Lab: Climatological Structure of the Atmosphere

Summary

The average of many individual weather events over time periods of a month or more defines the statistical characteristics of the atmosphere; this is referred to as "climate".

For example, some summer days are warm and dry, others are oppressively hot and humid; this is a weather statement. But summer in New York is always hotter than winter; this is a statement about New York's climate.

In this lab we are going to examine the monthly mean vertical and latitudinal structure of some of the basic variables that describe the atmosphere's climate and general circulation: temperature, humidity, zonal wind speed, and meridional wind speed. All of these are presented as average values over all longitudes (called a "zonal mean" since it is an average in the west-east, i.e. "zonal" direction) and over ten-year periods for each of the months of the year. The results can be thought of as representing typical cross sections of the atmosphere at one longitude.

The data that you will view were compiled from all available radiosonde (weather balloon) profiles over the ten year period. The data set contains numbers at all pressure levels and latitude bands because at least some observations have been made at all latitudes over this long a period of time. But the time average hides some important differences between one part of the world and another. In northern midlatitudes, where much of the latitude circle is covered by land and many of the nations have long been industrialized, the radiosonde network is dense and data are plentiful. But near the equator and in the Southern Hemisphere, where ocean covers a greater part of most latitude circles and many nations are just now developing, the radiosonde network is sparse and the averages are less reliable indicators of the true mean state of the atmosphere. In fact, the "Roaring 40's" of the Southern Hemisphere are almost entirely ocean, almost perpetually stormy, and are therefore rarely visited by humans. This part of the world is virtually unobserved by radiosondes. Thus, some parts of the climatology are more reliable than others. This sampling problem is the stimulus for the development of Earth-orbiting satellites that can observe every location on the planet and give us a true global picture.

Purpose

The purposes of this lab are to:

1. make you familiar with how meteorological parameters vary vertically, latitudinally (equator-to-pole and between the hemispheres), and seasonally,

2. make you think about how convective and baroclinic instability, and hence the occurrence of thunderstorms and synoptic-scale storms, vary over the world,

3. allow you to see the effects of differential insolation and the climate system's response to it, and

4. help you develop a deeper understanding of why different parts of the world have different climates.

5. introduce you to the use of the spreadsheet program Excel for the analysis of small data sets. If you jave never seen Excel, please go through the Introduction to Excel before coming to lab.

Reading List

• Peixoto, J.P., and A.H. Oort (1991). Physics of Climate. American Institute of Physics, New York.
• Legates, D.R., and C.J. Willmott (1990). Mean seasonal and spatial variability in gauge-corrected, global precipitation. International Journal of Climatology, Vol. 10, pp. 111-127.

Lab Instructions

Lab Report Instructions and Format

Excel Help - If you are unfamiliar with Excel, work through these Excel help pages.

Contributors:

• Audrey Wolf, GISS
• William Kovari, GISS