Weather pressure in Xiaoshan

Hangzhou is located in the middle subtropical transition zone, which is warm and humid, with four distinct seasons, abundant sunshine and rainfall. In a year, with the reverse transformation of winter and summer monsoon, the weather system, control air mass and weather conditions will change obviously seasonally, forming the climate characteristics of rainy spring, humid summer, fresh air in autumn and dry and cold winter. Due to the complex landform and uneven terrain, the geographical distribution of light, heat and water in Hangzhou is uneven, and the local microclimate resources are rich. However, due to the instability of monsoon advance and retreat time and duration, there are often anomalies of cold, hot, dry and wet, which lead to disastrous weather.

I. Solar radiation and sunlight

The annual average total solar radiation in Hangzhou is between100 ~10 kcal/cm2, the sunshine hours are 1800 ~ 2 100 hours, and the sunshine percentage (the percentage of actual sunshine hours in a certain period to theoretical sunshine hours in this area) is 4. Geographically, there are more plains than mountains. To the north of Tonglu and Fuyang, Xiaoshan, Yuhang and the northeast of the city are flat and sunny. The annual average total solar radiation is above 108 kcal/cm2, the sunshine hours are above 2000 hours, and the sunshine percentage is above 45%, which is a high-value area in the city. In the central part of the city, the Xin 'anjiang reservoir area and the valley plain in the east of Lin 'an County, the annual average total solar radiation is 106 ~ 108 kcal/cm2, the sunshine hours are 1950 ~ 2000 hours, and the sunshine percentage is about 45%. In hilly and mountainous areas, the annual average total solar radiation is generally below 100 kcal/cm2, the sunshine hours are less than 1.900 hours, and the sunshine percentage is less than 4 1%. In the pier with narrow ridge, the solar radiation and sunshine are only about 70% of those in the plain.

According to the observation of Tianmu Mountain Meteorological Station, the solar radiation and sunshine in mountainous areas below 500 meters above sea level become weaker and shorter with the elevation of the terrain; At an altitude of 500 ~ 1000 meters, due to more clouds and rain, the lowest value appears; Above the altitude of 1000 meters, it becomes stronger and longer with the elevation of the terrain. The seasonal changes of solar radiation and sunshine in Hangzhou are obvious. The total solar radiation, sunshine hours and sunshine percentage in summer half year (May ~ 10) are greater than those in winter half year (1 1 ~ April of the following year). Among them, July and August in midsummer have strong sunshine and long sunshine time. Except in mountainous areas, the monthly average total solar radiation in most parts of the city is 12.5 ~ 14.5 kcal/cm2, the sunshine hours are 230 ~ 260 hours, and the sunshine percentage is 55 ~ 60% or above. In winter, the solar radiation is weak and the sunshine is short. From June 65438 to February of the following year, the monthly average total radiation was below 6 kcal/cm2, the sunshine hours were less than 150 hours, and the sunshine percentage was less than 50%. Spring (March-April) and autumn (9-65438+1October) are transitional seasons, and the sunshine amount and sunshine amount are in the middle. In contrast, there are more rainy days in spring, and each value is smaller than that in autumn. In addition to the top of Tianmu Mountain, except July and August, the average sunshine hours in winter are also more, and the sunshine percentage in each month from165438+1October to 65438+1October of the following year exceeds 50%.

Second, the temperature

(1) annual average temperature and monthly average temperature. The annual average temperature in Hangzhou is 15.3℃ ~ 17℃. Geographically, the south is high and the north is low, and the plain is higher than the mountainous area. The highest annual average temperature in the city is in the south of Xin 'anjiang Reservoir Area, Shou Chang Basin and Meicheng Basin, which is above 17℃. North of Jiande Wulong Mountain Scenic Resort, the valley plains on both sides of Fenshui River, the northeast plain in the middle, the temperature16.0 ~16.9℃; Temperature in Changhua, flooded valley plain and low hilly valley in northwest China15.0 ~15.9℃; The annual average temperature in mountainous areas with an altitude of more than 250 meters, such as Tianmu Mountain, Yuling Mountain, Baiji Mountain and Qianligang, is below 65438 05℃. The annual average minimum temperature in the city is 8.9℃ at the top of Tianmu Mountain. In a year, the monthly average temperature of 65438+ 10 is the lowest, generally 3.0 ~ 5.0℃ (the temperature difference between north and south is about 2℃), and it is lower than 3℃ in mountainous areas. It is the highest in July, and the monthly average temperature is 28.0 ~ 29.0℃ (the temperature difference between north and south is about 65438 0℃). The average monthly temperature at the top of Tianmu Mountain is 6℃ lower in June and 9℃ lower in July. Spring and autumn are the seasons of temperature change. The temperature rises fastest in April, and the monthly average temperature is 6℃ higher than that in March. The temperature drops fastest from autumn to early winter, and the average temperature drops by more than 5.5℃ in June at 5438+00 and June at 5438+0 10. In terms of temperature, June 5438+0, April, July and June 5438+00 respectively represent winter, spring, summer and autumn in Hangzhou.

