The natural Navigation: The Right Course, Naturally

The northerly winds were carrying high cirrus and contrails down towards the coast this morning. They have brought colder air, as forecast yesterday. This gave us our first frost of the season. The feel and even the sounds of the grass underfoot have a relationship with the direction the air is moving.

We were in the hot and wet season in Phuket last week. The skies were in constant turmoil at all levels. The warm humid air accelerated upwards in an often fruitless search for some air at the same temperature.

The Thai fishermen’s longboats had seen it all before and bobbed nonchalantly as the storms built and subsided on all sides, through the day and night.

This is the full moon from two nights ago, rising amongst the clouds. The picture was taken at about 11 o’ clock and so we are looking close to southeast.

I took this picture a week ago. It shows the lower fair-weather cumulus clouds against the upper cirrus clouds. It is not at all unusual to watch the lower clouds and upper clouds move in different directions and to feel a third wind direction on your face at the same time.

I had been working on the chapter about the sea in my book last week, so was even more finely tuned to its vagaries than normal as we crossed to the Isle of Wight on Saturday morning.

The sea’s colour is influenced by its depth, the colour of the seabed, salinity, microorganisms, silt and light levels to name a few factors.

The subtle shift in colour can be seen as the sea shallows to the coast off Ryde. The dark horizontal strip in the middle distance is caused by a thin cumulus cloud.

This morning was filled with a breezy walk up to Halnaker Windmill. The sun was out for most of the way up the hill, but the sky also had a generous share of cumulus clouds.

Natural navigation is a mixture of art and science and this can be felt very strongly when the sun disappears behind the clouds. Science allows us to understand the direction that the sun will be and there is an art to reading the cloud edges to reveal the direction of the sun, even when we cannot see it.

The low trees on the exposed hilltop had been groomed by the prevailing southwesterly winds. There were green, grey and gold lichens layering the various sides of the brick.

This morning’s sun was a strong enough clue, but if we wanted to know which way was southeast then these aircraft contrails are pointing the way to the continent.

It looks like a particularly busy morning for aircraft, but this is just a reflection of atmospheric conditions. The hydrogen-rich jet fuel has mixed with oxygen, reacted in the engines and formed, among lots of other lovely and not so lovely things, water. In certain temperatures and humidity levels this water freezes into ice crystals. The high cirrus clouds that we normally see are also composed entirely of ice.

The length of time that a contrail survives depends on the humidity, if the air is dry it will sublimate away, but if saturated they will last as long as other cirrus clouds.

I can remember sitting at a restaurant in the small and perfectly formed fishing village of Trehiguier in southern Brittany last July. I had my back to the sun, which was setting behind the row of houses behind me. I watched the crisp edge of a chimney corner move upwards and to the right as the sun slipped down and to the left behind me. My poor wife had to watch me gauging the sun with a fist and then outstretched fingers and then listen to me predict when the chimney shadow would reach our table.

Last night my wife was spared such ordeals as I was working outside, in a small patch of woodland. I watched the sun’s light moving up the trees in front of me. Unlike the crisp edges of the chimney shadow, the edges were blended. The shadows were moving upwards but not following discrete lines. The…

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Tonight’s early evening sky is a feast of cloud types. Cumulus, passing low and darkened by the shade, perhaps the last of the fair-weather clouds for a bit. Higher there is cirrus, cirrostratus and altostratus all heralding the approaching warm front. Thrown in for a bonus there are some contrails from aircraft heading to and from the continent.

Last night was one of those occasions where the moon was the natural navigator’s best option. At about 10pm the sky overhead was overcast with broken clouds down to nearer the horizon. The western glow of dusk was gone and the only objects that could be seen were Jupiter and the three-quarter Moon. The cloud meant no Polaris, and the bright moon in the only patch of open sky blotted out the other stars. The Moon plays hard to get at first but on nights like this it can be a very good friend.