Observation of Clear-Air Echoes with 3.2-cm Radars

Takeda, Takeshi; Murabayashi, Shigeru

doi:10.2151/jmsj1965.59.6_864

Cited by 6 publications

(6 citation statements)

References 26 publications

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“…As a result of the analysis of the AMeDAS precipitation data (Figures not shown), it turned out that no precipitation was observed near the echoes around 1500 JST on the days. Therefore, it is possible that the echoes near the northeast of Nagoya are clear air echoes (Takeda and Murabayashi 1981;Kusunoki 2002), and then the present study can not judge whether the echoes represent precipitation and the clouds northeast of Nagoya can bring precipitation. However, Seko and Takeda (1987) observed quasi-steady radar echoes of an isolated organized cumulonimbus and a local heavy rainfall at the northeast of Nagoya (Kasugai City), in the afternoon on a summer day with no distinct fronts and strong disturbances around Japan.…”

Section: Cloud Distributionmentioning

confidence: 64%

Time Variation of Cloud Distribution near Surface Wind Convergence Zone in the Nobi Plain during Daytime on Summer Sunny Days

Tsunematsu

Kai

2004

Journal of the Meteorological Society of Japan

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The present study investigates the relationship between surface wind convergence and clouds by performing statistical analyses of time variations in surface wind field, its horizontal divergence, cloud distribution, and appearance frequency of radar echoes in the Nobi Plain in the daytime on summer sunny days using various observation data from 1990 to 1999. The 99 summer sunny days when general wind was weak were selected objectively in advance of the analyses. The results of analyses show that a westerly wind from the Biwa Lake direction and a sea breeze from Ise Bay converge in the north of Nagoya after 1300 JST on summer sunny days. In addition, clouds (cumulus) tend to be formed all over the Nobi Plain from late in the morning to about noon by thermal convections, and the formation of clouds continues near strong surface wind convergence zones until around 1500 JST on summer sunny days, although clouds are hardly formed in the afternoon in almost all parts of the plain due to the decline of the thermal convections. The continuation of the cloud formation is especially remarkable at the northeast of Nagoya. Thus, in the Nobi Plain on summer sunny days, the conditions where clouds are easily formed continue at the northeast of Nagoya until around 1500 JST, because of a strong surface wind convergence between a westerly wind from the Biwa Lake direction and a sea breeze from Ise Bay. The analysis of radar echoes observed around 1500 JST shows that the echoes occasionally appear near the northeast of Nagoya on summer sunny days. These results indicate that the strong surface wind convergence plays an important role in the formation of clouds, after thermal convection has weakened, on summer sunny days.

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Section: Cloud Distributionmentioning

confidence: 64%

Time Variation of Cloud Distribution near Surface Wind Convergence Zone in the Nobi Plain during Daytime on Summer Sunny Days

Tsunematsu

Kai

2004

Journal of the Meteorological Society of Japan

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“…Values of of insect echoes observed by Ka-band radars can be up to 0 dBZ (Luke et al 2008;Browning et al 2011), i.e., larger than observed in the present study (<−10 dBZ). It is considered that the difference in maximum reflects the difference in the backscattering cross section depending on the observed insect (Takeda and Murabayashi 1981;Martin and Shapiro 2007).…”

Section: Discussionmentioning

confidence: 99%

“…Knight and Miller (1993) examined the early stage of precipitation formation in clouds and highlighted that Bragg scattering can affect the equivalent radar reflectivity ( ) at magnitudes of <10, 0, and −10 dBZ for S-(10-cm), C-(5-cm), and X-band (3-cm) radars, respectively. Biological echoes have been observed associated with birds (Harper 1958;Russell et al 1998;Diehl et al 2003;Minda et al 2008; Van Den Broeke 2013), bats (Horn and Kunz 2008;Pennisi 2011;Rauber and Nesbitt 2018;Meade et al 2019), and insects (Glover et al 1966;Riley 1975;Takeda and Murabayashi 1981;Kusunoki 2002). Birds and bats show characteristic circular echoes when leaving their roost (Pennisi 2011; Van Den Broeke 2013; Rauber and Nesbitt 2018), whereas a flock of migrating birds typically shows as an irregular line in a radar echo when in V-shaped flight formation (Minda et al 2008;Rauber and Nesbitt 2018).…”