(2) The direct drop rate of temperature in mountainous areas. The temperature in mountainous areas decreases with the increase of topography, but it is greatly influenced by topography, slope direction and seasonal changes. In Zhongshan area, the direct temperature drop rate (the temperature drop value per 100 m altitude) is generally higher in the lower layer than in the upper layer, higher in the south slope than in the north slope, and higher in summer and autumn than in winter and spring. In the vicinity of Xin 'anjiang reservoir area, the change of direct temperature drop rate is more complicated due to the regulation of water body. In addition, cold air is easy to sink and accumulate in mountain basins in winter, and the radiation cooling effect is very strong in sunny nights, which often forms the phenomenon of "cold lake" and inversion (the temperature increases with altitude). The annual inversion frequency to the south of Tianmu Mountain is about 67%. According to different heights, it can be roughly divided into two inversion layers: the first layer, with an altitude of 150 ~ 500m and an average intensity of more than 0.7℃/100m; The elevation of the second floor is 800 ~ 1 100 meters, and the average strength is about 0.3℃/ 100 meters.

(3) Maximum temperature and minimum temperature. Jiande and Lin 'an Changhua are two high temperature centers in the city. The average maximum temperature in the hottest July is above 34℃, and the extreme maximum temperatures are 42.9℃ (1971July) and 41.9℃ (1August 6, 966) respectively. The extreme maximum temperature in Hangzhou once reached 42.1℃ (65438+ 10 on September 30th). Changhua, Lin 'an in the northwest, has the lowest temperature in winter, and the average lowest temperature in June is-1.3℃. The extreme minimum temperature often appears in the northeast plain where cold air in the south can directly drive in. 19771October 5, Xiaoshan recorded a low temperature of-15.0℃, which was nearly 2℃ lower than that in the northwest low-hilly valley. The monthly average minimum temperature and extreme minimum temperature in Xin 'anjiang reservoir area in southern China are 65438 0.9℃ and -8.0℃ respectively, which is the warmest area in winter in the city. The monthly average maximum temperature in the hottest month at the top of Tianmu Mountain is 23.8℃, and the extreme maximum temperature is only 30.6℃. The average minimum temperature in Leng Yue is -6. 1℃, and the extreme minimum temperature is-20.2℃ (65438+ 16 years in 096710,65438 in October), all of which are the lowest in the city. The five-year minimum temperature in Hangzhou (1951-198) is -9.6℃( 1969 February 6th).

(4) annual range and daily range of temperature. The annual average temperature difference (the difference between the average temperature in the hottest month and the average temperature in Leng Yue in a year) is 23.8 ~ 24.9℃. The annual amplitude of the northern and central plains is larger, above 24.5℃; The annual variation of Xin 'anjiang reservoir area and Meicheng basin in the south is small, generally not exceeding 24.0℃. The annual average daily range (the difference between the highest temperature and the lowest temperature in a day) is 7. 9 ~ 1 1.0℃. This value is higher in Shanliang Valley, and it reaches11.0℃ in Lin 'an Changhua. The low mountain valley is generally 9.0 ~10.0℃; The northeast plain area is small, about 8.0℃. The annual average daily range of each month is the largest in autumn and the smallest in winter. The annual average and daily range in mountainous areas are usually small, and the top of Tianmu Mountain is 22.5℃ and 7.3℃ respectively, which is the smallest in the city.

