pressure (Pa) at sea level

height of the 1000 hPa surface

question 1

height

lowhigh850855

Pressure decreases with height at about 10 mb every 100 m 𝑑𝑝𝑑𝑧 =− 𝜌𝑔

A B

start with pressure at 1500 m MSL

then use hydrostatic balance to estimate the height of the 855 mb surface at B

then draw the 855 mb isobar

use the same method to estimate the height of the 850 mb surface at A

and to draw the 850 mb isobar

Note: density variations are secondary – to a first order, density (thickness) can be assumed constant.

question 2

Jan 2010

DZ1000,500

DZ1000,500

Jul 2010

Z500

Z500

Jan 2010

Jul 2010

question 3sea-level pressure

NHwinter summer

SH

Jan 2010 Jul 2010

Schematic zonal-mean cross section (after Palmen & Newton)

ITCZ

The Palmen-Newton model has three meridional circulation cells in each hemisphere

Note that the three-cell pattern ignores seasonal variation and land-sea contrast.

How strong are the meridional cells? (zonal mean)

NH winter

NH summer

Jan

July

HadleyFerrel

NHHadley

Ferrel SHHadley

note the broad belt of subsidence (12-52ºN) in winter and the broad belt of ITCZ ascent (0-30ºN) in summer.

In the NH winter, over continents, the northern Hadley cell rising branch crosses the Equator into the SH ITCZ, and its sinking branch extends between 12-50ºN

Effectively ascent dominates in the summer hemisphere, and sinking in the winter hemisphere, and the Hadley cell that straddles the equator is the strongest.

ITCZ

ITCZ

Structure of SLP, winds, temperatureseasonal march of sea level pressure and sfc winds

observations:- A see-saw SLP variation dominates over the northern continents, with highs in winter and lows in summer. The seasonal variation of the polar lows and subtropical highs over the northern oceans is also large, and is in opposition to SLP variations over land at corresponding latitudes.- The southern hemisphere is far more zonally symmetric.- Note the extremely low SLP around the Antarctic ice dome.

northern oceans:- polar lows: Aleutian, Icelandic- subtropical highs: Pacific, Bermuda

northern continents: - winter highs: Siberian, Intramtn - summer lows: Pakistan, Sonoran

southern oceans: - circumpolar (southern) low - subtropical highs (3 oceans)

seasonal march of surface air temperature

note that the amplitude of the annual temperature range is higher at:- higher latitudes- over land rather than over water [this does NOT occur in terms of net radiation Rn]- over large land masses, especially their eastern side

question 4

Speed for 1 = 4.1 m/sSpeed for 2 = 16.4 m/sSpeed for 3 = 10.8 m/s