Moisture Origin Research Articles

Chemical and isotopic composition of rainwater in the eastern Yucatan peninsula, Mexico

Given that rain is the component of precipitation that reaches the surface of the earth, and aiming to contribute to the global efforts of rainwater monitoring, we present information regarding the origin of ions and their relationship with isotopic patterns and the source of moisture for rainwater in the Mexican Caribbean, which not only may be useful for pollution and atmospheric studies, but also for estimating groundwater recharges, understanding dust nuisances, and offering information about water quality for rainwater harvesting. In this paper, we describe the chemical composition of rainwater in terms of major ions, isotopic composition, and the most probable sources of moisture in the Caribbean coastal zone of Mexico, considering the three main climatic seasons in this area. The chemistry of rainwater displayed a noticeable influence from sea-salt spray, land-blown dust, and anthropogenic impacts such as agriculture and biomass burning. We identified the predominant terrestrial origin of calcium, namely anthropogenic contributions of sulfates and nitrates, plus potassium from sea spray and anthropogenic emissions. The local meteoric water line is δ2H = 8.2 δ18O + 13.8 (R² = 0.9601) suggesting enrichment due to evaporative losses, various moisture sources and local climatic effects. Although isotope composition was not different by site, it was by season, as opposed to water chemistry. We conclude that the water chemistry responds to the local conditions of the air column below the clouds, while the isotope composition is influenced by the origin of moisture and the physical conditions in which water evaporates and condenses as well.

The Role of Atmospheric Rivers Moisture Origin in the Seasonality of Extreme Precipitation in the Eastern United States

Abstract Regional patterns of the seasonal weather and atmospheric moisture origins can impact the seasonal activities of extreme precipitation in the eastern United States (eUS). At many locations, tracks of atmospheric moisture can have different influence on timing of extreme precipitation based on the moisture origin source. In this study we evaluate the contribution of Atmospheric Rivers (ARs), and their moisture origin sources to the distribution and seasonal effectivity of annual maximum precipitation (AMP) across the eUS during 1950–2021. Our results suggest that AR is a dominant mechanism of AMP in the eUS as they contribute to 75% (31,438 out of 41,976) of total AMP events recorded between 1950–2021. The seasonal analysis based on circular density approach shows that spring, summer and fall seasons display strong signals of seasonality of AMP-AR events. The spatial patterns of AMP associated with the four major moisture sources (the Pacific Ocean, the Atlantic Ocean, the combined source of Caribbean Sea and Gulf of Mexico, and the local source of moisture) reinforce the key role ARs play in transporting water vapor to eUS from both oceanic and inland originated moisture. The results additionally highlight the importance of moisture sub-sources (major sources sub-regions) in modulating the seasonality of extreme precipitation in the eUS.

A triggering mechanism of quasi-stationary convective bands in the vicinity of southwestern Japan during the summer season as deduced from moisture origins

To find a plausible initiation mechanism of quasi-stationary convective bands (QSCBs) that lead to disasters, we investigated an extreme heavy precipitation event in Kyushu, southwestern Japan, in the middle of August 2021, using a regional spectral model incorporated with isotopic tracers aided by a water-tagging method. In the synoptic environment, the horizontal pressure gradient at low levels between an eastward-migrating Baiu frontal depression (BFD) and the North Pacific subtropical high (NPSH) is intensified to the south of a synoptic-scale front. To the south of the front, QSCBs also lie from the East China Sea to inland Kyushu. We confirm that the merging of the Asian monsoon moisture and the NPSH moisture creates a deep moist layer reaching middle levels from the surface in the vicinity of the QSCBs, providing an extremely unstable condition. Although such an unstable condition is indispensable for the maintenance of the QSCBs, an initiation mechanism is required that accounts for why the QSCBs emerge around the oceanic region where the two primary moisture merges; that appears to be the Ekman pumping mechanism. The strong boundary layer inflow of the NPSH moisture origin enhances the convective instability to the south of the QSCBs. Since the horizontal pressure gradient is attenuated in the vicinity of the BFD's center, on the contrary, the boundary layer flow north of the QSCBs decelerates rapidly, giving rise to upwelling due to the Ekman convergence. The persistent upwelling estimated in this event can lift the air of the Ekman layer up to a few hundred meters in a few hours, allowing it to readily reach the level of free convection. It is reasonable to conjecture that the persistent upwelling triggers the release of enhanced convective instability, leading to the formation of QSCBs. Continuous merging of the two remote moisture origins under the pronounced horizontal pressure gradient will further contribute to the reinforcement of the QSCBs.

