A Novel Description of Weather: A Shock for Meteorologists? | Atmospheric Physics | 20240802 скачать в хорошем качестве

A Novel Description of Weather: A Shock for Meteorologists? | Atmospheric Physics | 20240802

This is Part 3 of my talks on air pressure near the surface of the Earth. It is proposed that the air pressure near the surface can be treated as a constant whenever the fluctuarions in air mass in a vertical unity column can be neglected. It is expected many viewers would think differently or could let me know what I am wrong. #atmosphericscience #weatherforecast #isobars #windspeed #densityexperiment We were used to watch weather forecasts at the end of a daily TV news, presented by a well-dressed weather man, such as Edwin Maher, who eventually worked for the CCTV in China. A weather map, often called as synoptic chart, is made by a number of irregular loops called isobars, meaning any locations on the same isobar curve should have the same surface air pressure. Two capital letters are often used, H and L, which represent, according to many a meteorology textbook, local maximum and local minimum pressures, respectively, presumably very close to the surface. By overlaying the surface temperature, it is clear that the places with L are relatively hotter than their surrounding areas, whilst the places with H are relatively colder than their surrounding regions, although the isobars and isothems are out of the phase., called baroclinic. 9.Similar to global mean surface temperature or GMST, it is impossible to obtain global mean surface pressure. Instead, mean sea level pressure, or MSLP for short, is frequently used for a short period of time. That’s why those isobar curves in a weather map are time dependent and must be updated every hour. 10.This is understandable, as weather forecasts are almost impossible without using such time-dependent isobars. Why? Because it is generally accepted that air currents, moist or dry, cold or hot, are initially driven by pressure-gradient forces.or PGF for short. 11.However, as discussed in my previous talk, the surface air pressure would be a constant if the total mass of air molecules in a vertical unity column above the surface is fixed. That’s the basis for my new description for weather. 12.Of cause, the atmospheric is a dynamic system. Therefore, fluctuations in the vertical column mass are inevitable, given the general circulation, that may affect the surface air pressure for sure. But it seems no quantitative justifications can easily be found. 13. Here, I would like to draw your attention to an important mechanism for weather change that has been omitted in many a meteorology textbook, namely, air diffusion caused by air density gradient without any PGF, the force arising from pressure difference in horizontal directions near the surface of the Earth. 14.Bearing in mind, I am not going to talk about the vertical pressure gradient due to gravity. Indeed, the air pressure 10 meter above the ground is only 1 hPa (hecto Pascal) weaker, compared with the mean surface air pressure 1,013 hPa. So, it is reasonable to to treat the thermodynamic process in the atmosphere near the surface as isobaric, meaning constant pressure. 15.Consider a small area near the surface, such as a football field. According to idea gas law, the product of the air temperature near the surface and the air density must be a constant if the air pressure is fixed, as shown in this diagram. The dependence of air density on the surface temperature is reciprocal. That’s to say, if air pressure is fixed, the air density near the surface would decrease as the local surface temperature increases. Let’s focus on the initial local response to the change of the surface temperature so that we can still use the gas law. 17.Perhaps you may ask, how could you explain weather.. 18.Because whenever air density distribution is not uniform, air currents can be formed due to diffusion processes, without PGF, from higher air density regions to lower air density areas, as shown in this CFD, or computational fluid dynamics, simulation for air flows in a hall due to air diffusion. 19.As air currents diffuse near the surface, forces show up, including Corioli, frictional, and centrifugal, in the same principle as that for air currents driven by PGF. Not a big deal. 20.In fact, we can still use those weather maps, provided the capital letters H and L now represent high air density and low air density, respectively, whilst the irregular loops of traditionally called isobar should be called as “equal-density curves”. 21.Ideally, to evaluate my new proposal, air density should be directly measured by simultaneously measuring the air pressure and air temperature at each position. If so, it is expected that the measured air pressure be a constant near, irrespective of the local surface temperature. 22.Alternatively, air density can be determined by measuring sound speed which depends on both air density and air temperature. In fact, this table show how the three dependent variables are determined, as used in this diagram.