Cycle Of Precipitation Research Articles

Clustering the Diurnal Cycle of Precipitation Using Global Satellite Data

AbstractThe diurnal cycle of precipitation (DCP) is a fundamental component of the precipitation cycles across various temporal scales. However, the absence of a comprehensive and intuitive clustering description of the DCP, including precipitation amount, frequency, intensity, and seasonality on the global scale, has impeded understanding of climate impacts on society. This study investigates the diurnal cycle and its seasonal differences in global precipitation using hierarchical clustering and high‐resolution satellite precipitation data. Results indicate that regions with coastal and topographic complexity exhibit intricate clustering patterns globally. Significant inter‐cluster differences suggest that the precipitation amount and frequency have stronger diurnal cycles than that of the precipitation intensity. Seasonal cluster transitions indicate that the global DCP exhibits significant seasonal differences. This study provides multiple sets of information‐rich and user‐friendly maps of the DCP, enhancing research on sub‐daily precipitation mechanisms and their climatic impacts.

Simulation of Thermal Nonequilibrium Cycles in the Solar Wind

Thermal nonequilibrium (TNE) is a condition of the plasma in the solar corona in which the local rate of energy loss due to radiation increases to the point that it cannot be sustained by the various heating terms acting on the plasma, precluding the existence of a steady state. The limit cycles of precipitation and evaporation that result from TNE have been simulated in 1D models of coronal loops, as well as 2D and 3D models of the solar chromosphere and lower corona. However, a careful study of TNE in the solar wind has not been performed until now. Here, we demonstrate that for suitable combinations of local and global heating rates, it is possible for the plasma to exhibit a TNE condition, even in the context of a transonic solar wind with appreciable mass and energy fluxes. This implies limits on the amount of footpoint heating that can be withstood under steady-state conditions in the solar wind, and may help to explain the variability of solar wind streams that emanate from regions of highly concentrated magnetic flux on the solar surface. The implications of this finding pertain to various sources of high-density solar wind, including plumes that form above regions of mixed magnetic polarity in polar coronal holes and the slow solar wind that emanates from coronal hole boundaries.

On the variability of the site-response parameters of the active rock slope in Brienz/Brinzauls (Switzerland)

Summary Unstable rock slopes, prone to collapse, pose an increasingly severe threat to both people and infrastructures, necessitating effective monitoring for risk mitigation. While many techniques rely on surface displacements to assess slope stability, seismic indicators such as resonant frequency, variations in seismic shear wave velocity, and site amplification offer valuable insights into the structural integrity of the slope, aspects not captured by surface deformation alone. Research has demonstrated that these site-response parameters can serve as monitoring tools to detect precursory signs of failure, such as a drop in resonant frequency and relative seismic velocity prior to collapse. Still, environmental factors like temperature, precipitation, snow melt, earthquakes, and freeze-thaw cycles transiently influence the seismic response. Our main objective is to understand the correlations and drivers between environmental parameters and seismic response, distinguishing between reversible and irreversible changes in dynamic behaviour. Over a five-year monitoring period, we continuously recorded ambient vibration data at the Brienz/Brinzauls landslide and monitored three different site-response parameters (resonant frequency, site amplification, relative seismic wave velocity variation) using enhanced frequency domain decomposition, site-to-reference spectral ratio, and single station ambient vibrations correlation techniques. Our results highlight a long-term increase in site amplification and a long-term decrease in first and second resonant frequencies, indicating ongoing structural weakening. Temperature was found to correlate with seasonal variations of seismic wave velocity with a few day’s time lag. Snow melting and rainfalls exerted a secondary influence, temporarily reducing relative seismic wave velocity during snowmelt and rainfall. Our findings suggest that single-station relative seismic velocity variations are mainly influenced by the shallow sub-surface (depth of about 30 m), limiting its application to study the stability of deep structures.

