Notes on Tephigram

A tephigram is a graphical representation of observations of pressure, temperature and humidity made in a vertical sounding of the atmosphere. Vertical soundings are made using an instrument called a radiosonde, which contains pressure, temperature and humidity sensors and which is launched into the atmosphere attached to a balloon.

The tephigram contains a set of process curves which are used to describe various processes in the atmosphere. These lines include:

Isobars - lines of constant pressure (horizontal slightly curving, grey)
Isotherms - lines of constant temperature (sloping left-right, orange with 0C in Blue)
Dry adiabats - related to dry adiabatic processes (potential temperature constant) (sloped right-left, purple)
Saturated adiabats - which are related to saturated adiabatic processes (wet bulb potential temperature constant). (curved, green)

On the tephigram there are two kinds of information represented:

The environment curves which describes the structure of the atmosphere. These are Temperature (Red) and Dew Point (Green)

The process curves which describes what happens to a parcel of air undergoing a particular type of process. (eg. Adiabatic process).

In addition, on the right hand side are wind direction and speed and heights at the standard levels. Wind is shown in wind-arrow format with the head of the pointing to where the wind is going and the strength given by the feathers – a long feather is 10kts, a short feather 5knots and a triangle 50kts. Add the feathers to get the speed.

Tephigrams can be used by the forecaster for the following purposes:

- to determine moisture levels in the atmosphere
- cloud heights
- to predict levels of convective activity in the atmosphere
- forecast maximum and minimum temperatures
- forecast fog formation and fog clearance
- detect the presence and height of inversions