Insights into the origin of precipitation moisture for tropical cyclones during rapid intensification process

In this study, we identified the moisture sources for the precipitation associated with tropical cyclones (TCs) during the rapid intensification (RI) process from 1980 to 2018 by applying a Lagrangian moisture source diagnostic method. We detected sixteen regions on a global scale for RI events distributed as follows: four in the North Atlantic (NATL), two in the Central and East Pacific Ocean (NEPAC), the North Indian Ocean (NIO) and South Indian Ocean (SIO), and three in the South Pacific Ocean (SPO) and the Western North Pacific Ocean (WNP). The moisture uptake (MU) mostly was from the regions where TCs underwent RI. The Western NATL, tropical NATL, Caribbean Sea, the Gulf of Mexico and the Central America and Mexico landmass supported ∼85.4% of the precipitating moisture in the NATL, while the latter source and the eastern North Pacific Ocean provided the higher amount of moisture in NEPAC (∼84.3%). The Arabian Sea, the Bay of Bengal and the Indian Peninsula were the major moisture sources in NIO, contributing approximately 81.3%. The eastern and western parts of the Indian Ocean supplied most of the atmospheric humidity in SIO (∼83.8%). The combined contributions (∼87.9%) from the western and central SPO and the Coral Sea were notably higher in SPO. Meanwhile, TCs in the WNP basin mostly received moisture from the western North Pacific Ocean, the Philippine Sea and the China Sea, accounting for 80.1%. The remaining moisture support in each basin came from the summed contributions of the remote sources. Overall, RI TCs gained more moisture up to 2500 km from the cyclone centre than those slow intensification (SI) and the total MU was approximately three times higher during RI than SI. Finally, the patterns of the MU differences respond to the typical pathways of moisture transport in each basin.

Quantifying the related precipitation and moisture sources in the lifecycle of subtropical cyclones in the South Atlantic basin

AbstractThis study applies a Lagrangian approach to identify the origin of moisture for subtropical cyclones (SCs) along their tracks in the South Atlantic Ocean (SAO) basin from 1980 to 2015. The analysis shows that the local evaporation cannot fully explain the moisture gained by SCs, highlighting the role of external sources in moisture support, mainly through the northeasterly winds associated with the South Atlantic Subtropical Anticyclone. Overall, the northwestern SAO was the principal moisture source for SCs. It was noticeable that its contribution (~40%–45%) remained quasi‐constant during the year. Conversely, the moisture supplied from the northeastern SAO, southwestern SAO and the terrestrial source southeastern Brazil exhibited a marked seasonal variability. While contributions from the southwestern SAO intensify (weaken) in austral winter (summer), the southeastern Brazil source is more intense (weak) in summer (winter). In addition, SCs predominantly gain atmospheric humidity from sources close to their position, which reduces the mean water vapor residence time to ~3.2 days. Interestingly, we also found that ~42%–47% of the moisture that reached the SCs precipitates. These findings constitute a further step toward improving our knowledge of mechanisms underlying SC activity in the SAO basin.

Drought, temperature, and moisture availability: understanding the drivers of isotopic decoupling in native pine species of the Nepalese Himalaya.

