Strong Moisture Research Articles

Combined Influence of 10–30‐Day Tropical and Mid–High‐Latitude Intraseasonal Oscillations on the Rapid Increases of Humid Heatwaves in Southern China

AbstractAs a typical hotspot of heatwaves, southern China experienced a marked shift from dry to humid heatwaves in the recent decade of 2013–2022. Significant 10–30‐day intraseasonal oscillation (ISO) in temperature and humidity is a major contributor to the humid heatwaves. Configuration of the 10–30‐day quasi‐barotropic wave train at mid–high latitudes with the dipolar pattern of tropical convection leads to the concurrence of strong moisture convergence and anomalous descents over southern China. The increased downward longwave radiation in association with moisture enhancement, shortwave radiation and adiabatic heating in association with descents bring about the persisting hot and humid conditions in humid heatwaves. Due to stronger barotropic energy conversion from mean flow to 10–30‐day circulation at mid–high latitudes, and stronger tropical convection activities in the recent decade, the occurrence of 10–30‐day circulation configuration induced humid heatwaves has increased by 13.3%, thus leading to the predominance of humid heatwaves.

Retrieval of Boundary Layer Precipitable Water from GOES ABI Using Machine Learning Techniques

Abstract Low-level moisture is an important ingredient for forecasting severe storms, especially over the Great Plains where severe storms often develop along the dryline. Although ground-based observation systems such as lidar or radiosondes on weather balloons provide accurate information on low-level moisture, data are provided at limited locations, and the low temporal resolution of radiosondes makes it difficult to track a rapidly developing dryline. Geostationary satellites provide high spatial and temporal observation, but the channels of current geostationary satellites are mostly sensitive to water vapor at mid- to upper levels. However, the split window difference (SWD) between the “clean” window channel (10.3 μm) and the “dirty” window channel (12.3 μm) is commonly used for estimating low-level water vapor. However, this estimation is complicated by surface temperature contributions, dependence on the lapse rate, and nonlinear relationships between SWD and moisture. This study applies machine learning techniques to infer boundary layer precipitable water (BLPW) from Geostationary Operational Environmental Satellite (GOES) Advanced Baseline Imager (ABI) data. Since there are few observations that cover wide regions for training convolutional neural networks, especially for the atmosphere above the surface, High-Resolution Rapid Refresh (HRRR) model outputs are used as the truth for training. Statistical results show that using ABI channel 13, 14, and 15 brightness temperatures, skin temperature, solar zenith angle, and GOES total precipitable water product as additional inputs shows the lowest mean-square error (MSE). Case study results show that the model developed in this study is good at capturing strong moisture gradients and depicting a dryline. Significance Statement Knowledge of low-level moisture is important for monitoring drylines and moisture convergence preceding convective initiation. Traditional observations lack the spatial resolution, spatial coverage, or temporal update frequency needed by forecasters. The latest generation of Geostationary Operational Environmental Satellite (GOES), the GOES-R series, provides high spatial resolution and rapid temporal updates. However, the estimation of low-level moisture using the Advanced Baseline Imager (ABI) is complicated by dependencies on other variables and nonlinear relationships. Machine learning is shown to provide good estimates of low-level moisture from ABI observations. This application of machine learning to GOES-R can improve the ability to monitor low-level moisture and forecast convective initiation.

Analysis of the biodrying and biostabilization efficiency of a continuous flow full-scale facility

