How to judge whether hail falls by radar echo

What are the echo characteristics of heavy hail on radar images?

The following is the echo characteristics of heavy hail on radar map, which is helpful to you:

What are the echo characteristics of heavy hail on radar map (1)

Analysis of radar echo characteristics of a hail process

Lingguandian Town, Shaodong, located in the middle of Shao Heng Basin, Hunan Province, belongs to the subtropical monsoon humid climate zone, and it is prone to strong convective weather from April to May every year, and hail in strong convective weather brings the most serious harm to agricultural production. In recent years, a new generation of Doppler weather radar has been built and put into operation in Shaoyang City, Hunan Province, which has played an important role in monitoring and early warning of disastrous weather.

In recent years, China has also carried out some research on supercell storms. Wu Chunxia et al. [1] studied the characteristics of a supercell storm, Wu Chunying et al. [2] thought that the headwind area was a strong signal of hail, Jiang Dunshuang et al. [3] thought that supercell storm was a direct influence system of hail, and Yuan Pengfei et al. [4] analyzed a strong hail weather, and thought that the echo height with intensity >: 55 dBz was higher than the height of -20℃ and the VIL value was >. 12 km, accompanied by the appearance of moderate cyclone, is a reliable signal of hail.

On April 30th, 20 12 16: 30 or so, hailstones suddenly fell in Lingguandian Town and Shizhuqiao Township, Qian Bao Township, Shaodong County, Shaoyang City, Hunan Province, with a hail diameter of10 ~ 20 mm. Bowl-shaped potholes can be seen everywhere in rice fields, and many crops such as rape, corn, grapes and vegetables are seriously damaged, with the affected area reaching 2 1 18 hm2. Hail * * * caused direct economic losses 1, 376, 1, 000 yuan. Based on NCEP 1× 1 reanalysis data and Shaoyang new generation Doppler weather radar data, this process is comprehensively analyzed from the aspects of large-scale circulation situation, physical quantity characteristics and radar echo evolution characteristics, and some conclusions are drawn to improve the monitoring, forecasting and early warning capabilities of severe convective weather such as hail.

1 weather background analysis

20 12 At 8: 00,500 hectopascals on April 30th, a short-wave trough moved rapidly eastward from eastern Gansu to northeastern Guizhou (Figure 1). There is a northeast wind behind the short wave trough and a southwest wind in front of the trough. Lingguandian Town in Shaodong County is located in the southwest airflow in front of the trough, with the southwest wind speed of 20 m/s and the southwest jet over Shaoyang area of 500 hPa of 18.

On April 30th 14: 00, the 500 hPa short-wave trough developed eastward from Chongqing to Guizhou, Lingguandian Town was in the southwest airflow in front of the trough, and the wind speed increased to 24 m/s. On the ground map, Lingguandian Town was controlled by the thermal low pressure, which indicated that the low-level southwest vortex shear line cooperated with the ground thermal low pressure, which strengthened the convergence and upward movement, triggered the energy release of convective instability, and produced hail.

2 physical quantity analysis

2. 1 Convective effective potential energy

Convection effective potential energy (CAPE) is a vertical integral index obtained by measuring the accumulated buoyancy energy in the free troposphere from the free convection height to the equilibrium height. The bigger the cape, the more favorable it is for the occurrence of strong convection and hail weather.

As can be seen from Figure 2, at 8: 00 on April 30th, the CAPE index of Lingguandian Town was 200 J/kg, 14:00, and the CAPE index of Lingguandian Town increased to 1 000 J/kg, an increase of 800 J/kg. On the 29th,

What are the echo characteristics of heavy hail on radar map (2)

Analysis of radar echo characteristics of a hail weather

Author: Yang Qunchao

Introduction to 0

In 2007, the "4. 14 Hail Disaster" in Chengdu occurred from 26: 30 to 23: 00 on April 14, and a strong convective weather process occurred in Pujiang, Pengzhou, Pixian and Meishan, lasting for 45 minutes, with the maximum diameter of hail of 5cm and the maximum wind speed of 650.