On the Importance of Precipitation‐Induced Surface Sensible Heat Flux for Diurnal Cycle of Precipitation in the Maritime Continent

AbstractThe Maritime Continent (MC) exhibits a pronounced diurnal cycle in precipitation, with many high‐resolution models overestimating the diurnal peak and predicting earlier precipitation over the islands than observed. We hypothesize that part of this model bias comes from ignoring precipitation‐induced surface sensible heat flux (QP). To test this conjecture, we performed simulations with and without QP for April 2009 and June 2006. The inclusion of QP reduced the bias in diurnal peak precipitation amplitude by 83% in April 2009 and 23% in June 2006. Similarly, the bias in precipitation peak timing decreased by 26% and 15%, respectively. This bias reduction was even more prominent during periods of heavier rainfall. This improvement in both the amplitude and phase of diurnal precipitation also led to a reduction in bias for total precipitation by ∼10%. These findings suggest that QP cannot be neglected over the MC, particularly during heavy precipitation.

Observed Variability in Convective Cell Characteristics and Near-Storm Environments across the Sea- and Bay-Breeze Fronts in Southeast Texas

Abstract During the DOE Atmospheric Radiation Measurement (ARM) Tracking Aerosol Convection Interactions Experiment (TRACER) IOP spanning June–September 2022, two fixed ARM sites and a mobile team concurrently sampled the airmass heterogeneity across sea- and bay-breeze fronts around the greater Houston metropolitan region. Here, we quantify the spatiotemporal variability between maritime (coastal/bay side of breeze fronts) and continental (inland side of breeze fronts) air masses over 15 IOP days characterized by strong sea-breeze forcing. We analyze environmental profile data from 177 radiosondes and use S- and C-band radar data to track and quantify the variability in attributes of more than 2300 shallow and transitioning cells across different air masses. The composite analysis of environmental profiles indicates that during the early afternoon, the sea-breeze maritime air mass exhibits lower convective available potential energy (CAPE) than the bay-breeze maritime air mass. As the sea breeze advances inland with time, CAPE within the maritime air mass exceeds that of the continental air mass to the north of the breeze fronts. In general, maritime cells have a larger mean composite reflectivity and cell widths than continental cells; however, the response varies between shallow and transitioning cells. Mean composite 20-dBZ echo-top heights, however, are similar across air masses for both shallow and transitioning cells. The continental and maritime inflow air mass for transitioning cells has significantly different mean values for mixed-layer entrainment CAPE, lifted condensation level, level of free condensation, boundary layer depth, and diluted equilibrium level. For shallow cells, only total precipitable water shows a significant difference. Significance Statement The greater Houston metropolitan area is a natural laboratory for understanding the individual impacts of background meteorology and aerosols on convective clouds. Due to its proximity to the Gulf Coast and Galveston Bay, the Houston region experiences a diurnal precipitation cycle in the summer, driven by convection triggered from sea- and bay-breeze fronts. These fronts act as a boundary between air masses with distinct thermodynamic and environmental characteristics. Convergence along these fronts and interactions between storm outflow and the fronts facilitate convection initiation in different mesoscale air masses. This study quantifies the heterogeneity among these air masses while investigating their influence on cloud microphysics. We find that the effect of airmass heterogeneity is more pronounced for the bulk microphysical properties in shallow clouds.

Effects of urban areas on the diurnal cycle of temperature and precipitation in a global climate simulation

