Low Precipitation Rates Research Articles

Simulation of the radiative effect of haze on the urban hydrological cycle using reanalysis data in Beijing

Abstract. Although increased aerosol concentration modifies local air temperatures and boundary layer structure in urban areas, little is known about its effects on the urban hydrological cycle. Changes in the hydrological cycle modify surface runoff and flooding. Furthermore, as runoff commonly transports pollutants to soil and water, any changes impact urban soil and aquatic environments. To explore the radiative effect of haze on changes in the urban surface water balance in Beijing, different haze levels are modelled using the Surface Urban Energy and Water Balance Scheme (SUEWS), forced by reanalysis data. The pollution levels are classified using aerosol optical depth observations. The secondary aims are to examine the usability of a global reanalysis dataset in a highly polluted environment and the SUEWS model performance. We show that the reanalysis data do not include the attenuating effect of haze on incoming solar radiation and develop a correction method. Using these corrected data, SUEWS simulates measured eddy covariance heat fluxes well. Both surface runoff and drainage increase with severe haze levels, particularly with low precipitation rates: runoff from 0.06 to 0.18 mm d−1 and drainage from 0.43 to 0.62 mm d−1 during fairly clean to extremely polluted conditions, respectively. Considering all precipitation events, runoff rates are higher during extremely polluted conditions than cleaner conditions, but as the cleanest conditions have high precipitation rates, they induce the largest runoff. Thus, the haze radiative effect is unlikely to modify flash flooding likelihood. However, flushing pollutants from surfaces may increase pollutant loads in urban water bodies.

Water chemistry and water quality of a tidal river system in relation with riverbank land use pattern and regional climate in the southwest Bengal Delta of Bangladesh

Water chemistry of BRRS (Bhairab-Rupsha River System) is defining the water quality of BRRS, which is seasonally changed from premonsoon (March–May) to postmonsoon (June–August). The study identified the relation in changes of water chemistry and water pollution with riverbank land use patterns and regional climate through four analytical frameworks including—Hydrochemical framework; GIS and RS framework; Statistical framework; Climatic framework. Integration of these four frameworks defines the changes of water chemistry as in water quality and explores the relation in-between water chemistry, water quality, riverbank land use pattern, and regional climate. The concentration of ions is higher in premonsoon with low precipitation rate and high daily temperature. The spatial distribution of water chemistry of BRRS explored in upper reach (upstream), middle reach, and lower reach (downstream) according to the riverbank land use patterns. Highest EC is measured in upper reach and in middle reach with high Na+ at postmonsoon and in lower reach with high Cl− at premonsoon. TDS is highest in upper reach with high Mg2+ at postmonsoon and in lower reach with high K+, Ca2+, Mg2+, and Cl− in premonsoon. Water chemistry of BRRS is controlling by continental weathering in postmonsoon, and by high salt concentration in premonsoon. The combination of Piper plot and mixing diagrams explored precipitation-runoff dominates in postmonsoon and lacks ample discharge in the premonsoon press the tidal front downwards and consequently dominated by increasing salt concentration. The degree of pollution estimates % of pollution in BRRS which increases in premonsoon and decreases in postmonsoon. SAR, Na%, TDS, and EC explored that BRRS water is suitable for daily purposes and irrigation only in postmonsoon.

The Al-Abiadh Valley Drainage Basin Environmental Aspects Extraction Using Quantitatively Morphometric Analyses of Shuttle Radar Topographic Mission Data

The accurate extracting, studying, and analyzing of drainage basin morphometric aspects is important for the accurate determination of environmental factors that formed them, such as climate, tectonic activity, region lithology, and land covering vegetation.
 This work was divided into three stages; the 1st stage was delineation of the Al-Abiadh basin borders using a new approach that depends on three-dimensional modeling of the studied region and a drainage network pattern extraction using (Shuttle Radar Topographic Mission) data, the 2nd was the classification of the Al-Abiadh basin streams according to their shape and widenings, and the 3rd was extracting then taking up the quantitative analysis technique to estimate the basin morphometric aspects and the basin's environmental parameters that created them.
 The Al-Abiadh valley basin is a six-order one with a dendritic, parallel, and deranged drainage network. The flood hazard is absent at the basin mouth because the valley runoff takes a long time to reach the sink (Al-Razaza Lake), located in the middle part of Iraq, with a low flow peak due to the high permeability soil, the arid to semi-arid climate, and the low annual precipitation rate.
 The region studied is an alluvial basin with similar geological structural solidity in most places. The drainage network was found to be controlled by lineaments and fracture traces; the basin has passed its youth geomorphic phase.

