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Lihong Wei
,
Xihui Gu
,
Louise J. Slater
,
Yangchen Lai
,
Dongdong Kong
,
Jianyu Liu
,
Jianfeng Li
, and
Xiang Zhang

Abstract

Precipitation induced by tropical cyclones (TCs) over cities is associated with both TC duration and urbanization; however, observational evidence of the impacts of TC duration and urbanization on precipitation in megalopolises is limited. In this study, the Yangtze River Delta (YRD) of eastern China is taken as a typical region because this region has been experiencing both rapid urbanization processes and frequent TC attacks. During 1979–2018, we find reduced translation speed and increased meandering of TCs over the YRD, resulting in increased TC duration and the proportion of TC stalling in this region. The correlation between TC duration and TC-induced precipitation amount is significant across the YRD region but is relatively weak in areas with faster urbanization expansion rates. Long-term increases in TC-induced precipitation are found in both rural and urban areas but are larger for urban areas. Urbanization plays an important role in enhancing TC-induced precipitation over urban areas of the YRD region. Areas with faster urbanization expansion rates and longer TC durations have larger TC-induced precipitation, suggesting that urban expansion and TC duration jointly amplify TC-induced precipitation. Our findings suggest that urban planners, in areas potentially affected by TCs, should consider adaptation measures to mitigate the impacts of urban rainstorms amplified by the combined effects of TCs and urbanization.

Significance Statement

The combined impacts of tropical cyclone (TC) duration and urbanization on precipitation have received limited attention, especially in populated urban areas. Here, we focus on the Yangtze River Delta (YRD) of eastern China, an urban agglomeration frequently impacted by TCs. We find that slowed translation and increased meandering of TCs have led to longer TC duration and stalling over the 500-km YRD buffer during 1979–2018. Significant positive correlation between TC duration and TC-induced precipitation indicates that longer-lasting TCs trigger greater precipitation. The greater TC-induced precipitation due to increased TC duration is further amplified by urban expansion.

Restricted access
Mengyu Wei
,
Jun Yang
,
Yongyun Hu
,
Yonggang Liu
,
Shineng Hu
,
Xiang Li
,
Jiawenjing Lan
,
Jiaqi Guo
,
Shuai Yuan
, and
Ji Nie

Abstract

Both observations and simulations show that under global warming there exists warming deficit in the North Atlantic, known as the North Atlantic warming hole (NAWH). Here we show that similar warming hole occurs in the sub-polar Pacific ocean of paleo-climate simulations. As solar constant is increased, local surface becomes substantially cooler rather than warmer in the sub-polar paleo-Pacific ocean under the land-sea configurations of 70, 90, and 150 million years ago (Ma). The warming hole has a magnitude of ≈3 °C and locates in the Northern Hemisphere in 70Ma and 90Ma. The warming hole in 150Ma has a magnitude of ≈1 °C and locates in the Southern Hemisphere. Both atmospheric and oceanic processes contribute to trigger the warming hole. For 70Ma and 90Ma experiments, atmospheric teleconnection along a great circle from tropics to extratropics intensifies surface winds over sub-polar ocean and thereby increases relatively cool seawater transport from high to low latitudes. Meanwhile, global meridional overturning circulation (GMOC) becomes weaker, causing a divergence of the meridional ocean heat transport in the warming hole region. An increasing of regional cloud shortwave cooling effect acts to further enhance the warming hole. For 150Ma experiments, the warming hole is related to the meridional shift of mid-latitude jet stream and the weakening of GMOC in the Southern Hemisphere. The strength and phase of the atmospheric teleconnection and the response of GMOC strongly depend on land-sea configuration, resulting to the paleo-Pacific warming hole to occur in special periods only.