AbstractAnalyses of global climate model results for urban impacts on temperature and precipitation are rare. Previous analyses of the global Conformal Cubic Atmospheric Model simulation results for 1985–2010 have revealed urban effects on minimum and maximum temperatures. Using the same dataset to derive time‐zone‐corrected three‐hourly local time period (LTP) data, averaged diurnal cycles of temperature and precipitation were calculated for grid cells with greater than 10% urban fraction (urban grid cells) globally. Three latitudinal bands were assessed: northern extratropics (NET, 274 urban grid cells), southern extratropics (SET, 39 urban grid cells), and the Tropics (26 urban grid cells). The largest statistically significant urban influences on temperature are consistently found at night, in agreement with many previous studies on urban heat islands. Signs of urban cooling were found for a few hours, from 09:00 to 15:00 LTP, most often in summer. Influences of urban areas on precipitation varied, with small increases and decreases in all latitudinal bands and seasons. For NET, increases were generally found. In the Tropics, increases were found from 21:00 to 09:00 LTP for all seasons except DJF, with decreases for all seasons from 15:00 to 18:00 LTP. In SET, all seasons had increases for 21:00 to 00:00 LTP and decreases for 15:00 to 18:00 LTP. DJF had decreases for all LTPs except 21:00 to 00:00 LTP and SON had increases for all times except 15:00 to 18:00 LTP. Differences in rainfall in the region surrounding the urban areas were broadly similar to local changes in NET. For the Tropics and SET, regional decreases were found for DJF and JJA, with a more varied pattern for other months. Regional effects appeared to be more restricted to near‐urban areas in the Tropics than in NET. The results indicate some influence of nearby urban areas on regional temperature and precipitation.

Environmental and ecological factors associated with stinging jellyfish at a tourism hotspot in the Gulf of Thailand

The waters of Thailand are associated with some of the most severe cases of envenomation from jellyfish in Asia, often attributed to the extensive marine recreational tourism industry it supports. The western Gulf of Thailand in particular has been shown to host among the highest abundances of box jellyfish, while also being home to some of the highest marine recreational tourism, such as along the Koh Samui archipelago. Here we utilise aspects of the same tourism industry to develop a deeper understanding of stinging jellyfish population dynamics, by combining citizen science at the island of Koh Tao, with dedicated in-situ surveys and remote sensing data. Our analyses of 170 box jellyfish sightings and 81 blooms of Pelagia sp. across a six-year period revealed a strong seasonal trend, with both groups being most abundant between July and December. Decision tree analysis of the complete observation dataset and multiple environmental variables revealed a combination of precipitation and lunar cycle to be the strongest predictors of the assessed stinging jellyfish at Koh Tao. Furthermore, blooms of Pelagia sp. were associated with extensive medusivory by a large diversity of predators, including reef building corals. These observations add to the growing literature showing that scleractinian corals are readily able to ingest larger prey items, either by solitary or protocooperative feeding strategies. Meanwhile, no consumption of box jellyfish medusae was recorded during the study. These findings may allow for improved tourism management practices while also supporting a wider biogeographic assessment of stinging jellyfish in south-east Asia.

A multi-scenario ensemble approach incorporating stepwise cluster analysis to reduce uncertainty in large-scale watershed precipitation projections: a case study of Pearl River Basin, South China.

Assessing and selecting climate models with lower uncertainty is necessary to predict future climate and hydrological risks at the watershed scale. In this study, we integrated stepwise cluster analysis (SCA) to propose a multi-model ensemble downscaling framework aimed at reducing the uncertainty of GCM-based precipitation projections in large-scale watersheds. The Pearl River Basin (PRB) in southern China was selected as the study area to validate the reliability of this framework. Spatially, we investigated the features of terrain-related spatial heterogeneity in precipitation simulation of different climate models using a stepwise cluster zoning approach. The spatial performance of most CMIP6 models was effective in capturing the annual mean precipitation from the source region to the downstream of the PRB. To further evaluate the model's skill in simulating precipitation patterns, we conducted a seasonal analysis for different periods throughout the year. However, the seasonal precipitation cycle exhibited a wet bias during cold seasons, and the most significant deviation of precipitation percentage intervals occurred during winter. The TSS ranking of CMIP6 models was used to select the top-performing models to construct an improved multi-model ensemble mean (MEM5), resulting in a more accurate precipitation simulation for PRB. Results showed consistent precipitation increases (p < 0.05) for all scenarios in the PRB, with the middle and lower reaches being the most sensitive to changes in precipitation. The improved MEM5 can serve as a valuable reference for accurately simulating hydrological regimes and extreme weather events in the PRB. The proposed multi-model ensemble downscaling framework, which incorporates SCA, offers a new approach for high-resolution and low-uncertainty climate simulations in other large-scale watersheds.