New insights into the interaction between heavy metals and struvite: Struvite as platform for heterogeneous nucleation of heavy metal hydroxide

During the struvite (MgNH4PO4·6H2O) recovery from agricultural or industrial wastewater, the extensive existence of heavy metals would pose great threats to the planting and environment. This work revealed the association of kinds of heavy metals, as possible substances in the wastewater, with the struvite. The struvite has been synthesized in situ and employed to contact with both high and low concentration heavy metal (including Cu, Ni, Pb, Zn, Mn, Cr(III)) wastewater. The heavy metal precipitation rates under different pH values from 6.0 to 10.0, and under a series of struvite addition amount have been investigated. The precipitation of heavy metals without addition of struvite is functioned as control experiments. The struvite’s presence can enhance the heavy metal precipitation rate under all pH values. The Ni and Mn have relatively lower precipitation rate compared with other metals. For extremely low heavy metal concentration the precipitation rate is 99.1%, 97.9%, 99.9%, 98.9%, 96.9%, and 98.3%, which is much higher than that of control group (10.5%, 8.7%, 13.2%, 14.1%, 6.7%, and 10.5%). Through XPS and TEM & EDS analysis, the heavy metal hydroxides is found to be precipitated on the struvite surface. Based on TEM observations, it has been found the copper hydroxides had nucleation and growth on the struvite’s surface. The heterogeneous nucleation mechanism has been proposed, which provides relationship model of sorption, nucleation, and precipitation of heavy metals in the form of hydroxides on struvite surfaces. It has been calculated that the △Gi value that thermodynamic activation energy barrier constraints on the metal hydroxide formation can be intensively abated through heterogeneous nucleation on struvite.

Postglacial alluvial fan dynamics in the Cordillera Oriental, Peru, and palaeoclimatic implications

AbstractAlluvial fans record climate-driven erosion and sediment-transport processes and allow reconstructing past environmental conditions. Here we investigate the sedimentation history of two alluvial fans located in formerly glaciated valleys of the Cordillera Oriental, Peru.10Be exposure ages from the fan surfaces and radiocarbon ages from the fan interiors constrain the final stages of fan formation. The10Be and14C ages cluster mainly between 13.3–9.3 ka and 11,500–9700 cal yr BP, respectively. Our age data set indicates that—after deglaciation—large amounts of fan sediment were deposited until ∼10 ka, when sedimentation rates declined rather abruptly. This pattern is supported by10Be erosion rates for the fan catchments, because under the assumption of constant erosion the time needed to erode the material stored in the fans significantly exceeds their age. Correlating our ages with regional climate records indicates that precipitation exerts the primary control on fan sedimentation. Two periods with elevated lake levels and increased precipitation between 18 and 14.5 ka and from 13 to 11.5 ka resulted in rapid deposition of large fan lobes. Subsequently, lower precipitation rates decreased erosion in the catchments and sediment delivery to the fans, which have remained largely inactive since ∼9.5 ka.

A Multiyear Analysis of Global Precipitation Combining CloudSat and GPM Precipitation Retrievals

