Why do we carry out vertical profile observation and what is the status quo and development of vertical profile observation of the China Meteorological Administration (CMA)?

This article will offer a thorough overview. Let's dig deeper.

1. Why do we carry out vertical profile observation？

Vertical meteorological observation refers to the three-dimensional and continuous detection of meteorological elements (such as temperature, humidity, wind, aerosol, water condensates) at different altitudes. Ground-based vertical profile observation system (VPOS) integrates millimeter-wave cloud radar, microwave radiometer, Global Navigation Satellite System/ Meteorology (GNSS/MET), wind profile radar and aerosol lidar. It realizes high spatio-temporal resolution continuous observation of meteorological elements at different altitudes such as temperature, humidity, wind, aerosol, and water condensates. This system is designed to characterize the variations in atmospheric vertical structure and provides critical data support for meteorological research, severe weather forecasting, and numerical weather prediction (NWP).

2. Composition of the VPOS

The VPOS is composed of five types of observation equipment, including millimeter-wave cloud radar, microwave radiometer, GNSS/MET, wind profile radar, aerosol lidar and a set of ground-based remote sensing vertical profile integrated system, which realizes the synergistic observation of temperature, humidity, wind, aerosol and water condensates profiles.

Fig. 1 Composition of the VPOS

3. What are the VPOS products?

a. Wind profile radar observation product

The wind profile radar continuously provides height-distributed variations in meteorological parameters, such as horizontal wind field and vertical airflow.

Fig. 2 Wind profile radar

Basic meteorological products: Horizontal wind (direction, speed), vertical velocity, and constant of refractive index of atmospheric structure（Cn2）

Temporal resolution: 6 min

Spatial resolution: at 120 m intervals

Sounding height:150 m to 6 km

Fig. 3 Wind profile radar horizontal wind products

Fig. 4 wind profile radar vertical velocity products

b. Millimeter-wave cloud radar observation product

Millimeter-wave cloud radar delineates the vertical evolution of cloud with high precision and retrieves cloud-base/cloud-top heights.

Fig. 5 Millimeter-wave cloud radar

Basic meteorological products: reflectivity factor, radial velocity, velocity spectrum width, and linear depolarization ratio

Temporal resolution: 1 min

Spatial resolution: 30 m

Sounding height: 150 m to 20 km

Fig. 6 Reflectivity factor

Fig. 7 Radial velocity

Fig. 8 Velocity spectrum width

Fig. 9 Linear depolarization ratio

c. Microwave radiometer observation product

The microwave radiometer provides continuous vertical profiles of temperature, relative humidity and water vapor density.

Fig. 10 Microwave radiometer

Basic Meteorological Products: Temperature, relative humidity, and water vapor density

Temporal resolution: 2 min

Spatial resolution: 25 m/50 m/ 250 m

Sounding height: 0 to 10 km

                    （A）                     （B）                      （C）

Fig. 11 Microwave radiometer products (A:Temperature B: Relative humidity C:Water vapor density)

Fig. 12 Characteristic level heights

(Red line: 0℃ level; Blue line: -20℃ level)

Fig. 13 Integrated water vapor (red line) and liquid water path (blue line)

d. Aerosol lidar observation product

Aerosol lidar can detect the optical and physical properties of aerosols, and monitor aerosol concentration and particle distribution in real time.

Fig. 14 Aerosol lidar

Basic meteorological products: Extinction coefficient, backscatter coefficient, and depolarization ratio

Temporal resolution: 1 min

Spatial resolution: at 30 m intervals

Sounding height: 0 to 10 km

Fig. 15 Extinction coefficient

Fig. 16 Backscatter coefficient

Fig. 17 Depolarization ratio

e. GNSS/MET observation product

Invert the water vapor content and vertical distribution profiles in the atmosphere by using the delay effect caused by water vapor and other factors when the GNSS satellite signal passes through the atmosphere.

Fig. 18 GNSS/MET

Basic Meteorological Products: Zenith total delay, and precipitable water vapor

Temporal resolution: 5 min

Fig. 19 Zenith total delay

Fig. 20 Precipitable water vapor

f. Multi-element integrated product

The VPOS is able to simultaneously observe temperature, humidity, wind, aerosols and water condensates, which can generate multi-element integrated products.

Fig. 21 Five vertical profiles in one plot (left) and temperature-logarithmic pressure diagram (right)

g. Low-level jet products

The horizontal wind field can be used to retrieve low-level jet products, including low-level jet surface products below 600 hPa, low-level jet vertical products and low-level jet index. The products can characterize water vapor conditions and uplift triggering mechanisms, which are mainly used in nowcasting services for severe convection.

Fig. 22 Low-level jet products

h. Multi-source fused cloud-top analysis product

Satellite brightness temperature information and cloud top height products from millimeter wave cloud radar observation are harnessed, performing spatiotemporal matching and data fusion to form a space-ground integrated cloud top height areal products.

Fig. 23 Cloud top height areal product of space-ground integration

i. Temperature advection product

Horizontal wind fields can be used to derive temperature advection product, which reflects the stability of atmospheric stratification. If the vertical variation rate of temperature advection is greater than 0, it indicates enhanced unstable stratification, which is favorable for the development of weather systems. This product is commonly used in monitoring cold wave.

Fig. 24 Temperature advection product

4. Application cases of the VPOS

a. Snowfall case in Beijing on February 20, 2024

Through the comprehensive analysis of relative humidity profile products and cloud/precipitation type products, it is evident that starting from 03:00 on February 20, influenced by a southwesterly warm moist airflow, humidity significantly increased around 3 km altitude. The moist layer expanded to 1-6 km, providing ample moisture conditions for snowfall. By 17:00, the precipitation phase was transformed to snow at the surface. The onset time of snowfall was detected earlier by the VPOS than by the surface stations.

Fig. 25 Millimeter wave cloud radar surface precipitation classification product

Fig. 26 Microwave radiometer temperature and humidity profile products

b. Haze case in Beijing from March 5 to 9, 2023

According to the comprehensive analysis of extinction coefficient, temperature profile, horizontal wind, boundary layer height, and humidity profile fusion products, the concentration of haze was higher during the morning of March 5 to March 6 and early morning of March 7 to March 8. From the night of the March 5 to the morning of March 6, and on the morning of March 7, the near-surface humidity was higher, which was conducive to the hygroscopic growth of haze particles. Between the morning of March 5 until 00:00 on March 6, and from the afternoon of March 6 to the afternoon of March 7, the middle and lower atmospheric layers were dominated by southerly wind, which were favorable for the transport and accumulation of haze with the help of the northern terrain. Temperature inversion layer existed during three critical periods: night of March 5 to morning of March 6, night of March 6 to morning of March 7, and night of March 7 to morning of March 8, and the boundary layer height was low, which was not conducive to the diffusion of haze.

Fig. 27 Aerosol lidar extinction coefficient product

Fig. 28 Microwave radiometer temperature profile product

Fig. 29 Integrated product of horizontal wind, boundary layer height, and humidity profile

In collaboration with Department of Integrated Observations of CMA and CMA Meteorological Observation Centre (MOC)

Image source: CMA MOC

Editor: LIU Shuqiao