neil Armstrong in selecting a landing site.

[kinteafrokunta]

Asking on PPRuNe instead of getting it from the horses mouth would be like Buzz Aldrin asking on PPRuNe the thinking process of Neil Armstrong in selecting a landing site.

Did they really land on the moon?:E

[BOAC]

Glad you asked here....................:rolleyes:

That should improve the 'quality' of this thread.

[Green Guard]

Did they really land on the moon?

actually that is a very good question
:hmm:

[underfire]

According to pprune pilots, I thought the Wx was just used to scare away birds on final. Now I find out one can even map the cloud tops!

I love this site!

:zzz:

[lifeafteraviation]

Oh OH!!! I know the answer to this one....

How to calculate cloud tops with wx radar...

(But you will have to depressurize the airplane)

Remove the radar display unit from the panel (although you may need to sneak a screwdriver on board because pilots aren't allowed to have screwdrivers).

Toss the unit out the window and start the timer...

When your unit disappears into the cloud tops, stop the timer...

Use the terminal velocity formula, v = the square root of ((2*m*g)/(ρ*A*C))

The rest is pretty academic.

(This really works by the way but I had to quick Google that last part)

[BOAC]

Yes, that would work, it is establishing 'C' that is the difficult bit.

That's probably how Nemrytter does it, I guess. Clever chap.

[underfire]

not if you are inverted....

[Nemrytter]

That's probably how Nemrytter does it, I guess. Clever chap.No, we just have more sophisticated processing than the standard cockpit display (even though the hardware is the same). Unless you are looking at a huge tropical convective cell then the returns are always very small and would be tricky to see on the tiny screen.

As someone said on the last page: It's "impractical." But it's not impossible. :)

[A Squared]

ATC should have asked some poor turboprop pilot slugging it out in the high teens, low 20s.

Admit it, you're feeling nostalgic about those days, aren't you.

[Green Guard]

There are always those who enjoy to confuse apples with bananas.

The thread subject is: "ATC requests cloud tops at night "
and not: ATC requests TO CALCULATE cloud tops at night.

All that ATC wants in this case is:
Pilot Visual report, using Pilot cockpit windows vs Pilot altimeters, during climb or descent. During level flight just say you are bellow,above or on top.
PS
If you can not make the difference between night-sky
(with or without moon, the darker the more stars should be there ! )
opposite to no-sky-visible due to in-cloud conditions then no calculation will help you.:cool::ooh:

[JammedStab]

of all the statements so far, compressor stall has the answer.

you should have asked him. why didn't you?

isn't it possible that he was using the radar to make a quick search for buildups before giving the answer based upon climbout visual observation?


Actually, I did ask him. He was playing with the tilt and a few small green splotches appeared. He used a straight forward formula based on tilt and distance to green splotches(it has been a while now so I don't remember the details). I just thought that I would ask on here as well as I was a bit skeptical but not sure. Hope you don't mind me trying to get a second opinion.

It did not appear to be a night of any buildups. There was midlevel cloud below with very little but some light with no real depth perception. I will say that we were flying over an area where public TV had said would have rain on the ground.

[zerozero]

Admit it, you're feeling nostalgic about those days, aren't you.

Never did get rid of the nervous twitch in my eye.

:8