What do OAT and RAT mean?

From FlightSim

OAT=Outside Air Temperature is the temperature of the undisturbed air stream. TAT=Total Air Temperature =RAT=Ram Air Temperature is the OAT plus the temperature rise due the complete slowing down of the air stream in the temperature sensor.

ISA= International Standard Atmosphere.

The measured temperature is in reality the Ram Air Temperature (RAT). It is the Outside Air Temperature (OAT) increased due forward speed. The difference is the ram air temperature rise.

A typical value is after take off with an indicated airspeed of 170 kts a rise of 3 degrees C which is 5.4 F.

At 30.000 ft with a DIAS of 280 kts or M.74 at OAT of - 45 degrees C ( -49 F) the rise is 26 degrees C or 46 degrees F.

The conversion from RAT to OAT is done electronically in the instrument system. In this atmosphere the sea level temperature is 15 deg Celsius or 59 deg Fahrenheit. This temperature decreases with 2 deg C or 3.6 deg F with every 1000 ft increase in altitude until reaching the tropopause altitude after which altitude the temperature is is assumed to stay constant. Dew point is the temperature at which the present humidity in the air would be 100%. so if the present temperature decreases due f.i. radiation you get closer to the dew point. And when dew point and temperature coincide you have a good chance of fog.

Saturated Air Temperature I'm not sure about.

I think it might be what in my language is called the wet bulb temperature. The thermometer bulb is surrounded by wet cotton. The water is evaporated by ventilation and thereby decreasing the temperature. The dryer the atmosphere the lower the subsequent temperature. The difference in temperature is a measure of the humidity.

Antoon Amesz