Restricted access
Jiawenjing Lan
,
Jun Yang
,
Yongyun Hu
,
Xiang Li
,
Jiaqi Guo
,
Qifan Lin
,
Jing Han
,
Jian Zhang
,
Shuang Wang
, and
Ji Nie

Abstract

For modern Earth, the annual-mean equatorial winds in the upper troposphere are flowing from east to west (i.e., easterly winds). This is mainly due to the deceleration effect of the seasonal cross-equatorial Hadley cells, against the relatively weaker acceleration effect of coupled Rossby and Kelvin waves excited from tropical convection and latent heat release. In this work, we examine the evolution of equatorial winds during the past 250 million years using one global Earth system model, the Community Earth System Model version 1.2.2 (CESM1.2.2). Three climatic factors different from the modern Earth—solar constant, atmospheric CO2 concentration, and land–sea configuration—are considered in the simulations. We find that the upper-tropospheric equatorial winds change sign to westerly flows (called equatorial superrotation) in certain eras, such as 250–230 and 150–50 Ma. The strength of the superrotation is below 4 m s−1, comparable to the magnitude of the present-day easterly winds. In general, this phenomenon occurs in a warmer climate within which the tropical atmospheric circulation shifts upward in altitude, stationary and/or transient eddies are relatively stronger, and/or the Hadley cells are relatively weaker, which in turn are due to the changes of the three factors, especially CO2 concentration and land–sea configuration.

Free access
Liangyi Wang
,
Xihui Gu
,
Louise J. Slater
,
Yangchen Lai
,
Xiang Zhang
,
Dongdong Kong
,
Jianyu Liu
, and
Jianfeng Li

Abstract

In July 2021, Typhoon In-Fa (TIF) triggered a significant indirect heavy precipitation event (HPE) in central China and a direct HPE in eastern China. Both these events led to severe disasters. However, the synoptic-scale conditions and the impacts of these HPEs on future estimations of return periods remain poorly understood. Here, we find that the remote HPE that occurred ∼2200 km ahead of TIF over central China was a predecessor rain event (PRE). The PRE unfolded under the equatorward entrance of the upper-level westerly jet. This event, which encouraged divergent and adiabatic outflow in the upper level, subsequently intensified the strength of the upper-level westerly jet. In contrast, the direct HPE in eastern China was due primarily to the long duration and slow movement of TIF. The direct HPE occurred in areas situated less than 200 km from TIF’s center and to the left of TIF’s propagation trajectory. Anomaly analyses reveal favorable thermodynamic and dynamic conditions and abundant atmospheric moisture that sustained TIF’s intensity. A saddle-shaped pressure field in the north of eastern China and peripheral weak steering flow impeded TIF’s movement northward. Hydrologically, the inclusion of these two HPEs in the historical record leads to a decrease in the estimated return periods of similar HPEs. Our findings highlight the potential difficulties that HPEs could introduce for the design of hydraulic engineering infrastructure as well as for the disaster mitigation measures required to alleviate future risk, particularly in central China.

Restricted access
Wenting Wang
,
Hongrong Shi
,
Disong Fu
,
Mengqi Liu
,
Jiawei Li
,
Yunpeng Shan
,
Tao Hong
,
Dazhi Yang
, and
Xiang’ao Xia

Abstract

Numerical weather prediction (NWP), when accessible, is a crucial input to short-term solar power forecasting. WRF-Solar, the first NWP model specifically designed for solar energy applications, has shown promising predictive capability. Nevertheless, few attempts have been made to investigate its performance under high aerosol loading, which attenuates incoming radiation significantly. The North China Plain is a polluted region due to industrialization, which constitutes a proper testbed for such investigation. In this paper, aerosol direct radiative effect (DRE) on three surface shortwave radiation components (i.e., global, beam, and diffuse) during five heavy pollution episodes is studied within the WRF-Solar framework. Results show that WRF-Solar overestimates instantaneous beam radiation up to 795.3 W m−2 when the aerosol DRE is not considered. Although such overestimation can be partially offset by an underestimation of the diffuse radiation of about 194.5 W m−2, the overestimation of the global radiation still reaches 160.2 W m−2. This undesirable bias can be reduced when WRF-Solar is powered by Copernicus Atmosphere Monitoring Service (CAMS) aerosol forecasts, which then translates to accuracy improvements in photovoltaic (PV) power forecasts. This work also compares the forecast performance of the CAMS-powered WRF-Solar with that of the European Centre for Medium-Range Weather Forecasts model. Under high aerosol loading conditions, the irradiance forecast accuracy generated by WRF-Solar increased by 53.2% and the PV power forecast accuracy increased by 6.8%.

