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Xiang Li
,
Dongliang Yuan
,
Zheng Wang
,
Yao Li
,
Corry Corvianawatie
,
Dewi Surinati
,
Asep Sandra
,
Ahmad Bayhaqi
,
Praditya Avianto
,
Edi Kusmanto
,
Dirham Dirhamsyah
, and
Zainal Arifin

Abstract

The ocean currents in the Halmahera Sea are studied using a subsurface mooring deployed in the Jailolo Strait from November 2015 to October 2017. The subtidal currents of the mooring measurements are characterized by a two-layer system, with the current variability below about 200 m in opposite phases to that in the upper layer. The mean along-strait velocity (ASV) is toward the Indonesian seas in the whole water column, producing an estimated mean transport of 2.44 ± 0.42 Sv (1 Sv ≡ 106 m3 s−1). The errors of the transport calculation based on the single mooring measurements are estimated to be less than 15% using simulations of high-resolution ocean models. A weak current is observed to flow northward during 2017 at the bottom of the strait. The ASV variability is found to be dominated by an annual cycle both in the upper and lower layers. The total transport, however, is dominated by semiannual variability because of the cancelation of the annual transports in the upper and lower layers. The variability of the transport is suggested to be driven by the pressure difference between the Pacific Ocean and the Indonesian seas, as evidenced by the agreement between the satellite pressure gradient and the two-layer transports. The transport of the Jailolo Strait during the 2015/16 super El Niño is found to be nearly the same as that during the 2016 La Niña, suggesting that the interannual variability of the transport is much smaller than the seasonal cycle.

Free access
Xiantong Liu
,
Huiqi Li
,
Sheng Hu
,
Qilin Wan
,
Hui Xiao
,
Tengfei Zheng
,
Minghua Li
,
Langming Ye
,
Zheyong Guo
,
Yao Wang
, and
Zhaochao Yan

Abstract

According to the high-accuracy linear shape–slope (μ–Λ) relationship observed by several two-dimensional video disdrometers (2DVD) in South China, a high-precision and fast solution method of the gamma (Γ) raindrop size distribution (RSD) function based on the zeroth-order moment (M 0) and the third-order moment (M 3) of RSD has been proposed. The 0-moment M 0 and 3-moment M 3 of RSD can be easily calculated from rain mass mixing ratio Q r and total number concentration N tr simulated by the two-moment (2M) microphysical scheme, respectively. Three typical heavy-rainfall processes and all RSD samples observed during 2019 in South China were selected to verify the accuracy of the method. Relative to the current widely used exponential RSD with a fixed shape parameter of zero in the 2M microphysical scheme, the Γ RSD function using the linear constrained gamma (C-G) method agreed better with the Γ-fit RSD from 2DVD observations. The characteristic precipitation parameters (e.g., rain rate, M 2, M 6, and M 9) obtained by the proposed method are generally consistent with the parameters calculated by Γ-fit RSD from 2DVD observations. The proposed method has effectively solved the problem that the shape parameter in the 2M microphysical scheme is set to a constant, and therefore the Γ RSD functions are closer to the observations and have obviously smaller errors. This method has a good potential to be applied to 2M microphysical schemes to improve the simulation of heavy precipitation in South China, but it also paves the way for in-depth applications of radar data in numerical weather prediction models.

Full access
Qiang Wang
,
Lili Zeng
,
Jian Li
,
Ju Chen
,
Yunkai He
,
Jinglong Yao
,
Dongxiao Wang
, and
Weidong Zhou

