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  • Author or Editor: Yuan Wang x
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Jinfeng Ding, Xiaoyong Zhuge, Xin Li, Zipeng Yuan, and Yuan Wang

Abstract

Two comparative studies have been performed to evaluate the accuracy of Chinese Aircraft Meteorological Data Relay (AMDAR) weather reports. The comparison between AMDAR reports and radiosonde observations shows that the root-mean-square differences (RMSDs) in temperature, wind speed, and wind direction are 1.06°C, 1.95 m s−1, and 22°, respectively, within a spatial range of ≤20 km and a temporal window of ≤15 min. The comparison between AMDAR reports collected by different aircraft reveals that observation uncertainties in temperature, wind speed, and wind direction are 0.59°C, 0.90 m s−1, and 12°, respectively. The spatial and temporal representativeness as well as the environmental factors that may affect the evaluation results are also discussed in detail in the two comparative studies. The results of the present study provide valuable information on and high confidence in the application of Chinese AMDAR in numerical weather prediction models.

Open access
Jinfeng Ding, Xiao-Yong Zhuge, Yuan Wang, and Anyuan Xiong

Abstract

Aircraft Meteorological Data Relay (AMDAR) weather reports are a type of high spatiotemporal data currently widely used in weather monitoring and prediction. A recent Chinese AMDAR project began in 2003 has made rapid progress. However, the assessment and accuracy of these Chinese AMDAR reports have yet to be thoroughly discussed. A comparison of temperature and wind observations between Chinese AMDAR reports and rawinsonde data between 2004 and 2010 is conducted in this paper. Results demonstrate that the root-mean-square error (RMSE) between these two sets of data is 1.40°C for temperature, 3.56 m s−1 for wind speed, and 28° for wind direction. Because of the particularity of observation and inversion method, comparison results are not only affected by AMDAR measurement and reporting error but also by spatial and temporal representativeness, flight phases, and the environment. This evaluation helps create a complete estimation of the accuracy of Chinese AMDAR in order to assist with data assimilation.

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Wei Wang, Jiaping Xu, Yunqiu Gao, Ivan Bogoev, Jian Cui, Lichen Deng, Cheng Hu, Cheng Liu, Shoudong Liu, Jing Shen, Xiaomin Sun, Wei Xiao, Guofu Yuan, and Xuhui Lee

Abstract

Performance evaluation of an integrated eddy covariance (EC) instrument called the IRGASON, with a separated EC for reference, was conducted in a desert riparian Populus euphratica stand in the lower Tarim River basin in northwestern China. The separated EC consisted of an open-path gas analyzer and a sonic anemometer separated by 20 cm. The IRGASON integrates an open-path gas analyzer and a sonic anemometer into the same sensing volume, thus eliminating sensor separation in comparison to the traditional open-path EC setup. Integrating the infrared gas analyzer’s sensing head into the sensing volume of the sonic anemometer had negligible effects on wind speed and friction velocity observations of the IRGASON. Physiologically unreasonable daytime CO2 uptake was observed by both systems during the cold winter season (mean air temperature of −6.7°C), when the trees were dormant without any photosynthetic activities. The mean midday CO2 flux was −1.65 and −1.61 μmol m−2 s−1 for the IRGASON and the separated EC setup, respectively. No evidence was found for sensor self-heating as the cause of the apparent uptake CO2 flux. Instead, the uptake CO2 flux appeared to be an artifact of the spectroscopic effect of the IRGASON’s gas analyzer. After adjusting for this spectroscopic effect using a relationship with the sensible heat flux, the wintertime IRGASON CO2 flux became physiologically reasonable (mean value of −0.04 μmol m−2 s−1).

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Jenn-Shyong Chen, Jian-Wu Lai, Hwa Chien, Chien-Ya Wang, Ching-Lun Su, Kun-I Lin, Meng-Yuan Chen, and Yen-Hsyang Chu

Abstract

A VHF pulsed radar system was set up on the Taoyuan County seashore (24°57′58″N, 121°00′30″E; Taiwan) to observe the sea surface in the northern Taiwan Strait for the first time. The radar used a four-element, vertically polarized Yagi antenna to transmit the 52-MHz radar wave. The receiving linear array consists of four vertical dipole antennas that were located 3 m apart and attached with four independent and identical receivers. With the multichannel echoes, the direction of arrival (DOA) of the radar echoes were determined by using an optimization beamforming approach—the Capon method. Echo intensity was observed to vary principally in semidiurnal oscillation, which matched well the time series of tide gauge measurements and sea level simulations. In addition, the oscillatory characteristics of Doppler/radial velocity of the VHF radar were generally consistent with that of the HF coastal ocean dynamics applications radar (CODAR) nearby. Nevertheless, the contributions of various tidal modes to the parameters of DOA, echo intensity, radial velocity, and spectral width, varied with the range and time period (e.g., neap or spring tides). For example, the semidiurnal tides governed the variation in the echo center only in the range interval between ~15 and ~25 km from the seashore but dominated other parameters throughout the detectable range. Correlations and phase relationships between these parameters were diverse; they varied with time and had dramatic changes at around the distances of 3 and 10 km. Possible causes of these features were discussed, including sea surface wind, nearshore current, sea level height, and bathymetric effect.

Open access