11.2: Air Masses
- Page ID
- 46268
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)An air mass is an extensive body of air featuring generally similar temperature and moisture characteristics. They can extend thousands of square kilometers. Air mass are identified based on their temperature and humidity characteristics as well as their geographical region of origin. For example, if an air mass is dry and warm and originated from the tropical region over a continent, it would be called a continental Tropical (cT) air mass. If an air mass is humid and cold and originated over the ocean in the high latitudes, it would be called a maritime Polar (mP) air mass. The air mass name will always begin with a lower-case letter signifying either continental (c) or maritime (m) and a second capital letter signifying Equatorial (E), Tropical (T), Polar (P), Arctic (A), or Antarctic (AA).
Maritime air masses are humid air masses originating from oceans or large bodies of water. Continental air masses are dry air masses originating from land. Equatorial air masses are warm moist air masses originating from the equatorial region. Tropical air masses are warm air masses originating from the lower latitudes. Polar air masses are cold air masses originating from the upper latitudes. Arctic air masses are composed of extremely cold air that originated from the poles. Arctic air masses are even colder and drier than Polar air masses, and Antarctic air masses are even more extreme than Arctic air masses.
The common types of air masses are maritime Tropical (mT), maritime Polar (mP), continental Polar (cP), continental Tropical (cT), and continental Arctic (cA).
- Maritime Tropical (mT) air masses are warm, humid air masses originating from the oceans in the tropics.
- Maritime Polar (mP) air masses are cold, humid air masses originating from the oceans in the polar latitudes.
- Continental Polar (cP) air masses are cold, dry air masses originating from land regions in the polar latitudes.
- Continental Tropical (cT) air masses are hot, dry air masses originating from land in the tropics.
- Continental Arctic (cA) air masses are cold, dry air masses originating from the North Pole.
- Continental Antarctic (cAA) air masses are extremely cold and dry air masses originating from land at the South Pole.
See the below image to visualize where these different types of air masses typically originate.
Creation of Air Masses
Air masses develop when air is present over a surface for an extended period of time. This typically occurs in a high pressure system with light wind. The areas where air masses develop are called source regions. Air masses over warm surfaces usually develop faster than those over colder surfaces because there is weaker turbulence in the stable air over the cold surface. When air masses shift from their source regions, they change over time due to the surfaces and terrain over which the air masses flow.
Movement of Air Masses
Air masses do not remain over their source regions permanently. Slight changes in weather patterns may shift the air mass to a new location. As air masses move, two things can occur. First, as the air shifts over the different surface characteristics, the air mass begins changing. This process is called air mass modification. For example, an mP airmass that moves from the Pacific ocean over the mountains in the western continental US will typically dry as it crosses the mountains, rains out its moisture, and warms over the land surface until it becomes a cT airmass. The second thing that happens when air masses move is that they may collide with other air masses. When a collision occurs, the two air masses develop a boundary called a front.