| There are many methods to determine the height of the atmospheric boundary layer.The most common method to determine the height of the atmospheric boundary layer is base on the temperature profile.At present,there are many methods based on the temperature profile,such as the temperature gradient method,the temperature jump method,the air block method,the Holzworth method and so on.What are the differences between these methods in the semi-arid regions of the Northwest? At the same time,in the northwestern semi-arid region with a special environment and climate background,what are its characteristics of the boundary layer height? Based on the above two issues,this paper uses Suizhong as the representative station of the northwestern semi-arid region,based on the sounding data of the national reference climatological station in Suizhong and the microwave radiometer data of the Lanzhou University Semi-Arid Climate and Environment Observatory(SACOL).First,the paper analyzes the differences in temperature and humidity data between the soundings of soundings and microwave radiometers in the semi-arid area.Second,based on the sounding data,the temperature gradient method,the combined method of air mass and Richardson number were used to determine the height of the boundary layer in the semi-arid area.While based on microwave radiometer data,the temperature gradient method,air block method,Holzworth method are used to determine the height and type of boundary layer in semi-arid areas.Then comparing the determined boundary layer heights to compare the difference of methods.At last the characteristics of the boundary layer in the semi-arid region are analyzed based on the microwave radiometer data using air-block method,and the following conclusions are drawn:(1)Both the temperature and specific humidity data of soundings and microwave radiometers have the highest degree of coincidence in August and September at the turn of the summer and autumn,and the correlation coefficient can reach above 0.9,and the degree of coincidence in December in winter is the lowest.Below 0.5,the degree of coincidence of the bit-temperature data of both types of data is higher than that of specific wet data.In the case of two types of data with good agreement,the temperature profiles of the two are well below 2000 m,and the agreement is poor at more than 2000 m.In the morning,the temperature profile of the lower layer is higher than that of the evening.At the evening,the high temperature profile of the high level in the evening is more consistent than that in the morning;in the case of two types of data with better fit than the wet data,the radiosonde data has a jump over the wet profile above 3000 m.The data is not higher than the wet profile,and at a height above 3000 m,the sounding of the sound is less than that of the microwave radiometer than wet.(2)Based on radiosonde data and microwave radiometer data,the temperature gradient method was used to determine the type of atmospheric boundary layer in the semi-arid area.The morning and evening atmospheric boundary layers are mainly SBL and NBL types.In the morning,the frequency of SBL types is characterized by low spring and summer and high autumn and winter temperatures.At night,the frequency of NBL types has the characteristics of high spring and summer and low autumn and winter temperatures.In the type of boundary layer determined based on radiosonde data using a bit-temperature gradient method,no CBL occurs in the morning and evening of the year,and in the type of boundary layer determined by the bit-temperature gradient method based on microwave radiometer data,in the spring and summer morning and evening CBL appears on the night of autumn and winter,which is more reasonable;the SBL type basically appears at night,the CBL type basically appears during the day,and the NBL type appears throughout the day.Affected by sunrise and sunset times and solar radiation,SBL and CBL types The frequency of occurrence has a distinctive feature of diurnal variation.After sunrise,the frequency of CBL types suddenly increases,the frequency of SBL types decreases sharply,and after sunset,the frequency of CBL types suddenly decreases,and the frequency of SBL types suddenly increases,from winter to spring and summer.The monthly increase of the frequency of CBL's sudden increase in time is advanced in advance,and the time of sudden decrease is successively pushed back.The time for the monthly SBL frequency to decrease sharply is earlier and the time for sudden increase is increased.After bolus,both the frequency of occurrence of mutations consistent time base,frequency of occurrence of the NBL and SBL similar trend.(3)The height of the boundary layer determined by the temperature gradient method is high,especially in the autumn and winter,the monthly variation of the height of the boundary layer is above the block method and the Holzworth method.This is mainly due to the use of the temperature gradient method to determine the boundary layer.The height is greatly affected by the choice of the threshold temperature gradient,while the Holzworh method estimates that the height of the boundary layer at night does not change much,and is basically around 100 m.This is mainly because the boundary layer type is SBL at night,and the boundary layer height is largely falling.At the top of the ground inversion layer,the vertical resolution of the microwave radiometer temperature data 0~1000m is only 100 m at the same time,and the night boundary layer height determined by the Holzworh method is basically 100 m.Influenced by the selection of the critical value of Ri,the height of the boundary layer determined by combining the gas block and the Richardson number based on sounding data is particularly high in the morning.Its high value is much higher than the high value of the boundary layer height determined by the temperature gradient method.It is far lower than the low boundary layer height determined by the temperature gradient method.At the same time,the Richardson number method cannot effectively estimate the height of the boundary layer due to the partial loss of the wind profile data of the sounding data.(4)In the semi-arid region,the height of the atmospheric boundary layer has significant seasonal variation characteristics in spring and summer and autumn and winter.The average height of the spring boundary layer reaches a maximum of 900 m,and the average height of the boundary layer in autumn and winter is relatively low,only 300 m.The monthly average height of the layer reached a maximum of 1100 m in June and a minimum of only 300 m in December.In clear weather conditions in May,June and July,a deep boundary layer of more than 4000 m can occur.(5)The atmospheric boundary layer height in the semi-arid area has a significant daily variation in each month and every season.The average morning rising period,the night conversion period,and the appearance and maximum height of the maximum average have periodic changes..At the same time,the degree of fluctuation of the boundary layer during the day is more severe than at night,and the degree of difference between the two is characterized by high spring and summer temperatures and low autumn and winter temperatures.From December 2008 to November 2009,the morning rise of the boundary layer advanced from 9:00 in December to 7:30 in July and was postponed until 8:30 in November;The lowest conversion period was postponed from 18:30 in December to 21:00 in June,and then back to 19:00 in November;the maximum average height in the boundary layer generally appeared in the afternoon from 14:00 to 15:00.During the period,the maximum height increased from 500 m in December to 3200 m in June,and then dropped to 450 m in November;meanwhile,the morning rise of the boundary layer was postponed from 7:30 in spring and summer to 9:00 in winter.The period from early spring to summer at 20:30 to winter at 18:30,the average height of the boundary layer occurs from 14:45 in spring to 14:00 in winter,and the maximum decreases from 2600 m in spring to 475 m in winter..(6)Based on the microwave radiometer data,the atmospheric boundary layer height in the semi-arid region determined by the air block method has a significant diurnal variation characteristic under fine weather conditions.Under cloudy weather conditions,the diurnal variation characteristics are not obvious,and its temperature profile The daily change on the line is less severe than on sunny conditions. |
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