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Dongqian Wang
,
Ying Sun
,
Ting Hu
, and
Hong Yin

Abstract

The anthropogenic forcing and anomalous atmospheric circulation have increased the occurrence probability of 2022-like extreme heat by approximately 62.0 and 2.6 times, respectively.

Open access
Biyin Xie
,
Yang Yang
,
Hailong Wang
,
Pinya Wang
, and
Hong Liao

Abstract

Fire emissions from the Maritime Continent (MC) over the western tropical Pacific are strongly influenced by El Niño–Southern Oscillation (ENSO), posing various climate effects to the Earth system. In this study, we show that the historical biomass burning emissions of black carbon (BCbb) aerosol in the dry season from the MC are strengthened in El Niño years due to the dry conditions. The eastern Pacific type of El Niño exerts a stronger modulation in BCbb emissions over the MC region than the central Pacific type of El Niño. Based on simulations using the fully coupled Community Earth System Model (CESM), the impacts of increased BCbb emissions on ENSO variability and frequency are also investigated in this study. With BCbb emissions from the MC scaled up by a factor of 10, which enables the identification of climate response from the internal variability, the increased BCbb heats the local atmosphere and changes land–sea thermal contrast, which suppresses the westward transport of the eastern Pacific surface water. It leads to an increase in sea surface temperature in the eastern tropical Pacific, which further enhances ENSO variability and increases the frequency of extreme El Niño and La Niña events. This study highlights the potential role of BCbb emissions on extreme ENSO frequency, and this role may be increasingly important in the warming future with higher wildfire risks.

Restricted access
Kai Wang
,
Hong Ye
,
Feng Chen
,
Yongzhu Xiong
, and
Cuiping Wang

Abstract

Based on the 1960–2009 meteorological data from 559 stations across China, the urbanization effect on the diurnal temperature range (DTR) was evaluated in this study. Different roles of urbanization were specially detected under solar dimming and solar brightening. During the solar dimming time, both urban and rural stations showed decreasing trends in maximum temperature (T max) because of decreased radiation, suggesting that the dimming effects are not only evident in urban areas but also in rural areas. However, minimum temperature (T min) increased more substantially in urban areas than in rural areas during the dimming period, resulting in a greater decrease in the DTR in the urban areas. When the radiation reversed from dimming to brightening, the change in the DTR became different. The T max increased faster in rural areas, suggesting that the brightening could be much stronger in rural areas than in urban areas. Similar trends of T min between urban and rural areas appeared during the brightening period. The urban DTR continued to show a decreasing trend because of the urbanization effect, while the rural DTR presented an increasing trend. The remarkable DTR difference in the urban and rural areas showed a significant urbanization effect in the solar brightening time.

Full access
Jinqing Zuo
,
Hong-Li Ren
,
Weijing Li
, and
Lei Wang

Abstract

Interdecadal variations in the relationship between the winter North Atlantic Oscillation (NAO) and surface air temperature in China are investigated using observational and reanalysis data. Focus is on south-central China, in which temperature variability is strongly related to the NAO. It is revealed that the relationship shows clear interdecadal variations in midwinter during 1951–2015. A relatively weak in-phase relationship occurs before the early 1970s (P1), but a significant out-of-phase relationship dominates in the last two decades of the twentieth century (P2), though it is clearly weaker from the late 1990s onward. Observational evidence shows that such interdecadal variations are related mainly to variations in the spatial pattern and amplitude of the NAO. The northern center of the NAO shifted eastward over the second half of the twentieth century. In addition, the amplitude of the center strengthened from P1 to P2, resulting in a perturbation in the atmospheric circulation response pattern over Eurasian mid-to-high latitudes. During P2, the eastward shift and amplitude intensification of the NAO favored a north–south dipole structure in circulation anomalies over the Asian continent, which tended to produce cold temperature anomalies in south-central China during the positive NAO phase and warm anomalies during the negative phase. However, in the past two decades the northern center of the NAO has weakened and retreated westward. This was concurrent with a weakening relationship between the NAO and temperature anomalies in south-central China and northern Eurasia, indicating weaker downstream impacts of the NAO in midwinter.

Full access
Hangzhou Wang
,
Ying Chen
,
Hong Song
, and
Samuel R. Laney

Abstract

A fiber optic–based spectrometry system was developed to enable automated, long-term measurements of spectral irradiance in sea ice environments. This system utilizes a single spectrometer module that measures the irradiance transmitted by multiple optical fibers, each coupled to the input fiber of the module via a mechanical rotary multiplexer. Small custom-printed optical diffusers, fixed to the input end of each fiber, allow these probes to be frozen into ice auger holes as small as 5 cm in diameter. Temperature-dependent biases in the spectrometer module and associated electronics were examined down to −40°C using an environmental chamber to identify any artifacts that might arise when operating these electronic and optical components below their vendor-defined lower temperature limits. The optical performance of the entire system was assessed by freezing multiple fiber probes in a 1.2-m-tall ice column, illuminating from above with a light source, and measuring spectral irradiance distributions at different depths within the ice column. Results indicated that the radiometric sensitivity of this fiber-based system is comparable to that of commercially available oceanographic spectroradiometers.