The Himalayas experienced long-term climate changes and recent extreme weather events that affected plant growth and the physiology of tree species at high-elevation sites. This study presents the first statistically robust δ18OTR chronologies for two native pine species, Pinus roxburghii, and Pinus wallichiana, in the lower Nepalese Himalaya. The isotope chronologies exhibited 0.88‰ differences in overall mean isotope values attributed to varying elevations (460-2000m asl). Comparative analysis of climate response using data sets from different sources and resolutions revealed the superiority of the APHRODITE (Asian Precipitation - Highly-Resolved Observational Data Integration Towards Evaluation) data set calibrated for the South Asian Summer Monsoon (SASM)-dominated region. Both species exhibited negative correlations with monsoon precipitation and positive correlations with temperature. However, during the peak monsoon season (July-August), daily resolved climate data disentangled statistically insignificant relationships, and revealed that δ18OTR is influenced by atmospheric moisture. Both congeneric species showed a decoupling between the chronologies after 1995. However, no significant change in air moisture origin and monsoon regime between the study sites was observed, indicating a consistent dominant moisture source during different monsoon seasons. Besides, we also observed the decreased inter-series correlation of both δ18OTR chronologies after 1995, with P. wallichiana experiencing a steeper decrease than P. roxburghii. The weakening correlations between and within the chronologies coincided with a regional drought during 1993-1995 in both sites, highlighting the strong regulation of local climate on the impact of regional extreme climate events. Our findings emphasise the importance of employing climate data with optimal spatial and temporal resolution for improved δ18OTR-climate relationships at the intra-annual scale while considering the influence of site-specific local environmental conditions. Assessing climate data sets with station data is vital for accurately interpreting climate change's impact on forest response and long-term climate reconstructions.

Moisture source differences between the 2020 and 1998 super Meiyu-flood events in the Yangtze River Valley

Two historic Meiyu events in 1998 and 2020 hit the Yangtze River Valley (YRV), causing catastrophic damage to the socio-economy. By tracking moisture supplies to the extreme precipitation events using Water Accounting Model-2Layers and ERA5 reanalysis, the moisture origins and their differences in feeding the YRV precipitation were revealed. Climatologically, the southwest monsoon channel is the most important moisture channel with the Indian Ocean contributing ∼45% and the Indo-China Peninsula contributing ∼16% of the YRV precipitation. During the two super Meiyu events, the Indian Ocean and the Indo-China Peninsula dominated the excessive moisture supply, which together contributed more than 65% of the extra precipitation. Moisture supply anomalies in 1998 and 2020 showed a robust spatial pattern of “west increase-east decrease”. When the YRV precipitation is higher than the normal, moisture mainly comes from the southwest sources, and moisture contribution from the northwestern Pacific is relatively small. We also found that the intensity of the western Pacific subtropical high is a major influencing factor that explained ∼47% of the YRV precipitation variation during 1991–2020. When it intensifies, an anomalous anticyclone is formed in the mid-lower troposphere around the tropical Northwest Pacific. In its northwestern flank, a strong southwesterly in the upwind of the YRV helps bring in more moisture through the southwest monsoon. In the downwind, it inhibits moisture supply from the northwestern Pacific Ocean. Compared with 2020, a drier condition over Indo-China Peninsula and YRV in 1998 led to a substantially less (∼29%) moisture supply to the YRV precipitation, resulting in a less strong Meiyu event in 1998.

Impact of Atmospheric Circulation Variability on U.S. Midwest Moisture Sources

Abstract Elevated spring and summer rainfall in the U.S. Midwest is often associated with a strong Great Plains low-level jet (GPLLJ), which transports moist air northward to the region from the Gulf of Mexico. While the intensity of hourly precipitation extremes depends on local moisture availability and vertical velocity, sustained moisture convergence on longer time scales depends on horizontal moisture advection from remote sources. Therefore, the magnitude of moisture convergence in the Midwest depends in part on the humidity in these moisture source regions. Past work has identified the time-mean spatial distribution of moisture sources for the Midwest and studied how this pattern changes in years with anomalous rainfall. Here, using reanalysis products and an Eulerian moisture tracking model, we seek to increase physical understanding of this moisture source variability by linking it to the GPLLJ, which has been studied extensively. We find that on interannual time scales, an anomalously strong GPLLJ is associated with a shift in the distribution of moisture sources from land to ocean, with most of the anomalous moisture transported to—and converged in—the Midwest originating from the Atlantic Ocean. This effect is more pronounced on synoptic time scales, when almost all anomalous moisture transported to the region originates over the ocean. We also show that the observed positive trend in oceanic moisture contribution to the Midwest from 1979 to 2020 is consistent with a strengthening of the GPLLJ over the same period. We conclude by outlining how projected changes in a region’s upstream moisture sources may be useful for understanding changes in local precipitation variability. Significance Statement In this work, we study how the origin of moisture that forms precipitation in the U.S. Midwest covaries with large-scale atmospheric circulation. Our results show that an intensification of the mean winds tends to increase the proportion of total rainfall that originates from the ocean. This analysis may help to constrain future projections of rainfall extremes in the central United States, as projected changes in humidity over the ocean are typically more robust and better understood than those over land.

