Abstract: Automatic station and manual observation are two main bases for collecting meteorological elements. Due to the differences in instrument principle, observation time and space, sampling method and sample number, observation time and other factors, there are many differences in meteorological data obtained by these two observation technologies. Starting with the differences between the two observation methods, this paper sorts out and compares the observation data of Nanxiong Station, and seeks an effective way to improve the accuracy and scientificity of the observation data.

Keywords: automatic station and manual station? Observation data? The difference? Nanxiong national benchmark climate station

Before the automatic observation station is put into operation, the ground atmospheric sounding station shall conduct comparative observation of meteorological elements for two years. Up to now, Nanxiong National Reference Climate Station still retains two sets of atmospheric sounding instruments and equipment, namely automatic station observation instruments and equipment and manual observation instruments and equipment. 24 hours a day, both manual stations and automatic stations need to regularly observe the meteorological element values and compare the observation data of manual stations and automatic stations. It is generally believed that the difference is normal within a reasonable range, otherwise it is a suspected erroneous record.

First, the difference between automatic station and artificial observation factors

1, the instrument principle is different.

In principle, the meteorological sensors used in automatic weather stations are different from the instruments used for manual observation. These sensors have smaller time constants, and can observe smaller meaningful fluctuations in the atmosphere, which makes the obtained extreme values more representative, such as temperature extreme value, humidity extreme value, wind speed extreme value and so on. These sensors have high resolution, and the wind direction observed manually is only 16 directions, while the wind direction observed by automatic stations is 36 directions. These sensors have high measurement accuracy, such as temperature sensor (especially ground temperature sensor), wind sensor and humidity sensor at low temperature.

Automatic weather stations can avoid subjective errors and human errors in manual observation. In manual observation, observers often have habitual errors, and occasionally there may be large reading errors when reading, which affects the human body's temperature when measuring temperature. The average value of 2-minute wind is influenced by people's subjective judgment. When observing the deep ground temperature manually, the readings are taken from the ground due to the errors caused by environmental changes, and these problems do not exist in automatic observation. These are better than manual observation, and there are essential differences between them.

However, automatic meteorological observation also has some shortcomings, especially in special weather conditions, such as humidity measurement under high temperature and high humidity, rainfall measurement above rainstorm, extreme ground temperature measurement under snow, etc., which is quite different from manual observation and true value.

2. Temporal and spatial differences

Surface meteorological observation is carried out in the near-surface layer, but in the near-surface layer, there are great fluctuations in time and space, that is to say, there are great gradient changes.

According to the requirements of the Standard for Surface Meteorological Observation on time, artificial observation should observe clouds, visibility, air temperature and humidity, precipitation, wind power, air pressure and ground temperature in 45-60 minutes; Evaporation can be observed between 40 minutes after punctuality and 10 minutes. Because manual observation is carried out item by item by observers, the time span is long.

Under normal circumstances, the time from the punctuality of artificial observation is about: the temperature and humidity difference is about 8 minutes, and the wind direction and speed difference is 5 minutes; The air pressure difference is 2 minutes; The ground temperature difference is at least 10 minute. In the above time difference, the numerical values of meteorological elements will change to varying degrees. From the observation, it is found that when the temperature rises in summer, the observation time is 8 minutes different, which can cause a difference of 0.2-0.3℃. When the ground temperature is 0cm, there is no cloud at the zenith of the station during artificial observation, but after the observation, there is a cloud moving to the zenith before the punctuality, which blocks the sunlight. At this time, the observed data may be different by several degrees. When observing precipitation at artificial stations, there will be rainfall loss and so on. According to the order of temperature, humidity, precipitation, wind direction, wind speed, air pressure, ground temperature, sunshine and evaporation, automatic meteorological observation can be completed almost instantly.

It can be seen that because the observation time of the two observation systems is not synchronous, the observation results are bound to be different.

In terms of space, although the installation requirements of sensors in automatic meteorology are basically the same as those in manual observation, the installation location and location are slightly different. For elements closely related to the installation location, such as ground temperature, the difference in location may lead to significant differences in measured values.

3. Sample differences

Manual observation is point reading, that is, the observer only reads the instructions of the instrument once during observation. However, automatic observation is different, and each observation value is the average of multiple sample values. Different sample numbers will inevitably lead to different measurement results.

4. Time difference

Automatic meteorological observation data are stored once every hour, 24 times a day, while ordinary weather stations carry out manual observation 3 times a day, supplemented by self-recording records at 02: 00, and observe ***4 times a day, so the observation data density of automatic stations is higher than that of manual stations.