The technological solution adopted for aerobic treatment of Waste Organic Fraction (WOF) can influence the evolution of the physical parameters of the process making the facility acting as a biostabilization or a biodrying system. In the present study, the continuous flow biological section of the full-scale mechanical biological treatment plant was experimentally investigated by means of evolution, during treatment period (day), of temperature (T) (° C), volatile solids (VS) (%TS) and oxygen uptake of the WOF under treatment. Oxygen uptake was measured by the Dynamic Respirometer Index Potential (DRIP) (mgO2/kgVSh). Main findings were that T (° C) and VS %TS remained quite constant among inlets and outlets of the biological treatment sections, about 70° C and 50 (%TS), respectively. DRIP (mgO2/kgVSh) values measured by several samples withdrawn along the basin width increased significantly in the first half portion of the basin of the aerobic section, remaining quite constant in the second half. This was mainly caused by the strong moisture reduction that rapidly achieved values lower than 40% causing inhibition to microbial activity. The simulation model developed in this work showed that the mean retention time (day) of the WOF inside the aerobic basin was about 14-16 days, this parameter being strongly influenced by the WOF inlet rate (tonnes/day). Finally, experimental evidence pointed out that the reduction of WOF DRIP (mgO2/kgVSh) stopped after the first days of treatment indicating that the facility operates mainly as biodrying system. Based on simulations, biostabilization can also be pursued by maintaining the moisture of WOF to proper values not lower than 40 (% w/w).

The stannides SrPdSn and m-BaPtSn

Abstract The stannides SrPdSn (TiNiSi type, orthorhombic space group Pnma) and m-BaPtSn (EuNiGe type, monoclinic space group P21/c) were synthesized from the elements in sealed tantalum ampoules in a high-frequency furnace. Their structures were refined from single-crystal X-ray diffraction data. SrPdSn crystallizes directly from the melt and is stable upon annealing at T = 1073 K. A BaPtSn sample quenched from the melt adopts the cubic LaIrSi-type structure, cubic space group P213 (c-BaPtSn) and shows a temperature induced (annealing at 1070 K) structural phase transition leading to a EuNiGe-type low-temperature modification m-BaPtSn. The phase transition leads to a reconstruction within the polyanionic [PtSn] δ− network. The latter is three-dimensional and composed of ten-membered Pt5Sn5 rings in c-BaPtSn, while the polyanion is two-dimensional in m-BaPtSn and is composed of condensed Pt4Sn4 and Pt2Sn2 rings. The two-dimensional substructure leads to a strong moisture sensitivity for m-BaPtSn. The Pt–Sn distances in both modifications range from 257 to 267 pm, indicating substantial covalent bonding.

Effect of water occurrence in coal reservoirs on the production capacity of coalbed methane by using NMR simulation technology and production capacity simulation

The occurrence of gas and water is a critical factor affecting the production capacity of coalbed methane. Therefore, occurrence and dynamic interaction between gas and water in coal reservoirs need to be studied. T2 spectrum of all the samples were studied by NMR technique at 0, 5, 9, and 28 h of natural evaporation. Then, multifractal model was used to characterize water distribution heterogeneity, and a novel evaluation coefficient was proposed to characterize distribution heterogeneity of water content, the correlation among evaluation coefficient, water distribution heterogeneity and pore structure parameters was analyzed. The results are as follows. In the saturated state, the moisture distribution of three types is heterogeneous. Type A of adsorption pore-developed exhibits strong moisture variation heterogeneity of small pores, in contrast to the uniform moisture variation in large pores. Type B of fracture-developed has the highest coefficient of variation in moisture distribution. The coefficient of variation A1 for moisture content can determine the speed of moisture transport and evaporation in the pore structure. A lower A1 indicates a greater moisture transport volume and faster moisture transport rate over the same time. The coefficient of variation A2 for moisture distribution represents the heterogeneity of moisture content variation in the pore structure. That is, a smaller A2 indicates better heterogeneity in the distribution of moisture content in the pore structure. Numerical simulation indicates the average gas production and the peak gas production time increase and decrease with the initial moisture content (Sgrw) increases, respectively. These findings provide practical guidance for coalbed methane development, especially in optimizing coalbed methane production capacity prediction and improving recovery efficiency.