1 circulation background analysis

At 08: 500hPa on April 14, 2007, the Sichuan area was basically controlled by the northwest airflow, and the western Sichuan Plateau fluctuated slightly. At 20: 500hPa, Chengdu Railway Station turned to the west wind, and at 700hPa, there was weak shear in the west of Chengdu, with abundant water vapor, and there was convergence area at 850hPa and on the ground map.

2 unstable energy analysis

At 08: 00 on June 5438+04, the index SI of sand is-1.3℃, and the air mass index K is 25℃. By 20: 00, the SI is -3.6℃ and the K index gradually rises to 38.0℃, indicating the possibility of strong thunderstorm. At the same time, the unstable energy Ek changes from negative to positive, and from stable state to unstable state.

According to the temperature-logarithmic pressure chart at 20 o'clock, there is obvious vertical wind shear in Chengdu Railway Station, which is beneficial to the occurrence of convective weather. There is an inversion layer near 650hPa, which is beneficial to the accumulation of unstable energy. The 0℃ layer is near the isobaric surface of 600hPa, with a corresponding height of 3.7km, and the -20℃ layer is near the isobaric surface of 450hPa, with a corresponding height of 6.5km, which is beneficial to the formation of hail.

What are the echo characteristics of heavy hail on radar map (3)

Radar test questions and answers

1. When the wave source moves relative to the observer, the frequency received by the observer is different from that of the wave source, and its (frequency change) is related to (relative motion speed). This phenomenon is called Doppler effect.

2. The most effective way to judge the severe hail is to check whether the strong echo (≥45dBZ) can develop to (0℃), especially above the isotherm height of (-20℃).

5. The main reason for the limited detection ability of the new generation weather radar is the existence of static cone area.

6. The main radar parameters of weather radar are (radar wavelength), (pulse repetition frequency PRF), pulse duration (τ) and pulse width (h), (peak power) and (beam width).

9. The scattering of electromagnetic waves to precipitation particles is the basis of (weather radar detecting precipitation).

1 1. The most essential feature of supercell is that it has a (deep and persistent mesocyclone). What are the echo characteristics of heavy hail on radar images?

12. There is an area (ring with high reflectivity factor) in the echo of precipitation reflectivity factor of layered cloud or mixed cloud, which is called zero-degree bright area.

13, the non-meteorological conditions that may lead to the increase of spectral width are (antenna speed) (distance) (radar

Signal to noise ratio)

15. The Doppler velocity characteristics of mesoscale convective echoes producing heavy rain are (strong wind shear), (strong convergence deformation), (deep cumulus convection) and (rotating circulation).

2 1. On the radial velocity diagram, the small-scale cyclone (or anticyclone) in the airflow appears as one (maximum and minimum radial velocity pair), but the connecting line of the two extreme centers is perpendicular to the radar ray.

23. The convergence line of the boundary layer shows (narrow band echo) on the reflectivity factor diagram of the new generation weather radar, and the intensity varies from several dBZ to more than ten dBZ.

24. In the case of large vertical wind shear in the environment, there are many single-cell storms, squall lines and super-single-cell storms that produce linear gale on the ground, and one of their early warning indicators is * * *.

(Intermediate air flow convergence).

28. The sum of backscattering cross sections of cloud and rain particles in unit volume is called the (reflectivity) of meteorological target.

29. For the same pulse repetition frequency, the measuring range of C-band radar is about that of S-band radar (1/2).

3 1, the echo ceiling height (less than the cloud ceiling height) in the echo ceiling height products of the new generation weather radar.

33.VWP is a vertical wind profile product, which can be used for analysis (high and low level jet, vertical wind shear, thermal advection type).

34, cyclone is a storm scale circulation, it can be composed of (shear scale, duration scale, vertical

The thickness extends in a straight line).

35. Early warning indicators of wet downburst are (convergence of airflow above the cloud bottom, decrease of reflectivity factor core).

36. Compared with rain gauge to estimate precipitation, radar has the advantages of high spatial resolution.

(wide range).

38. Squall lines (fractures) are often places where strong weather is easy to occur.

39. Relative storm helicity is the potential measured by a physical quantity (storm rotation).

4 1 and squall line are convective monomer families (linear arrangement), and the aspect ratio is greater than (5: 1).