Abstract

Cross-shelf flow induced by mesoscale eddies has been investigated in the northern South China Sea (NSCS) using velocity observations from Long Ranger ADCP moorings. Mesoscale eddies influenced the three mooring stations during almost all the observation period. Four quadrants have been defined with the mooring location as the origin, and it is found that warm (cold) mesoscale eddies induce onshore (offshore) movement in the eastern two quadrants and offshore (onshore) movement in the western two quadrants. When an eddy propagates past a mooring station, net cross-shelf flow at the mooring station can be induced by asymmetry in the horizontal and vertical structure of the eddy and by its evolution. As an eddy propagates westward, its shape changes continually and the vertical modes also transform from high to lower modes, which contributes to the net cross-shelf flow. Based on the quasigeostrophic potential vorticity equation, it is confirmed that the net cross-shelf flow is mainly induced by the eddy evolution and suppressed by nonlinear effect. Because of dispersion characteristics of the mesoscale eddy, barotropic mode will restructure at the baroclinic mode area after separating from the baroclinic mode, which will be enhanced by topography slope.

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Qingjing Hu
,
Peiran Yu
,
Yujiao Zhu
,
Kai Li
,
Huiwang Gao
, and
Xiaohong Yao

Abstract

In this paper, the concentration, the size distribution, and the formation of dimethylaminium (DMA+) and trimethylaminium (TMA+) ions in atmospheric particles were studied during a cruise campaign over the Yellow Sea and the Bohai Sea of China in May 2012. The concentrations of DMA+ and TMA+ in particles smaller than 11 µm were 4.4 ± 3.7 and 7.2 ± 7.1 nmol m−3, respectively. The two ions had a good correlation (R 2 = 0.86), and both had a moderately good correlation with chlorophyll a fluorescence (R 2 = 0.66–0.67). The observed concentrations were from one to three orders of magnitude larger than the concentrations reported in other marine atmospheres. They were also much larger than the values observed at a coastal site neighboring the Yellow Sea in May–June 2013. The high concentrations of DMA+ and TMA+ observed in the marine atmosphere were probably associated with local biogenic activity instead of the long-range transport of these species from adjacent continents. The calculated mole ratios of (DMA+ + TMA+) to in different-sized particles over the seas indicated that (DMA+ + TMA+) most likely played an important role in neutralizing acidic species in particles less than 0.43 µm but not in particles of other sizes. Size distributions of DMA+ and TMA+ in the marine and coastal atmospheres were analyzed in terms of the respective contribution of gas–particle partitioning, cloud/fog processing of TMA+ and DMA+, bioaerosols, and sea-salt aerosols to the observed concentrations of the two ions over the seas.

Full access
Xudong Liang
,
Yanxin Xie
,
Jinfang Yin
,
Yi Luo
,
Dan Yao
, and
Feng Li

Abstract

Dealiasing is a common procedure in radar radial velocity quality control. Generally, there are two dealiasing steps: a continuity check and a reference check. In this paper, a modified version that uses azimuthal variance of radial velocity is introduced based on the integrating velocity–azimuth process (IVAP) method, referred to as the V-IVAP method. The new method can retrieve the averaged winds within a local area instead of averaged wind within a full range circle by the velocity–azimuth display (VAD) or the modified VAD method. The V-IVAP method is insensitive to the alias of the velocity, and provides a better way to produce reference velocities for a reference check. Instead of a continuity check, we use the IVAP method for a fine reference check because of its high-frequency filtering function. Then a dealiasing procedure with two steps of reference check is developed. The performance of the automatic dealiasing procedure is demonstrated by retrieving the wind field of a tornado. Using the dealiased radar velocities, the retrieved winds reveal a clear mesoscale vortex. A test based on radar network observations also has shown that the two-step dealiasing procedure based on V-IVAP and IVAP methods is reliable.