Identifying the pathways of extreme rainfall in South Africa using storm trajectory analysis and unsupervised machine learning techniques

Abstract This study has utilised National Oceanic and Atmospheric Administration (NOAA) NCEP/NCAR Reanalysis 1 project meteorological data and the HYSPLIT model to extract the air parcel trajectories for selected historical extreme rainfall events in South Africa. The k-means unsupervised machine learning algorithm has been used to cluster the resulting trajectories, and from this, the spatial origin of moisture for each of the rainfall events has been determined. It has been demonstrated that rainfall events on the east coast with moisture originating from the Indian Ocean have distinctly larger average maximum daily rainfall magnitudes (279 mm) compared to those that occur on the west coast with Atlantic Ocean influences (149 mm) and those events occurring in the central plateau (150 mm) where moisture has been continentally recirculated. Further, this study has suggested new metrics by which the HYSPLIT trajectories may be assessed and demonstrated the applicability of trajectory clustering in a region not previously studied. This insight may in future facilitate improved early warning systems based on monitoring of atmospheric systems, and an understanding of rainfall magnitudes and origins can be used to improve the prediction of design floods for infrastructure design.

Contrasting Seasonal Isotopic Signatures of Near‐Surface Atmospheric Water Vapor in the Central Arctic During the MOSAiC Campaign

AbstractThe Arctic is experiencing unprecedented moistening which is expected to have far‐reaching impact on global climate and weather patterns. However, it remains unclear whether this newly sourced moisture originates locally from ice‐free ocean regions or is advected from lower latitudes. In this study, we use water vapor isotope measurements in combination with trajectory‐based diagnostics and an isotope‐enabled atmosphere general circulation model, to assess seasonal shifts in moisture sources and transport pathways in the Arctic. Continuous measurements of near‐surface vapor, δ18O, and δD were performed onboard RV Polarstern during the Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition from October 2019 to September 2020. Combining this isotope data set with meteorological observations reveals that the spatiotemporal evolution of δ18O mimics changes in local temperature and humidity at synoptic to seasonal time scales, while corresponding d‐excess changes suggest a seasonal shift in the origin of moisture. Simulation results from the particle dispersion model FLEXPART support these findings, indicating that summer moisture originates from nearby open ocean, while winter moisture comes from more remote sources with longer residence time over sea‐ice. Results from a nudged ECHAM6‐wiso simulation also indicate that evaporative processes from the ocean surface reproduce summer isotope values, but are insufficient to explain measured winter isotope values. Our study provides the first isotopic characterization of Central Arctic moisture over the course of an entire year, helping to differentiate the influence of local processes versus large‐scale vapor transport on Arctic moistening. Future process‐based investigations should focus on assessing the non‐equilibrium isotopic fractionation during airmass transformation over sea‐ice.

Variations in triple oxygen isotope of speleothems from the Asian monsoon region reveal moisture sources over the past 300 years

Characterization of moisture origins is crucial to understanding hydroclimatic processes. Nevertheless, documenting past atmospheric moisture contents and their sources remains challenging partially due to insufficient moisture-tracing proxies. Here, we present triple oxygen isotope compositions in 21 cave speleothems from monsoonal Asia to examine spatial moisture origin differences in eastern Asia over the past 300 years. Our data suggest an isotopic equilibrium fractionation during speleothem formation, and thus parent water 17O anomalies (Δ′17O) values reconstructed from speleothems preserve information on moisture origins and recycling across space. Notably, speleothem Δ′17O records exhibit a distinct geographical distribution, with low values in central-eastern and southern China, high values in northwestern and northern China, and relatively high values in the Yangtze River region. This spatial pattern underscores the diverse influence of different moisture sources regulated by regional hydrological circulation, and demonstrates the potential use of speleothem Δ′17O in reconstructing the moisture cycle at spatial scales.