Remote Forcing for a Circulation Pattern Favorable to Surface Melt over the Ross Ice Shelf

Abstract The Ross Ice Shelf (RIS) experiences surface melt events in summer, which could accelerate ice loss and destabilize the ice sheet in a warming world. This study links the interannual variability of RIS surface melt to the northerly wind anomaly over the Ross Sea sector, which is established in association with the quasigeostrophic barotropic Rossby wave trains from the tropical Pacific and subtropical Australia toward West Antarctica. Atmospheric general circulation model experiments suggest that these Rossby wave trains are regulated by El Niño–related sea surface temperature (SST) anomalies in the tropical central–eastern Pacific and atmospheric heating anomalies over western Australia. El Niño provides an important forcing of the atmospheric circulation anomalies over the Ross Sea via inducing a Rossby wave train, and most surface melt events over the RIS happen during El Niño years. In addition, the anomalous atmospheric heating over western Australia, which is independent of El Niño, is another important forcing that triggers a Rossby wave train extending from subtropical Australia to the Ross Sea. The northerly flow toward the Ross Sea induces strong poleward moisture and heat transport, which further contributes to surface melt over the RIS. Significance Statement During austral summer, surface melt occurs over the Ross Ice Shelf, accelerates ice loss, and poses ice-sheet destabilization risks in a warming world. The northerly wind anomaly over the Ross sector provides strong poleward heat and moisture transport and is favorable for the surface melt. This wind anomaly is influenced by two remote forcings, El Niño and heating anomaly over western Australia, through generating Rossby wave trains from the tropics and subtropical Australia. This study reveals a previously unexplored relationship that atmospheric heating over western Australia influences large-scale circulation, contributing to surface melt.

Nocturnal Extreme Rainfall over the Central Yungui Plateau under Cold and Warm Upper-Level Anomaly Backgrounds during Warm Seasons in 1980–2020

The spatiotemporal and cloud features of the extreme rainfall under the warm and cold upper-level anomalies over the central Yungui Plateau (YGP) were investigated using the hourly rain gauge records, ERA5 reanalysis data, TRMM, and Fengyun satellite data, aiming to refine the understanding of different types of extreme rainfall. Extreme rainfall under an upper-level negative temperature anomaly (cold events) presents stronger convective cloud features when compared with the positive temperature anomaly (warm events). The maximum rainfall intensity and duration in cold events is much larger than that of warm events, while the brightness temperature of the cloud top is lower, and the ratio of convective rainfall is higher. In cold events, the middle-to-upper troposphere is dominated by a cold anomaly, and an unstable configuration with upper (lower) cold (warm) anomalies is observed around the central YGP. Although the upper-level temperature anomaly is positive, the anomalous divergence and convergence of southerly and northerly winds, as well as the strong moisture center and upward motions, are also found over the central YGP in warm events. The stronger atmospheric instability and higher convective energy under the upper-level cold anomalous circulation are closely associated with the rainfall features over the central YGP. The results indicate that the upper tropospheric temperature has significant influences on extreme rainfall, and thus more attention should be paid to the upper tropospheric temperature in future analyses.

Evaluation of near‐surface and boundary‐layer meteorological conditions that support cold‐fog formation using Cold Fog Amongst Complex Terrain field campaign observations

AbstractCold fog refers to a type of fog that forms when the temperature is below 0°C. It can be composed of liquid, ice, and mixed‐phase fog particles. Cold fog happens frequently over mountainous terrain in the cold season, but it is difficult to predict. Using observations from the Cold Fog Amongst Complex Terrain (CFACT) field campaign conducted in Heber Valley, Utah, in the western United States during January and February of 2022, this study investigates the meteorological conditions in the surface and boundary layers that support the formation of wintertime ephemeral cold fog in a local area of small‐scale mountain valleys. It is found that fog formation is susceptible to subtleties in forcing conditions and is supported by several factors: (1) established high pressure over the Great Basin with associated local clear skies, calm winds, and a stable boundary layer; (2) near‐surface inversion with saturation near the surface and strong moisture gradient in the boundary layer; (3) warm (above‐freezing) daytime air temperature with a large diurnal range, accompanied with warm soil temperatures during the daytime; (4) a period of increased turbulence kinetic energy (above 0.5 m2·s−2), followed by calm conditions throughout the fog's duration; and (5) supersaturation with respect to ice. Then, the field observations and identified supporting factors for fog formation were utilized to evaluate high‐resolution (˜400 m horizontal grid spacing) Weather Research and Forecasting (WRF) model simulations. Results show that the WRF model accurately simulates the mesoscale conditions facilitating cold‐fog formation but misses some critical surface and atmospheric boundary conditions. The overall results from this paper indicate that these identified factors that support fog formation are vital to accurately forecasting cold‐fog events. At the same time, they are also critical fields for the NWP model validation.