Abstract Satellite-based instruments are essential to the observation of precipitation at a global scale, especially over remote regions. Each instrument has its own strengths and limitations in accurately determining the rate of precipitation at the surface. By using the complementary strengths of two instruments, a more complete analysis of global precipitation can be performed. The Global Precipitation Measurement (GPM) Core Observatory’s Dual-Frequency Precipitation Radar (DPR) is capable of measuring precipitation at high and medium precipitation rates by using Ku-band (13.6 GHz) radiation. The CloudSat satellite’s Cloud Profiling Radar (CPR) uses higher-frequency W-band (94 GHz) radiation and is therefore capable of measuring precipitation at low rates not detected by the GPM DPR. CloudSat observations from January 2007 to December 2016 and DPR observations from March 2014 to February 2018 are combined and the results examined. Since these datasets are not completely coincident, this study is conducted as a multiyear analysis. Observed precipitation from CloudSat is used starting at the lowest precipitation rates and increasing rates until the occurrence observed by GPM surpasses that of CloudSat, at which point data from GPM are used. The precipitation rate at which this change occurs contains important information on the amount of precipitation missed by each instrument and implications as to the size of the hydrometeors present. Liquid precipitation retrieval from CloudSat is not performed over land; analysis over land is produced here using the information available. By combining the two datasets, a more complete picture of precipitation occurring globally is obtained.

Review on Solar Thermal Desalination in Libya

Libya is suffering from a freshwater shortage as most of its land is semi-arid to arid with very low precipitation rates and too limited freshwater sources. Libya is in one of the driest regions of the world with an annual rainfall ranging from just 10 mm to 500 mm, and only 5% of its land receives more than 100 mm annually. This review summarizes the most important published studies related to solar thermal desalination research in Libya. A brief description of the most thermal desalination technologies is also presented. The study has shown that only a few in-completed pilot projects were carried out for desalination using renewable energy.The research activities in the field of using renewable energy especially solar thermal energy to desalinate water are limited and do not give a comprehensive idea on the potential of different thermally driven solar desalination technologies. However, most of the recent pilot studies refer to using CSP desalination in providing most of the future water demand in Libya by 2035. A lot of efforts need to be done to carry-on genuine research to put strategic plan to tackle the deficit water issue in Libya through using desalination driven by conventional and renewable energies

Population structure, spatial distribution and phenology of Anacardium humile A. St.-Hil. (Anacardiaceae) in cerrado stricto sensu

ABSTRACT This study determined the size structure, spatial distribution, and phenology of individuals from a population of Anacardium humile A. St.-Hil. in a cerrado stricto sensu area. Four sample plots (100 × 100 m each) were randomly selected in the Quilombola Kalunga land. Within the plots, we counted the number of individuals and measured the height, basal diameter, number of tree branches and recorded their location and the presence of rocky outcrops. For the phenological analysis, sixteen individuals were monitored between May 2016 and April 2017. A total of 417 individuals were inventoried, which resulted in an average density of 104.25 ind ha-1 (± 60.35). The abundance of individuals was higher in the rocky outcrops and with an aggregate spatial distribution. The population is self-regenerating. Phenological changes were concentrated in the dry season and were influenced by lower precipitation rates, maximum temperature, and relative humidity.

Delimitation of Agricultural Areas with Natural Constraints in Greece: Assessment of the Dryness Climatic Criterion Using Geostatistics

The Less Favored Areas (LFAs) scheme has existed in various forms since 1975 and it is a broad mechanism supporting rural development in agricultural areas with natural constraints (ANC). Within the programme period 2014–2020, the European Commission developed a common set of biophysical criteria (soil, climate, and terrain) to meet the requirement for a robust and harmonized approach of delimiting ANC throughout the EU Member States. Soil and terrain criteria can be derived directly from soil maps using geospatial analysis techniques based on the provided guidelines. However, the assessment of climatic criteria can be challenging especially in regions characterized by increased spatial variability and data scarcity. In this paper, the assessment of the dryness climatic criterion in a data-scarce region (Greece) as well as the challenges, limitations, and solutions are presented. Daily data-series from 140 meteorological stations for a 30-year reference period were analyzed and the spatial distribution of the precipitation and the potential evapotranspiration for each year were estimated in order to make the final assessment of the dryness criterion. Climate variability and the presence of trends were investigated as well. The obtained results indicated that most of the utilized agricultural area is affected by dryness due to a combination of low precipitation and high evapotranspiration rates. The extreme spatial variability especially in precipitation was also highlighted. An important temporal variability was observed as well, including indications of decreasing trends in precipitation and aridity index. Climate variability and possible trends should be investigated in more detail using longer time series in order to evaluate their impact in agricultural production.