Moisture sources and climatic effects controlling precipitation stable isotope composition in a western Mediterranean island (Pianosa, Italy)

The Mediterranean basin is indicated as a hot spot of climate change, which is an area whose climate is especially responsive to variations. The insular environment is one of the most threatened by the current climate change, especially in terms of drought events, with serious consequences for water scarcity and water stress. This issue is even enhanced in small islands, whose ecosystems are among more sensitive to climatic changes and water availability. The stable isotope composition of hydrogen (δ2H) and oxygen (δ18O) in precipitation is globally recognized as a powerful natural tracer in the water cycle and represents the starting point to investigate hydrological processes. The understanding of the prevailing factors that drive the isotopic variability of precipitation in the Mediterranean is therefore essential to unravel the hydrological processes and to ensure proper and sustainable management of potentially vulnerable resources to climate change. Here, we discuss the results of multi-year isotopic monitoring in the period 2014–2021 of monthly precipitation collected on Pianosa Island (Italy), a small island located in the northern Tyrrhenian (western Mediterranean). The lower slope and intercept of the Local Meteoric Water Line of the island compared to the Global Meteoric Water Line indicated warmer and drier climatic conditions, suggesting the existence of sub-cloud evaporation processes of raindrops during precipitation, especially in summer. The mean δ18O of precipitation was lower with respect to other sites placed at higher elevation in this Mediterranean region, due to the lack of summer precipitation which were generally enriched in heavy isotopes. Temperature and amount effects may explain part of the δ18O variability observed at the monthly and seasonal scale. An HYSPLIT-based moisture uptake analysis indicated the area between the western Mediterranean basin, Italy, and the Adriatic Sea as the region that supplied most of the humidity associated with monthly precipitation samples on Pianosa Island. Less moisture was picked from the northwestern areas of Europe, the North Atlantic Ocean, the proximal Atlantic Ocean, the Iberian Peninsula and North Africa. Consistently with the rainout effect, the higher the moisture fraction picked from the more proximal regions, the more positive the δ18O of precipitation occurring on Pianosa Island; conversely, the higher the percentage of moisture sourced from more distal regions, the more negative the δ18O. A multiple linear model was proposed to predict the δ18O of monthly precipitation from temperature, precipitation amount and moisture origin data, which explained 45% of the δ18O variability. The deuterium excess variability on the island was partly controlled by the local climatic variables, whose effect potentially modifies the original d-excess signature imprinted at the moisture source. No relationship was found between the precipitation deuterium excess and moisture sources, suggesting that more attention should be paid when using the deuterium excess as a tracer of moisture origin, especially in the Mediterranean.

The moisture origin of dew: Insights from three sites with contrasting climatic conditions

AbstractDew is one of the important moisture sources in many arid and semiarid regions. The knowledge of moisture origin of dew under various climatic conditions is still lacking. Isotopic variations can preserve information about moisture origin and formation mechanisms. Therefore, the isotopic compositions of dew and precipitation (δ2H, δ18O, δ17O, d‐excess, lc‐excess and 17O‐excess) were investigated at three sites with different climatic conditions (i.e., Gobabeb with extremely dry climate, Nice with Mediterranean climate and Indianapolis with humid continental climate). The results showed that there were three types of dew at Gobabeb: advective dew, groundwater‐derived dew, and shallow soil water‐derived dew, accounting for 27.3%, 45.4% and 27.3% of the dew events, respectively. The ultimate moisture sources of advective dew and the other two types of dew at Gobabeb were from the South Atlantic Ocean and a mixture of the Indian and South Atlantic Oceans, respectively. Dew in Nice included ocean‐derived dew from the North Atlantic Ocean with local evapotranspiration replenishment, and local‐derived dew, mainly from the continental Europe and Mediterranean Sea, accounting for 39.1% and 60.9% of the dew events, respectively. All the Indianapolis dew were likely local‐derived dew. Based on the moisture origins, the future dew trends were speculated under global warming. Dew frequencies at Gobabeb and Indianapolis under future climates are uncertain due to the concurrent increases in atmospheric water vapour and temperature. The local‐derived dew in Nice would likely decrease due to the decreasing precipitation and increasing drought, and the ocean‐derived dew under future climates is uncertain. This study provides a practical method to distinguish dew moisture sources, and such information is useful for future prediction of dew trends under climate change.