(5) The first frost day, the last frost day and the frost-free period. The average first frost sunrise in Hangzhou is now1mid-late October 1 1, and the final frost sunrise is around mid-March, and the frost-free period is generally 230 ~ 260 days. The cold air in the valley north of Fuyang is easy to invade. The first and last frost days are 5 ~ 10 and 5 days earlier and 10 ~ 15 days later than those in the south, respectively, and the frost-free period is shortened by about 20 days. Especially in the valley ridge area of Changhua, Lin 'an in the north, the advection cooling effect of cold air at night and the radiation cooling effect of the surface are strong and easy to overlap. The first frost is early, the last frost is late, and the frost-free period is short, only about 232 days. Jiande and Chun 'an near Xin 'anjiang Reservoir in the south have the latest first frost day and the earliest final frost day, and the frost-free period can reach 254 ~ 263 days. The number of frost days in all parts of the city is generally 23 ~ 26 days. There are more valley plains in the north than coastal plains, and coastal plains are more than Xin 'anjiang reservoir area in the south. The annual temperature in mountainous areas is low, the first frost day is advanced and the last frost day is postponed. 10 The average first frost day at the top of Tianmu Mountain in October is 1 1, the average last frost day is April 4, and the average frost-free day is only about 209 days.

(six) the first day, the whole day and the accumulated temperature of 65438 00℃ is stable. The first day and the whole day when the daily average temperature in Hangzhou passes (≥ 10℃) appear in late March to early April and 1 1 in the middle and late October respectively, and the duration is 230 ~ 250 days. ≥ 10℃ Accumulated temperature is 4700 ~ 5700℃. The average first day ≥ 10℃ in Xin' anjiang reservoir area and southern valley plain appeared on March 20 ~ 25, lasting for more than 240 days, and the accumulated temperature ≥ 10℃ was 5300 ~ 5700℃, making it the best area in the city. The average date of the first day of ≥ 10℃ in the central valley plain and the northeast plain appeared from March 25th to March 3rd1,lasting for 235 to 240 days, and the accumulated temperature of ≥ 10℃ was 5000 ~ 5300℃. The first day average sunrise of ≥ 10℃ in hilly areas of the west and southeast is from the end of March to the beginning of April, lasting for 230 ~ 235 days, and the accumulated temperature of ≥ 10℃ is 4700 ~ 5000℃. The average dates of the first day and the whole day appear after April 3rd and before June165438+1October1,respectively, and the duration is less than 230 days, and the accumulated temperature ≥ 10℃ is less than 4700℃, which is the heat condition of the whole city.

Third, precipitation

(1) Average precipitation and rainy days. The average annual precipitation in Hangzhou is1100 ~1600 mm, and the annual rainy days are 130 ~ 160 days. However, due to the influence of circulation and topography, precipitation and rainy days vary greatly from place to place, and the general distribution trend is decreasing from southwest to northeast, and increasing from valley plain and Xin 'anjiang reservoir area to hilly and mountainous areas. The mountainous areas in the northwest, middle and southwest of the city are rich in rainfall, with the annual average precipitation exceeding 1 500mm and rainy days exceeding 1 0,60 days, which is a rainy area. Especially in Shiling and Shuangshi on the east and west sides of Tianmu Mountain, Mashan in the north of Yuling Mountain, Chenjiacun and Zhang Cun in the east of Bletilla striata, Baima in former Khan Lee, Xiling and Dakeng in Jiande, the annual average precipitation exceeds 65,438 0.800 mm, and the rainy days exceed 65,438 0.65 days. South of Lin 'an and Fuyang, along the river to Shou Chang basin, Meicheng basin and Xin 'anjiang reservoir area, the annual average precipitation is 1350 ~ 1500mm, and rainy days are 145 ~ 155 days. The average annual precipitation in the Northeast Plain is below 1400 mm, and the rainy days are less than 150 days, which is a rainy area in the city. The average annual precipitation is less than 1200mm, and the rainy days are less than 140 days in the coastal areas of Xiaoshan and Yuhang.