Section: Introductionmentioning

confidence: 99%

Clear-Air Echoes Observed by Ka-band Polarimetric Cloud Radar: A Case Study on Insect Echoes in the Tokyo Metropolitan Area, Japan

Ohigashi

Maesaka

Suzuki

et al. 2021

Journal of the Meteorological Society of Japan

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In this study, the polarimetric variables of clear-air echoes (CAEs), that appeared on May 21, in the Tokyo metropolitan area, Japan, were investigated using Ka-band (8.6-mm-wavelength) polarimetric cloud radar capable of detecting non-precipitating clouds. The objective was to establish the potential for distinguishing CAEs and hydrometeor echoes in the initial stage of cloud formation using Ka-band polarimetric cloud radar. On the studied day, CAEs showed evident diurnal variation. There were no CAEs before sunrise. The equivalent radar reflectivity () increased with time after sunrise and horizontally widespread echoes (max. value > −15 dBZ) occurred within the radar observation range in the early afternoon. After sunset and into the early part of the night, decreased rapidly. Range-height indicator observations showed CAEs were restricted to heights of <1.5 km. The differential reflectivity () values of the CAEs were largely positive (1.8 dB) with large standard deviation at 18:00 local time, i.e., considerably larger than those of cloud/weak precipitation echoes (0.4 dB) observed simultaneously. In comparison with cloud/precipitation echoes, the copolar correlation coefficient () of the CAEs was smaller (<0.9), while the variability of the total differential phase (Ψ) in the range direction was larger. The upper limit of and the distributions of and were inconsistent with the characteristics of Bragg scattering observed by S-band (10-cm-wavelength) radar in previous studies. However, the larger , smaller , and larger variability of Ψ in the range direction, 3 associated with the horizontally widespread echoes, were consistent with the characteristics of insect echoes. The depolarization ratio, defined using and , could be effective in distinguishing this type of CAE and hydrometeor echoes observed by Ka-band polarimetric cloud radar. The polarimetric variables obtained by Ka-band polarimetric cloud radar are useful in distinguishing between CAEs and hydrometeor echoes.

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Section: Methodology 221 Bayesian Approach For the Identification Of Catsmentioning

confidence: 99%

“…Clear air turbulence echoes (hereafter CATs) can be observed by X-band radar [4][5][6]. The CATs of five X-POLs are source of contaminations for radar precipitation estimations, it is need to remove CATs and only retain the precipitation echoes.…”

Section: Introductionmentioning

confidence: 99%

Clear-Air Turbulence (CAT) Identification with X-Band Dual Polarimetric Radar Based on Bayesian Approach

Ma¹,

Luo²,

Chen³

et al. 2021

Atmosphere

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The echo of weather radar is seriously disturbed by clear-air turbulence echo (CAT) which needs identifying and eliminating to improve the data quality of weather radar. Using the data observed with the five X-band dual polarimetric radars in Changping, Fangshan, Miyun, Shunyi, and Tongzhou, Beijing in 2018, the probability density distribution (PDD) of the horizontal texture of four radar moments reflectively factor (ZH), differential reflectivity (ZDR), correlation coefficient (ρHV), differential propagation phase shift (ΦDP), and then the CAT is identified and removed using Bayesian method. The results show that the radar data can be effectively improved after the CAT has been eliminated, which include: (1) the removal rate of CAT is more than 98.2% in the analyzed cases. (2) In the area with high-frequency distribution of CAT, the CAT can be effectively suppressed; in the area with low-frequency distribution, some weather echo in the edge with SNR < 15 dB may be mistakenly identified as CAT, but the proportion of meteorological echoes to the total echoes is more than 85%, which indicate that the error rate is very low and does not affect the radar operation.

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Observation of Clear-Air Echoes with 3.2-cm Radars

Abstract: Clear-air echoes were observed in Nagoya with two radars of 3.2 cm in wavelength. Most of echoes were dot echoes.

Cited by 6 publications

References 26 publications

Time Variation of Cloud Distribution near Surface Wind Convergence Zone in the Nobi Plain during Daytime on Summer Sunny Days

Time Variation of Cloud Distribution near Surface Wind Convergence Zone in the Nobi Plain during Daytime on Summer Sunny Days

Clear-Air Echoes Observed by Ka-band Polarimetric Cloud Radar: A Case Study on Insect Echoes in the Tokyo Metropolitan Area, Japan

Clear-Air Turbulence (CAT) Identification with X-Band Dual Polarimetric Radar Based on Bayesian Approach

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