A Comparative Analysis Between The Data From Automatic Observation And The Data From Manual Observation In Winter Half Year Of Jilin Province

With the progression of meteorological modernization, the automatic observation system has gradually replaced the manual observation system. However, the two systems inevitably differ in data, especially under the particular climate condition of Jilin Province in winter. How to make reasonable revisions to these differences so as to eliminate the effect from the transformation of observation systems to the greatest extent is an issue to be emphasized on when the materials are used in the future.The thesis firstly introduces the domestic analysis on manual and automatic observation data, the current situation of the observation network in China and Jilin Province, and the difference of observation instruments. It investigates the difference of winter meteorological elements between manual and automatic observation data in Jilin Province based on the meteorological observation materials in winter half year(October-April) of 2008-2012 provided by the 4 national benchmark climate stations in Jilin Province. In analyzing the observation materials, it gives an introduction to the temperature, relative humidity, air pressure and 2-minute wind direction and speed of the 4 national benchmark climate stations, i.e. Baicheng, Changchun, Dunhua and Donggang, in winter half year(October-April) of 2008-2012 as well as the precipitation data in winter half year of 2012-2013; meanwhile, it delves into the change of temperature and relative humidity in cold wave, freezing and snowstorm weather in Jilin Province. The thesis probes into the revisions to the materials through analyzing the temperature difference. The conclusions are drawn as follows:(1) As for temperature, it is indicated that the comparative difference between the data from automatic observation and the data from manual observation suffers an obvious diurnal change, which reaches a positive maximum at 8-9:00 and a negative maximum at 17-20:00; the turning point for comparative difference is after sunrise and sunset and the comparative difference increases and decreases along with the rise and fall of temperature.The difference between the two diminishes as far as monthly change is concerned.and the comparative difference is centered between-0.5? and 0.5?. The peak in Baicheng Station is around 0? and the temperature from automatic observation is higher than that from manual observation on the whole. However, the comparative balance in Changchun Station, Donggang Station and Dunhua Station is inclined to be a negative value, indicating that the temperature from automatic observation is lower than that from manual observation. When the temperature changes dramatically, the difference between the two increases significantly due to the sensitivity of instruments and the difference in observation time.(2) The monthly percentage error of precipitation is centered between-4.85% and 5.56% and the error in January and February is comparatively larger than that in other months.the difference between the data from manual observation and the data from automatic observation diminishes year by year and the difference is centered on ±0.3mm, the variation range of daily precipitation difference was between-2.9mm and 2.3mm. The samples testifying that the daily precipitation from manual observation is smaller than that from automatic observation account for 25.3%, the samples testifying that the daily precipitation from manual observation is larger than that from automatic observation account for 34.5%; the samples testifying a difference of 0.0mm account for 40.2%, which indicates that the precipitation from manual observation is comparatively larger than that from automatic observation.(3) As for relative humidity, the comparative difference shows a distinctive feature in diurnal change, which reaches a minimum level at 8-9:00 and a maximum level at about 18:00, and the turning point is before and after sunrise and sunset. Owing to different geographic locations, the range of diurnal change in Dunhua Station and Donggang Station is larger than that in Changchun Station and Baicheng Station. In monthly comparative difference, 75% of the samples shows a negative value and the data in Changchun and Dunhua are entirely negative, indicating that the relative humidity from manual observation is generally higher than that from automatic observation. The period with largest gross error ratio is before and after January every year and in case of an observation at low temperature in winter, the data from manual observation are subject to an evident increase in error and when the relative humidity changes quickly, the difference between the data from automatic observation and the data from manual observation becomes even more apparent owing to the sensitivity of instruments and the discrepancy in observation time.(4) As for wind speed, the monthly comparative difference shows an overall trend of yearly decrease and the wind speed from automatic observation is higher than that from manual observation.It can be seen from the dairly change that the change of wind speed is obviously. With the incase of turbulence at 8 am to 9, the difference turn to the peak,and it fall off with decline of The snowfall turbulence until to the mimnium at 4pm to 5pm. Dunhua, Donggang in the eastern mountains of contrast is significantly greater than the difference between the stations located in the plains of Changchun, Baicheng. As for wind direction, the coincidence rate for wind direction in the 4 stations ranges from 24% to 65%, which is relatively low.(5) The comparative difference in air pressure shows distinctive features in diurnal change and there are two high values and two low values in a day; the high value appears about 8:00 and 20:00 respectively and the low value appears about 3:00 and 12:00 respectively; the difference increases along with the rise of air pressure. As for air pressure, the comparative difference in the station changes around ±1.2hPa and the value is centered between-0.2hPa and 0.5hPa; the air pressure from automatic observation is higher than that from manual observation. The comparative difference of Donggang Station and Changchun Station is positive, while the comparative difference of Baicheng Station and Dunhua Station is mostly negative. From the perspective of monthly comparative difference, the influence from the change of instrument is larger than that from the instruments itself.(6) It is indicated through an analysis over the temperature and relative humidity in cold wave, severe cold and snowstorm weather that the comparative difference in temperature and relative humidity increases toward the positive value area when the value of observation factors rises and towards the negative value area when the value of observation factors falls, and the maximum value appears when the value of the observation factor changes. Due to the sensitivity of manual observation instruments and the discrepancy in observation time, the comparative difference is subject to an evident fluctuation when the speed of rise and fall changes.(7) In the revision to data series, an attempt has been made to revise the temperature from automatic observation by referring to the instrument error revision table for manual observation instrument and adopting the simplified method of comparative difference. The verification result shows that positive effects have been achieved on the whole but the revision for Baicheng Station after 2009 shows a negative effect, which indicates that this method is effective but should be further analyzed and testified.