Archive for the ‘Meteorological’ Category

2014, July, Noctilucent Clouds

Wednesday, July 9th, 2014

Spaceweather.com, and other observers, predicted that Noctilucent Clouds may be visible in early July 2014. From Ardgay the evening sky “just looked right/promising”.

In the night of 7th July both Phil in Ardgay and Pat in Balintore were, for an unknown reason, looking at the northern sky and saw noctilucent clouds at about 01:30 +/-. The view was basically to the north, in Ardgay slightly eastward.

Here are their proofs:

2014, July 7 Noctilucent Clouds by Pat RaeClick image to view

2014, July 7 Noctilucent Clouds by Phil

Simplified Geometry for observing NLC’s

Noctilucent Cloud Sighting Geometry

Spaceweather.com has this to say about Noctilucent Clouds:

NLCs are Earth’s highest clouds. Seeded by “meteor smoke,” they form at the edge of space 83 km above Earth’s surface. When sunlight hits the tiny ice crystals that make up these clouds, they glow electric blue.

In the northern hemisphere, July is the best month to see them. NLCs appear during summer because that is when water molecules are wafted up from the lower atmosphere to mix with the meteor smoke. That is also, ironically, when the upper atmosphere is coldest, allowing the ice crystals of NLCs to form.

The natural habitat of noctilucent clouds is the Arctic Circle. In recent years, however, they have spread to lower latitudes with sightings as far south as Utah and Colorado. This will likely happen in 2014 as well. Observing tips: Look west 30 to 60 minutes after sunset when the Sun has dipped 6o to 16o below the horizon. If you see blue-white tendrils zig-zagging across the sky, you may have spotted a noctilucent cloud.

It seems our ’sunset / sunrise’ lasts all night as far as seeing phenomena like noctilucent clouds.  It just remains for you be awake, there to be few obscuring clouds, and tiny ice crystals at just the right position between you and the sun.

Aurora, October 2012

Wednesday, October 10th, 2012

Russell managed to see the northern lights on Monday night as a large parcel of cosmic rays ejected from the sun came sweeping through our atmosphere. Continue reading “Aurora, October 2012” »

Cloud Iridescence

Tuesday, January 17th, 2012

Before dawn on 12th January, 2012 observant watchers of the southeastern sky would have seen two persistent, small clouds which held the imagination.  They were of a lenticular shape but their colour was classic ‘mother of pearl’.

2012-01-12-Iridescent-01Viewed from Tain.Click image to view

3463-first-sightViewed from Ardgay.

These clouds were very bright even though sunrise was 20 or 30 minutes away.  This timing and the presence of other small, low, very dark clouds in the same view indicated these iridescent clouds were, from a very high position, catching (and refracting) sunlight that the darker, lower clouds were not.

An additional special feature was virga below both clouds.  This developed as one watched and succeeded the clouds, being faintly visible after the original cloud was all but vanished.

Additionally, a clear anvil developed at the top of one cloud – shown in the picture gallery by clicking an image.

There are a few names that could be attached to these clouds: Lenticular, Nacreous, Polar Stratospheric, Iridescent.

Nacreous clouds typically look very filamentous and cover wide areas of the sky, and have the same mother of pearl colouring seen here and are similarly very high in the sky, visible after sunset or before sunrise.

Iridescent clouds are ‘normal’ but sunlight passes through them at the precise angle to display a spectrum of colour, as in this case.  The spectrum can be affected by the cloud composition as well – that may be water droplets, ice crystals, or nitric or sulfuric acids in water.

Here are some references for these types of cloud:

Iridescent Clouds

Polar Stratospheric Clouds, or also Nacreous Clouds

Cloud Iridescence

Virga , or fallstreaks, or precipitation shafts

Lenticular Clouds, HERE or HERE

This whole cloud performance was over in 15 minutes.  Watchers before or after would have no idea what took place.

EPOD ( a service of NASA’s Earth Science Division and the EOS Project Science Office (at Goddard Space Flight Center), and the Universities Space Research Association ) has suggested that these clouds were Nacreous Clouds and they have published David’s photo as their photo of the day on Valentine’s Day – see comment, below, of 15th February.

Visible virga
From Ardgay, start of virga
2012-01-12-Iridescent-03
3474-virga-and-anvil
2012-01-12-Iridescent-04
3478-nonzoom
3482-virga-afterward

Nacreous Clouds over Sutherland

Friday, July 30th, 2010

Last night, 29th – 30th July, there was a great display of Nacreous Clouds, or 2, at 03:00, early morning of the 30th. Continue reading “Nacreous Clouds over Sutherland” »