42. (Stability and persistence) are the main differences between supercells and other severe storms.

43. Supercell storms with heavy precipitation usually have rich water vapor and low LFC (free

Convection height) and the top cover of weak convection front inversion layer.

44. The central cyclone is closely related to the (updraft) and the back side (downdraft) of severe convective storms.

Connected small-scale vortices meeting certain criteria (shear, vertical extension and persistence).

46. The occurrence of heavy hail is related to (the intensity and scale of storm updraft) and crossing updraft.

Relating to airflow (as opposed to storm airflow). What are the echo characteristics of heavy hail on radar images?

47. Lightning is caused by ice crystals in cumulonimbus clouds (temperature difference electrification) and other electrification effects.

Discharge between clouds and earth or between clouds. Generally, when the cloud top develops above the (-20℃) isotherm height, there are enough ice crystals in the cloud, so lightning will appear.

49. In the echo mode of strong typhoon radar, there is always an echo area (spiral rain area).

1. Indicates what kind of refraction each electromagnetic wave belongs to.

2. Definition of backscattering cross section σ

A: An ideal scatterer, whose cross section is σ, can receive all the electricity incident on it.

Electromagnetic waves, and all evenly scattered, scatter electromagnetic energy to the radar antenna.

The current density is exactly equal to the energy of the actual scatterer returning to the radar antenna at equal distance.

Flow density, cross section σ is backscattering cross section.

3. What is the antenna gain?

Answer: The energy flow density and uniform scattering time per unit area at a certain distance in the antenna direction.

The ratio of energy flow density at the same distance

4. What is the pulse repetition frequency?

A: The number of trigger pulses generated per second.

How many units of reflectivity factor does 5.0 dBZ represent? How many units do the reflectivity factors do- 10 dbz, 30dBZ and 40dBZ represent respectively?

Answer: 0. 1, 1000, 10000(mm6/m3).

6. What are the volume scanning methods currently used by radar?

Answer: VCP 11-VCP11(scanning strategy # 1, version1) stipulates.

Scanning mode with a specific elevation angle of 14 within 5 minutes.

VCP2 1-VCP2 1 (scan strategy # 2, version 1) stipulates that

Scanning mode with 9 specific elevation angles in 6 minutes.

VCP3 1-VCP3 1 (scan strategy # 3, version 1) stipulates that

/kloc-scanning mode with five specific elevation angles in 0/0 minute.

VCP32-VCP32 (Scan Policy # 3, Version 2).

The five specific elevation angles completed in 10 minutes are the same as VCP3 1. The difference is that VCP3 1 uses long radar pulses and VCP32 uses short pulses.

WSR-98D does not define VCP32.

10, clutter characteristics of common ground objects:

A: It refers to the ground objects such as towers or mountains caused by the normal propagation of radar beams.

Clutter usually appears near radar. For any specific elevation angle, the typical fixed clutter pollution rarely changes from one body scan to the next, and it will appear most of the time. Generally, the reflectivity is high and the radial velocity is close to zero.

1 1, the difference between clutter signal and meteorological signal:

Answer: Clutter signals are characterized by high echo power and radial velocity of.

Zero is a central distribution with a narrow spectral width. Meteorological signals have varying echo power, and the radial velocity is rarely distributed near zero.

13, meaning of "purple" on radar velocity chart.

Answer: In the case of multi-pass echo superposition, for the echo superposition library,

If the power ratio exceeds the threshold, the target position corresponding to the smaller echo will be marked as purple; If the power ratio does not exceed the threshold, the target distances corresponding to all superimposed echoes will be marked as purple.

14. Briefly describe the wind field near the radar station shown on the right.

trait

Answer: The wind direction rotates clockwise with height.

Wind speed does not change with height.

15. Briefly describe the radar station near the right.

Characteristics of empty wind field

Answer: The wind direction does not change with height.

The wind speed first increases and then decreases with height.

There is a low-level jet stream.

16. Briefly describe the location of the weather system shown on the right.

And the characteristics of wind field near the radar station.

