BARIC GRADIENT PRESSURE STEP Done by student of RSHU Evgeniya Durneva MA-283
Introduction Concept of baric gradient and pressure step are studied in the part of meteorology – Static. Structure of atmosphere is explored in the static when there is no motion relative to the Earth.
Static equation Let’s have the part of atmosphere at rest relative to Earth, then horizontal baric gradient (G₂) equals 0. z p+dp z+dz P z p p Volume of air = 1 m² z, z+dz – isobaric surfaces; p, p+dp – pressure; P = ρgdz – gravity force;
Static equation Let’s have projections of all these forces: p - (p+dp) – P. Whereas the volume of air at rest. We obtain: p - (p+dp) – P = 0. -dp - gρdz = 0 or -dp = gρdz -dp/dz = gρ – equation of static. -dp/dz = G₁ - vertical baric gradient When we have the static equilibrium: G₂=0 but G₁=G ( G – total baric gradient )
Static equation -dp/dz = gρ. So, this equation expresses the balance of two forces – gradient of pressure and gravity. We can make an important conclusion: If the height increases ( dz>0 ) and gρ >0 then –dp>0 or dp<0. If the height increases, atmospheric pressure decreases.
Pressure step – the height, one must ascend to in order to decrease the atmospheric pressure by 1 h. Pa. [ h ] – m/h. Pa. h= dz/(-dp)= -dz/dp h= 1/gρ. This formula shows us, that: h only depends on density of air (ρ). ρ h
Pressure step If we compare two pressure steps on the same isobaric surfaces (p=const) but in the different air masses (hot and cold), we obtain: h h > hc If the pressure step is small, atmospheric pressure decreases faster.
Conclusion We have learned about the important concepts in static. Static equation; Baric gradient; Pressure step. All of these parameters are used in the meteorology. And we must know them!
References “Physics of Atmosphere” – L. T. Matveev.
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