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Meteorologists frequently refer to thermodynamic diagrams called "Tephigrams". These show the vertical distribution of temperature, moisture and winds in the atmosphere over a place and at a specific time. The diagram can comprise pure model data from sophisticated computer models or they may be a snapshot of the atmosphere over a particular place made up of actual readings made by a weather balloon carrying a small radiosonde and launched over a particular location.

As the balloon ascends the radiosonde transmits its precise location from an on board GPS locator, it also transmits its temperature and relative humidity from tiny probes on board, and its pressure as read by an on board miniature aneroid barometer. By knowing the radiosonde's precise location in time and space its is easy to calculate the wind and each level of the atmosphere as it ascends.

The radiosonde data is streamed constantly to a receiving station (from where the balloon was released) and then coded into a standard format before being sent around the globe by a sophisticated global telecommunications system (GTS).

Radiosonde data is ingested into computer model systems, together with surface observations, satellite, aircraft, ship and ocean buoy data to assist with the production of short term and long term weather forecasts. Such data from all around the globe is facilitated by the World Meteorological Organisation's global data monitoring system - an international border-free exchange of weather information.

In the image we can see on the left a cross-section of the the atmosphere over the lower North Island as observed by the Paraparaumu balloon flight which was launched around midnight last night. The tephigram from the balloon flight shows the winds on the right hand side as barbs, showing that the winds were all pretty much blowing from west to northwest with speeds between around 35-65km/h.

Also on the tephigram we see two traces, the air temperature (on the right) and the dew-point temperature, derived from the humidity as measured by the radiosonde (on the left). Where the temperature and dew-point are close together, the diagram indicates clouds in the atmosphere.

On the right hand side we see an image captured by the Masterton webcam. I have indicated the clouds on the webcam corresponding to their positions on the Paraparaumu tephigram and there is very good agreement. The heights of each cloud layer as seen on the webcam are labeled on each arrow, which corresponds to their position on the tephigram.

Read more about clouds and the tephigram at ^AB

Original author: New Zealand Weather Network
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