Crepuscular rays in desert dust

After the twilights had been getting normal through the past three weeks, where hardly any volcanic aerosoles from Sarychev volcano had been measured, I was very astonished when I saw an intense purple light with crepuscular rays about half an hour before sunrise (sun elevation at -6°) in the morning of November 17. The crepuscular rays crossed the whole sky near the horizon, converging at the antisolar point (1 - 2 - 3).

Of course I immediately asked my colleagues from the Hohenpeissenberg observatory about the phenomenon. And I got a very surprising answer:
At that moment there were two different layers of dust from the Sahara desert above us, a lower one at an altitude of about 8.5 kms with dust from the western parts of the Sahara, and a higher one at about 11 kms, which contained dust from the eastern part of the Sahara. There were two different currents of air at higher levels which overlapped each other above the Alps.
It is new for me to learn that such twilights are also possible in desert dust, just as this dust up to now only caused a kind of certain dimness in the air. But at that moment there was no desert dust directly above us; I only looked into the layers of dust.

However, there was an extra bonus on the next morning. Unfortunately could only watch it from the valley:

Twinned rainbow

Mark Worme observed this rainbow today at around 3.15 pm Atlantic Standard Time in central Barbados facing east. At first he only noticed the double rainbow, but then he realized the lower one was split.

During a heavy rainshower, a twinning of the upper part of a rainbow can sometimes be observed, which often lasts from a few seconds up to several minutes. As for a long time there were only few observations of this phenomenon available, only speculations could be made about its origin. Only in the past few years, this twinning could be registered more often by continuous observations, and due to some detailed descriptions, new theories could be advanced. As in all observations both bows are of equal brightness, light refraction on ice particles can be ruled out. Most probably is that raindrops of a non-spherical shape produce one of these bows or even both of them. Due to surface-tension, small rain droplets hardly change their shape when falling, but large drops can be flattened by the air resistance. The more flattened they become, the smaller is their refractive index. So the sunlight has to fall upon water drops of different size at the same time to make the twinning appear. As this twinning was up to now observed under big shower or thunder clouds which formed in hot air, it can be supposed that the small, not flattened raindrops evaporate at a short distance below the cloud basis. This would explain why the twinning can only be seen for a short time and exclusively in the upper part of the rainbow. It should be important to determine the radius of the rainbow when the twinning is observed, and to record the weather situation at the time the twinning appears as exactly as possible.

Shadows and lights of a flight

Many people find flights boring - but not all! If you are lucky to be seated by a window you can always find something interesting in the air beside or below the airplane. David Lukacs from Hungary took this picture on 2nd November 2009 on a flight from Rome to Budapest, about 15 minutes after the departure. A thin layer of haze was between the plane and the sea so the sun shining on the right side above the plane could cast radial shadows on the left below. The beams of shadow and light join at the antisolar point.



A bit later when the plane travelled above a cloud layer David also noticed a nice glory below them:



Even the shadow of the airplane appeared in the middle:

Thunderstorm shadows

In the evening of June 29, 2009, several thunderstorms formed unexpectedly over northwestern Germany, from the Ruhr area northward to southern Lower Saxony. They brought rainfalls up to 30 liters per square meter.

As the sun was almost setting, the shadows of the storm clouds reached a length of several hundred kilometers. The satellite picture taken at 19.15 UTC = 21.15 CEST shows the shadows extending even up to Thuringia and northern Bavaria.

Unfortunately, there are no reports on crepuscular rays from the area southeast of the thunderstorms.

Author: Peter Krämer, Bochum, Germany
Satellite image with kind permission of DWD (German Weather Office)

Interference Phenomena on Soap Bubble Surface

Inspired by my daughter who was playing with soap bubbles, I one day got the idea to take photographs of the surface of soap bubbles.

For this purpose I filled a big dark frying pan with water and put some dishwashing liquid in it. I mounted my little digicam on a clamp pod (figure 2) and aligned it roughly with the pan.
Then I blew some bubbles into the water using a drinking straw. Now I aligned the camera exactly with the vernier adjustment of the clamp pod and started photographing.

Already the first pictures turned out well, and a short while later I had made a considerable amount of pictures. I soon noticed a remarkably large variety in the positioning of the different colours on the soap bubbles. At first, the distribution of colours on the bubbles looked like a piece of abstract art, but later the colours arranged to parallel stripes, similar to a rainbow.

The reason for this play of colours:

The physical reason for these colours is the so called two-beam interference. This is remarkably well explained at http://www.itp.uni-hannover.de/~zawischa/ITP/zweistrahl.html (German) and http://www.itp.uni-hannover.de/~zawischa/ITP/twobeams.html(English).

