Wx + Turb benefit

[Molesworth]

Can any of the radar gurus help with this one? I've tried a search but have not found an answer that relates specifically to this question:
Most modern wx radars have 'wx' and 'wx + turb' settings, with the 'turb' function only active at ranges below 40nms. What is the benefit of using the 'wx' function? Does the turb function attenuate the least powerful returns? Does it use less power? Is there a reason to not use 'wx + turb' all the time? If not, why was the 'wx' function provided?
I believe that in older radars there was some attenuation with turb selected, and observation using the 767 radar does show a small reduction in the area of green returns when going from 'wx' to 'wx + turb'
Thanks for any answers or references.

[vapilot2004]

The turbulence function using doppler calculation has value only when a wet target is in range. WX mode alone is optimised for scanning ahead for precipitation and obstructions.

Also, some radars in T mode will lose level 4 indications on the WX display. (magenta)


Perhaps an actual guru can expand on my offering.

[HotDog]

The present sytem is the pre-cursor of the NASA evaluation of the Turbulence prediction & warning system TPAWS.

The TPAWS technology is an enhanced turbulence detection radar system that detects atmospheric turbulence by measuring the motions of the moisture in the air. Researchers have already tested TPAWS on a NASA Boeing 757 research aircraft. The TPAWS equipped plane searched for turbulence activity around thunderstorms for eight weeks. The aircraft flew within a safe distance of storms, so researchers could experience the turbulence and compare the radar prediction to how the plane responded to the encounters. After one severe patch of turbulence, a NASA research pilot said his confidence in the enhanced radar had "gone up dramatically," since the plane's weather radar did not show anything, while the same time the TPAWS display showed rough skies ahead.

This evaluation started in 2004 and I do not possess any current data but would imagine it is already in production for new aircraft. Your radar could well be the latest with TPAWS. My last experience of Wx Radar on the Classics only had WX or Map capability.

[ICT_SLB]

Weather radars with turbulence detection have very stable frequency transmitters that allow the receiver section to see returns that differ in frequency caused by the doppler shift as precipitation or dust particles move towards or away from the aircraft. To avoid spurious returns, airspeed is fed into the radar to provide a speed range gate. Obviously the returns from such moving particles are much lower in energy to the main one from static targets hence turbulence only working at closer ranges. In the WX position, only the main (non-doppler) return is used. Both WX & WX+TURB may use other processing techniques to better show what's out there - exactly what seems to depend more on manufacturer than pure physics.

[Apollo 100]

I have found the Wx+T mode on our aircraft of limited practical value due to its very short range (40nm), and I usually just leave the display on Wx only. As previously mentioned, the fourth level of precipitation (Magenta) is replaced by turbulence detection (the same colour magenta) and the doppler function becomes active. I my experience I have found that the turbulent precipitation has to be pretty severe to get any reading at all on the display and I feel more comfortable seeing the standard wx radar colours and making my own assessment of where the worst turbulence is likely to be. I find Ground Clutter Supression (GCS) a more useful tool than +T to be honest.

cheers

[maui]

The FAA/Boeing approved AFM on the 777's and 747-4 at my company, state quite clearly that Turb mode has not been properly evaluated, and should be used only on a non interference basis. It goes on to state that WX mode is the proper mode for weather avoidance.

Having said that, and having pointed it out to Flt Ops/Safety and Standards, about 80% of our pilots still fly around with Turb selected for all operations. Go figure!
(ref AFM, Normal Operations, Weather Radar with turbulence mode)

Maui

[sameep]

hi.. not sure if i am right but wx mode is the one generally used.. if the whole screen is red and bad wx has to be penetrated we use wx+t to penetrate through areas of least turbulence. this is what i have been told.. any feedback?

[I-2021]

if the whole screen is red maybe it is better to go somewhere else.