Science Facts - Lapse Rate Overview

Lapse Rate refers to the decrease in temperature with altitude ... unless a specific qualifier is used - such as pressure, wind, humidity, and the like. *

Lapse Rate = -dT/dh 
The negative of the change in temperature divided by the change in height

For scientific purposes, the lapse rate is expressed as °C/km, for aviation purposes, it is expressed as °F/1,000 ft

On these pages, I prefer to use the incorrect change in temperature with height which provides a negative value when the temperature decreases with height. (By definition, Lapse Rate is a positive value.)

Layer		dT/dh
Layer		°C/km	°F/1,000 ft
Troposphere	DALR	-9.8	-5.4	Computed
	SALR	-4.9	-2.7	Variable, -3 to -9.8
	ELR	-6.5	-3.6	Defined average
Tropopause		0.0	0.0	Ideal
Stratosphere 1964		3.0	1.6	Warmer with height
Stratosphere 1976	Lower	1.0	0.55	Warmer with height
Stratosphere 1976	Upper	2.8	1.5	Warmer with height

Interactive Graphs

I have provided several interactive graphs to help demonstrate these concepts.

Seasons	This compares the seasons - winter, spring, summer - and has notes explaining DALR, SALR, ELR
Winter	2 days in February
Summer	4 days in August

These graphs plot real data from NOAA.
The graphs include 2 representations of the standard atmosphere - 1964 & 1976
3 adjustable controls allow you to move the DALR, SALR, and ELR lines left and right

Additional user interface features

Individual series can be hidden via the checkboxes
Series colors are user configurable - click the color boxes
The lower graph provides zoom and scroll control

The data comes from noaa - just navigate using

Maps/Charts / By Station / United States / Jacksonville

I just picked a few records for Jacksonville, Florida that appeared to not have any clouds. They are representative for a coastal city near sea level - Winter, Spring, Summer.

The data files are typically for 00:00 UTC and 12:00 UTC. (The standard collection times are 0000, 0600, 1200, 1800 UTC.) Because Jacksonville is 5 hours earlier, these should be 7:00 pm and 7:00 am local time, respectively ... ignoring daylight savings time. As a result, the 00:00 (7pm) surface temperature is almost always warmer than at 12:00 (7am).

Notes

The graphs are a little weird - the temperature is on the x-axis, and the altitude is on the y-axis. On the one hand, this makes a lot of sense. However, it took a while to get use to the lapse rates. Because the lapse rate is the change in temperature over the change in height, and because temperature is on the x-axis, the lapse rate lines have a slope of one over the specified value.

This means that the DALR (Dry Adiabatic Lapse Rate = 9.8°C/km) has a slope of

1/(-9.8°C/km) = -0.10km/°C

As the Lapse Rate increases (from 5 to 9) the slope decreases. This is counter intuitive and takes a while to get use to.

The SALR varies from about 3°C/km to the DALR (9.8°C/km), depending on the temperature, pressure, and humidity. In the graphs, it is shown as having a slope of

1/(-4.0°C/km) = -0.25km/°C

a good value for the lower troposphere.

When you actually measure the temperature at various heights, the average slope is between the DALR and the SALR. By international agreement, the ELR is 6.5°C/km. One of the reasons for providing adjustable lapse rate lines is so that you can see how close the ELR is to the measured values.

The graphs also let you see that the surface and tropopause temperatures differ significantly from the standard model. This was a consideration in selecting those specific data sets.

The tropopause is interesting - by definition, the temperature is constant, but that is seldom observed. Both the height and thickness of the tropopause varies with season and latitude.

Author: Robert Clemenzi