The main statement in this explanation is that the colours depend directly from the optical length of way (and so from the thickness) inside the the soap layer. This is an explanation as well for the black “holes” at the highest point of the bubbles, as also for the colourful rings below these “holes”. The colourful flaws, which can be seen especially on “fresh” bubbles, are areas of different thickness of the soap layer, which are (still) positioned irregularly. Following the force of gravity, they slowly flow downwards causing the soap layer to be thinner at the top and thicker at the bottom of the bubbles. The constantly the thickness of the soap layer increases from the top to the bottom of the bubbles, the more regularly is the positioning of the colourful rings.

The Picture above show a detail on the surface of a soap bubble.

Figure 2: Camera mounted on a c-clamp. The distance between the camera lens and the soap surface is here about 4 cms.

Figure 3: Abstract play of colours on the surface of fresh soap bubbles.

Figure 4: The lesser the flaws in the soap layers are, the more regular is the increase of the thickness of the soap layer towards the bottom of the bubbles, and so is the play of colours. The spotted dark areas on top of the bubbles indicate that the bubbles are about to burst.

More pictures: 5 - 6 - 7

Author: Reinhard Nitze, Barsinghausen, Germany

Intense colours of a lightrefraction on fireweed seeds

This year the season of my firweed-hunt began earlier than last year because in hope of a better lightrefraction on early seeds. It was about mid-july when I saw the first seeds falling and I was very surprised when i moved the seeds beetween the sun and my camera. The effect was extremely strong. I guess this came from the fresh seeds, they were not sticked together like last year and showed real bright colours. I shot about 20 pictures and afterwards I went alomost crazy when I saw these intense clours on my PC. The pictures (1-2-3-4-5-6-7-8) were taken with a Canon EOS 350D and a Tamron AF 70-300mm Makro lense near Langgoens in Germany.

Author: Rolf Kohl, Langgöns, Germany

Reflected light dewbow on water surface

I and my wife Eliisa Piikki got a hint about a light phenomenon on a lake nearby. Eliisa took some photos and there was a dewbow and a reflected light dewbow in those photos. They were formed on the waterdroplets that were settled down on the Chrysomyxa ledi needle rust (Small-spored spruce-Labrador-tea rust).

That rust can't be seen in Finland every year, but this year it is very common especially in the Eastern and in the Northern Finland. Because of the rust the young needles of some spruces are brown.

Author: Jari Piiki, Finland

Reflection rainbow (Lahti, Finland)

On the evening 5th of August 2009, there was a reflection bow observed at city of Lahti. Marja Wallin saw and photographed a small fragment of reflection primary bow.
For the moment, the precise location of sun ray reflection is not yet analysed... To see her other rainbow photos for same evening, look at here.

Update (11th Aug 2009):
There is another gallery existing of the reflection rainbow, in same date and location, taken by Sami Luoma-Pukkila.

image (c) Marja Wallin

Volcanic Twilights

On June 12, 2009, one of the most active volcanoes of the Kuril islands near Kamtschatka, which is situated near the northwestern end of the island of Matua, Sarychev Peak, erupted.

A NASA picture taken from the ISS gives an impressive sight of the eruption. Ashes have been ejected up to 20 kms into the atmosphere. Only a few hours after the eruption, the sulfur dioxide cloud of the volcano covered an area of 2.407 kms in width and 926 kms in length above the island. During the following weeks, the aerosoles spread over the whole northern hemisphere.

Since the end of June, also in Central Europe unusual twilights are observed. The up-to-date Lidar measurement from the Hohenpeissenberg observatory in Bavaria shows three aerosol layers in altitudes of 15, 18 and 22 kms in comparison to the eruption of Mt. Pinatubo. It is very interesting that the layers in 15 and 18 kms have come here with westerly winds passing over Alaska, Canada and the Atlantic Ocean, while the layer in 22 kms has been transported to us by stratospheric easterly winds passing over Asia (Russia/China). So the volcanic aerosoles have travelled around half of the planet in two different directions (the lower layers eastward and the upper one westward), meeting again here over Europe. I think this is worth to be mentioned.

On July 4, Peter Krämer observed the caracteristic crepuscular rays (picture above). On July 13, Reinhard Nitze photographed the most spectacular volcanic twilight in Barsinghausen near Hanover (Fig. 3). In his picture, the high aerosol clouds can easily be recognized. These clouds still receive sunlight while normal cirrus clouds are already within the shadow of the earth.








During the past few days, there were also noctilucent clouds visible, which passed over to the reddish aerosol clouds in lower layers. There should be unusual twilights visible also during the following weeks.

COMPOUND EYE OF A HORSEFLY

July 11, 2008:

I was very astonished when I was working and suddenly a horsefly fell upon my workbench.
The animal was about 3.5 cms in length. It was a very hot day, and the “flying fellow” had obviously lost his way, landed up in the workshop and could not find the way out. Well, the animal was lying there without moving, and the sunlight caused nice diffraction colours in its big compound eyes.

Author: Michael Großmann, Kämpfelbach, Germany