Answer: The cold front moved over the radar station.

Behind the cold front is the northwest wind, and the wind direction follows.

The height rotates counterclockwise, and the southwest wind is before the cold front.

What are the echo characteristics of heavy hail on radar map (4)

Comprehensive analysis of a hail weather process

Based on conventional weather data, satellite cloud images and radar echo data, this paper analyzes the hail weather that mainly occurred in Bayannaoer, Baotou and Hohhot on1August 1998 12. The analysis shows that (1) the hail weather occurred at the strong center of the gale axis at 08: 500 hPa, the negative center of Shaughnessy index SI and the difference between 850 hPa and 500 hPaθse. (2) The satellite cloud image is a convective cumulonimbus cloud with neat and smooth edges; (3) The radar echo has obvious V-shaped notch and suspended echo characteristics. Key words: satellite cloud images that affect the physical quantities of the system; Radar echo; Classification number: P4

Document ID: a

Article number:1672-3791(2013) 07 (b)-0237-01August, 998/afternoon of kloc-0/2nd. Hail is concentrated between 106 E and10l e, and the narrow strip north of the Yellow River and south of Daqing Mountain is basically east-west, with the phenomenon of "toad jumping" every several tens of kilometers. 16 ~ 17, the hail cloud moves southeast from Xiwugaigou and Bashi in Wuhou Banner to Lianglang Pass in Wuzhong Banner. After coming out of the mountain, it invaded the Hetao agricultural area and began to hail. The maximum hail particle size is 2.5 ~ 3.0 cm, and the longest duration is more than 20 minutes, which causes disasters in Sumu, 9 towns in Wu Zhongqi, He Lin and Wuyuan County, with a total disaster area of 9 1 168 mu, 50 dead sheep and injuries 1 person. At around 19: 30, hail fell on National Day and Dongyuan in Baotou area, and the largest hail was the size of an egg. 12000 mu of crops were affected, and even the harvest was severe. At 20 o'clock, there was a soybean hail in Hohhot, and there was no disaster. 1 analysis of large-scale environmental field and its influence system on the weather map108: 300 hectopascals on August 2, 2, the middle reaches of the Yellow River reach Mongolia in the north and northeast China in the east. Most areas (north of 42 N, 98 ~130 E) are wide low trough areas, and they are also low trough areas on the 500 hPa weather map, coming from Lake Baikal. There is a cold center at-16℃ on the Bayanmao Road from Mongolia to Ameng (40 ~ 45 N,105 E), and there is another short wave trough from Baotou to Chengdu. Hetao area is located in the stepped trough and at the front of the northern trough area, which is controlled by northwest-west airflow. With the low trough from Lake Baikal to Hami, there are relatively forward-leaning troughs on the 700 hPa and 850 hPa maps. At the same time, the low trough area has an obvious narrow wind axis from west to south, from 300 hPa to 700 hPa, and the wind direction changes are basically concentrated in Hetao area. On the gale axis, 500 hPa is located near the northwest of Hetao, and the wind speed center is strong. In addition, on the 700 hectopascal map, there is obvious wind speed shear along the middle line of the Yellow River (near 40 N), and there is southwest or southerly airflow in the 850 hectopascal area, which plays a role in conveying warm and humid air. On the ground map, there is a low pressure area near the border between China and Mongolia (105 E, 42 N), which matches a straight cold and warm front. From the above analysis, it can be seen that there is a southwest warm and humid airflow in the lower layer of the hail area, while there is a cold advection in the middle and upper layers, which conforms to the weather conditions of dry top, cold bottom and warm and humid bottom. 2. Condition analysis of physical quantities 2. 1 Shaughnessy index SI is a quantitative index indicating the stability of the lower troposphere. On the Charcot index distribution map at 08: 00 on August 12 (omitted), there is a large-scale low-value center of -4℃ in the northwest corner of Hetao, indicating that there is instability in the middle and lower layers. This hail happened just downstream of this low center. From the advection point of view, this area is unstable and will become unstable. 2.2 500 hPa wind field and humidity ratio effective potential energy field The analysis of 500 hPa wind field and low-level energy field shows that there is a strong wind speed center of 16 m/s in the northwest corner of Hetao. On the vertical profile of effective potential energy of wet ratio, there is a high-energy tongue in the lower layer of strong wind speed center, and hail occurs in the downwind of wind speed center and high-energy tongue. 