(2) Seasonal distribution of precipitation. Hangzhou has two rainy seasons and one rainy season in a year. The first rainy season starts around the beginning of May and ends from the end of June to the beginning of July, commonly known as Meiyu period, which is mostly caused by the northward movement of the polar front (Meiyu front) and the stagnation of the middle and lower reaches of the Yangtze River and the Jiang Nanyu belt. During this period, the rainfall was concentrated, with heavy rain, and the average precipitation was 350 ~ 550 mm, accounting for about 25 ~ 365,438+0% of the annual total. Rainy areas are mainly distributed in mountainous areas from southwest to northwest, with an average of more than 500 mm The second rainy season occurs from the end of August to the end of September, which is caused by typhoon or polar front moving southward, commonly known as typhoon autumn rain period, with an average precipitation of 120 ~ 220mm, accounting for 8- 13% of the annual total. Rainy areas are mainly distributed in the northwest mountainous areas and the northeast plain. The east side of Tianmu Mountain is the frequent center of typhoon and rainstorm, with an average of more than 200 mm. In addition, March-April is a rainy period, which is called spring rain period. The average precipitation is 200-300mm, accounting for about 13-23% of the annual total. July, August and 10 to February are two relatively dry seasons. The first dry season is midsummer and summer drought, that is, summer drought. The city is controlled by subtropical high, with extremely high summer monsoon, high temperature and little rain. Except for the average precipitation of 250-300mm in Tianmu Mountain area in the northwest and Yuling Mountain area in the middle, the average precipitation in most areas is 250-300mm, and the average precipitation from Qiantang River basin to Xin 'anjiang reservoir area in the northeast plain is the least, less than 250mm. The last dry season was winter dry season, because the south of Mongolia is a polar continent.

(3) The interannual variation of precipitation and the relative variability of annual precipitation. The precipitation in Hangzhou varies greatly from year to year, and the relative variability of annual precipitation (the average absolute value of the difference between annual average precipitation and annual average precipitation accounts for the percentage of annual average precipitation) is 12 ~ 17%. Among them, Lin 'an, Chun 'an, the west and southwest of Jiande, and the east of Xiaoshan are more than 15%, and other areas are 12 ~ 15%. The relative variability of each month in the whole year is the smallest in March-June, which is 25-35%, indicating that the amount of spring rain and plum rain is relatively stable, while the annual precipitation in March-June is half of the total annual precipitation, which is easy to cause floods and wet damage in different degrees. There is less precipitation in July and August, and the relative variability increases (35 ~ 50%) compared with the previous period, which is prone to summer drought. Only under the influence of typhoon precipitation and autumn rain in September can the drought be alleviated or lifted. During the winter dry period from 10 to February of the following year, the precipitation changes greatly, with the largest relative variability (50-80%), and "dry winter" or "rotten winter" years often appear.

(4) Distribution of rainstorm days. Except in winter, there may be rainstorm days with daily precipitation ≥50 mm in all parts of Hangzhou, with an average of 2 ~ 5 days per year. June is the most, followed by September. The regional distribution of rainstorm days is the least in the northeast river network plain and coastal plain, with an average of about 2 days per year; Low-hilly valley and Xin 'anjiang reservoir area in south-central China, with an average of 3-4 days per year; Mountain areas are the most, with an average of more than 4 days a year, and several rainstorm centers have reached or exceeded 5 days. The daily precipitation is ≥ 100 mm, and the average annual rainstorm days are less than 2 days. Among them, the northeast plain area and Xin 'anjiang reservoir area are less than 0.5 days. The maximum daily precipitation in the western mountainous area during the plum flood season can reach more than 200 mm; During the typhoon autumn rain, there were 300 ~ 400 mm heavy rains, which often appeared in the east side of Tianmu Mountain and the eastern plain.

Four. Evaporation and humidity

(1) evaporation. The average annual evaporation in Hangzhou is1150 ~1400 mm, which is greater in the south than in the north, greater in Jiande and Chun 'an near Xin 'anjiang reservoir area, and less than150 mm in Lin 'an town in the south of Tianmu Mountain ... It is the largest in summer (June-August), sunny and hot in July-August in midsummer, and the average monthly evaporation is 170 ~ 230mm. Spring (March-May) and autumn (9-165438+1October) take the second place, and the average monthly evaporation is 75- 150 mm ... and the minimum is 65438+/kloc in winter (65438+February to the following February).