Moisture origins of the Amazon carbon source region

The southeastern Amazon has recently been shown to be a net carbon source, which is partly caused by drying conditions. Drying depends on a number of factors, one of which is the land cover at the locations where the moisture has originated as evaporation. Here we assess for the first time the origins of the moisture that precipitates in the Amazon carbon source region, using output from a Lagrangian atmospheric moisture tracking model. We relate vegetation productivity in the Amazon carbon source region to precipitation patterns and derive land-cover data at the moisture origins of these areas, allowing us to estimate how the carbon cycle and hydrological cycle are linked in this critical part of the Amazon. We find that, annually, 13% of the precipitation in the Amazon carbon source region has evaporated from that same area, which is half of its land-derived moisture. We further find a moisture-recycling-mediated increase in gross primary productivity of roughly 41 Mg carbon km−2 yr−1 within the Amazon carbon source region if it is fully forested compared to any other land cover. Our results indicate that the parts of the Amazon forest that are already a net carbon source, still help sustain their own biomass production. Although the most degraded parts of the Amazon depend mostly on oceanic input of moisture, further degradation of this region would amplify carbon losses to the atmosphere.

Evaluating Changes in the Moisture Sources for Tropical Cyclones Precipitation in the North Atlantic That Underwent Extratropical Transition

AbstractIn this study, we investigated the changes in the origin of moisture for the precipitation associated with tropical cyclones (TCs) after extratropical transition (ET) over the North Atlantic Ocean basin from 1980 to 2018. We analyzed the 24 hr before and after the occurrence of ET events. By applying a TC‐centric methodology we found that the moisture uptake (MU) occurred predominantly in the south and southwest sectors within ∼2,000 km of TC center before ET and from the southwest and west sectors after ET. In addition, the development of the cold front and the warm conveyor belt after ET induces changes in the moisture transport pattern. Overall, the secondary circulation of TCs favored the moisture flux inward for TCs precipitation, while the large‐scale baroclinic environment controlled the MU after ET.

Application of Stable Isotopic Compositions of Rainfall Runoff for Evaporation Estimation in Thailand Mekong River Basin

The Mekong River Basin comprises approximately 38% of Southeast Asia. Our study area comprises the right-bank tributaries, which drain a substantial portion of Northeast Thailand. This study aimed to estimate the evaporative losses from streams during the 2013–2015 period. The normal and warm El Niño–Southern Oscillation (ENSO) phases caused higher temperatures and low rainfall in the 2014–2015 period. The results show that the local meteoric water line for precipitation isotopes had seasonal variation due to variable precipitation. The enrichment of river isotopes indicated that streams lost an average of 4% of their water through evaporation. During the cooling ENSO phase, significant evaporation occurs due to the deep convection that typically occurs in tropical regions. In contrast, evaporation was low during the warm ENSO phase because of its geographic location. The El Niño year’s isotope values were significantly more enriched than the La Niña year’s, showing that precipitation and positive temperature anomalies affected the isotopic compositions in the continental basin. Furthermore, the deuterium excess helped distinguish the relative contributions of the wet and dry seasonal sources to the moisture origin, indicating that the predominant source of moisture is inland evaporation, with a small contribution from the ocean.

Moisture Origin and Transport for Extreme Precipitation over Indonesia’s New Capital City, Nusantara in August 2021