Heterogeneity of the diurnal cycle of precipitation in the Amazon Basin

Heterogeneity of the diurnal cycle of precipitation in the Amazon Basin

Diurnal Cycle of Precipitation and Extremes in Nepal

This study examines the spatio-temporal distribution of hourly precipitation across Nepal using Integrated Multi-Satellite Retrievals for Global Precipitation Measurement (IMERG) data from 2015 to 2021. The findings indicate that hourly precipitation intensity during the monsoon season can reach up to 0.7 mm/hr, while pre-monsoon intensities peak at 0.2 mm/hr. These intensities are predominantly concentrated in mid- and low-elevation areas of central and eastern Nepal. Post-monsoon and winter seasons exhibit high-intensity precipitation patches over high-elevation regions in the western, central, and eastern peripheries of the country. The annual distribution of hourly precipitation shows a pronounced peak during the monsoon season, indicating that a significant portion of the total annual precipitation occurs during this period. Extreme precipitation events follow a similar seasonal distribution, with monsoon extremes exceeding 15 mm/hr. The diurnal cycle of monsoonal precipitation shows unique characteristics, peaking at 0.65 mm/hr around midnight and decreasing to 0.2 mm/hr by late morning, then increasing steadily in the afternoon and evening. Additionally, the study contrasts hourly heavy precipitation extremes (≥10 mm/hr or day) with daily extremes, noting that hourly extremes, despite being accumulated into daily measures, present a higher frequency, and pose greater short-term hazard risks. This analysis over a seven-year period suggests the need for continued research to determine spatial and temporal trends in hourly versus daily extreme precipitation patterns, particularly in the context of climate change and its impacts on regional hydrology and meteorology.

Climatic characteristics of centennial and extreme precipitation in Hangzhou, China

The precipitation characteristics in Hangzhou of Zhejiang Province, China under the background of global climate change are analyzed using the meteorological observation data obtained from the Hangzhou base station in this study. We investigate the climate characteristics of precipitation in Hangzhou from several aspects, such as centennial trend, seasonal change, periodicity and the variation of extreme precipitation. Our results show a linear decreasing trend and obvious interdecadal characteristics in the precipitation of Hangzhou on a centennial timescale. Significantly increased amplitude of precipitation fluctuation was observed since the beginning of the 21st century. For the interdecadal variation of seasonal precipitation on a centennial timescale, precipitation in autumn showed a decreasing trend of 8.1 mm/10a, whereas the trends for the other three seasons were statistically insignificant. The precipitation in Hangzhou showed a decreasing trend in spring and an increasing trend in winter over the past 30 years. Our analyses reveal distinct precipitation cycles, including a quasi-30-year cycle since the 1960s and a quasi-10-year cycle since the 1980s. However, the periodicity has weakened in the past 10 years. In addition, the occurrence of torrential rain has increased rapidly in the past 10 years. Furthermore, influenced by global climate change and regional processes, the variation of extreme precipitation in Hangzhou has changed, which shows strong correlations with the overall trend of annual precipitation. The annual maximum daily precipitation in Hangzhou was mainly in the range of 0–40 mm from 1951 to 1980 and in the range of 40–80 mm from 1981 to 2010 with the maximum daily precipitation occurrence rate of 4.7 times/10a and 6.3 times/10a, respectively. This study emphasizes the risk of urban waterlogging caused by short-term heavy rainfall and provides useful reference to the assessment of extreme meteorological and hydrological disaster risk in Hangzhou.