(2) Relative humidity. The annual average relative humidity and monthly average relative humidity in Hangzhou are 75-85%, which is generally greater in the north than in the south. The average relative humidity in Xiaoshan, Yuhang, Lin 'an and Fuyang is about 80% in summer and autumn, and most of them are below 80% in Chun 'an, Jiande and Tonglu. The annual relative humidity is the highest in rainy season (June), with the monthly average humidity above 80%, and the lowest in dry winter period (65438+ 10), with the monthly average humidity not exceeding 78%. The annual change of relative humidity at the top of Tianmu Mountain is the most obvious, reaching about 90% in July and August, which is the largest in the city. 12 and 1 are lower than 65% in February, which is the smallest in the city.

Verb (abbreviation for verb) wind and air pressure

(1) wind

Wind direction The prevailing wind direction in the northern and central plains of Hangzhou and mountainous areas above 1000m above sea level has obvious monsoon characteristics. With the change of winter and summer seasons, the maximum wind direction also changes in the opposite direction (the intersection angle is above 120). Every February and March (at the turn of winter and spring), the wind direction begins to turn from north to east and then to south; Southwestern southerly winds have prevailed since June (early summer); In August (midsummer), the east wind strengthened; From September (autumn) to February of the following year, and even the whole winter half year, northerly winds predominate. Among them, around 65438+ 10, the north-northwest wind is particularly prevalent. The above rules are most obvious at the top of Tianmu Mountain.

In low mountains, hills and valley plains, the prevailing wind direction has local characteristics due to local topographic interference. Jiande, Chun 'an and Lin 'an Changhua are prone to easterly winds all year round. The easterly wind is the most in the east of Lin 'an in spring, and the southwest wind is the main wind in summer, autumn and winter.

The monthly maximum wind direction frequency in all parts of the city is generally 10 ~ 25%, which is higher in winter and summer than in spring and autumn.

Wind speed. The average annual wind speed in most parts of Hangzhou is 1.3 ~ 2.4m/s, the northeast plain and Xin 'anjiang reservoir area are flat, and the average annual wind speed is higher than 2m/s, especially in the coastal plains on both sides of Qiantang River, and the average annual wind speed exceeds 3m/s. In low hills and valleys, especially in narrow hills and valleys orthogonal to the wind direction, the wind speed is relatively low, such as Lin 'an and Changhua. The annual average wind speed is only 1.3m/s, and the static wind frequency is as high as 52%, which is 20-30% higher than other areas. The wind speed on hilltops, hills and windward slopes is much higher than that in plain areas. The annual average wind speed at the top of Tianmu Mountain is 6.3m/s, and the static wind frequency is less than 4%.

The monthly average wind speed is between 1. 1 ~ 2.7 m/s, which is usually higher in winter and lower in summer. The wind speed in the central and northern regions is slightly higher in spring than in autumn, but there is little difference near the Xin 'anjiang reservoir area in the south.

The annual maximum wind speed and monthly maximum wind speed are generally between 10 ~ 20m/s, and the highest wind speed in Tianmu Mountain can reach 25 ~ 30m/s ... The strong winds in winter and spring mainly appear when the cold air (cold wave) in the north goes south, mostly in the northwest direction; However, strong winds in summer and autumn are often affected by strong convection (hot thunderstorms, squall lines, etc.). ) and typhoons in some areas, the wind direction is chaotic. ?

(2) Air pressure

Annual average air pressure. According to the record of Hangzhou Meteorological Observatory 196 1 ~ 1980, the annual average pressure in Hangzhou is101.6 hectopascals, which is lower than the standard pressure10/kloc-0. The average maximum pressure in 1953 and 1970 is10/6.5 hectopascals, and the average minimum pressure in 1974 is10/0.9 hectopascals. The maximum difference of annual average air pressure is 5.6 hectopascals.

Monthly mean air pressure. In a year, the monthly average air pressure in Hangzhou changes with the monthly average temperature. The lowest monthly mean air pressure appeared in July, which was 999.2 hectopascals, and the highest monthly mean air pressure appeared in June 5438+February and June 5438+1October, which was 102 1.6 hectopascals.

Extreme changes in air pressure. In winter, it was attacked by Siberian cold high pressure (strong cold wave), and the air pressure reached its maximum. Hangzhou was affected by cold high pressure at 198 15438+02, and the air pressure rose sharply to 1038.2 hectopascals. At the turn of autumn and winter, due to the strong typhoon, the air pressure has a minimum value. 1On the morning of August 2, 956, due to a strong typhoon in Hangzhou, the air pressure plummeted to 958.7 hectopascals, which was the first time in 40 years.

