Base reflectivity versus composite reflectivity

"Icebound" wrote in message
...


Based on NOAA's description, Composite is just *the strongest* of the
echoes from the scans at many elevations.

My server rejected this post last night with an error... then magically it
appeared only after I posted a repeat. The repeat is somewhat more
accurate. Ignore this one.

iflyatiger wrote:
"iflyatiger" wrote in message
...

Peter ,

I am also interested in the weather.
Here is 2 screen shots I just took of a composite and a base reflectivity
radar. Maybe someone can describe what we are lookin at.

How about posting them at alt.binaries.pictures.aviation [hope that's the right
name, my news server here at work doesn't have the binaries groups] and then
posting a pointer to them back here?... or better yet, put them on a web server.

Dave

"Jay Beckman" wrote in message
news:kowie.10549$Fv.335@lakeread01...
In light of the fact that summer thunderstorm activity is coming quickly
(and our traditional "monsoon" season) here in the desert, this subject is
very interesting.

In reading the descriptions of "Base" vs "Composite" at the NWS website,
am I taking away the right idea:

Base: Image derived from a single radar azimuth
Composite: Image derived from multiple radar azimuths then, well,
composited into one 2D top-down view?

Jay Beckman
PP-ASEL
Chandler, AZ


No, like Iceman says, the composite shows the most intense echo over a range
of antenna tilts (elevations). The base image shows one elevation. Both
composite and base images show all azimuths. The antenna on a NEXRAD site
is so large (resulting in a very narrow beam) that it can easily scan above
or below the area of the storm holding the water. You could have a massive
supercell and the beam might pass right under the storm at low tilt angles
(elevation). The composite would show the storm unless it is directly over
the antenna.

Mike
MU-2

"Mike Rapoport" wrote in message
ink.net...
No, like Iceman says, the composite shows the most intense echo over a
range of antenna tilts (elevations). The base image shows one elevation.
Both composite and base images show all azimuths. The antenna on a NEXRAD
site is so large (resulting in a very narrow beam) that it can easily scan
above or below the area of the storm holding the water. You could have a
massive supercell and the beam might pass right under the storm at low
tilt angles (elevation). The composite would show the storm unless it is
directly over the antenna.

Mike
MU-2


Thanks Mike and "Ice" good explanations...

Jay B

The comment that "even airplanes can be lifted uncontrollably"
deserves a real world example, for those of you that have never
experienced it.

During one flight in the south during the summer thunderstorm
season, I was using my Strikefinder and input from ground
controllers to fly through what appeared to be a 80 to 100nm
wide gap in a line of thunderstorms. I was at 6,000' MSL and
got into the soup as I entered the area. A few minutes into it,
the rain picked up, it got dark, the rain got harder, it got darker,
etc. But the ride was smooth and I was nicely centered up the the
gap with cells off to both sides.

All of a sudden, the VSI pegged indicating a climb of greater than
4,000 FPM. With both throttles closed and a picth angle of about
20 degrees down, I was still going up at better than 4,000 FPM.
This was in a Piper Aztec that weighted in at about 4800 pounds
at that moment in time.

The updraft persisted about 30 seconds and resulted in a +2,000'
altitude deviation even after my best efforts to stop it, which I reported
to ATC as time permitted along with asking for an update on what he
was seeing on his radar. The response was that I was about through
the stuff and sure enough, I popped out into nice weather in another
couple of minutes.

Don't underestimate the power of a building convective storm. It can
suck you up in a hurry. Likewise, understand the even more dangerous
downdrafts when the storm is dissapating. Flying along down low and
encountering a 4,000 FPM to 6,000 FPM downdraft would ruin your
whole day.


"Stan Gosnell" wrote in message
...
"Peter R." wrote in news:1116341209.145697.282000
@z14g2000cwz.googlegroups.com:

First, a rather basic question: Why is it that all of the moisture
that appears in a composite reflectivity map is not all falling? Is
this due to the strength of the updrafts within the cell? It seems to
me that moisture that appears that heavy on radar would be heavy enough
to all fall out of the cloud.

The updrafts can be very intense. How do you think baseball-sized hail
occurs? Water drops get lifted so high they freeze, then eventuall fall,
only be lifted again after picking up more water, and the process repeats
until the ice ball gets large enough to finally fall through the updrafts
or else (more likely) gets thrown completely out of the updrafts
horizonally, and falls. If thunderstorm updrafts can lift huge chunks of
ice, they can certainly hold up water drops, and even airplanes can be
lifted uncontrollably.

--
Regards,

Stan

"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." B. Franklin