Second, the difference analysis

1, air pressure

As can be seen from Table 2, the difference between the observation data of manual station and automatic station is only 0. 1hpa, which is quite close. As we know, air pressure is related to altitude, atmospheric temperature and atmospheric density. Generally, with the increase of altitude, the air pressure decreases. Therefore, in the same climate environment, it is inevitable that the measured values of outdoor automatic stations will deviate slightly from those of manual stations, as long as they are within ≤0.8hpa specified by the provincial bureau, they can be regarded as correct values.

2. Temperature

In the atmosphere, the temperature fluctuates greatly, and the radiation error caused by solar radiation can not be ignored. From the table 1, although the observation data of the two are close, it is better to see the comparison result of a relatively complete data series than to compare single comparison data simply and randomly. So it is best to compare the data in months.

3. Relative humidity

In automatic meteorological observation, humidity is measured by humidity-sensitive capacitor in the whole process, and its measuring principle is very different from manual observation data.

When the relative humidity is lower than 80%, the humidity sensitive capacitor has good linearity and humidity measurement performance. As can be seen from Table 2, the contrast difference is very small. As can be seen from Table 2, the contrast difference is 0.5 when the relative humidity of high temperature and high humidity is above 80%. The relevant provisions of the provincial bureau do not give a specific range of differences, so it must be considered in sections in daily work.

4. Wind direction and speed

The electric anemometer used for manual observation is quite different from the wind sensor used for automatic weather station in principle, resolution and accuracy, and the observation time is not synchronous because of the uncertainty of wind speed in the atmosphere. The data of annual wind direction and speed show that the static wind (C) and ENE, E and W winds have the highest frequency in manual observation and automatic station observation. Generally, when the wind speed is small, the comparison error between automatic station wind speed and manual observation is large. The reason is that the automatic station adopts low inertia and light metal wind sensor, and its starting wind speed is only 0.3 m/s, which has the characteristics of small inertia, fast starting and sensitive sensing. The starting wind speed of the artificial station wind sensor is1.5 m/s.

Step 5 rain

In artificial observation, it is generally believed that the results measured by rain gauge are reliable, but they are not. When it rains, there is rainfall loss in the process of manual observation, which is a problem that should be paid attention to when analyzing the errors of automatic observation and rain measurement. Coupled with the difference in observation time, the comparison error is very large.

As can be seen from Table 3, the contrast difference of 4% is within the difference range given by the provincial bureau. However, as can be seen from Table 3, the precipitation difference between June and February in 5438 reached 6%, far exceeding the' difference range (3%) given by the provincial bureau. In the maximum difference between the primary process and the related literature, the difference of the heavy precipitation process can even reach 10%. Therefore, when the contrast of precipitation is quite different, this value cannot be judged as a doubtful record mechanically, but depends on the magnitude of precipitation. It must be pointed out here that the precipitation process is the best choice when comparing the two.

6. Ground temperature

The complexity of geothermal measurement After solar radiation heats the underlying surface, the soil temperature rises rapidly. Because of the different physical and chemical properties of soil, that is, different specific heat, the same heat, temperature appreciation is also different. According to the experiments of relevant institutions, the horizontal temperature field in the soil is unevenly distributed, and the vertical temperature gradient is very large, especially on sunny days in summer. In addition, in soil, radiation heat transfer is weak; Convective heat transfer is almost nonexistent; Soil is not a good conductor of heat and conducts heat slowly. This makes it difficult for the horizontal inhomogeneity and vertical gradient of temperature in soil to achieve the proper balance. In addition, the surface temperature measurement is influenced by strong solar radiation, so it is difficult to obtain representative measured values, and it is also difficult to judge which instrument is more reliable in geothermal measurement.

As can be seen from Table 5, the contrast difference of 0~20cm is gradually decreasing, which is within the allowable range given by the provincial bureau.

7. Evaporation

Manual and automatic evaporation measurement are carried out in the same large evaporation device. As can be seen from Table 2, the evaporation of automatic stations is much larger than that of manual stations, and there are obvious differences in evaporation. The evaporation of automatic station is mainly affected by precipitation, humidity, wind, sunshine, temperature and instrument accuracy.

Some precipitation weather records on July 15 and June 16, 2006 were randomly selected for analysis. The average temperature of 24 times on July 15 and June 16 was 26.0℃, and the sunshine hours were 0.0 h.. The hourly precipitation, hourly evaporation, hourly humidity and hourly wind speed data of these two days are listed in Table 3.

Three. conclusion

According to theoretical analysis, there will inevitably be differences in meteorological element data observed by manual stations and automatic stations. By comparing the observation data of manual station and automatic station in Nanxiong National Reference Station, it is found that the differential interval given by the relevant regulations of the provincial bureau can be applied in general weather conditions, but it is obviously smaller than the actual situation in special weather conditions, which should be paid attention to in future work.

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