A Two-parameter Representation of the Normal Temperature Distribution of the 1,000—500 mb Layer

Height normals for 1,000, 700 and 500 mb, published by U.S. Weather Bureau, have been used to study the normal temperature field of the 1,000—500 mb layer by means of a simple model. In this model the normal temperature-height curve is replaced by one having a temperature lapse-rate independent of height in such a way that the thicknesses of the sub-layers 1,000—700 and 700—500 mb are correctly represented by the model. As a consequence, the temperature as well as its horizontal gradient and the thermal wind all have a linear variation with height and may be described in terms of two parameters, the temperature lapse-rate k and a “representative” 1,000 mb temperature τ₀.

Hemispheric maps for these parameters as well as the thermal wind at 1,000 and 500 mb have been prepared for the months January and July. The major frontal zones of the atmosphere appear clearly on the τ₀-maps in positions which agree essentially with those shown earlier by a number of meteorologists. The July map reveals, however, a strong baroclinic zone in high latitudes, surrounding the polar cap, not shown clearly in earlier presentations of the low-level baroclinity.

The k-charts disclose large horizontal variation in the temperature lapse-rate, and the charts for the thermal wind show that its variation with height is very pronounced in middle and high latitudes.