Significance Statement

Numerical weather prediction (NWP) is the “go-to” approach for achieving high-performance day-ahead solar power forecasting. Integrating time-varying aerosol forecasts into NWP models effectively captures aerosol direct radiation effects, thereby enhancing the accuracy of solar irradiance forecasts in heavily polluted regions. This work not only quantifies the aerosol effects on global, beam, and diffuse irradiance but also reveals the physical mechanisms of irradiance-to-power conversion by constructing a model chain. Using the North China Plain as a testbed, the performance of WRF-Solar on solar power forecasting on five severe pollution days is analyzed. This version of WRF-Solar can outperform the European Centre for Medium-Range Weather Forecasts model, confirming the need for generating high spatial–temporal NWP.

Restricted access
Bin Wang
,
Juan Li
,
Mark A. Cane
,
Jian Liu
,
Peter J. Webster
,
Baoqiang Xiang
,
Hye-Mi Kim
,
Jian Cao
, and
Kyung-Ja Ha

Abstract

Predictions of changes of the land monsoon rainfall (LMR) in the coming decades are of vital importance for successful sustainable economic development. Current dynamic models, though, have shown little skill in the decadal prediction of the Northern Hemisphere (NH) LMR (NHLMR). The physical basis and predictability for such predictions remain largely unexplored. Decadal change of the NHLMR reflects changes in the total NH continental precipitation, tropical general circulation, and regional land monsoon rainfall over northern Africa, India, East Asia, and North America. Using observations from 1901 to 2014 and numerical experiments, it is shown that the decadal variability of the NHLMR is rooted primarily in (i) the north–south hemispheric thermal contrast in the Atlantic–Indian Ocean sector measured by the North Atlantic–south Indian Ocean dipole (NAID) sea surface temperature (SST) index and (ii) an east–west thermal contrast in the Pacific measured by an extended El Niño–Southern Oscillation (XEN) index. Results from a 500-yr preindustrial control experiment demonstrate that the leading mode of decadal NHLMR and the associated NAID and XEN SST anomalies may be largely an internal mode of Earth’s climate system, although possibly modified by natural and anthropogenic external forcing. A 51-yr, independent forward-rolling decadal hindcast was made with a hybrid dynamic conceptual model and using the NAID index predicted by a multiclimate model ensemble. The results demonstrate that the decadal changes in the NHLMR can be predicted approximately a decade in advance with significant skills, opening a promising way forward for decadal predictions of regional land monsoon rainfall worldwide.

Open access
Xianan Jiang
,
Baoqiang Xiang
,
Ming Zhao
,
Tim Li
,
Shian-Jiann Lin
,
Zhuo Wang
, and
Jan-Huey Chen

Abstract

Motivated by increasing demand in the community for intraseasonal predictions of weather extremes, predictive skill of tropical cyclogenesis is investigated in this study based on a global coupled model system. Limited intraseasonal cyclogenesis prediction skill with a high false alarm rate is found when averaged over about 600 tropical cyclones (TCs) over global oceans from 2003 to 2013, particularly over the North Atlantic (NA). Relatively skillful genesis predictions with more than 1-week lead time are only evident for about 10% of the total TCs. Further analyses suggest that TCs with relatively higher genesis skill are closely associated with the Madden–Julian oscillation (MJO) and tropical synoptic waves, with their geneses strongly phase-locked to the convectively active region of the MJO and low-level cyclonic vorticity associated with synoptic-scale waves. Moreover, higher cyclogenesis prediction skill is found for TCs that formed during the enhanced periods of strong MJO episodes than those during weak or suppressed MJO periods. All these results confirm the critical role of the MJO and tropical synoptic waves for intraseasonal prediction of TC activity. Tropical cyclogenesis prediction skill in this coupled model is found to be closely associated with model predictability of several large-scale dynamical and thermodynamical fields. Particularly over the NA, higher predictability of low-level relative vorticity, midlevel humidity, and vertical zonal wind shear is evident along a tropical belt from the West Africa coast to the Caribbean Sea, in accord with more predictable cyclogenesis over this region. Over the extratropical NA, large-scale variables exhibit less predictability due to influences of extratropical systems, leading to poor cyclogenesis predictive skill.