2.3 Distribution Diagram of the Difference between Pseudo-equivalent Potential Temperature 850 hPa and 500 HPA θse (omitted) From the mountain, it can be seen that there is a positive center in the northwest corner of the Hetao, indicating that there is an unstable layer in the middle layer, which has the conditions of dry and cold upper part and warm and wet lower part, and hail has also appeared in the downwind of this center. Satellite cloud image analysis From the GMS satellite cloud image sent every hour on August 12, it can be seen that the process affecting the hail weather is mainly convective cumulonimbus clouds. 14, a discontinuous Cloud belt consisting of small cloud clusters or monomers appeared from the north to the northwest of Hetao, and the small cloud cluster cl near the northwest of Hetao developed rapidly. When 15, it developed into a relatively large cloud group, which showed an east-west trend. 16, the range of the cloud cluster is expanded. Under the influence of high-altitude wind, the upwind edge of the cloud cluster is clear, the structure is compact, and the downwind edge is fuzzy. Some clouds extend eastward, and cloud top temperature is below -30℃, indicating that the clouds are deep and have strong convection. At this time, it is located in the cloud C 1 According to relevant data, around 16, hail occurred in Wuyuan and Wuzhongqi of Bashi. 17, Cloud C2 merges into cl (the figure is omitted), and cloud C 1 develops to the southeast, with a wider range. From west to northwest, the edge of the cloud is smoother and neater. At this time, the river is on the windward edge of the cloud, and it begins to hail around 17. At 18, the cloud C 1 continued to move eastward, and the temperature in cloud top temperature was about -39℃. 19: 00, Cloud cl moved eastward over Baotou city, and cloud top temperature in the southwest of the cloud dropped slightly, with a compact cloud structure. At around 19: 30, it began to hail in Baotou. By 20 o'clock, the structure of the northwest part of the cloud began to loosen, while the edge of the southwest to the south part was clear and the structure was tight. In the east, there seems to be a cloud anvil extending eastward, and the range of clouds begins to decrease. At this time, the cloud has entered the sky above Hohhot, and there is hail in Hohhot, but there is no disaster. At 2 1, the clouds weakened obviously and the hail weather ended. The convective cloud lasts for 8 hours from 14 to 2 1. 4 Radar Echo Analysis When the convective cloud C 1 is located over Baotou City, a series of echo images were observed by the 7 1 1 3 cm wavelength digital radar in Baotou City before and after the hail. The most characteristic hail cloud echoes are 19: 00, 10 and 19: 25. On the PPI map (abbreviated) 19: 00, there is a composite unit between the northeast of the station 10 ~ 40km, and the strongest echo center is located in the southwest of the composite unit, between the northeast of the station 12 ~ 18km, with the central intensity of 60 ~ 65dBz, the main area. The main echo height 1 1.5km, echo intensity 60 ~ 65dbz, and echo height 8km at 50 dbz on the RHI map (omitted). On the PPI map of 19: 25, the main echo is distributed between 20 and 55 kilometers east of the station, and the strong center is located between 2 1 ~ 30 kilometers east of the station, with an intensity of 60 ~ 65 dbz and an area of about 25×20 square kilometers. On the RHl diagram, the echo height of the main body is 12km, the intensity is 60 ~ 65dbz, and the echo structure of the suspended body is obvious. These are typical features of hail clouds. Conclusion (1) The hail occurred at 08: 00 in the gale center of 500 hPa gale axis, the negative center of SI, the positive center of the difference between 850 hPa and 500 hPaθse, the downwind side of the low-level wet ratio effective potential energy tongue, and in the narrow strip north of the Yellow River and south of Daqing Mountain. (2) Hail occurs in convective cumulonimbus clouds with neat and smooth edges. This cloud was generated near the downwind of the above three centers at 14, developed eastward, and weakened to death after 2 1, lasting for 8 hours. (3) The radar echo of this hail is a composite single rupture, with the center intensity of 60 ~ 65 dbz and the height of 1 1 ~ 12 km, which has obvious V-shaped and suspended echo characteristics. References [1] Bai, Xu, et al. Weather in Northwest China [M]. Beijing: Meteorological Press, 199 1, 3. [2] Gu Runyuan. Manual of weather forecast in Inner Mongolia Autonomous Region [M]. Beijing: Meteorological Press, 20 18.

