A Method for Retrieving Vertical Air Velocities in Convective Clouds over the Tibetan Plateau from TIPEX-III Cloud Radar Doppler Spectra
Abstract
:1. Introduction
2. Materials and Methods
2.1. Experiment, Instrument, and Measurements
2.2. Data Processing of Cloud Radar Doppler Spectra
2.3. Retrieval Method
2.3.1. Essential Idea
2.3.2. Integrated Retrieval Technique Using Multimode Doppler Spectra
- (1)
- The three operational modes have different sensitivities, detectable height ranges, Nyquist velocities, and spectral velocity resolutions. These key performance parameters are crucial for the estimation of vertical air velocity. Thus, comprehensive usage of the multimode data needs to be considered to obtain more reasonable and accurate results.
- (2)
- Convective clouds over the TP commonly vary rapidly with small scales, and, thus, the measured radar Doppler spectra in a sampling volume can be broadened by the active turbulence, wind shear, and inhomogeneous horizontal wind, which will cause bias to the retrieval results. Therefore, spectral broadening needs to be further revised.
- (3)
- Because of a low melting layer altitude of approximately 1 km on the TP, hydrometeors in the interior of convective cells exist mostly in the ice phase, which typically involves greater diameters than the liquid phase. Furthermore, the rain droplets under the cloud base also have relatively large diameters. Therefore, as the fall velocities of the traced targets in the radar sampling volume cannot be neglected, the possible biases that this introduces to the small-particle-traced idea need to be documented.
3. Results
3.1. Two Typical Cases
3.2. Comparing with Retrieval Resulst from a Disdrometer
4. Discussion
5. Conclusions
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Items | Technical Specifications |
---|---|
Radar system | Doppler, solid-state, depolarization, multi-mode |
Frequency | 33.44 GHz |
Wavelength | 8.9 mm |
Transmitted peak power | ≥100 W |
Sensitivity | −38 dBZ at 5 km |
Antenna diameter | 2 m |
Antenna gain | ≥53 dB |
Pulse width | 0.2 , 12 |
Beam width | 0.3° |
Pulse repetition frequency | 8333 Hz |
Range gate number | 510 |
Detection range | Height: 150 m ~ 15.3 km |
Measurable reflectivity range: −50 ~ 30 dBZ | |
Unambiguous velocity range: −18.54 ~ +18.54 m·s−1 (maximum) | |
Resolution | Temporal resolution: ~9 s (adjustable) |
Vertical resolution: 30 m | |
horizontal resolution: 26 m at 5 km | |
Measurements | Original data: Doppler spectra |
Spectral moments: reflectivity (Z), mean Doppler velocity (MV), spectrum width (), linear depolarization ratio (LDR), skewness (), kurtosis (), etc. |
Parameters | Mode | ||
---|---|---|---|
BL | CI | PR | |
Detectable range (km) | 0.12–7.5 | 2.04–15.3 | 0.12–12 |
Pulse width () | 0.2 | 12 | 0.2 |
Pulse period () | 120 | 120 | 120 |
Pulse repetition frequency (Hz) | 8333 | 8333 | 8333 |
Number of coherent integrations | 4 | 2 | 1 |
Number of incoherent integrations | 16 | 32 | 64 |
Sensitivity | −24 dBZ at 5km | −38 dBZ at 5km | −18 dBZ at 5km |
Spectral bin number | 256 | 256 | 256 |
Nyquist velocity (m·s−1) | ±4.635 | ±9.27 | ±18.54 |
Velocity resolution (cm·s−1) | 3.64 | 7.27 | 14.54 |
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Zheng, J.; Liu, L.; Zhu, K.; Wu, J.; Wang, B. A Method for Retrieving Vertical Air Velocities in Convective Clouds over the Tibetan Plateau from TIPEX-III Cloud Radar Doppler Spectra. Remote Sens. 2017, 9, 964. https://doi.org/10.3390/rs9090964
Zheng J, Liu L, Zhu K, Wu J, Wang B. A Method for Retrieving Vertical Air Velocities in Convective Clouds over the Tibetan Plateau from TIPEX-III Cloud Radar Doppler Spectra. Remote Sensing. 2017; 9(9):964. https://doi.org/10.3390/rs9090964
Chicago/Turabian StyleZheng, Jiafeng, Liping Liu, Keyun Zhu, Jingya Wu, and Binyun Wang. 2017. "A Method for Retrieving Vertical Air Velocities in Convective Clouds over the Tibetan Plateau from TIPEX-III Cloud Radar Doppler Spectra" Remote Sensing 9, no. 9: 964. https://doi.org/10.3390/rs9090964