Large‐Scale Drivers of Tropical Extreme Precipitation Events: The Example of French Overseas Territories

AbstractDue to their severity and lack of predictability, understanding and forecasting extreme precipitation events (EPEs) is critical for disaster risk reduction. The present work documents the large‐scale environment of tropical EPEs based on a 42‐year data set combining dense rain‐gauge networks that cover several tropical small islands and coastal regions. Approximately 10%–30% of EPEs are associated with a tropical storm or cyclone (TC), except for Reunion, for which its high topography makes it reach 55%. TCs multiply the EPE probability by a factor of 4–15, especially during TCs of category 1 or higher. A composite analysis demonstrates that the remaining large part of EPEs occurs within large‐scale and strong moist, convective, and cyclonic wind anomalies resulting from the superimposition of intraseasonal, seasonal‐to‐annual, and interannual timescales. These intense anomalies come essentially from intraseasonal variability, and lower frequencies improve the effect of intraseasonal events in creating a favorable environment for EPEs.

Contrasting extremely warm and long-lasting cold air anomalies in the North Atlantic sector of the Arctic during the HALO-(𝒜 𝒞)3 campaign

Abstract. How air masses transform during meridional transport into and out of the Arctic is not well represented by numerical models. The airborne field campaign HALO-(𝒜𝒞)3 applied the High Altitude and Long-range Research Aircraft (HALO) within the framework of the collaborative research project on Arctic amplification (𝒜𝒞)3 to address this question by providing a comprehensive observational basis. The campaign took place from 7 March to 12 April 2022 in the North Atlantic sector of the Arctic, a main gateway of atmospheric transport into and out of the Arctic. Here, we investigate to which degree the meteorological and sea ice conditions during the campaign align with the long-term climatology (1979–2022). For this purpose, we use the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis v5 (ERA5), satellite data, and measurements at Ny-Ålesund, including atmospheric soundings. The observations and reanalysis data revealed two distinct periods with different weather conditions during HALO-(𝒜𝒞)3: the campaign started with a warm period (11–20 March 2022) where strong southerly winds prevailed that caused poleward transport of warm and moist air masses, so-called moist and warm air intrusions (WAIs). Two WAI events were identified as atmospheric rivers (ARs), which are narrow bands of strong moisture transport. These warm and moist air masses caused the highest measured 2 m temperatures (5.5 °C) and daily precipitation rates (42 mm d−1) at Ny-Ålesund for March since the beginning of the record (1993). Over the sea ice northwest of Svalbard, ERA5 indicated record-breaking rainfall. After the passage of a strong cyclone on 21 March 2022, a cold period followed. Northerly winds advected cold air into the Fram Strait, causing marine cold air outbreaks (MCAOs) until the end of the campaign. This second phase included one of the longest MCAO events found in the ERA5 record (19 d). On average, the entire campaign period was warmer than the climatological mean due to the strong influence of the ARs. In the Fram Strait, the sea ice concentration was well within the climatological variability over the entire campaign duration. However, during the warm period, a large polynya opened northeast of Svalbard, untypical for this season. Compared to previous airborne field campaigns focusing on the evolution of (mixed-phase) clouds, a larger variety of MCAO conditions was observed during HALO-(𝒜𝒞)3. In summary, air mass transport into and out of the Arctic was more pronounced than usual, providing exciting prospects for studying air mass transformation using HALO-(𝒜𝒞)3.

