Regarding weather radar?

[Switchfoot]

So flying home from an all-nighter we come across this situation regarding weather radar:

Ground observations indicated cells in the 20 thousand foot range at the halfway point and the same near home (but dissipating). We get to the halfway point at FL240 and there is nothing on the airborne unit; nothing being painted, no colour, and visibly, nothing except scattered clouds around the area.

Getting closer to home, still nothing being painted on the airborne unit, but can see lightening in the distant (not close to landing airport from altitude), ground observer at the MF cannot see any lightening, just showers, and centre has is not showing anything.

In the descent thru 12000' ASL, get into heavy precipitation, lightening and moderate turbulence. Basically flew thru a dissapating thunderstorm cell. When you're fatigued after flying all night, not a good time!

So my question is why? Why would the airborne unit not paint anything until we were already in the storm? The unit works, and tilt and range functions were used correctly. Is it possible that precipitation was so heavy (and trust me, it was), that embedded CB's behind it were not being painted? I'm sort of new to this IFR stuff and wondering if someone can shed some information.

Thanks.


Switchfoot.

[Hedley]

This is why I like both stormscope and radar. Either one alone only shows you part of the picture. Together, they are a very powerful combination.

[C-GPFG]

doesn't heavy precipitation show as a black hole?

[2R]

Black holes are usually Radar Shadows.Radar shadows should be avoided .Radar shadows are made by really wet area's that absorb the radar energy creating the UNKNOWN .Usually the unknown in an area of convective activity is bad and can kill.Black holes can indicate that the wet area is growing in intensity and can be a weather monster. Depending on the temperature and moisture content of the cell/line depends on how bad it will get. Temperature of the cell /line and height can tell you alot about whether to avoid that weather.
A 30,000 foot cell above 20 c will have a lot of energy in it and may spawn tornado's in it.

In the southern states they issue convective weather sigmets it may look nice but if the weather guesser says it is going to be bad it usually is .So do not fly over any trailer parks in a sigmet area as that is where most tornado' s as everone knows that is where the tornado's like to go.

There are some excellent dvd's out on weather radar worth the money .

Use your radio to get weather updates from ATC and the FSS stations to help avoid the stuff that can develope enroute ,long after you get your weather preflight brief.Those guys and gals have better radar weather information in real time and really like to help .They have saved me grief on more than one occasion.

[Swamp Donkey]

When you are flying during in the daytime, and you have build-ups or isolated cells, practice using the weather radar. Try the tilt, gain and different range settings to make youself more comfortable using the unit. That way when you can't see them at night, you'll know what to expect on the screen.

[pika]

Is it possible that precipitation was so heavy (and trust me, it was), that embedded CB's behind it were not being painted?

Yes, it's called attenuation.

"Micro-waves used in weather radars can be absorbed by rain, depending on the wavelength used. For the 10 centimeter radars, this attenuation is negligible. That is the reason why countries with high water content storms are using 10 centimeter wavelength like in the United Sates with NEXRAD. The cost of a larger antenna, klystron and other related equipments is offset by the benefice.

For a 5 centimeter radar, absorption becomes important in very heavy rain and this attenuation leads to underestimation of echoes in and beyond a strong thunderstorms line. Canada and other northern countries use this less costly kind of radars as their precipitations are usually less intense. However, users have to remember this effect when interpreting data. The images above show how a strong line of echoes seems to vanish as it moves over the radar. To compensate for this behaviour, radar sites are often chosen to somewhat overlap in coverage in order to give different point of view to the same storms.

Shorter wavelength are even more attenuated and are only useful on short range. Many television stations in United States have 3 centimeters radars to cover their listening audience. Knowing their limitations and using them with the local NEXRAD can add information to a meteorologist."

http://en.wikipedia.org/wiki/Weather_radar

(near the bottom)

Archie Trammell is the weather radar authority.

EDIT PART

http://www.artietheairplane.com/radar.htm

Go here for a further description and a look at the PAC Alert Bar that appears on modern radar units during attenuation.

[flyinhigh]

Be advised that in the centres (all centres across Canada) we only see lightning strike information on our displays, and do not see very much cell information, if any.

We only get cell information from those radar sites that have PSR colocated with the SSR, which in most cases are only those radars serving a terminal airspace. Even then, we only see dark blue and light blue shading, neither of which are very consistent in accurately identifying weather requiring deviations.

In short, don't rely on Centre to be able to steer you clear of Wx.

First with what atc wrote about steering clear of wx, I'd like to thank the guys at yyz departures for the other day, they vectored me around a system and took all thinking out of it on my part, excellent job.

Now a question for cp atc-
So if I am flying and ask you the controller if you are showing anything on your radar along my flight path, do you actually paint the system that I am painting and know whats there?

By the way I read your post you don't see them only lightning strikes.

[water wings]

First with what atc wrote about steering clear of wx, I'd like to thank the guys at yyz departures for the other day, they vectored me around a system and took all thinking out of it on my part, excellent ...

and this differs from the every day...ummm. how?

this isn't be nice to your captain day is it?

[TOGA Descent]

So flying home from an all-nighter we come across this situation regarding weather radar:

Ground observations indicated cells in the 20 thousand foot range at the halfway point and the same near home (but dissipating). We get to the halfway point at FL240 and there is nothing on the airborne unit; nothing being painted, no colour, and visibly, nothing except scattered clouds around the area.

At a minimum, you should have been displaying Ground Returns on the outer edge of the Weather Radar Unit. Why?

By adjusting the tilt to display ground returns on the outer edge of the Weather Radar Display Unit, you have done a number of things, including:

1. Ensuring that the unit itself is working,
2. That the tilt is properly calibrated (More on this shortly),
3. Having a method to detect a “Black Hole” (Explanation below)

Explanations.