What are the echo characteristics of heavy hail on radar map (5)

Application of satellite cloud image and radar echo in rainstorm analysis and forecast

In view of the annual rainstorm and rainstorm weather from July 2009 1995 to June 2009, the practical experience accumulated by satellite cloud picture and rainstorm forecast is fully utilized in each rainstorm weather process forecast, and the method of forecasting heavy precipitation by combining satellite cloud picture, cloud system characteristics and radar echo with weather situation is explored, and the cloud field model before rainstorm is summarized, which improves the accuracy of rainstorm forecast.

Satellite cloud picture; Keywords; Radar echo; Heavy rain; App application

China library classification number P457.6 document identification number a1007-5739 (2016) 04-0226-02.

The rainstorm is sudden and difficult to predict. It can accurately forecast the process of heavy precipitation, which plays an important role in improving the visibility of meteorological departments and reducing the loss of people's lives and property. In the practice of forecasting, we make full use of the practical experience accumulated by satellite cloud image analysis and rainstorm research and forecast, explore the method of forecasting rainstorm by combining satellite cloud image, cloud system characteristics and radar echo with weather situation, summarize the cloud field model before rainstorm, and improve the accuracy of rainstorm forecast. From July 1995 to May, 2009, there were five rainstorms and 1 rainstorm at this station, all of which were accurately predicted. The application of satellite cloud image and radar echo in rainstorm analysis and forecast is discussed.

1 forecast heavy precipitation by combining satellite cloud images and weather situation.

1.65438+

This is very effective for forecasting a single weather system with slow changes. The central intensity of the rainstorm can be estimated by the enhanced cloud image or the 1 h rainfall of the observation station in the bright cloud cluster of the automatic station at that time [1-2]. For example, in July 2005 1 1 day, the rainstorm weather process was characterized by the rapid start and end of the local precipitation process, strong rainfall and short duration of heavy precipitation. Thunderstorm, gale, hail and strong convective weather occurred in Chaoyang, with heavy precipitation time 15: 50- 17: 52 and precipitation of 65438. According to the record of precipitation, 16: 00- 17: 00, the precipitation reached 104.5 mm, and the wind speed reached 19 m/s and 16: 27-65438+.

The satellite cloud image shows that the unstable cloud system in the southwest warm and humid airflow at the edge of the subtropical high blocked the high pressure in front of the short wave trough and met the stable cloud system in the north-south direction, forming a cloud system with a large bending state. There is a new white cloud around the corner, which is located in the south of Chaoyang, which is the range of the rainstorm area. The process of cold air going south is complicated. Using cloud images to analyze the shape of high and low level jet in rainstorm forecast. Different regions have experienced frontogenesis and frontogenesis, and there are three cold air diffusion in the middle of the cold front, which stimulates the emergence of convective precipitation.

1.2 determining the position of jet axis in high and low altitude by using the characteristics of jet cloud system in satellite cloud image [1]

