pressure (Pa) at sea level
description
Transcript of pressure (Pa) at sea level
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