1. Self explanatory,

2. Radar antennas come in a variety of sizes, and each size provides an inversely proportional radar beam (a cone).

a. Larger Transport Category Antenna (typically 30 inch) produce a 3 degree beam (cone)

b. A 10 inch antenna would produce a beam of approximately 18 degrees,

c. Diameters between 30 inches, and 10 inches provide various beam diameters between greater that 3 degrees, and less than 18 degrees.

d. To determine the beams diameter at any distance, simply recall the old 1 in 60 rule.

e. For example, in a Transport Category Aircraft, with a 30 inch antenna, the radar beam diameter would be approximately 18000 feet, at 60 miles. (1 in 60, with a 3 degree beam, means 3 statute miles of diameter at 60 miles) 1 SM equates to approx 6000 feet. So, we have approx 18000 feet of beam at 60 miles. BUT, remember that with tilt set to Zero, half of that beam is above the horizon, and half is below(assuming a gyro stabilized unit).

f. Not understanding this can lead to over-scan or under-scan.

3. By painting ground returns, AT MOST TIMES, you protect yourself against attenuation problems (Black Hole).

a. When a radar unit displayes weather returns, and then, also provides a ground return BEHIND that weather, you can be confident that the weather displayed is accurate, and that the unit is not attenuating. A black area behind a weather return, where a ground return should be displayed, indicates clearly that the “Black Hole” exists.

b. Also, by painting a ground return you can almost guarantee that your weather radar beam is scanning the freezing level somewhere along your track. This also helps to prevent over-scan and under-scan

c. When weather returns appear on the outer edge with the ground returns, you can properly use the tilt function to scan the weather mass vertically. This will give you a better understanding of that weathers properties.

Getting closer to home, still nothing being painted on the airborne unit, but can see lightening in the distant (not close to landing airport from altitude), ground observer at the MF cannot see any lightening, just showers, and centre has is not showing anything.

I would guess that the freezing level was not in the radar beams field of view (Line of sight), and Weather Radar is not so good at detecting ice. (Ice Crystals, Hail, etc).

In the descent thru 12000' ASL, get into heavy precipitation, lightening and moderate turbulence. Basically flew thru a dissapating thunderstorm cell. When you're fatigued after flying all night, not a good time!

Now I’m convinced of this...

So my question is why? Why would the airborne unit not paint anything until we were already in the storm? The unit works, and tilt and range functions were used correctly. Is it possible that precipitation was so heavy (and trust me, it was), that embedded CB's behind it were not being painted? I'm sort of new to this IFR stuff and wondering if someone can shed some information.

I hope this answers the question. I’ve taught Weather Radar at several airlines over the past years. It’s not a complicated devise to fully understand, but does require a technique, and you will have to develop several weather avoidance strategies.

That said, sorry for the short explaination, but I’m flying today, and don’t have much time now. If you like, you can email me for more details. aa321486@yahoo.co.uk


Cheers, and fly safe.

[co-joe]

The gain could be set too low. Sometimes a cell won't stand out from its surroundings so if you turn down the gain the cell itself will become more obvious. If you then forget to turn it back up to zero you might miss weaker liquid water content. You can also try turning it up to +3 from time to time to check for more subtle wx.

My undersatnding about attenuation is that something will show, but not the wx behind it. You'll get "hooks" and "fingers" with black areas behind them which in fact are the places to avoid. But it doesn't sound like that's what you are saying. If you got no return at all, the problem could be elsewhere. Possibly in the hardware.

[TOGA Descent]

The gain could be set too low. Sometimes a cell won't stand out from its surroundings so if you turn down the gain the cell itself will become more obvious. If you then forget to turn it back up to zero you might miss weaker liquid water content. You can also try turning it up to +3 from time to time to check for more subtle wx.

True. Gain is a very misunderstood radar control. Typically, the unit has an "Auto", "Cal", or similar setting. the unit is best left in this setting.

That said, "Gain" is normally used all you to find the weaker cell, in a line of cells. Thus, determining the "Least-Worst" area. The suggestion I mentioned earlier, of displaying the ground return beyond the weather, is a much safer method of completing the same task.

Obviously, if enough radar energy can penetrate the storm cell, and then provide a ground return, you have a good idea of the true extent of that weather.

My undersatnding about attenuation is that something will show, but not the wx behind it. You'll get "hooks" and "fingers" with black areas behind them which in fact are the places to avoid. But it doesn't sound like that's what you are saying. If you got no return at all, the problem could be elsewhere. Possibly in the hardware.

True again. Attenuation is all the energry being absorbed by the weather, and none returning to the unit in the aircraft.
And, the the first indicator of possible attenuation will be an extremely steep gradiate on the back side of the cell that has absored that last amount of energy.

[Hedley]

I know this is just too easy, but:

http://www.garmin.com/products/gpsmap396/

Now back to your regularly scheduled obfuscation.

[Dust Devil]

will the 396 display canadian weather?

[2R]

I could not see the magic TSO numbers .That allow use in commercial ops

[Switchfoot]

Thanks for all of the replies. I haven't been flying since but the next time I am out there I will try a few of the methods you guys/gals have suggested.

When I spoke with one of our other pilots they mentioned that the unit seemed to work better at a lower range setting, which makes me wonder if there is something wrong with it? Because obviously we would like to see further ahead.

Having said that though, our maintanence team is pretty good, so perhaps it was a mistake on the crews (our) fault. A learning experience, and more to brush up on! Keep the answers coming.


Switchfoot.