Absolute instability of moisture‐coupled waves on the equatorial beta‐plane

AbstractThe instabilities produced by a linear model of the tropical atmosphere coupled to a prognostic equation for water vapour are investigated. The basic model with no meridional wind supports unstable eastward‐propagating waves. For parameter regimes relevant to the Indo‐Pacific warm pool, the long‐time asymptotic behaviour of the unstable waves is found to be absolutely unstable, so that the amplitude of disturbances will grow in time at every point in the domain. The absolute instability of the system is realized at planetary length‐scales and intraseasonal frequencies. Other parameter choices for the system do not produce this same behaviour at these length‐ and time‐scales. It is shown that the resultant long‐time behaviour of the instability is characterized by roughly equal roles for temperature and moisture fluctuations in setting the thermodynamic tendency of the waves. With the inclusion of momentum damping, the phase speed of the absolutely unstable solution is about 7 ms. Addition of a strong background meridional moisture gradient, as in recent studies on the Madden–Julian Oscillation (MJO), appears to remove the absolute instability from the system. In a background state that varies slowly in the zonal direction, it is shown analytically that localized regions of instability may be formed, again using parameter choices relevant to the warm pool. The dynamics and thermodynamics of these local instabilities show some correspondence with the observed development of the MJO as it propagates through the warm pool.

Examining Atmospheric River Life Cycles in East Antarctica

AbstractDuring atmospheric river (AR) landfalls on the Antarctic ice sheet, the high waviness of the circumpolar polar jet stream allows for subtropical air masses to be advected toward the Antarctic coastline. These rare but high‐impact AR events are highly consequential for the Antarctic mass balance; yet little is known about the various atmospheric dynamical components determining their life cycle. By using an AR detection algorithm to retrieve AR landfalls at Dumont d'Urville and non‐AR analogs based on 700 hPa geopotential height, we examined what makes AR landfalls unique and studied the complete life cycle of ARs reaching Dumont d'Urville. ARs form in the mid‐latitudes/subtropics in areas of high surface evaporation, likely in response to tropical deep convection anomalies. These convection anomalies likely lead to Rossby wave trains that help amplify the upper‐tropospheric flow pattern. As the AR approaches Antarctica, condensation of isentropically lifted moisture causes latent heat release that—in conjunction with poleward warm air advection—induces geopotential height rises and anticyclonic upper‐level potential vorticity tendencies downstream. As evidenced by a blocking index, these tendencies lead to enhanced ridging/blocking that persist beyond the AR landfall time, sustaining warm air advection onto the ice sheet. Finally, we demonstrate a connection between tropopause polar vortices and mid‐latitude cyclogenesis in an AR case study. Overall, the non‐AR analogs reveal that the amplified jet pattern observed during AR landfalls is a result of enhanced poleward moisture transport and associated diabatic heating which is likely impossible to replicate without strong moisture transport.

Moisture sources of precipitation over the Pearl River Basin in South China

AbstractMoisture sources and transport processes play a critical part in hydrological cycle and determine regional precipitation. This paper utilizes the Water Accounting Model‐2layers (WAM‐2layers) and the ERA5 reanalysis data to track the sources of precipitation over the Pearl River Basin (PRB). The contribution of external moisture and the role of local recycling are investigated. The results show that during the period from 1980 to 2020, oceanic sources including the western North Pacific and Indian Oceans serve as the primary moisture sources of precipitation over the PRB. The contributions to total seasonal precipitation are respectively 62.57% in MAM, 54.79% in JJA, 43.70% in SON and 60.88% in DJF. By contrast, the contribution of local recycling is generally below 5.50%. In the dry years of 1994, 1997 and 2001, the contribution of terrestrial sources is about 19.22%; in the wet years of 1989, 2009 and 2011, the contribution is about 16.31%. The summer precipitation anomalies are mainly attributable to moisture anomalies from the Equatorial Indian Ocean in the wet years and from Southeast Asia in the dry years. Furthermore, vertically integrated moisture flux anomalies over the boundaries of the PRB are generally the result of anomalous wind rather than anomalous moisture. In the wet years, low‐pressure systems induce strong cyclonic moisture transports, increasing the PRB precipitation. In the dry years, high‐pressure anomalies over the PRB block the moisture transports from the Indian Ocean and western North Pacific.