Factors Affecting the Inland and Orographic Enhancement of Lake-Effect Precipitation over the Tug Hill Plateau

The factors affecting the inland and orographic enhancement of lake-effect precipitation are poorly understood, yet critical for operational forecasting. Here we use nine cool seasons (16 November–15 April) of radar data from the Montague/Ft. Drum, New York (KTYX), WSR-88D, the North American Regional Reanalysis (NARR), and observations from the Ontario Winter Lake-effect Systems (OWLeS) field campaign to examine variations in lake-effect precipitation enhancement east of Lake Ontario and over the Tug Hill Plateau (hereafter Tug Hill). Key factors affecting the inland and orographic enhancement in this region include the strength of the incident boundary layer flow, the intensity of the lake-induced convective available potential energy (LCAPE), and the mode of the lake-effect system. Stronger flow favors higher precipitation rates, a precipitation maximum displaced farther downwind, and greater inland and orographic enhancement. The effects of LCAPE depend upon the strength of the flow. During periods of weak flow, higher LCAPE favors lower precipitation rates, a maximum closer to the shoreline, and lesser inland and orographic enhancement. During periods of strong flow, higher LCAPE favors higher precipitation rates, a maximum displaced farther downwind, and greater inland and orographic enhancement. Banded (nonbanded) modes favor higher (lower) precipitation rates, lesser (greater) inland and orographic enhancement, and a maximum closer to the shoreline (over Tug Hill). These results, for both manually measured and radar-estimated precipitation, are robust when many lake-effect events are considered, but substantial variability exists during individual events.

Effects of different oxyanions in solution on the precipitation of jarosite at room temperature

The effects of five different oxyanions, AsO4, SeO3, SeO4, MoO4, and CrO4, on the precipitation of jarosite at room temperature were investigated by X-ray diffraction, scanning electron microscopy, and chemical analysis. Different amounts (2, 5, and 10 mol%) of oxyanions in the starting solution and different aging times (1 h–40 days) were used for the experiment. In the initial stage, only the amorphous phase appears for all samples. With increasing aging time, jarosite and jarosite with oxyanions start precipitating at room temperature with different precipitation rates and crystallinities. Jarosite with AsO4 shows the lowest precipitation rate and lowest crystallinity. With increasing amounts of oxyanions, the crystallization rate decreases, especially for jarosite with AsO4. The jarosite samples with CrO4 and SeO4 show the fastest precipitation and highest crystallinities. For the jarosite samples with a low precipitation rate and low crystallinity, the amorphous phase contains high concentrations of oxyanions, probably because of the fast precipitation of the amorphous iron oxyanion phase; however, the phase with fast jarosite precipitation contains fewer oxyanions. The results show that coprecipitation of jarosite can play a more important role in controlling the behavior of CrO4 than AsO4 in acid mine drainage.

Observational Constraint for Precipitation in Extratropical Cyclones: Sensitivity to Data Sources

AbstractUsing cyclone-centered compositing and a database of extratropical-cyclone locations, the distribution of precipitation frequency and rate in oceanic extratropical cyclones is analyzed using satellite-derived datasets. The distribution of precipitation rates retrieved using two new datasets, the Global Precipitation Measurement radar–microwave radiometer combined product (GPM-CMB) and the Integrated Multisatellite Retrievals for GPM product (IMERG), is compared with CloudSat, and the differences are discussed. For reference, the composites of AMSR-E, GPCP, and two reanalyses are also examined. Cyclone-centered precipitation rates are found to be the largest with the IMERG and CloudSat datasets and lowest with GPM-CMB. A series of tests is conducted to determine the roles of swath width, swath location, sampling frequency, season, and epoch. In all cases, these effects are less than ~0.14 mm h−1 at 50-km resolution. Larger differences in the composites are related to retrieval biases, such as ground-clutter contamination in GPM-CMB and radar saturation in CloudSat. Overall the IMERG product reports precipitation more often, with larger precipitation rates at the center of the cyclones, in conditions of high precipitable water (PW). The CloudSat product tends to report more precipitation in conditions of dry or moderate PW. The GPM-CMB product tends to systematically report lower precipitation rates than the other two datasets. This intercomparison provides 1) modelers with an observational uncertainty and range (0.21–0.36 mm h−1 near the cyclone centers) when using composites of precipitation for model evaluation and 2) retrieval-algorithm developers with a categorical analysis of the sensitivity of the products to PW.