Full access
Hong-Bo Liu
,
Jing Yang
,
Da-Lin Zhang
, and
Bin Wang

Abstract

During the mei-yu season of the summer of 2003, the Yangtze and Huai River basin (YHRB) encountered anomalously heavy rainfall, and the northern YHRB (nYHRB) suffered a severe flood because of five continuous extreme rainfall events. A spectral analysis of daily rainfall data over YHRB reveals two dominant frequency modes: one peak on day 14 and the other on day 4 (i.e., the quasi-biweekly and synoptic-scale mode, respectively). Results indicate that the two scales of disturbances contributed southwesterly and northeasterly anomalies, respectively, to the mei-yu frontal convergence over the southern YHRB (sYHRB) at the peak wet phase. An analysis of bandpass-filtered circulations shows that the lower and upper regions of the troposphere were fully coupled at the quasi-biweekly scale, and a lower-level cyclonic anomaly over sYHRB was phase locked with an anticyclonic anomaly over the Philippines. At the synoptic scale, the strong northeasterly components of an anticyclonic anomaly with a deep cold and dry layer helped generate the heavy rainfall over sYHRB. Results also indicate the passages of five synoptic-scale disturbances during the nYHRB rainfall. Like the sYHRB rainfall, these disturbances originated from the periodical generations of cyclonic and anticyclonic anomalies at the downstream of the Tibetan Plateau. The nYHRB rainfalls were generated as these disturbances moved northeastward under the influence of monsoonal flows and higher-latitude eastward-propagating Rossby wave trains. It is concluded that the sYHRB heavy rainfall resulted from the superposition of quasi-biweekly and synoptic-scale disturbances, whereas the intermittent passages of five synoptic-scale disturbances led to the flooding rainfall over nYHRB.

Full access
Hong Wang
,
Liang Gao
,
Lei Zhu
,
Lulu Zhang
, and
Jiahao Wu

Abstract

Accurately assessing cyclone intensity changes due to global warming is crucial for predicting and mitigating sequential hazards. This study develops a high-resolution, fully coupled air-sea model to investigate the impact of global warming on Super Typhoon Mangkhut (2018). A numerical sensitivity analysis is conducted using the Pseudo-Global Warming (PGW) technique based on multiple global climate models (GCMs) from the Coupled Model Intercomparison Project Phases 6 (CMIP6). Under ocean warming scenarios, the increasing average sea surface temperature (SST) by 2.26 °C, 2.44 °C, 3.45 °C, and 4.53 °C result in reductions in minimum sea-level pressure by 9.2 hPa, 10.6 hPa, 15.7 hPa, and 19.4 hPa, respectively, compared to the original state of Typhoon Mangkhut. Rising SST increases turbulent heat flux, to be specific, an average SST increase of 2.26-4.53 °C changes the turbulent heat flux into 177% to 272% of the original value. Besides, stronger winds enhance SST cooling, including upwelling and entrainment, leading to an increase in the mixed layer depth (MLD). Tropical cyclone heat potential (TCHP) tends to be enhanced under the combined influences as the SST rises. An average increase in SST of 2.26 °C, 2.44 °C, 3.45 °C, and 4.53 °C leads to increase in TCHP of 9.94%, 9.85%, 14.67%, and 15.30%, respectively. However, future changes in atmospheric temperature and humidity will moderate typhoon intensification induced by ocean warming. Considering atmospheric conditions, the maximum wind speed decreases by approximately 10% compared to only considering ocean warming. Nevertheless, typhoon intensity is projected to strengthen under future climate change.

Restricted access
Hong Wang
,
Fubao Sun
,
Tingting Wang
,
Yao Feng
,
Fa Liu
, and
Wenbin Liu

Abstract

Pan evaporation (E pan) serves as a monitorable method for estimating potential evaporation, evapotranspiration, and reference crop evapotranspiration, providing crucial data and information for fields such as water resource management and agricultural irrigation. Based on the PenPan model, the monthly E pan was calculated over China during 1951–2021, resulting in an average R 2 of 0.93 ± 0.045 and an RMSE of 21.48 ± 6.06 mm month−1. The trend of E pan over time was characterized by an initial increase before 1961, followed by a decrease from 1961 to 1993, and a subsequent increase from 1994 to 2021. However, the sustained duration and magnitude of the decreasing trend led to an overall decreasing trend in the long-term dataset. To better understand the drivers of E pan trends, the E pan process was decomposed into radiative and aerodynamic components. While radiation was found to be the dominant component, its trend remained relatively stable over time. In contrast, the aerodynamic component, although smaller in proportion, exhibited larger fluctuations and played a crucial role in the trend of E pan. The primary influencing factors of the aerodynamic component were found to be wind speed and vapor pressure deficit (VPD). Wind speed and VPD jointly promoted E pan before 1961, and the significant decrease in wind speed from 1961 to 1993 led to a decrease in E pan. From 1994 to 2021, the increase in VPD was found to be the main driver of the observed increase in E pan. These results show the complex and dynamic nature of E pan and underscore the need for continued monitoring and in-depth analysis of its drivers.