The position of the low-level jet axis is determined by the wind field of 700 HPA or 850 HPA, and then the rainstorm forecast is made according to the configuration (parallel or cross) of the high-level and low-level jet axis. For example, during the local rainstorm on July 14, 2008, the actual rainfall was 23.3 mm, and the rainfall in Sihedang and Goumenzi towns was 70.5 mm and 75.0 mm respectively. The cirrus line of southwest-northeast subtropical jet appears on the infrared cloud image and extends northward to the northwest of North China, indicating that the jet is strengthened. This cirrus line represents the upper jet axis, and when it tends to be parallel to the lower jet axis, it is a sign that there may be heavy rain. According to the white bright cloud area with heavy infrared and visible light cloud images, combined with the position of 700 hPa (or 850 hPa) low-level jet axis on the weather map, the approximate position, direction and path of the rainstorm area can be determined. The rainstorm area is located on the left side of the low-level jet axis, and the trend is consistent with the low-level jet axis, which is located in the high-low jet axis area in front of the low-level jet center and on the right side of the high-level jet center. The future path of the rainstorm area is along the high-altitude jet axis, that is, the direction of the jet cirrus line on the cloud map. The cumulus belt on the edge of subtropical high pressure of this rainstorm is the image reflection of the southeast water vapor conveyor belt, which is very clear on the cloud image. The configuration of high and low jets also has certain reference value for the forecast of rainstorm area.

1.3 Analysis of interaction between mid-low latitude system and rainstorm

The rainstorm in Chaoyang is mainly related to the interaction of the mid-low latitude system [2], and typhoon and low pressure are the main participants in the mid-low latitude system. This is clearly reflected in the satellite cloud image, so the cloud image is a powerful tool to analyze the interaction between middle and low latitudes. However, due to the complexity of the interaction process, we can't just rely on cloud images. It is best to make comprehensive use of satellite cloud images, weather maps and physical quantity distribution maps to achieve better rainstorm forecasting effect. For example,1June 65438+June 65438+June 09, 1996, the precipitation was 52.8 mm, and some towns were flooded (because there was no rainfall point at that time). After the typhoon weakens into a low pressure, it often combines with the northern cold front cloud belt, and the weakened typhoon cloud system strengthens at this time. Near or north of the typhoon, the airflow convergence is the most obvious and the vertical movement is the strongest. In addition, there is a temperature contrast between cold and warm air, and the high-altitude westerly jet accompanied by the cold front is located just to the north of the typhoon, which provides favorable divergence conditions for the rainstorm area. Therefore, there is heavy precipitation where the cold front cloud system intersects with the typhoon cloud system, and the main precipitation area is located in the north or northeast of the typhoon [3-4].

2. Forecast heavy rainfall by combining the characteristics of cloud system and weather situation.

(1) When there may be a situation of heavy precipitation on the weather map, use the characteristics of local cloud system and the development and evolution of other situation fields to judge whether there is a strong precipitation system influence in the local area in the next 24 hours.

(2) When the precipitation system has moved to the local area and the local area has developed from high clouds to medium clouds, the precipitation capacity of the cloud system is diagnosed according to the macroscopic physical characteristics of the cloud system, and the rainfall trend forecast for the next 24 hours is made. Affected by cold air and subtropical high, a regional rainstorm occurred in Chaoyang on July 5, which was the most extensive and intense since the flood season. The precipitation in all towns and villages exceeds 50 mm, and the precipitation in Siguanyingzi Town is 67.3 mm. On the afternoon of the 4th, it was found from the satellite cloud image of 1 time/hour and the local cloud system that a precipitation cloud moved slowly from southwest to northeast, so it was reported that there would be a relatively large precipitation process in the next 24 hours. At 2 1: 00 on the 4th, there was no doubt that the trail of the rainstorm was revealed, thus further clarifying the exact location of the rainstorm. At 2 o'clock on the 5th, the "front" of the rainstorm reached the edge of Chaoyang City, and it began to rain in the western region, followed by the precipitation of this station. Heavy rain occurred in some rainfall stations, and at 6: 48, the precipitation in five places exceeded 50 mm. According to the macroscopic physical characteristics of the cloud system, diagnose the precipitation capacity of the cloud system, determine that there will be 20 ~ 30 mm precipitation in the next 6 hours, and issue an early warning signal.

(3) If conditions permit, analyze the intensity of cloud field with the conventional cloud and cloud cover data in this area, and make the forecast of rainstorm area in the next 6 ~ 12 h (used to issue rainstorm warning signals). The rainstorm on June 9, 2003, the actual rainfall was 50.7 mm, which was based on the activity of a North China cyclone detected at (1) and (2). The method was used to forecast a local rainstorm on July 14, 2008, and good results were obtained.