Modeling aquifer behaviour under climate change and high consumption: Case study of the Sfax region, southeast Tunisia

The water resources are exhausted by the increasing demand related to the population growth. They are also affected by climate circumstances, especially in arid and semi-arid regions. These areas are already undergoing noticeable shortages and low annual precipitation rate. This paper presents a numerical model of the Sfax shallow aquifer system that was developed by coupling the geographical information system tool ArcGIS 9.3 and ground water modeling system GMS6.5’s interface, ground water flow modeling MODFLOW 2000. Being in coastal city and having an arid climate with high consumption rates, this aquifer is undergoing a hydraulic stress situation. Therefore, the groundwater piezometric variations were calibrated for the period 2003–2013 and simulated based on two scenarios; first the constant and growing consumption and second the rainfall forecast as a result of climate change scenario released by the Tunisian Ministry of Agriculture and Water Resources and the German International Cooperation Agency “GIZ” using HadCM3 as a general circulation model. The piezometric simulations globally forecast a decrease that is about 0.5 m in 2020 and 1 m in 2050 locally the decrease is more pronounced in “Chaffar” and “Djbeniana” regions and that is more evident for the increasing consumption scenario. The two scenarios announce a quantitative degradation of the groundwater by the year 2050 with an alarming marine intrusion in “Djbeniana” region.

Flash Flood Risk Assessment for Kyushu Island, Japan

Using advanced geospatial analysis technologies, flash flood risk is assessed for the island of Kyushu, Japan. In this study, the flash flood risk is redefined in terms of the flash flood potential index (FFPI) and the flash flood residential hazard (FFRH). The island experiences rainy weather, especially in the summer (June–August), when catastrophic flash flood events have historically occurred. Studies of the surface hydrological properties of the island are very rare and localized; hence, geospatial techniques are most appropriate for the assessment process. The Soil Conservation Service rainfall-runoff model was used to estimate hydrological responses on the island. Four factors were included in the flash flood assessment. A multi-criteria analysis was carried out to map the FFPI and FFRH from the evaluation factors. The results show that the highest flash flood risk occurs in the northern parts of the island, where the soil displays relatively low infiltration rates and relatively high curve numbers, despite the comparatively low precipitation rates that occur there. The results indicate that soil hydrological properties are the main driving forces of flash floods, especially in regions with low precipitation rates. The results of this research are consistent with previous in situ measurements of runoff made at several sites on the island. The results also show a strong geographic correlation with historical flash flood events on the island. This research validates the use of geospatial analysis for large geographic regions where in situ measurements cannot be taken due to time or cost constraints. The results of this study provide decision makers with the information needed to select a management strategy to address possible future flash flood events that considers safety and water harvesting.

Análise Ambiental da Ocorrência das Queimadas na Porção Nordeste do Cerrado

Com a crescente demanda nos últimos anos por áreas agricultáveis ainda não exploradas, o bioma Cerrado se tornou um dos ambientes mais favoráveis para a expansão da fronteira agrícola. Uma das consequências consiste no desmatamento e no aumento do número de queimadas, ocasionando a degradação e supressão de extensas áreas de ecossistemas naturais do bioma. Neste contexto, o presente trabalho teve como objetivo principal analisar a distribuição espacial das áreas queimadas na porção nordeste do bioma Cerrado. Desta forma, foi realizado o mapeamento das áreas queimadas em imagens do sensor Moderate Resolution Imaging Spectroradiometer (MODIS), da plataforma Terra e Aqua, nos anos de 2012 a 2015 a partir do uso do Modelo Linear de Mistura Espectral (MLME). Os dados de precipitação do Tropical Rainfall Measuring Mission (TRMM) do produto 3B43 foram utilizados para verificar a influência das chuvas na ocorrência das queimadas. Além disso, analisou-se a ocorrência das queimadas com o uso e cobertura da terra, com as Unidades de Conservação (UC) e com os municípios da área de estudo. Foi verificado que as áreas mais atingidas por queimadas são de Savana, Savana Lenhosa e Gramíneas e os anos que apresentaram menores índices de precipitações também foram os anos que ocorreram maior incidência de queimadas. A unidade de conservação mais atingida foi a Estação Ecológica Uruçuí-Uma no Piauí, com uma média de 36,5% de sua área queimada e os municípios mais atingidos estão localizados principalmente nos estados do Piauí e Maranhão, apresentando em média metade de suas áreas queimadas.

