Five Basic Laws Used by Meteorologists to Understand

the Evolution of Atmospheric Flow Patterns



1.      Ideal Gas Law (Equation of State) -- expresses the relationship of the pressure a gas exerts to the volume it occupies and its temperature. (The product of the pressure a gas exerts and the volume the gas occupies is directly proportional to the temperature of the gas).


         Heating the atmosphere causes it to expand (special application of the gas law)




2.      Newton's Second Law of Motion (Equation of Horizontal Motion) -- states that the acceleration experienced by an object is due to the sum of the forces acting on the object .  (An object at rest will be accelerated in proportion to the forces that act on the object).  (F = ma)


How Wind Develops: --  air motion can be understood on the basis of the forces that cause air to move.  In the absence of all other forces, at a given elevation (say, sealevel or at 18000 feet), air tends to be accelerated horizontally from regions of higher pressure to regions of lower pressure.





3.      Hydrostatic Law (Obtained from the Equation of Vertical Motion) -- the upwards directed pressure gradient force acting on an air parcel (explained in class) is balanced by the weight of the air parcel.


         How Vertical Winds Can Develop [special case of (2)]




4.      First Law of Thermodynamics -- the temperature changes experienced by an air parcel can be put into two general categories:  i.  those related to direct heating or chilling of the air parcel (termed sensible or diabatic heating or cooling; and, ii. those related to non-direct heating or chilling associated with expansion or contraction of the air parcel (termed adiabatic  heating or cooling).


         How temperature changes




5.      Conservation of Mass Applied to the Atmosphere (Equation of Continuity ) -- with respect to the sealevel weather map, pressure changes occur because of net accumulation  or net deficit of air in the air column above. (In simplified form, this is termed Dine's Compensation by synoptic meteorologists -- which states the result of this principle on atmospheric flow -- upper level divergence tends to be balanced by lower level convergence and vice versa).


How pressure changes at a given level develop--creation of high and low pressure area.   Also, upper tropospheric divergence tends to be larger than the compensating lower level convergence:  hence, surface low pressure areas develop under regions of upper tropospheric divergence.