Specific systems or specific weather phenomena in the flow field, pressure field, temperature field and humidity field that have an important impact on weather formation.In the flow field, there are waves, cyclones, anticyclones, shear lines, convergence zones, typhoons, jet streams, squall lines, tornadoes, etc;In the pressure field, there are low pressure, high pressure, low pressure trough, high pressure ridge, etc;There are air masses and fronts in the temperature field;In the humidity field, there are dry areas, wet tongue, dew point front, etc;The combination of various meteorological element fields includes cold high pressure, hot low pressure, cold trough, warm ridge, energy front, etc;The weather system of specific weather phenomenon includes thunderstorm, hail storm, cloud cluster, etc.[1]
Another definition is the atmospheric motion system with typical characteristics (usually the system composed of the spatial distribution of atmospheric pressure) divided according to the spatial distribution of meteorological elements, such as high (gas) pressure, low (gas) pressureHigh pressure ridge, low pressure tank, etc.Sometimes refers to the system of wind distribution, such ascycloneCirculationAnticyclone circulation、Shear lineEtc.Sometimes refers to the system of temperature distribution, such as high temperature zone, low temperature zoneFrontal zoneEtc.Sometimes refers to the system of weather phenomenon distribution, such asthunderstorm、Tropical cloud clusterEtc.There is often a certain configuration relationship between this element system and another element system.
Pneumatic systemGood relationship with wind field: low pressure andCyclonic circulationPhase configuration, sometimes called low pressure, sometimes called cyclone;High pressure andAnticycloneThe phase configuration is sometimes called high pressure, sometimes called anticyclone.The air pressure system and the temperature system often have a certain configuration relationship.For example, low pressure and low temperature zone phase configuration is calledCold low pressureorCold vortex；Low pressure and high temperature zone phase configuration, calledThermal low pressure。The atmospheric pressure system can also have certain configuration relationship with weather phenomena, such as thunderstorm and (small) high pressure configuration, calledThunderstorm high pressure。The weather system canSynoptic chartandsatellite cloud chartAnd other analysis tools.
Characteristic scale
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atmospheric circulation
Various weather systems have certain characteristic scales.Spatial scaleIt is mainly measured by the size of the horizontal scale of the weather system, which refers to the wavelength or disturbance diameter of the weather system;time scale Measured by the length of the life cycle of the weather system,lifeHistory refers to the rise and fall of the weather system from birth to death.The larger the horizontal scale of the general weather system is, the longer its time scale is.
During the study of convective disastrous weather around the 1950s, many high and low pressure systems with a horizontal range of one or two hundred kilometers, dozens of kilometers or even several kilometers were found, collectively referred to asMesoscale and small-scale weather system。To analyze such systems, it is necessary to establish a dense observation network, such as the so-called α, β and γ observation networks in the United States, with station distances of about 50km, 8km and 2.5km respectively.In the 1970s, it was carried out at a grid distance of 300-400kmNumerical weather forecastWhen the grid spacing is too large, it is often impossible to analyze someConvective weatherThe prediction effect is affected by the system of.When the grid spacing is reduced to 100~200km, it can be analyzed. Later, the system of this scale is calledMesoscale weather system。
The characteristic scales of various weather systems in the atmosphere vary greatly, ranging from tens of thousands of kilometers, such asUltralong wave、Subtropical high, and some as small as several hundred meters, such as a scroll.According to the characteristic scale, it can be roughly divided into five categories, namely:Planetary scale weather system、Synoptic scaleWeather systemMesoscale weather systemMesoscale weather system and small-scale weather system.The classification of weather systems is not completely unified internationally.
scale effect
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Scale effect of weather system
Spatial scale (horizontal and vertical) andtime scale , and the characteristic horizontal wind speed are determined according to the actual observation.However, some quantities cannot be directly observed until the beginning of the 21st century, and can only be measured according toAtmospheric dynamic equationCalculate.In progressnumerical calculationSelect the appropriatespaceThe grid distance, whose size is determined by the characteristic scale of the system, is calledscale effect 。For example, the characteristics of the weather system are verticalMovement speed, can be based onContinuity equationBy horizontal scale and characteristic levelwind speedCalculated.The vertical motion speed of various weather systems has certain characteristic values, such asPlanetary scaleThe weather system is 10-1 cm/s,Synoptic scaleThe weather system is 10 ° cm/s,small scaleThe vertical speed of the weather system is about 100 times that of the synoptic scale weather system, i.e. 102 cm/s.
