Vertical profile of cloud microstructure in moderate smoky conditions was done some 100 km to the SW of JPR. Clouds again had droplets concentrations exceeding 3000 cm 3 in smoke. The concentrations reduced to 2000 cm-3 at 15 kft. There was little coalescence and no warm rain processes at all. On the way back we crossed an intense squall line and made a nice cross section of the clouds microstructure at 7 kft, from the smoky leading edge to the transition zone into stratiform. The clouds remained with high droplet concentrations throughout the width of the squall line, even in the heavy rain.

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3 Νοε 2013 (πριν από 3 χρόνια και 7 μήνες)

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Summary of cloud physics flight, 28 September 2002



Overview:


Vertical profile of cloud microstructure in moderate smoky conditions was done
some 100 km to the SW of JPR. Clouds again had droplets concentrations
exceeding 3000 cm

3 in smoke. The concen
trations reduced to 2000 cm
-
3 at 15
kft. There was little coalescence and no warm rain processes at all.

On the way back we crossed an intense squall line and made a nice cross section
of the clouds microstructure at 7 kft, from the smoky leading edge to t
he
transition zone into stratiform. The clouds remained with high droplet
concentrations throughout the width of the squall line, even in the heavy rain.



The planned mission for today was documenting the gradient of smoke between Ji
Parana (JPR) and Vilh
ena (VLH). The INPE aircraft (Aerosol instruments) took off at
12:17, and reported a sharp transition to smoky conditions some 20 minutes flight to
the south east of JPR, and two coordinates of fires between that location and VLH.

Based on this report we t
ook off with the UECE cloud physics aircraft at 13:41,
planning to do vertical profiles from cloud base to 15 kft. Oxygen masks were
available, which made it possible. Lack of deicing device on the aircraft prevented
working at greater altitudes.


Visibili
ty at JPR was 10 km, and a huge squall line was visibly approaching from the
west, drowning the territory where we aimed to work with the fires. We had to fly
SSW instead of SE to bypass the huge storm.

The local cloud base near JPR was at 4.5 kft, reachin
g pick concentrations of 3000
droplets cm
-
3. I was amazed by the large concentrations for not heavily smoky
conditions, but the visibility was quickly reducing to a point where the ground was
only poorly seen from cloud base level.


0
500
1000
1500
2000
2500
3000
3500
4000
0
0.5
1
1.5
2
2.5
3
3.5
4
64200
64220
64240
64260
64280
64300
SPA20020928_173713_Spect ra
Ntot
Def f*100
LWCsp
KLWC
Xmax mm
Ymax mm
N [cm
-3
], Deff [
m
m*100]
LWC [g m
-3
], Max Size [mm]
Nsec
175128-175008_1700m

Fig. 1: Clouds in th
e growing part of the squall line, at 5.5 kft, at

S
662.11

W
1621.6
.


A few large raindrops fell already, and we reached an area where everything was
growing towers all around us. We could not conduct organized penetrations in this
stuff, so I requested th
e pilots simply to gain altitude up to 15 kft while going through
non precipitating clouds, using the aircraft radar to avoid precipitation.

We continued climbing towards the SW, penetrating convective elements and
intervening less convective pieces of clo
uds. The convective cores had only moderate
updrafts of about 1000’ min, although the pilots were concerned of the turbulence.
The convective elements reached up to 2000 drops cm

3, whereas to more mature
detrained cloud elements contained 1000
-
1500 dropl
ets cm
-
3.

The widening of the droplet spectra (Fig. 4) was slow with height, ut somewhat less
extreme than the clouds on 24 September. The broadening was insufficient to produce
warm rain at the 15 kft level.


0
500
1000
1500
2000
2500
3000
3500
4000
0
1
2
3
4
5
6
65515
65520
65525
65530
65535
65540
SPA20020928_173713_Spect ra
Ntot
Def f*100
LWCsp
KLWC
Xmax mm
Ymax mm
N [cm
-3
], Deff [
m
m*100]
LWC [g m
-3
], Max Size [mm]
Nsec
181157-181218_4465m

Fig. 2: The highest cloud that we measured,
at 15 kft, at

S
66
2
366

W
16
2
963.





Fig. 3: The area that we penetrated the cloud in Figure 2. Photo taken at 15 kft, 18:14
GMT. The clouds do not look very vigorous and produced only modest updrafts.


0.01
0.1
1
10
100
1000
0
10
20
30
40
50
DSD20020928
1487m
1721m
2035m
2332m
3774m
4431m
N [cm
-3
]
Drop size [
m
m]

Fig. 4: Vertical evolution of cloud droplet spectra
.

The aircraft radar showed echoes only in clouds with tops well above our flight level
of 15 kft. The few precipitation particles that we hit sounded as graupel. We
transmittd to the INPE aircraft the coordinates of our work area, for them to monitor
the
aerosols. However, when they came after two hours, the clouds have precipitated
and the extensive downdrafts changed the whole boundary layer.

Again the 200X probe detected already near cloud base about 0.5 particles per liter at
the size range of 50 to 40
0 micron, with peak at about 170 micron. The concentrations
of these particles increased to about 1 per liter at 15 kft, their maximum size increased
slightly, but the mode remained below 200 micron. The making of these particles is
an outstanding question

that needs an answer.



0
500
1000
1500
2000
2500
3000
3500
4000
0
0.5
1
1.5
2
2.5
3
3.5
4
68650
68700
68750
68800
68850
68900
SPA20020928_173713_Spect ra
Ntot
Def f*100
LWCsp
KLWC
Xmax mm
Ymax mm
N [cm
-3
], Deff [
m
m*100]
LWC [g m
-3
], Max Size [mm]
Nsec
190440-190805_2000m

Fig. 5: Passage across a smoky squall line at 7 kft, from
S
66
2
809
W
16
2
264 to
S
66
2
659
W
16
2
202. The front part (left) smelled very smoky. It became very dark with the
continued penetration at 19:07:00, but still did not precipitate
d. Large raindrops fell
towards the last part, as detected by the 200Y probe and vividly heard and seen on the
windshield.



We descended through clouds continuing to the SW. At 18:41 we passed through at
cloud which smelled smoky (2100 m, at

S
66
2
872

W
16
2
146). It reached a peak
concentrations of 3350 drops cm
-
3. The SPP100 was grossly overestimating the
water contents in the high concentrations, suggesting a serious problem of
coincidence. I estimate that there is an undercounting by a factor of at least
1.6 in te
more severe cases, which brings the peak concentrations to exceed 5000 droplets cm
-
3. The drop size is overestimated respectively.


On the way back to JPR we had to cross the squall line, because it has propagated
through JPR and was between us a
nd JPR. The cross section took us through a very
dense and dark cloud, which made it feel pretty dark. We should have had a dense
cloud with small drops and large water contents for many km above us to cause such a
dramatic darkening. The cloud was quite s
moky after entry, and reached a peak
concentrations of 3400 droplets cm

3. From this point the concentrations decreased
gradually to about 2000 cm

3 at the rear part of the squall line, bordering the
stratiform rainfall. The droplet effective diameter at

7 kft increased from 5 to 15
micron, which is still way below the size allowing warm rain processes. The small
starting diameter suggests that the front of the gust front cloud was a shelf cloud, with
roots above the boundary layer, which lowered gradual
ly. This squall line produced
very strong winds in JPR. Earle Williams counted at the radar site 5 lightning flashes
per second, using the filed mill.


The last leg to JPR took place in an extensive trailing stratiform precipitation with low
stratus clouds
, and fog patches coming out of the forest.

We landed in stratiform rain at 19:38 (15:38 local time).