Significance Statement

The primary objective of this study is to explore the spatiotemporal patterns and potential driving factors of pan evaporation in China based on constructing a comprehensive dataset of pan evaporation. This is important because pan evaporation is an important indicator of the water cycle, which is currently undergoing modifications and is expected to become more pronounced as the climate continues to warm. Our findings showed that the patterns of pan evaporation were characterized by its drivers. As the drivers are numerous and continuously changing under climate change, it is necessary to pay attention to the pattern and attribution of pan evaporation.

Restricted access
Hong Wang
,
Fubao Sun
,
Fa Liu
,
Tingting Wang
,
Yao Feng
, and
Wenbin Liu

Abstract

The most basic features of climatological normals and variability are useful for describing observed or likely future climate fluctuations. Pan evaporation (E pan) is an important indicator of climate change; however, current research on E pan has focused on its change in mean rather than its variability. The variability of monthly E pan from 1961 to 2020 at 969 stations in China was analyzed using a theoretical framework that can distinguish changes in E pan variance between space and time. The E pan variance was decomposed into spatial and temporal components, and the temporal component was further decomposed into interannual and intra-annual components. The results show that the variance in E pan was mainly controlled by the temporal component. The time variance was mainly controlled by intra-annual variance, decreasing continuously in the first 30 years, and slightly increasing after the 1990s. This is mainly due to the fact that the decrease of wind speed and the increase of water vapor pressure deficit with the temperature increase offset each other and inhibit the variability of E pan. The variance decreased more in the northern region, whereas it exhibited a small decrease or slight increase in the southern region. The reduction in seasonality was dominated by spring, followed by summer. The differences in E pan variability in space and season were mainly caused by the differing rates of change in evaporation driving forces, such as a greater reduction in wind speed in the northern region and spring.

Significance Statement

The purpose of this study is to better understand how the variability of evaporation changes rather than in mean under climate change. This is important because the variability is useful to describe the observed or likely future fluctuations, and a small fluctuation may have large impacts on water practices, such as agricultural production. Our findings showed that the temporal and spatial variability of evaporation decreased due to its drivers offsetting each other. However, because the drivers are numerous and continuously changing under climate change, it is necessary to pay attention to its mean and variability for serving water resources practice.

Restricted access
Yushan Qu
,
Shengpeng Wang
,
Zhao Jing
,
Yu Zhang
,
Hong Wang
, and
Lixin Wu

Abstract

Tropical Pacific quasi-decadal (TPQD) climate variability is characterized by quasi-decadal sea surface temperature (SST) variations in the central Pacific (CP). This low-frequency climate variability is suggested to influence extreme regional weather and substantially impact global climate patterns and associated socioeconomics through teleconnections. Previous studies mostly attributed the TPQD climate variability to basin-scale air–sea coupling processes. However, due to the coarse resolution of the majority of the observations and climate models, the role of subbasin-scale processes in modulating the TPQD climate variability is still unclear. Using a long-term high-resolution global climate model, we find that energetic small-scale motions with horizontal scales from tens to hundreds of kilometers (loosely referred to as equatorial submesoscale eddies) act as an important damping effect to retard the TPQD variability. During the positive TPQD events, compound increasing precipitation and warming SST in the equatorial Pacific intensifies the upper ocean stratification and weakens the temperature fronts along the Pacific cold tongue. This suppresses submesoscale eddy growth as well as their associated upward vertical heat transport by inhibiting baroclinic instability (BCI) and frontogenesis; conversely, during the negative TPQD events, the opposite is true. Using a series of coupled global climate models that participated in phase 6 of the Coupled Model Intercomparison Project with different oceanic resolutions, we show that the amplitude of the TPQD variability becomes smaller as the oceanic resolution becomes finer, providing evidence for the impacts of submesoscale eddies on damping the TPQD variability. Our study suggests that explicitly simulating equatorial submesoscale eddies is necessary for gaining a more robust understanding of low-frequency tropical climate variability.

Significance Statement

Submesoscale ocean eddies inhibit the development of quasi-decadal climate variability in the equatorial central Pacific, according to a high-resolution global climate simulation.

Open access