Extreme Seasonal Droughts and Floods in the Madeira River Basin, Brazil: Diagnosis, Causes, and Trends

The Madeira River, a major tributary of the Amazon River, often undergoes severe flood and drought conditions. This study seeks to investigate the climate processes associated with the opposing extreme precipitation events in the Madeira River basin and to relate them to river discharge variability based on a flood awareness dataset. Despite the uncertainty in the observational datasets, the annual precipitation cycle exhibits a rainy season from November to March. A significant result is the high correlation between the rainy season variability in the Madeira River basin and the sea surface temperature (SST) anomalies in the tropical North Atlantic Ocean and the southwestern South Atlantic Ocean. This result indicates that improving the Atlantic SST representation in climate modeling allows for capturing extreme precipitation events in the region. In addition to this impact, certain Madeira River tributaries present significant climate trends. The river discharge variability reveals an increase in hydrological extremes in recent years in the upper sector, but more significantly, in the lower basin, where it has reduced by more than 400 m3/s per decade. These findings highlight the need to improve in situ data and climate and hydrological modeling, with a focus on describing the intense climate variability and trends in river discharges.

Reaction pathway, mechanism and kinetics of thermochemical sulfate reduction: insights from in situ Raman spectroscopic observations at elevated temperatures and pressures

In Earth’s crust, thermochemical sulfate reduction (TSR) is a common organic–inorganic interaction, which is in close association with the carbon cycle in sedimentary basins and metal sulfide precipitation in Mississippi Valley-type deposits. However, the reaction pathway and mechanism of TSR need further investigation, mainly due to the complex sulfur species involved in this reaction. Here we applied in situ Raman spectroscopy to disclose the stepwise transformation from sulfate to sulfide and the reaction kinetics in the CH4-Na2SO4/MgSO4/H2SO4-H2O systems at elevated temperatures and pressures. Our results indicate that sulfate is transformed to H2S through a series of reduction and disproportionation reactions. Once dissolved H2S reaches a certain concentration, it reacts with sulfate to form intermediate valence sulfur species (S0 and S3−), which quickly oxidize methane to generate CO2 and H2S. The formation of S3− and S0 is responsible for the autocatalytic effect in TSR. The sulfur speciation significantly affects the reaction kinetics, which could be divided into three stages based on the in situ observations. Extrapolated kinetic data show that TSR could proceed fast under the catalysis of H2S, and the half-life of methane is ∼7.10 million years at 200 °C. Subsequent numerical modeling strongly supports that in situ sulfate reduction could provide sufficient reduced sulfur for the formation of giant Mississippi Valley-type deposits, thus serving as an efficient mineralizing mechanism.

The Zonal Seasonal Cycle of Tropical Precipitation: Introducing the Indo-Pacific Monsoonal Mode

Abstract The intertropical convergence zone (ITCZ) is associated with a zonal band of strong precipitation that migrates meridionally over the seasonal cycle. Tropical precipitation also migrates zonally, such as from the South Asian monsoon in Northern Hemisphere summer (JJA) to the precipitation maximum of the west Pacific in Northern Hemisphere winter (DJF). To explore this zonal movement in the Indo-Pacific sector, we analyze the seasonal cycle of tropical precipitation using a 2D energetic framework and study idealized atmosphere–ocean simulations with and without ocean dynamics. In the observed seasonal cycle, an atmospheric energy and precipitation anomaly forms over South Asia in northern spring and summer due to heating over land. It is then advected eastward into the west Pacific in northern autumn and remains there due to interactions with the Pacific cold tongue and equatorial easterlies. We interpret this phenomenon as a “monsoonal mode,” a zonally propagating moist energy anomaly of continental and seasonal scale. To understand the behavior of the monsoonal mode, we develop and explore an analytical model in which the monsoonal mode is advected by low-level winds, is sustained by interaction with the ocean, and decays due to the free tropospheric mixing of energy. Significance Statement Regional concentrations of tropical precipitation, such as the South Asian monsoon, provide water to billions of people. These features have strong seasonal cycles that have typically been framed in terms of meridional shifts of precipitation following the sun’s movement. Here, we study zonal shifts of tropical precipitation over the seasonal cycle in observations and idealized simulations. We find that land–ocean contrasts trigger a monsoon with concentrated precipitation over Asia in northern summer and near-surface eastward winds carry this precipitation into the west Pacific during northern autumn in what we call a “monsoonal mode.” This concentrated precipitation remains over the west Pacific during northern winter, as further migration is impeded by the cold sea surface temperatures (SSTs) and easterly winds of the east Pacific.

