WMONEX 17 December 1978. Airborne cloud photographs

Charles Warner 18 Jan 2013

In the same manner as with page2.html, and supplementary to it, this study of winter monsoon clouds follows earlier collaboration with Joanne and Robert Simpson at the University of Virginia. This page shows various interesting cloud formations, notably "slender" cumulus humilis (Warner 1982). This was an error; the cumulus were narrow rather than slender, and the semantic error is now corrected. Slides by Joanne and Robert Simpson together with Warner's black and white film have been used here. A weak vortex disturbance occurred off Borneo on 16 and 17 December. One may go straight to the findings of this study. (back to main page).

1330 local time, 17 Dec 1978. Infrared satellite image. The line of latitude 10°N is shown, and the longitude 110°E. The size of the view is about 1400 km N-S by 1600 km E-W. Bands of cloud down the South China Sea persisted with minor changes of shape and intensity during the period. The track of the aircraft is shown, at altitude 6.4 - 7.8 km (pressure 470 - 390 mb). Along this track, arrows show the locations and directions of view of photos following, labelled occasionally with local times (UTC + 7.5 h). Click on times or selected arrows to go to the indicated photo. The infrared channel is here found to be sensitive to dense high overcast, and not low clouds. Patterning was dominated by diurnal influences.

0928. 3.4°N, 103.5°E, altitude 6.4 km on 060° azimuth.
A pan of two slides by RHS at the coast. (back)

After much flight near stratus layers and above shallow cumulus, an overcast was briefly encountered below flight level:
0348
1118. about 10.1°N, 111.4°E, altitude 6.8 km on 320° azimuth. (back)

At the northern extremity of the aircraft track conditions remained undisturbed with many layers of cloud:
0427
1157. 11.9°N, 113.8°E, altitude 7.4 km on 060° (left) and 240° (right) azimuth. (back)

0439
1209. 10.8°N, 114.4°E, alitude 7.4 km on 060° azimuth.
Lines of small cumulus aligned roughly N-S, mostly confined below the level of stratus. (back)

0446
1216. 10.4°N, 114.7°E, altitude 7.4 km on 030° azimuth.
Cumulus confined below the level of stratus, and arcs of stratiform cloud oriented towards the east. (back)

0448
1218. 10.3°N, 114.8°E, altitude 7.4 km looking N.
Looking back on arc seen above. (back)

0449
1219. 10.2°N, 114.8°E, altitude 7.4 km on 240° azimuth.
Cumulus humilis at quite large number density were sheared towards azimuth 330, indicating relative winds below this level from the opposite direction.
The coastline of an atoll may be seen in the middle of Joanne's view. (back)

0455
1225. 9.7°N, 115.1°E, altitude 7.4 km on 030° azimuth.
Narrow small cumulus sheared towards the north. From the narrow widths, unstable stratification and an absence of subsidence at the level of the clouds is inferred. Note (in stereo) the presence of stratus between the top of the largest cumulus and flight level. (back)

0459
1229. 9.4°N, 115.3°E, altitude 7.4 km on 060° azimuth.
Note the evident feebleness and intermittency of cumulus updrafts, and the arrest of ascent at a stable layer where the cloud is spread out. (back)

0500
1230. 9.3°N, 115.3°E, altitude 7.4 km on 140° azimuth.
By RHS from the cockpit. The anvil was towards roughly azimuth 250. Note the absence of marked wind shear through flight level:
local cumulus towers were nearly vertical. (back)

0505a
1235.05. 8.9°N, 115.55°E, altitude 7.4 km on 240° azimuth.
The top of a cumulus evaporating at flight level. The last remnant of updraft may be perceived, with fallout below.
Cumulus were rising gently through unstable stratification. (back)

0505b
1235.09. 8.9°N, 115.55°E, on 240° azimuth.
The same view taken a few seconds later. The interval between right and left eye views was minimal, about a second.

0509
1239. 8.65°N, 115.7°E, altitude 7.4 km on 040° azimuth.
A small patch of narrow cumulus humilis, denoting locally an absence of subsidence accompanying unstable stratification.
The humilis were sheared towards about azimuth 050, indicating a low level wind maximum from 050. (back)

0515
1245. 8.3°N, 116°E, altitude 7.4 km on 045° azimuth.
Photos by Joanne Simpson. Linear features of narrow cumulus fractus and humilis. Winds were not strong near the surface.
Note the areas with a total absence of cumulus. The tall congestus was very roughly 70 km distant. (back)

053009
1300. 8°N, 115.2°E, altitude 7.8 km on 180° azimuth. Left half of pan by RHS.
05301230
1300. 8°N, 115.2°E, on 270° azimuth. Right half of pan by RHS. Strong ascent. (back)

0531
1301. 8°N, 115.2°E, altitude 7.8 km on 160° azimuth.

0540
1310. 8°N, 114.3°E, altitude 7.8 km on 210° azimuth.
Strong ascent. (back)

0548
1318. 7.7°N, 113.6°E, altitude 7.8 km on 140° azimuth.
Quite a thick anvil at altitudes through flight level. (back)

Much of the return part of the flight was in cloud, with no photos taken.

0725
1455. 3.5°N, 106°E, altitude 7.8 km .
Pan from cockpit by RHS. On azimuth 165° (150 left and 180 right). Streets are of orientation 230 - 050°
and suggest relatively strong winds from 050° at low levels. (back)

0735
1504. 3.4° N, 105.4° E, altitude 7.8 km on 040° azimuth.
Similar to the view following, a difficult partial cross-eye stereo-pair between a color slide by RHS and black and white film by Warner.
Taken at the time of a loop for tests of wind measurement. (back) (back to main page) (back to web design)

0736
1506. 3.5°N, 105.6°E, altitude 7.8 km on 030° azimuth.
Near the surface, streets were aligned along 320-140°, probably close to the wind orientation. Rows of narrow humilis were aligned along 290-110°. The tops of the cumulus humilis were sheared towards 330°, implying relative flow from this direction.

Findings

This case is consistent with others in that strong ascending motion occurred in very restricted areas, and in that there was great variety in formations of clouds.

Several instances have been shown here of narrow cumulus humilis, stemming from shallowness of roots in the sub-cloud layer. This appears to accompany both unstable stratification and an absence of subsidence. Systematic search for appearances of narrow cumulus humilis has shown no particular circumstances of occurrence. They appeared occasionally on nearly every mission in WMONEX. There is a variety of mechanisms of response to forcings on larger scales. (back to main page)