Potential risk of weed outbreak by increasing biochar's application rates in slow-growth legume, lentil (Lens culinaris Medik.).

Biochar amendment is a promising tool to improve the soil quality and, consequently, higher crop yield has received more attention during last decades. The positive effects of biochar have been attracting more attention especially in the areas with low precipitation rates, such as the Middle East, due to low soil organic carbon content, higher drought intensity, and increasing demands for food production. However, biochar can lead to lower herbicide efficacy, resulting in higher consumption of herbicides. In this study, the impact of two biochars on soil properties, plant growth, and fomesafen efficacy under rain-fed condition was investigated. Biochar amendment at the rate of 5 t ha-1 improved soil quality and plant growth by 40-200% and 46-57%, respectively, compared to the control. The increase of biochar application rate from 5 t ha-1 to 15 t ha-1 showed small additional positive effects on soil and lentil as the tested crop plant, whereas the growth of weeds elevated by 200% in this case. Albeit biochar application could be an effective way to improve the soil fertility, the potential risk of weed outbreak in the long term should be evaluated carefully before the use of biochar amendment at field scale. © 2017 Society of Chemical Industry.

Spatiotemporal heterogeneity of the palaeoecological record in a large temperate palaeolake, Šúr, southwest Slovakia: Comparison of pollen, macrofossil and geochemical data

Aquatic macrophytes living within shallow lakes are particularly sensitive to climate change and fluctuations in water depth. In the Dabubian Lowland of southwestern Slovakia, sediments from the large, shallow palaeolake, named Šúr, provide a unique opportunity to reconstruct changes in water depth to analyse succession within local aquatic and terrestrial vegetation. Here, we used a multi-core, multi-proxy approach (macrofossils, pollen, and geochemistry) in order to reconstruct water depth changes and its influence on aquatic and terrestrial vegetation succession during the Holocene. Additionally, we also consider how heterogeneity in proxy data varied across time and space. Using particular macrophyte taxa found in the macrofossil assemblage, which have specific water depth requirements, our results demonstrate changes in water depth created a long-term mosaic of vegetation succession. In the Early Holocene, aquatic macrophytes suggest the water column was high (>100cm). During the Middle Holocene, water depths decreased creating mosaics of aquatic succession. By ca 4200calyrB.P., terrestrialization had occurred in the former lake area. Regional vegetation succession was likely more influenced by the presence of fluvial sands and/or by low precipitation and high evaporation rates, which delayed the expansion of temperate trees and favoured Pinus until 8850calyrB.P. Macrofossils exhibit the lowest temporal variation among all proxies, which suggests a rather stable macrophyte community when water depth was high. Pollen data show very low spatial variation given by the size of the accumulation basin, which reflects regional pollen rain. Higher spatial variation was observed in the geochemistry and macrofossil data compared to the pollen data, which could be the result of different mosaics of aquatic plants, local dispersion of propagules, or changes in sediment types. We conclude that changes in water depth were not homogenous, but rather heterogeneous in space and time.

Effects of catalase on chloroplast arrangement in Opuntia streptacantha chlorenchyma cells under salt stress

