What Is the Troposphere?

The troposphere is the layer of the earth's atmosphere close to the ground. It is also the highest density layer in the earth's atmosphere, and it contains about 75% of the mass of the entire atmosphere, as well as almost all water vapor and aerosols.

The earth's troposphere is located in the lowest layer of the atmosphere, which concentrates about 75% of the mass of the atmosphere and more than 90%

The troposphere contains the following components:

Nitrogen (N2)

Oxygen (O2)

Carbon dioxide (CO2)

Methane (CH4)

Nitrous oxide (N2O)

Carbon monoxide (CO)

Ozone (O3)

Sulfuric acid (SO4)

Nitrogen dioxide (NO2)

Hydroxide (OH-)

Division within the troposphere

Although the atmosphere in the lower troposphere will cause friction with the surface, the air in the upper layer is not affected by this friction. Therefore, the weather phenomena in the upper and lower troposphere will be different. Based on the difference in this phenomenon, the troposphere will be separated into three more layers. The ground layer is from 0 to 100 meters from sea level, the Ekman layer from 100 to 1 km, and 11 kilometers from 1 to 11

Tropospheric mode

Excludes cloud and precipitation effects.

The main propagation modes or effects in the troposphere are:

Measurement of tropospheric radio-meteorological data. Tropospheric detection is divided into two types: refractive index measurement and water vapor condensate measurement. The former includes measurements of temperature, humidity, pressure, refractive index, turbulence, and stratification; the latter includes measurements of clouds, fog, and especially precipitation. Tropospheric sounding data is the physical basis for tropospheric radio wave propagation research.

Tropospheric refractive index

The refractive index is often determined by the measurement data such as temperature, humidity and pressure as follows

Where N is the refractive index (N units); T is the temperature (K);

N = ( / × 10 is the water vapor pressure (millibars); P is the atmospheric pressure (millibars). The refractive index can also be directly measured by using a refractive index meter. There are many kinds of refractive index meters. In a refractometer whose shaft cavity is a sensitive element, the change in the refractive index N of the air causes the cavity resonance frequency to change (), and the relationship is

Therefore, by measuring the change in the resonant frequency of the cavity, the change in the refractive index can be determined. Some refractometers use air capacitors as sensitive components.

The short-term average of the refractive index of the ground, the refractive index gradient of 1 km above the ground, and the short-term average of the refractive index gradient within 100 meters and its distribution can generally be obtained by using the ground temperature, humidity, pressure records and sounding data of conventional weather stations and stations. However, the fine refractive index structure and its changes require special measurements to obtain. There are two methods of measurement: direct measurement and remote sensing.

Direct measurement: Place the measuring instrument on a meteorological tower, a captive balloon or an airplane, and directly measure the refractive index of the point where the instrument is located. Meteorological towers can obtain continuous and simultaneous refractive index or temperature, humidity, and pressure records, but are limited by height and location; tethered balloons can make finer measurements of refractive index structures within 500 meters, but only for better Weather; the airborne refractometer has a large range of measurement heights, which can perform fairly fine measurements of stratification and turbulence, but not all-weather measurements.

Remote sensing: Measure the refractive index with radiometer, lidar, sodar or microwave radar remote sensing. Radiometers generally invert the vertical distribution of atmospheric temperature by measuring the radiation intensity of the 60 GHz oxygen radiation band. The solar radiation attenuation of the water vapor absorption band or the measurement of atmospheric bright point temperature is used to determine the height distribution of water vapor density; Lidar uses nitrogen The temperature is measured by Roman backscatter. This backscattering intensity is related to the temperature of the scattering point. If the lidar works at two wavelengths, one of which has a water vapor absorption attenuation, the water vapor content can be calculated by comparing the echo attenuation of the two wavelengths. The response of sound waves to changes in temperature and water vapor is much more sensitive than that of radio waves. The intensity and location of the inversion layer can be detected using a single-station sound wave system. The radio acoustic wave system uses radio waves to measure the speed of sound waves traveling through the air, thereby obtaining a high degree of temperature distribution. Since the absorption of water vapor by sound waves is a function of frequency and humidity, a multi-frequency sound wave system can be used to measure the humidity profile; microwave radar can also measure stratification and turbulent structures.