Full access
Baoqiang Xiang
,
Shian-Jiann Lin
,
Ming Zhao
,
Shaoqing Zhang
,
Gabriel Vecchi
,
Tim Li
,
Xianan Jiang
,
Lucas Harris
, and
Jan-Huey Chen

Abstract

While tropical cyclone (TC) prediction, in particular TC genesis, remains very challenging, accurate prediction of TCs is critical for timely preparedness and mitigation. Using a new version of the Geophysical Fluid Dynamics Laboratory (GFDL) coupled model, the authors studied the predictability of two destructive landfall TCs: Hurricane Sandy in 2012 and Super Typhoon Haiyan in 2013. Results demonstrate that the geneses of these two TCs are highly predictable with the maximum prediction lead time reaching 11 days. The “beyond weather time scale” predictability of tropical cyclogenesis is primarily attributed to the model’s skillful prediction of the intraseasonal Madden–Julian oscillation (MJO) and the westward propagation of easterly waves. Meanwhile, the landfall location and time can be predicted one week ahead for Sandy’s U.S landfall, and two weeks ahead for Haiyan’s landing in the Philippines. The success in predicting Sandy and Haiyan, together with low false alarms, indicates the potential of using the GFDL coupled model for extended-range predictions of TCs.

Full access
Shenjia Ma
,
Chaohui Chen
,
Hongrang He
,
Jie Xiang
,
Shengjie Chen
,
Yi Li
,
Yongqiang Jiang
,
Dan Wu
, and
Hao Luo

Abstract

In this study, a convection-allowing ensemble prediction experiment was conducted on a strong convective weather process, based on the local breeding growth mode (LBGM) method proposed according to the strongly local nature of the convective-scale weather system. A comparative analysis of the evolution characteristics of the initial perturbation was also performed, considering the results from the traditional breeding growth mode (BGM) method, to enhance understanding and application of this new initial perturbation generation method. The experimental results showed that LBGM results in the perturbation distribution exhibiting characteristics more evident of flow dependence, and an initial perturbation with greater definite kinetic significance was derived. Information entropy theory could well measure the amount of information contained in the perturbation distribution, indicating that the innovative initial perturbation generation method can increase the amount of local information associated with the initial perturbation. With regard to the physical perturbation quantities, the LBGM method can improve the dispersion of the ensemble prediction system, thereby solving the problem of insufficient ensemble spread of prediction systems obtained by the traditional BGM method. Simultaneously, the root-mean-square error of the prediction can be further reduced, and the predicted precipitation distribution is closer to the observed precipitation, thereby improving the prediction effect of the convection-allowing ensemble prediction. The LBGM method has advantages compared to the traditional method and provides a new theoretical basis for further development of initial perturbation technologies for convection-allowing ensemble prediction.

Full access
Fan Mei
,
Hailong Wang
,
Zihua Zhu
,
Damao Zhang
,
Qi Zhang
,
Jerome D. Fast
,
William I. Gustafson Jr.
,
Xiang-Yu Li
,
Beat Schmid
,
Christopher Niedek
,
Jason Tomlinson
, and
Connor Flynn

Abstract

The spatial distribution of ambient aerosol particles significantly impacts aerosol–radiation–cloud interactions, which contribute to the largest uncertainty in global anthropogenic radiative forcing estimations. However, the atmospheric boundary layer and lower free troposphere have not been adequately sampled in terms of spatiotemporal resolution, hindering a comprehensive characterization of various atmospheric processes and impeding our understanding of the Earth system. To address this research data gap, we have leveraged the development of uncrewed aerial systems (UAS) and advanced measurement techniques to obtain mesoscale spatial data on aerosol microphysical and optical properties around the U.S. Southern Great Plains (SGP) atmospheric observatory. Our study also benefits from state-of-the-art laboratory facilities that include three-dimensional molecular imaging techniques enabled by secondary ion mass spectrometry and nanogram-level chemical composition analysis via micronebulization aerosol mass spectrometry. Through our study, we have developed a framework for observation–modeling integration, enabling an examination of how various assumptions about the organic–inorganic components mixing state, inferred from chemical analysis, affect clouds and radiation in observation-constrained model simulations. By integrating observational constraints (derived from offline chemical analysis of the aerosol surface using collected samples) with in situ UAS observations, we have identified a prominent role of organic-enriched nanometer layers located at the surface of aerosol particles in determining profiles of aerosol optical and hygroscopic properties over the SGP observatory. Furthermore, we have improved the agreement between predicted clouds and ground-based cloud lidar measurements. This UAS–model–laboratory integration exemplifies how these new advanced capabilities can significantly enhance our understanding of aerosol–radiation–cloud interactions.

Open access