In arid and semiarid regions, low precipitation rates lead to soil salinity problems, which may limit plant establishment, growth, and survival. Herein, we investigated the NaCl stress effect on chlorophyll fluorescence, photosynthetic-pigments, movement and chloroplasts ultrastructure in chlorenchyma cells of Opuntia streptacantha cladodes. Cladodes segments were exposed to salt stress at 0, 100, 200, and 300 mM NaCl for 8, 16, and 24 h. The results showed that salt stress reduced chlorophyll content, Fv/Fm, ΦPSII, and qP values. Under the highest salt stress treatments, the chloroplasts were densely clumped toward the cell center and thylakoid membranes were notably affected. We analyzed the effect of exogenous catalase in salt-stressed cladode segments during 8, 16, and 24 h. The catalase application to salt-stressed cladodes counteracted the NaCl adverse effects, increasing the chlorophyll fluorescence parameters, photosynthetic-pigments, and avoided chloroplast clustering. Our results indicate that salt stress triggered the chloroplast clumping and affected the photosynthesis in O. streptacantha chlorenchyma cells. The exogenous catalase reverted the H2O2 accumulation and clustering of chloroplast, which led to an improvement of the photosynthetic efficiency. These data suggest that H2O2 detoxification by catalase is important to protect the chloroplast, thus conserving the photosynthetic activity in O. streptacantha under stress.

An evaluation of gravity waves and gravity wave sources in the Southern Hemisphere in a 7 km global climate simulation.

In this study, gravity waves (GWs) in the high-resolution GEOS-5 Nature Run are first evaluated with respect to satellite and other model results. Southern Hemisphere winter sources of non-orographic GWs in the model are then investigated by linking measures of tropospheric non-orographic gravity wave generation tied to precipitation and frontogenesis with absolute gravity wave momentum flux in the lower stratosphere. Finally, non-orographic GW momentum flux is compared to orographic gravity wave momentum flux and compared to previous estimates. The results show that the global patterns in GW amplitude, horizontal wavelength, and propagation direction are realistic compared to observations. However, as in other global models, the amplitudes are weaker and horizontal wavelengths longer than observed. The global patterns in absolute GW momentum flux also agree well with previous model and observational estimates. The evaluation of model non-orographic GW sources in the Southern Hemisphere winter shows that strong intermittent precipitation (greater than 10 mm h-1) is associated with GW momentum flux over the South Pacific, whereas frontogenesis and less intermittent, lower precipitation rates (less than 10 mm h-1) are associated with GW momentum flux near 60°S. In the model, orographic GWs contribute almost exclusively to a peak in zonal mean momentum flux between 70 and 75°S, while non-orographic waves dominate at 60°S, and non-orographic GWs contribute a third to a peak in zonal mean momentum flux between 25 and 30°S.

Coherent tropical-subtropical Holocene see-saw moisture patterns in the Eastern Hemisphere monsoon systems

The concept of a Global Monsoon (GM) has been proposed based on modern precipitation observations, but its application over a wide range of temporal scales is still under debate. Here, we present a synthesis of 268 continental paleo-moisture records collected from monsoonal systems in the Eastern Hemisphere, including the East Asian Monsoon (EAsM), the Indian Monsoon (IM), the East African Monsoon (EAfM), and the Australian Monsoon (AuM) covering the last 18,000 years. The overall pattern of late Glacial to Holocene moisture change is consistent with those inferred from ice cores and marine records. With respect to the last 10,000 years (10 ka), i.e. a period that has high spatial coverage, a Fuzzy c-Means clustering analysis of the moisture index records together with “Xie-Beni” index reveals four clusters of our data set. The paleoclimatic meaning of each cluster is interpreted considering the temporal evolution and spatial distribution patterns. The major trend in the tropical AuM, EAfM, and IM regions is a gradual decrease in moisture conditions since the early Holocene. Moisture changes in the EAsM regions show maximum index values between 8 and 6 ka. However, records located in nearby subtropical areas, i.e. in regions not influenced by the intertropical convergence zone, show an opposite trend compared to the tropical monsoon regions (AuM, EAfM and IM), i.e. a gradual increase. Analyses of modern meteorological data reveal the same spatial patterns as in the paleoclimate records such that, in times of overall monsoon strengthening, lower precipitation rates are observed in the nearby subtropical areas. We explain this pattern as the effect of a strong monsoon circulation suppressing air uplift in nearby subtropical areas, and hence hindering precipitation. By analogy to the modern system, this would mean that during the early Holocene strong monsoon period, the intensified ascending airflows within the monsoon domains led to relatively weaker ascending or even descending airflows in the adjacent subtropical regions, resulting in a precipitation deficit compared to the late Holocene. Our conceptual model therefore integrates regionally contrasting moisture changes into the Global Monsoon hypothesis.