Six or four seasons

According to the climatic index (1 for five days), the average climate temperature is less than 10℃ in winter, more than 22℃ in summer and 10 ~ 22℃ in spring and autumn. Hangzhou has four distinct seasons, with a long time distribution in winter and summer and a short time in spring and autumn.

(1) Spring

From the fourth to the sixth waiting in March, the fifth waiting in May to the first waiting in June. It lasted about 68 days, with a difference of about 10 and 7 days respectively. After the beginning of spring every year, the cold and warm air flow intensifies alternately, and the wind direction is changeable due to cyclone and frontal activity, but it is mainly easterly; The weather is cold and warm, and the temperature difference is very large; The rain is increasing and the rain is uncertain; Therefore, Hang Yan has a saying that children's faces change three times a day in spring. During the "Qingming" season in April, when strong cold air goes south, there will often be "cold spring" weather with continuous low temperature and rainy weather. There are strong convective weather such as thunderstorms and hail in late spring. The average temperature in spring is about 65438 07℃, and the precipitation is 330 ~ 450 mm.

(2) Summer

From the sixth waiting in May to the second waiting in June, and finally to the third waiting in September to the end of the fifth waiting. Duration 1 15 ~ 120 days. The south starts early, the north ends late, the south ends late and the north ends early, with a difference of 5-7 days. In the early summer, with the gradual strengthening of the subtropical high in the North Pacific, the southerly wind is increasing day by day, and the warm and humid airflow is very active. Influenced by the Meiyu front, it rained continuously and the temperature and humidity rose synchronously, but the wind was small and the weather was sultry. At this time, Huangmei is ripe and the goods are easy to mildew, commonly known as Meiyu period or mildew period. Due to concentrated rainfall and frequent rainstorms, floods occur from time to time. From the beginning of July, the rainy season stopped and all localities entered the midsummer period. Until the end of August, the summer monsoon was extremely strong. Under the control of subtropical high, except for some thunderstorms, the weather is sunny and hot, which is a relatively dry and hot period all year round. Due to the continuous high temperature and little rain, strong sunshine and large evaporation, drought is formed. In the meantime, it is often affected by tropical weather systems such as typhoons, including heavy rain and windy weather. In summer, the average temperature is 26 ~ 27℃ and the precipitation is 530 ~ 630mm.

(3) Autumn

It started from the fourth day of September to the fifth day, and lasted for about 63 days from the fourth day of June to the fifth day. 165438+. The first day is early in the north and late in the south, with a difference of 5 ~ 7 days. Around the "autumnal equinox", the cold air in the north moves southward rapidly, the wind direction is northerly, and the temperature drops rapidly, which is prone to low temperature in autumn. Sometimes, cold and warm air flows alternate again, which will produce a rainfall process. From mid-October of 65438/kloc-0 to mid-October of165438+10, under the control of the cold and high-pressure ridge front in Mongolia, the air layer is stable, the rainfall is obviously reduced, and there are often crisp autumn weather with less clouds and more sunshine, large temperature difference between day and night and low relative humidity. In late autumn, the cold air is powerful and the first frost will appear. Autumn average temperature 16 ~ 17℃, precipitation 140 ~ 200mm. ?

(4) Winter

From 165438+ 10 to the beginning of the fifth quarter in October, and finally to the end of the third quarter to the fifth quarter in March of the following year, it lasted 1 10 ~ 120 days. It starts in the north and ends in the south, ends in the north and ends in the south, with a difference of 5 ~ 10 days. In early winter, the cold air in the north frequently goes south, the northerly wind increases, and the temperature drops suddenly. In June 5438+10, the winter wind was the most abundant, controlled by the cold high pressure in Mongolia, and mainly sunny and cold weather. After "beginning of spring", the wind weakened in winter, the temperature slowly rose, and the rain and snow gradually increased. Under the attack of strong cold air or cold wave, there will often be strong winds and strong cooling weather, and sometimes there will be serious freezing damage and snow damage. The average temperature in winter is 6 ~ 7℃, and the precipitation is 260 ~ 290 mm.

Authentic hangzhou dishes is absolutely light. Famous snacks such as Zhang Shengji and clay casserole are also exquisite, with a sense of taste and so on. Those spicy and greasy dishes are all imported.