Full access
Jun Yang
,
Weitao Lyu
,
Ying Ma
,
Yijun Zhang
,
Qingyong Li
,
Wen Yao
, and
Tianshu Lu

Abstract

The macroscopic characteristics of clouds in the Tibetan Plateau are crucial to understanding the local climatic conditions and their impact on the global climate and water vapor cycle. In this study, the variations of cloud cover and cloud types are analyzed by using total-sky images of two consecutive years in Shigatse, Tibetan Plateau. The results show that the cloud cover in Shigatse presents a distinct seasonal difference that is characterized by low cloud cover in autumn and winter and high cloud cover in summer and spring. July is the month with the largest cloud coverage, and its average cloud cover exceeds 75%. The probability of clouds in the sky is the lowest in November, with an average cloud cover of less than 20%. The diurnal variations of cloud cover in different months also have considerable differences. Specifically, cloud cover is higher in the afternoon than that in the morning in most months, whereas the cloud cover throughout the day varies little from July to September. The dominant cloud types in different months are also not the same. The proportion of clear sky is large in autumn and winter. Stratiform cloud occupies the highest percentage in March, April, July, and August. The probability of emergence of cirrus is highest in May and June. The Shigatse region has clear rainy and dry seasons, and correlation analysis between precipitation and clouds shows that the largest cumulative precipitation, the highest cloud cover, and the highest proportion of stratiform clouds occur simultaneously in July.

Full access
Chundi Hu
,
Qigang Wu
,
Song Yang
,
Yonghong Yao
,
Duo Chan
,
Zhenning Li
, and
Kaiqiang Deng

Abstract

In this study, the authors apply a lagged maximum covariance analysis (MCA) to capture the cross-seasonal coupled patterns between the Southern Ocean sea surface temperature (SOSST) and extratropical 500-hPa geopotential height anomalies in the Southern Hemisphere, from which Niño-3.4 signals and their linear trends are removed to a certain extent. Statistically significant results show that the dominant feature of ocean–atmosphere interaction is likely the effect of atmosphere on SOSST anomalies, with a peak occurring when the atmosphere leads the SOSST by 1 month.

However, the most eye-capturing phenomenon is that the austral autumn atmospheric signal, characterized by a negatively polarized Antarctic Oscillation (AAO), is significantly related to the gradual evolution of preceding SOSST anomalies, suggesting that the SOSST anomalies tend to exert an effect on the Southern Hemisphere atmospheric circulation. A regression analysis based on SOSST anomaly centers confirms these features. It is also demonstrated that the gradual evolution of changes in SOSST is mainly driven by internal atmospheric variability via surface turbulent heat flux associated with cold or warm advection and that the atmospheric circulation experiences a change from a typical positive AAO to a negative phase in this process. These findings indicate that such a long lead cross-seasonal covariance could contribute to a successful prediction of AAO-related atmospheric circulation in austral autumn from the perspective of SOSST anomalies, with lead times up to 6–7 months.

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Chunyan Zhang
,
Donghai Wang
,
Lebao Yao
,
Zhenzhen Wu
,
Qianhui Ma
,
Yongsheng Li
, and
Peidong Wang

Abstract

This study investigates and compares large-scale moisture and heat budgets over the eastern rainy sea area around Dongsha, the western rainless sea area around Xisha, and the northern coastland of the South China Sea. Ten-year (2011–20) surface, balloon-sounding, satellite measurements, and ERA5 reanalysis are merged into the physically consistent data to study annual and vertical variations of the budgets. It shows that the surface and column-integrated heat and moisture budgets have the smallest annual evolution over the coastland. The latent heat as a key heat contributor in summer is mainly offset by total cold advection and partially offset by net radiative cooling. The horizontal moisture advection below 700 hPa presents moistening over the sea whereas drying over the coastland during rainy months, in which the vertical moisture advection presents moistening up to 250 hPa for all three subregions. The horizontal temperature advection is weak throughout the year over the sea but displays strong top warming and bottom cooling in summer and nearly the opposite in winter over the coastland. The diabatic cooling with a peak at ∼700 hPa in winter is largely due to the enhanced radiative cooling and latent cooling. While the diabatic heating with a peak at ∼500 hPa in summer is largely due to the enhanced latent heating. The earliest atmospheric heating and moistening occur in spring over the coastland, inducing the earliest precipitation increase. The enhanced heating and moistening over Xisha have a 1-month lag relative to Dongsha, resulting in lagging precipitation.

