| Type of case | cumulus | ||||||
| Complexity | complex | ||||||
| Convection | line of convection | ||||||
| Electric field kV/m | Min Em_m = 0.458 Max Em_m = 59.475 Mean Em_m = 17.173 | ||||||
| Microphysics #/Liter |
| ||||||
| Location | (x,y) ~ (40,50) | ||||||
| Storm Motion | 3.8 m/s East, 2.4 m/s S, gives: 4.5 m/s SE | ||||||
Brief Description | comment |
| Type of case | anvil | ||||||
| Complexity | moderate | ||||||
| Convection | weakening line of convection | ||||||
| Electric field kV/m | Min Em_m = 0.180 Max Em_m = 46.261 Mean Em_m = 5.823 | ||||||
| Microphysics #/Liter |
| ||||||
| Location | (x,y) ~ (40,20) | ||||||
| Storm Motion | 3.8 m/s East, 2.4 m/s S, gives: 4.5 m/s SE | ||||||
Brief Description | comment |
| Type of case | cumulus | ||||||
| Complexity | complex | ||||||
| Convection | strengthening convection | ||||||
| Electric field kV/m | Min Em_m = 0.276 Max Em_m = 47.804 Mean Em_m = 11.341 | ||||||
| Microphysics #/Liter |
| ||||||
| Location | (x,y) ~ (30,10) | ||||||
| Storm Motion | 0 | ||||||
Brief Description | The reflectivity appears to stop at the radar. Perhaps due to some coastal effect? |
Investigator: Jim Dye
[presented on Mar 21, 2002]
Between 1700 and 1730 a pair of
cells NE of KSC near (-50,75) start producing both IC and CG lightning.
This convection quickly intensifies and by 1730 the LDAR plots show almost
continuous lightning.
By 2000 (the time of the first radar plots) the storm has
produced a stratiform region extending 75 or more km to the NE of the active
cores.
radar_1958_7km
The main core is to the SW of the complex with reflectivities exceeding
55 dBZ at 10 km. The stratiform regions extends from at least 4 km to
above 10 km and probably has precip to the surface.
Between 1900 and 1930 lightning begins to extend into this
stratiform region producing large areas with lightning.
Case 1: Ez
showed moderate values during the climb until about 2128 when they increased to
~+20 kV/m at –1C (~4.5 km), then shortly after reversed polarity with –50 kV/m
by 2130. Reflectivity above at and below the A/C were 20 to 40 dBZ. The
Citation, now at ~8 km, turned 2137 –2138 in reflectivities of 10-15 dBZ with
Ez near zero. to return to the SW. This pass was centered more along the axis
of the reflectivity at 7 km. Ez had moderate values of 5 to10 kV/m even though
reflectivities just below the A/C were 30 dBZ or more most of the time. As the
A/C got closer to the core near 2144 Ez increased in magnitude to –30 kV/m by
2145:30, then switched polarity to +20 kV/m by 2147.
ANALYSIS:
At the time of takeoff near 2115 UTC there was an arm of stratiform debris
extending 125 km to the NE. This debris had considerable shear to the SE
especially between 7 and 10 km but also some displacement between the 4km level
(which had patches of 35 to 40 dBZ) and 7 km (which had very small patches of
25-30 dBZ). Reflectivities were weaker at 10 km. (~ 15-20 dBZ). After takeoff
the Citation flew to the NE climbing in this arm of stratiform debris with the
track near the axis of the reflectivity at 4 km.
Near
2148 the A/C turned to begin another pass to the NE again along the axis of
the reflectivity arm at ~ 8km (-25C). This showed similar features to the
2138-2148 pass but Ez and reflectivities were somewhat less. Both small and
large particles tended to decrease as the A/C flew toward the NE end of the
arm. Another
pass to the SW was flown from 2156 to 2204, again along the axis of
max reflectivity at ~8km. By this time there was more horiz separation between the 4
and 7 km levels. I have the impression that the arm of debris was pushed out by
the very active convection earlier between 1900 and 2000. As the main core
weakened and was undercut by the long line approaching from the West, this arm
of debris drifted with the wind at the different altitudes as it decayed in
both E fields, particles and reflectivity. By 2220 the strongest Emag was ~8
kV/m for a brief period. After that the E fields were weak in this debris cloud
efield_2210-2220
efield_2220-2230
From
2221 until the Citation left this drifting debris slightly after 2245, Emag was
no more than 1-2kV/m (including offset) at the A/C altitude. By this time the
debris at 7 to 10 km had drifted ~30 to 40 km from the debris at 4 km.
Case 2:
Stratiform Region Associated with Line Moving from the West
At ~2250 the Citation moved west to investigate this separate stratiform region. The western part of the A/C passes through this region consistently showed strong E fields until the Citation left to return to PAFB.
In the two MER plots below as well as others afterwards, NOTE THE VOID IN RADAR COVERAGE
IN A CONE ABOVE PAFB (see the hor plot) results in a region on the right
side of MER 2252 with no apparent reflectivity but many particles and beginning
of high E fields. In MER 2300 on the left side you can actually see the inverted
cone of the radar void.
SUMMARY:
Case 2 investigated a stratiform region attached to active convection. The western
portion of all A/C passes for this case showed strong E fields as we neared the
active convection. We must be
careful in trying to examine E field versus reflectivity values for this case
because of the voids in radar coverage above the PAFB radar.
From looking at the reflectivity patterns and the location of radar cores relative to PAFB,
there was no apparent radar attenuation in the areas in which the Citation worked.
However, it is quite
likely that there was attenuation to the NW of the early very strong
convection and also to the west of the long line of convection.
The MER plots for Case 2 clearly show effects of the INVERTED CONE of
VOID in the RADAR DATA.
END OF SYNTHESIS
A region of very active convection NW of KSC with copious lightning produces
a stratiform region probably extending from the surface to above 10 km to
the NE of the storm cores. The Citation taking off near 2115 climbs out in this
stratiform arm or region. There is considerable shear between low and mid and
upper levels, resulting in an anvil-like structure extending to the SE with weaker
reflectivities at upper levels. By about 2200 the convection from these original cores
is weakened and then cut off by a long line of intense convectve cells moving
from the West
and the lightning in the stratiform region ceases. But there is copious
lightning in the line moving from the West.
The debris of this
stratiform arm drifts
to the SE and the Citation follows this debris as both the reflectivity,
microphysics and E fields decay. By the time the Citation leaves this debris
near 2250, the E fields have become quite weak and the largest reflectivities are
10 to 15 dBZ.
Even in the early and mid stage of the Citation investigations with lightning
still occurring in this system, when the A/C was
at the NE extent of the stratiform arm or debris the E fields were
weak in reflectivities of 15 to 20 dBZ. In the investigation of Case 1 of drifting
anvil-like debris, no instances were seen
in which there were strong E fields but weak reflectivity, i.e. <10 dBZ.
This first Case of the A/C study is a good case to compare E fields
with reflectivity and following the
decay of the electric field to weak fields. But it is hard to quantify the
time to decay because it is hard to identify the
time of the last lightning in either the stratiform region and especially in
the cores of the cells. It appears to be aproximately 2200.
Some lightning does occur in the stratiform arm
between 2115 and 2130 as the Citation climbs out to the NE.
