Characteristic Analysis of the Downburst in Greely, Colorado on 30 July 2017 Using WPEA Method and X-Band Radar Observations
Abstract
:1. Introduction
2. Data and Methods
2.1. Data Sources
2.2. Method
3. Case Study
3.1. Atmospheric Circulation Situation
3.2. Atmospheric Environmental Conditions
3.3. Dual-Polarization Radar Observations
4. Conclusions
- (1)
- Features of the atmospheric environmental field: The most important feature of downburst occurrence was the uneven distribution of heat in the external atmosphere. The distribution structure determines the degree of instability of the atmosphere. Before the onset of the downburst, the 3θ diagram showed the angles of tilt of the θsed and θ* lines becoming larger relative to the T-axis, and the unstable layer before the onset of the downburst was at an altitude below the 780-hPa level (about 2.3 km). Furthermore, analysis of the wind field of the downburst system showed that the height of the downburst, at around 2.4 km, was highly consistent with that of the unstable layer of the atmospheric environmental fields. Therefore, a new finding in this paper is that the important locations to monitor for downbursts can be determined by studying the atmospherically unstable areas using the WPEA method.
- (2)
- The release of unstable energy was found to have strong correlation with the impending weather process. The distribution and content of water vapor are very important in the occurrence of a downburst. In the case study, water vapor continuously accumulated in the mid- and high-altitude layers before the onset of the downburst, while there was no obvious change of water vapor in the lower atmosphere. Thus, it can be asserted qualitatively that the downburst was a weather process that involved low precipitation accompanied by localized hail precipitation. Based on the information from the WPEA method, and combined with the dual-polarization characteristic variables (Zh (>50 dBz), Zdr (3–6 dB), Kdp (2–4°/km)) and CC (0.9–0.95), we can better distinguish the phase distribution of the hydrometeor in the process and greatly enhance the judgment of the possibility of the downburst.
- (3)
- It was clearly observed in the initial stage of the downburst that the ‘Zdr column’ thrust upward beyond the zero-degree layer. Furthermore, the strong upward movement was indicative of the continuous formation and growth of supercooled water droplets and small ice particles. These were similar to the conclusions from previous studies. But in this paper we further discovered that the formation of the downburst was found closely associated with the occurrence of and the extended height of the ‘Zdr column’. However, no downburst process was found in the position where there is no obvious ‘Zdr column’ in the upper atmosphere. Therefore, we can regard the ‘Zdr column’ as an important early warning indicator of the location of the downburst in this case. However, the validity of this conclusion needs more case studies to verify in the future.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Gain | 53 dBi |
---|---|
Beamwidth | 0.3° |
Sidelobe level | <36 dB |
Frequency | 9.41 GHz ± 30 MHz |
PRF max | 2.00 kHz |
Sensitivity (dual-wavelength mode) | −15 dBz, 10 km |
Range sampling | 1.5–192.0 m |
Dynamic range | 90 dB |
Scan type | PPI (360°, sector), RHI, fixed pointing, vertically pointing |
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Wang, H.; Chandrasekar, V.; He, J.; Shi, Z.; Wang, L. Characteristic Analysis of the Downburst in Greely, Colorado on 30 July 2017 Using WPEA Method and X-Band Radar Observations. Atmosphere 2018, 9, 348. https://doi.org/10.3390/atmos9090348
Wang H, Chandrasekar V, He J, Shi Z, Wang L. Characteristic Analysis of the Downburst in Greely, Colorado on 30 July 2017 Using WPEA Method and X-Band Radar Observations. Atmosphere. 2018; 9(9):348. https://doi.org/10.3390/atmos9090348
Chicago/Turabian StyleWang, Hao, Venkatachalam Chandrasekar, Jianxin He, Zhao Shi, and Lijuan Wang. 2018. "Characteristic Analysis of the Downburst in Greely, Colorado on 30 July 2017 Using WPEA Method and X-Band Radar Observations" Atmosphere 9, no. 9: 348. https://doi.org/10.3390/atmos9090348