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Yingbin He
,
Dongmei Liu
,
Yanmin Yao
,
Qing Huang
,
Jianping Li
,
Youqi Chen
,
Shuqin Shi
,
Li Wan
,
Shikai Yu
, and
Deying Wang

Abstract

In this paper, an integrated indicator-based system is established to map the suitability of spring soybean cultivation in northeast China. The indicator system incorporates both biophysical and socioeconomic factors, including the effects of temperature, precipitation, and sunshine on the individual development stages of the spring soybean life cycle. Spatial estimates of crop suitability derived using this indicator system are also compared with spring soybean planting areas to identify locations where there is scope for structural adjustment in soybean farming. Results of this study indicate that northeast China is moderately suited to spring soybean cultivation. Areas classified as suitable, moderately suitable, and unsuitable for soybean cultivation, respectively, occupy approximately 9.09 × 104, 11.45 × 104, and 7.99 × 104 km2, accounting for 11.5%, 10.11%, and 14.49% of the total area of northeast China. The Songnen and Sanjiang Plains are identified as the most and least suitable places, respectively, for spring soybean growth. A comparative analysis indicates that the suitable, moderately suitable, and unsuitable areas account for 24.78%, 46.30%, and 28.92%, respectively, of the total area presently under soybean cultivation. The analysis suggests that soybean cultivation in Heilongjiang Province is generally unfavorable, with equivalent percentages of 15.39%, 51.70%, and 32.91%. Results suggest that agricultural structural adjustment may be required to encourage farmers to grow spring soybeans. It is anticipated that this study will provide a basis for follow-up studies on crop cultivation suitability.

Full access
Yongliang Jiao
,
Ren Li
,
Tonghua Wu
,
Lin Zhao
,
Xiaodong Wu
,
Junjie Ma
,
Jimin Yao
,
Guojie Hu
,
Yao Xiao
,
Shuhua Yang
,
Wenhao Liu
,
Yongping Qiao
,
Jianzong Shi
,
Erji Du
,
Xiaofan Zhu
, and
Shenning Wang

Abstract

Climate changes significantly impact the hydrological cycle. Precipitation is one of the most important atmospheric inputs to the terrestrial hydrologic system, and its variability considerably influences environmental and socioeconomic development. Atmospheric warming intensifies the hydrological cycle, increasing both atmospheric water vapor concentration and global precipitation. The relationship between heavy precipitation and temperature has been extensively investigated in literature. However, the relationship in different percentile ranges has not been thoroughly analyzed. Moreover, a percentile-based regression provides a simple but effective framework for investigation into other factors (precipitation type) affecting this relationship. Herein, a comprehensive investigation is presented on the temperature dependence of daily precipitation in various percentile ranges over the Qinghai–Tibet Plateau. The results show that 1) most stations exhibit a peaklike scaling structure, while the northeast part and south margin of the plateau exhibit monotonic positive and negative scaling structures, respectively. The scaling structure is associated with the precipitation type, and 2) the positive and negative scaling rates exhibit similar spatial patterns, with stronger (weaker) sensitivity in the south (north) part of the plateau. The overall increase rate of daily precipitation with temperature is scaled by Clausius–Clapeyron relationship. 3) The higher percentile of daily precipitation shows a larger positive scaling rate than the lower percentile. 4) The peak-point temperature is closely related to the local temperature, and the regional peak-point temperature is roughly around 10°C.

Significance Statement

This study aims to better understand the relationship between precipitation and surface air temperature in various percentile ranges over the Qinghai–Tibet Plateau. This is important because percentile-based regression not only accurately describes the response of precipitation to warming temperature but also provides a simple but effective framework for investigating other factors (precipitation type) that may be affecting this relationship. Furthermore, the sensitivity and peak-point temperature are evaluated and compared among different regions and percentile ranges; this study also attempts to outline their influencing factors. To our knowledge, this study is the first integration of percentile-based analysis of the dependence of daily precipitation on surface air temperature.

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