Nusantara, Indonesia’s new capital city, experienced a rare extreme rainfall event on 27–28 August 2021. This heavy rainfall occurred in August, the driest month of the year based on the monthly climatology data, and caused severe flooding and landslides. To better understand the underlying mechanisms for such extreme precipitation events, we investigated the moisture sources and transport processes using the Lagrangian model HYSPLIT. Our findings revealed that moisture was mostly transported to Nusantara along three major routes: from Borneo Island (BRN, 53.73%), the Banda Sea and its surroundings (BSS, 32.03%), and Sulawesi Island (SUL, 9.05%). Overall, BRN and SUL were the main sources of terrestrial moisture, whereas the BSS was the main oceanic moisture source, having a lower contribution than its terrestrial counterpart. The terrestrial moisture transport from BRN was mainly driven by the large-scale high vortex flow, whereas the moisture transport from the SUL was driven by the circulation induced by boreal summer intraseasonal oscillation (BSISO) and low-frequency variability associated with La Niña. The near-surface oceanic moisture transport from BSS is primarily associated with prevailing winds due to the Australian monsoon system. These insights into moisture sources and pathways can potentially improve the accuracy of predictions of summer precipitation extremes in Indonesia’s new capital city, Nusantara, and benefit natural resource managers in the region.

Defining a Precipitation Stable Isotope Framework in the Wider Carpathian Region

The eastern part of Europe is very poorly represented in the Global Network for Isotopes in Precipitation (GNIP) database, mainly because the monitoring of the stable isotopes in precipitation started only recently compared with other regions. In this respect, the main objective of this article is to fill the gap in the GNIP database over the eastern part of Europe and show the temporal variability and potential drivers of an extended network of δ18O values in precipitation collected from 27 locations in Romania and the Republic of Moldova. We also present the first high-resolution map of the spatio-temporal distribution of δ18O values in precipitation in Romania and the Republic of Moldova, according to an observational dataset. According to our results, the stations from western and northern Romania tend to have LMWLS with higher values than those from southwestern Romania. The monthly variation of the δ18O and δ2H showed a clearly interannual variation, with distinct seasonal differences, following the seasonal temperatures. The analysis of the spatial distribution of stable isotopes in precipitation water was made on the basis of both observational data and modeled data. This allowed us to study the origin of the air moisture and the interaction with regional and local patterns and to analyze the link between the spatial δ18O variations and the large-scale circulation patterns on a seasonal scale.

Origin of Moisture for the Precipitation Produced by the Exceptional Winter Storm Formed over the Gulf of Mexico in March 1993

On 12–15 March 1993, a severe winter storm (SC93) formed over the Gulf of Mexico, affecting the Caribbean Islands and the eastern coast of the United States (US) and Canada with a notable amount of precipitation, snow and severe local storms. In this study, we investigate the origin of the precipitation generated by SC93 by applying a widely used Lagrangian moisture source diagnostic method. Our findings revealed that most of the moisture came from the western North Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico. Moreover, the eastern US and Mexico acted as notable terrestrial moisture sources. Overall, the moisture contribution from the oceanic origin was higher than the terrestrial counterpart, and the moisture sources progressively shifted northward as the storm moved. In addition, the moisture uptake mainly occurred in the cyclone–anticyclone interaction region.

Where does the moisture for North Atlantic tropical cyclones come from?

Abstract In this study, we identified the origin of the moisture associated with the tropical cyclones (TCs) precipitation in the North Atlantic Ocean basin during their three well-differentiated life stages between 1980 and 2018. The HURDAT2 database was used to detect the location of 598 TCs during their genesis, maximum intensification peak, and dissipation phases. The global outputs of the Lagrangian FLEXPART model were then used to determine the moisture sources. Using a K-means cluster analysis technique, seven different regions were identified as the most common locations for the genesis and maximum intensity of the TC phases, while six regions were found for the dissipation points. Our results showed that the origin of moisture precipitating was not entirely local over the areas of TC occurrence. The North Atlantic Ocean to the north of the Inter Tropical Convergence Zone at 10°N (NATL) -especially from tropical latitudes, the Caribbean Sea and the Gulf of Mexico- provides most of the moisture for TCs (∼87%). The Atlantic Ocean basin southward the ITCZ (SATL) played a non-negligible role (∼11%), with its contribution being most pronounced during the TC genesis phase, while the eastern tropical Pacific Ocean made the smallest contribution (∼2%). The moisture supported by TCs varied depending on their category, being higher for hurricanes than for major hurricanes or tropical storms. Additionally, the approach permitted to estimate the mean residence time of the water vapour uptake that produce the precipitation during TC activity, which ranged between 2.6 and 2.9 days.