Since the advent of scale analysis in the late 1940s, people have oftenEquation of motion, simplify according to the characteristic scale of various weather systems, and study various systemsAtmospheric motionAnd the movement of the system.For example, research on synoptic scale weather system can apply quasiGeostrophic balanceAnd statics, while the mesoscale and small-scale weather systems do not meet the geostrophic balance andStatic equilibrium。
Scale division
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According to the size of the horizontal range and the length of the survival time, the weather system can be divided into different scales.There is no uniform standard for scale division.
The weather system with a general horizontal range of about 10km is called small-scale weather system (tornado, convection cell, etc.), and its survival time is from several minutes to several hours.The mesoscale weather system (strong thunderstorm, squall line, sea and land breeze, etc.), which is tens to 500 kilometers long, has a survival time of several hours to more than ten hours.The 500~3000 km weather system is called synoptic scale weather system (front, cyclone, anticyclone, typhoon, etc.), and its survival time is from one day to several days.3000~10000 km long wave weather system (blocking high pressureSubtropical high), the survival time is from a few days to more than ten days.The weather system over 10000 kilometers is called ultra long wave weather system, and the survival time is more than 10 days.Sometimes the weather systems equal to or larger than the synoptic scale are collectively referred to as large-scale weather systems.The weather systems of different scales have different characteristics. They are interrelated, restricted and transformable.Through the analysis of the characteristics of different weather systems and their interrelationships, we can understand the law of the evolution of weather phenomena and make weather forecasts.[1]
Small systems tend to develop under the nurture of large systems, and after the growth of small systems, it will react to large systems.All kinds of weather systems are formed and developed in a certain geographical environment, with certain geographical environment characteristics.If the high latitude area is cold and dry all the year round, it is a necessary condition for the formation of the cold high in the lower polar layer and the polar vortex in the upper polar layer;The low latitude area is hot and humid all the year roundConvective weatherThe foundation of system development;In the middle latitudes, the cold and warm air masses in Jiaosui are conducive to the formation and development of fronts and cyclones.Therefore, it is extremely important to grasp the structure of the weather system and its change rules for forecasting weather changes and understanding the shape and characteristics of the climate.stayweather forecastThrough the prediction of various systems, we can roughly predict the weather changes in the future.The combination of many weather systems forms a large-scaleWeather situation, constituting the hemisphere or even the globeatmospheric circulation。[2]
Evolution and extinction
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cyclone
The weather system is always in the process of rebirth, development and extinction.Various weather systems have different birth and death conditions and energy sources.Even if the characteristic scales belong to the same class of systems, their generation and dissipation conditions and energy sources are different.such asExtratropical cycloneThe development conditions ofVorticity advectionThe strength of the induced air divergence determines that its energy comes from the effective potential energy stored by the baroclinicity of the atmosphere.The occurrence and maintenance of typhoon is due toTropical disturbanceOflatent heatAnd the release of latent heat is the same as the potential instability andConvective instabilityThe energy mainly comes from thesteam, onCondensation processLatent heat released in.
Strong convectionThe meso and small scale weather system is mainly due to geopotentialUnstable airIts energy also comes from the release of latent heat.Moreover, the weather system is often not closed. The air in one system often exchanges with the air in the surrounding system. With this exchange, momentum, energy, etc. between systems are exchanged, resulting in the generation and elimination of systems and the interaction between systems.
Generally speaking, the large weather system restricts and breeds the occurrence and development of the small weather system, and the small weather system can feed back the maintenance and strengthening of the large weather system after its emergence.One of the main tasks of synoptic science is to study the conditions and energy sources of the generation and dissipation of the weather system, as well as the interaction between the systems.Weather system andatmospheric circulationBetween, not onlyflow patternIt is related to and has internal connection.For example, the activities of large-scale weather systems play an important role in maintaining the atmospheric circulation through the north-south transport of heat and momentum and the conversion of energy.The thermal condition of the atmospheric circulation and the characteristics of the basic wind system, such as the horizontal and vertical changes of the westerly flow, in turn restrict the large-scale weather system and directly affect the development of the large-scale weather system.
Evolution of weather system combination, such asZonal circulationRecovery ofGroup velocityThe dissemination of, andPlanetary scale weather systemThe development ofatmospheric circulationChanges.The change of atmospheric circulation is the condition and mechanism that causes large-scale and long-term weather changes.The short-term weather forecast can mainly consider the changes of a single weather system, while the medium-termlong-range weather forecastIt is necessary to study the evolution law of weather system combinationUltralong waveAnd the evolution law of the whole atmospheric circulation.