People have measured the global distribution of the ground refractive index and the monthly average of the refractive index gradient within a range of 1 km above the ground; there are also various empirical models for the statistical distribution of the refractive index gradient within 100 meters above the ground; in some areas it is also more detailed Atmospheric stratification, waveguides, and small inhomogeneities were investigated. ^[4]

Tropospheric precipitation measurement

Includes rainfall and snow measurements. The measurement items include the rainfall rate or snowfall rate and its temporal and spatial changes, and the microstructure of the rainfall or snowfall (particle shape, inclination, terminal velocity, and titer distribution, etc.). Rainfall rate measurements are often made with fast-response rain gauges or dump gauges with fairly high time resolution. The normal rainfall data of the meteorological department can be used as a wide range of data after the integration time is corrected, and the preliminary long-term distribution of the reference rainfall rate and the temporal and spatial variation of the rainfall rate have been proposed for various rain climate regions in the world. Raindrop shape and inclination can be measured by photography. Raindrops are generally oblate. The larger the raindrop, the flatter the shape. In the research of radio wave propagation, the Proupche-Pitt raindrop shape mode is mostly used. Generally, the size of the raindrop does not exceed 8 mm, the axis of symmetry is close to the vertical line, and it is slightly tilted by the vertical gradient of wind speed.

R. Geng and GD Kenze used electronic devices to measure the final velocity of raindrops and achieved good results. The electrified water droplet of the selected titer passes through the two induction coils for the second time during the landing, and two potential pulses are generated in the grid of the vacuum tube connected to the induction coil. The final speed of the water droplet can be determined based on the distance of the induction coil and the time difference between the two pulses. The final velocity of the raindrops increases with the increase of the raindrops, and the initial rate increases rapidly, and it slows down when the titer exceeds 2 mm.

There are many methods for measuring the rainfall rate distribution, including powder method, filter paper method, impact sensor method, electrostatic sensor method and optical detection method. The powder method and the filter paper method respectively determine the size of the raindrops according to the size of the powder balls formed by the raindrops in the face plate and the spots formed on the filter paper with the dye. The impact sensor is generally called a raindrop distribution meter, which converts the impulse or water acting on a rigid diaphragm into electrical pulses. Since the mass, final velocity, and impact time of the raindrop are all functions of the raindrop titer, the raindrop titer distribution can be converted based on the electrical pulse amplitude distribution. The electrostatic sensor and optical detector determine the size of the raindrop by measuring the charge of the raindrop and the size of the shadow formed by the raindrop passing through the beam. Rainfall titer distribution patterns that are more commonly used in propagation studies are the Rolls-Parsons distribution and the Marshall-Palmer negative exponential distribution.

Snowfall occurs in the form of snowflakes, with diameters ranging from a few millimeters to a dozen millimeters. Photographic measurements show that the ratio of the maximum horizontal grain size to the height of the snowflakes varies widely, averaging close to one. The angular variation is generally below 10 °, and the final speed increases with the increase of the granularity and mass of snow, which is generally a few meters / second. For the snowflake particle size distribution, KLS Geng and JS Marshall proposed a negative exponential model that is completely similar in form to the Marshall-Palmer rain titer distribution, with only different parameters.

Multi-parameter radars, including dual-frequency radars, dual-polarization radars, and Doppler radars, have become very important tools in precipitation measurement. Doppler radar can measure the frequency shift spectrum corresponding to various raindrop velocities. Raindrop velocity is a function of titer, so the frequency shift spectrum can be converted into raindrop titer distribution. Dual polarization radar can measure the reflectance of at least two orthogonal polarizations, which can be used to determine two parameters in the particle size distribution mode of negative exponential particles. If the correlation and relative phase shift of the two polarized received signals are measured simultaneously, the orientation of precipitation particles can also be determined at the same time. The dual polarized differential reflectance and attenuation of hail is different from rain, so the dual polarization and dual frequency radar can be used to separate hail and rain. ^[1]