On the relationship between mesoscale cellular convection and meteorological forcing: comparing the Southern Ocean against the North Pacific

Abstract. Marine atmospheric boundary layer (MABL) clouds cover vast areas over the ocean and have important radiative effects on the Earth's climate system. These radiative effects are known to be sensitive to the local organization, or structure, of the mesoscale cellular convection (MCC). A convolutional neural network model is used to identify the two idealized classes of MCC clouds, namely open and closed, over the Southern Ocean (SO) and Northwest Pacific (NP) from high-frequency geostationary Himawari-8 satellite observations. The results of the climatology show that MCC clouds are evenly distributed over the mid-latitude storm tracks for both hemispheres, with peaks poleward of the 40∘ latitude. Open-MCC clouds are more prevalent than closed MCC in both regions. An examination of the presumed meteorological forcing associated with open- and closed-MCC clouds is conducted to illustrate the influence of large-scale meteorological conditions. We establish the importance of the Kuroshio western boundary current in the spatial coverage of open and closed MCC across the NP, presumably through the supply of strong heat and moisture fluxes during marine cold-air outbreaks events. In regions where static stability is higher, we observe a more frequent occurrence of closed MCCs. This behavior contrasts markedly with that of open MCCs, whose formation and persistence are significantly influenced by the difference in temperature between the air and the sea surface. The occurrence frequency of closed MCC over the SO exhibits a significant diurnal cycle, while the diurnal cycle of closed MCC over the NP is less noticeable.

Role of atmospheric resonance and land–atmosphere feedbacks as a precursor to the June 2021 Pacific Northwest Heat Dome event

We demonstrate an indirect, rather than direct, role of quasi-resonant amplification of planetary waves in a summer weather extreme. We find that there was an interplay between a persistent, amplified large-scale atmospheric circulation state and soil moisture feedbacks as a precursor for the June 2021 Pacific Northwest "Heat Dome" event. An extended resonant planetary wave configuration prior to the event created an antecedent soil moisture deficit that amplified lower atmospheric warming through strong nonlinear soil moisture feedbacks, favoring this unprecedented heat event.

Circulation patterns in the middle and upper troposphere and their relationships with summer precipitation in the Jianghuai River Basin

AbstractThe upper and lower‐level circulations can be divided into four distinct modes based on ERA5 daily reanalysis data. The impact of these patterns on the summer persistent precipitation (SPP) in the Jianghuai River Basin (JRB) is investigated, with the ‘−SR (Silk Road)/+EAP (East Asia‐Pacific)’ mode identified as the most favourable for triggering SPP. The main manifestations are as follows: (1) From 1981 to 2020, 29.4% (30.7%) of extreme precipitation days (the frequencies of persistent extreme precipitation) are related to the ‘−SR/+EAP’ mode, indicating the importance of the ‘−SR/+EAP’ mode to the SPP in the JRB. (2) The ‘−SR’ pattern accelerates the westerly jet, leading to strong divergence over the JRB. Concurrently, the eastward movement of the South Asia High and westward shift of the Western Pacific subtropical high (WPSH) create conditions favourable for SPP in the JRB. (3) Abundant water vapour, facilitated by strong moisture convergence and upward motion, significantly contributes to SPP in the JRB.

Open-air, green-solvent processed organic solar cells with efficiency approaching 18% and exceptional stability

H75-2F, a fluorinated cathode material, boosts organic solar cell efficiency, achieving 19.44% PCE in controlled conditions and 17.78% with open-air green-solvent processing, while offering strong thermal and moisture stability.