Diurnal cycle of precipitation in Brazil

Diurnal cycle of precipitation in Brazil

A preliminary investigation of the small rockfall triggering conditions along a road network in Slovenia

AbstractRockfalls are among the natural hazards that endanger infrastructure, cause major economic disruptions, and threaten human lives. These phenomena result from long-term geological processes such as tectonic rock deformation or weathering, but the actual rockfall itself occurs suddenly, usually without warning. The triggering mechanisms are complex and difficult to trace. In this study, we investigated the triggering mechanisms of more than 2100 small rockfalls that occurred in 2021 in Slovenia, Europe, along the 51,000 km long national road network. We analyzed their spatial and temporal characteristics, as well as the triggering mechanisms of their occurrence, based on different weather scenarios. Multiple data mining methods were used to investigate triggering conditions, and scenario analyses were used to understand the triggering mechanisms. Most small rockfalls in 2021 were recorded in winter and spring at a density of 1 rockfall per 10 km2. The results show that winter weather conditions have the greatest potential for triggering small rockfalls in Slovenia, both in terms of spatial extent and frequency of triggering weather conditions. The analysis showed that summer storms are an important but indeterminant factor for the occurrence of small rockfalls. Among the scenarios tested, the winter scenario, which includes a combination of antecedent precipitation, snowmelt, and freeze‒thaw cycles a few days before the event, was able to predict 72% of the events in the colder season.

Human Activities Have Altered Sediment Transport in the Yihe River, the Longest River Originating from Shandong Province, China

Climate change and human activities affect regional sediment transport and ecological environment construction. Investigating sediment transport and its influencing factors in the Yihe River Basin (YHRB) will provide guidance for regional soil and water conservation and sustainable development. We analyzed the chronological changes, cycles, spatial distribution and influencing factors using Mann–Kendall (M-K) trend analysis, wavelet analysis, and the Pettitt mutation point (PMP) test, then quantified the role of precipitation and human activities in sediment transport changes. The results showed that annual precipitation decreased marginally, whereas sediment load has noticeably declined. Four precipitation cycles were observed: 4–8a, 9–14a, 16–19a, and 20–28a, where 9–14a was dominant; sediment transport cycles were tracked: 3–5a, 9–15a, and 30a, where 30a was dominant with a decreasing trend. The sediment load was higher in the central, northern, and southwestern sub-basins of the YHRB, while it was lower in the southeast. The contribution of human activities and precipitation changes to sediment transport was 73.14% and 26.86% in transitional phase I (1965–1980) and 71.97% and 28.03% in transitional phase II (1981–2020), respectively. Hydraulic engineering construction, water resource development, land-use changes, and soil and water conservation measures intercepted precipitation and sediment, making them the primary factor affecting sediment transport changes in the YHRB.

The performance of the CoMorph‐A convection package in global simulations with the Met Office Unified Model

AbstractThe impact on global simulations of a new package of physical parametrizations in the Met Office Unified Model is documented. The main component of the package is an entirely new convection scheme, CoMorph. This has a mass‐flux structure that allows initiation of buoyant ascent from any level and the ability for plumes of differing originating levels to coexist in a grid box. It has a different form of closure, where the mass flux of initiation is dependent on local instability, and an implicit numerical solution for detrainment that yields smooth timestep behaviour. The scheme is coupled more consistently to the cloud, microphysics, and boundary‐layer parametrizations and, as a result, significant changes to these have also been made. The package, called CoMorph‐A, has been tested in a variety of single‐column and idealized regimes. Here we test it in global configurations and evaluate it against observations using a range of standard metrics. Overall it is found to perform well against the control. Biases in the climatologies of the radiative fluxes are significantly reduced across the Tropics and subtropics, tropical and extratropical cyclone statistics are improved, and the Madden–Julian oscillation and other propagating tropical waves are strengthened. It also improves overall scores in numerical weather prediction trials, without revisions to the data assimilation. There is still work to do to improve the diurnal cycle of precipitation over land, where the peak remains too close to the middle of the day.

