Setting: Flight passing the Cumulonimbus cloud "Hector"
above the Tiwi-Islands in the north of Darwin. AreaMap3.bmp shows
the flight track of the airplane and the setting. The images were
taken between 5:21 p.m. and 5:45 p.m. local time at Darwin. So they
cover a period of 24 minutes which means a flight path of around
200 km. By this time the airplane reached its cruising altitude
of 11580 m at an outside temperature of - 58 deg C.
Background: The cloud system Hector was investigated during the SCOUT-O3 field campaign in November/December 2005 with two research aircrafts. These were the Russian high-altitude research aircraft Geophysica and the German research airplane Falcon, operated by German Aerospace (DLR). Hector is a tropical, high-ranging Cumulonimbus cloud system that almost regularly arises each day over the Tiwi-Islands near Darwin. The Tiwi-Islands are located offshore in the north of Australia. They have a size that allows two land-sea wind systems to occur simultaneously, so that both flows converge on the island. Therefore extremely strong upward convection is formed where both flows meet each other.
In figure AreaMap.jpg the green line shows the typical flight track
of the high-altitude research aircraft Geophysica. According to
its development stage Geophysica was able to reach the Hector complex
from the green line. In order to make in-situ measurements of particle
properties and several trace gases, Geophysica descended from a
cruising altitude of 21 km and dived into the anvil from the top.
During the SCOUT-O3 field campaign the upper limit of the anvil
varied between 16 and 19 km altitude.
Series of images: The aircraft flew towards the Tiwi Islands (start CbHector0.jpg) and then passed them on the west (from CbHector20.jpg on). The central tower ("hot tower") as well as the anvil can be clearly seen. For example in CbHector17.jpg, the form of the clouds reflect the direction of the land sea-wind flow. The anvil is asymmetric and covers a large area. The airplane travelled below the major area of the anvil and moved further below it a long way in direction to Singapore (look at CbHector 34.jpg). You can recognize at the last images of the series that the anvil of the Hector Cb clouds is located above the cruising altitude of 11580 m.
The airplane was still recognizable below the cirrus shield of
the anvil 45 minutes after the first image was taken. Depending
on the flight velocity this corresponds to over 450 km. Because
of the outside temperature of - 58 deg C at the cruising altitude
of the QF81 it can be concluded that the cloud layer of the anvil
consists of ice particles. During the SCOUT-O3 field campaign the
measured temperatures at the upper limits of the anvil were between
-70 and -85 deg C. This is so low that liquid water even cannot
exist in form of small droplets anymore. In chapter Cb
Hector II it is shown how "Hector" looks like from
Geophysica.jpg: S. Borrmann, Darwin, Northern Territories, Australia,
25 November 2005, 12:29 p.m. local time
CbHector0-34. jpg: S. Borrmann, Flight Quantas QF81 from Darwin,
Northern Territories, Australia to Singapore, 5 December 2005, start
5:10 p.m. local time