Multifunctional modification polyester with Au@Cu2O-ZnO ternary heterojunction fabricated by in situ polymerization.

In situ polymerization has been proven to be an effective method to introduce functional materials into polymers. In this work, a nano-heterojunction material was prepared successfully and evenly dispersed in PET by in situ polymerization methods to yield multifunctionally modified PET. The modified PET fibers showed excellent antibacterial activity and strong moisture absorption and perspiration, which could efficiently expel moisture from humans. Significantly, these prepared PET textiles demonstrate a strong safety without any cytotoxicity. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the uniform dispersion of heterojunctions and well-defined truncated octahedra including nano-gold rods. A series of characterizations including FTIR, XPS, XRD and DSC showed that the nano-heterojunction participates in the reaction during polymerization. It is interesting that the SEM images of the modified PET fiber presented an intriguing organ fold structure, which makes a significant contribution to moisture absorption and perspiration. The formation mechanism is discussed preliminarily.

The role of drylines in thunderstorm initiation and record rainfall during an anomalously convective early summer season in South Africa

An average of 12 drylines are associated with thunderstorm development (convective drylines) during December in the western plateau of subtropical southern Africa. During December 2021, 20 convective drylines occurred. This was the highest number since the record began in 2010. December 2021 was also unusually wet over a large part of the summer rainfall region in South Africa. Monthly rainfall records were broken in the Northern Cape, Northwest and Free State provinces. Above-average rainfall had dire consequences for the maize industry over the central interior. The large-scale circulation during December 2021 was very conducive to dryline formation over the western plateau with a deeper than usual surface trough and strong low-level northeasterly moisture flux towards the climatologically dry western plateau region. Above normal wind speeds of mid-tropospheric northwesterlies and large-scale uplift contributed to a favorable environment for strong thunderstorms, as seen during a 6-day convective dryline event. Thunderstorms which were triggered along the dryline travelled east and contributed to the above normal rainfall observed during December 2021. Dryline and rainfall frequencies show large inter-annual variability. However, a positive Pearson correlation (r = 0.45; p < 0.05) between the number of dryline days and rainfall amounts were found between 1979 and 2021. This correlation increased (r = 0.53; p < 0.05) when rainfall amounts immediately east of the western plateau domain were also included, suggesting that dryline-related convection can have a significant influence on rainfall over the western plateau and further downstream.

Intraseasonal variations of precipitation over southern China during boreal winter and their two primary influencing factors

AbstractThis paper utilizes reanalysis data and statistical methods to elucidate the physical mechanisms of intraseasonal variations of precipitation over southern China during the boreal winter, as well as the two primary factors influencing these variations. Anomalous southerly (northerly) wind over southern China will result in the strong moisture convergence (divergence) in enhanced (suppressed) scenarios, and the stronger positive (negative) horizontal advection of absolute vorticity at upper troposphere induces the anomalous ascending (descending) motion in enhanced (suppressed) scenarios. The Madden–Julian oscillation (MJO) in the tropics and a wave train over the North Atlantic and Eurasia with four activity centres in the mid–high latitudes (referred as NAE‐wave train) are the two primary factors that modulate the intraseasoanl precipitation over southern China. The intraseasonal circulation induced by MJO and NAE‐wave train exhibits distinct features, resulting in different physical mechanisms of their influences. The moisture flux divergence anomalies over southern China associated with MJO mainly stem from the meridional moisture convergence, whereas the meridional moisture advection is the first contributor in the influence of NAE‐wave train. The anomalous vorticity advection at upper troposphere associated with MJO is primarily influenced by the meridional advection, but that associated with NAE‐wave train is dominated by the zonal advection. Anomalous precipitation induced by MJO is concentrated mainly over South China, while that caused by NAE‐wave train is primarily located in the mid–lower Yangtze River basin. Therefore, different phases locking of MJO and NAE‐wave train could lead to various precipitation anomalies over southern China.