Integrated Effects of Site Hydrology and Vegetation on Exchange Fluxes and Nutrient Cycling at a Coastal Terrestrial‐Aquatic Interface

AbstractThe complex interactions among soil, vegetation, and site hydrologic conditions driven by precipitation and tidal cycles control the biogeochemical transformations and bi‐directional exchange of carbon and nutrients across the terrestrial–aquatic interfaces (TAIs) in coastal regions. This study uses a highly mechanistic model, Advanced Terrestrial Simulator (ATS)‐PFLOTRAN, to explore how these interactions affect exchanges of materials and carbon and nitrogen cycling. We used a transect in the Chesapeake Bay region that spans zones of open water, coastal wetland, transition, and upland forest. We designed several simulation scenarios to parse the effects of the individual controlling factors and the sensitivity of carbon cycling to reaction rate parameters derived from laboratory experiments. Our simulations reveal an active zone for carbon cycling under the transition zones between the wetland and the upland. Evapotranspiration is found to enhance the exchange fluxes between the surface and subsurface domains, resulting in a higher dissolved oxygen concentration in the TAIs. The transport of organic carbon derived from plant leaves and roots provide an additional source of organic carbon needed for the aerobic respiration and denitrification processes in the TAIs. The variability in reaction rate parameters associated with microbial activities is also found to play a dominant role in controlling the heterogeneity and dynamics of the simulated redox conditions. This modeling‐focused exploratory study enabled us to better understand the complex interactions among soil, water and microbes that govern the hydro‐biogeochemical processes at the TAIs, which is an important step toward representing coastal ecosystems in larger‐scale Earth system models.

An Investigation on Potential Dispersal of Airborne Pollen Over China and Their Impact on Climate as Ice Nuclei Using RegCM‐Pollen

AbstractPollen can serve as an effective ice‐nuclei (IN), altering cloud microphysical and radiative properties, thus precipitation and cloud life cycles. Here, a nationwide pollen emission inventory with a horizontal resolution of 5 km was established based on a parameterization scheme of mass balance of pollen grain fluxes surrounding the plant crowns, and using satellite observational data sets (including leaf area index and fractional vegetation cover) as well as pollen emission rates. The potential emission is then implemented in RegCM‐pollen model which treated pollen as aerosol tracers. Besides, pollen‐IN parameterization schemes were incorporated in RegCM‐pollen to simulate the interactions between pollen and ice clouds. Investigations show that the mean annual pollen emission in China is 2.65 × 107 grains m−2 yr−1, mainly distributed in the south and northeast of China. The IN magnitude is mainly determined by a combination of temperature and pollen concentration. Notably, an increasing number concentration of pollen grains produces opposite effects in Southern China (SC) and Northern China (NC). The weakened upward motion and vertical transport of water vapor in NC made ice clouds hardly form, resulting in cloud forcing (CF) of +0.86 W/m2. In contrast, it generates a CF of −0.84 W/m2 in SC mainly owing to expanded cloud cover. The changes in shortwave radiative forcing is more significant compared to longwave radiative forcing in the two regions. At the surface, the net radiative forcing in NC is +0.74 W/m2, while it is a −0.51 W/m2 in SC. Among them, downward shortwave radiative forcing is approximately twice that of upward longwave radiative forcing in SC and 1.4 times in NC. Surface temperature shows rising over NC, ranging from 0.05 to 0.25 K. In SC, it is primarily decreasing by −0.12 to −0.03 K. The pollen‐IN effect also causes a decline of precipitation in NC (−0.17 mm/day) and a rise in SC (0.09 mm/day). Our results suggest that the pollen effect on ice clouds is complex, yet significant in understanding its impact on radiation and climate of the atmosphere.