Precipitation Isotopes Associated with the Duration and Distance of Moisture Trajectory in a Westerly-Dominant Setting

A Lagrangian diagnostic adjusted using specific humidity, with 6 h intervals along the trajectory and with lifting condensation level as cloud base height, was employed to identify the moisture source regions around the Tianshan Mountains, northwest China. Then, the relationship between precipitation stable isotopes and diagnosed duration–distance of moisture trajectory was analyzed. In this region, the median value of transport duration from moisture source to precipitation sampling site is approximately 3 days, and most moisture sources are closer than 1000 km. According to the Lagrangian diagnosed moisture sources, the higher precipitation summer months usually have rapid air mass movement, and remotely sourced moisture can be delivered to arid central Asia; in the dryer winter months, the moisture loading is weak, and longer transport duration and shorter source distances are observed. As trajectory duration increases, δ18O in sampled precipitation shows a positive trend, especially on the northern slope, and the short-duration events are usually significantly impacted by local recycled moisture with depleted isotopic signatures. The northern slope usually shows relatively shorter duration and longer distance, and more distant sources have more enriched isotopic values.

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Spatial–Temporal Distribution of Tropospheric Specific Humidity in the Arid Region of Northwest China

Atmosphere ◽

10.3390/atmos12030349 ◽

2021 ◽

Vol 12 (3) ◽

pp. 349

Author(s):

Hao Zhang ◽

Meiping Sun ◽

Xiaojun Yao ◽

Zhilan Wang ◽

Lei Zhang

Keyword(s):

Spatial Distribution ◽

Arid Region ◽

Temporal Distribution ◽

Northwest China ◽

Atmospheric Temperature ◽

Reanalysis Data ◽

Dew Point ◽

Specific Humidity ◽

Positive Trend ◽

Weather Forecasts

Based on the atmospheric temperature and dew point temperature difference series of mandatory levels in the arid region of northwest China, we calculated the specific humidity of stations at 200, 300, 400, 500, 700, and 850 hPa and analyzed the spatial and temporal distribution. The specific humidity of radiosonde is compared with two sets of reanalysis data (ERA-interim from European Centre for Medium Range Weather Forecasts and Modern Era Retrospective Analysis for Research and Applications: MERRA-2). The annual specific humidity and summer specific humidity show a positive trend in the vertical atmospheric levels during the period 1958–2018. Taking the middle of the 1980s and 2002 as boundaries, the selected levels show the trend of “declining-gentle rising-fluctuation rising”. The maximum specific humidity is observed at the level of 850–700 hPa during the warm months of the year, and the most vertical expansion in specific humidity is in July. In terms of spatial distribution, the specific humidity is greatly influenced by the topography and underlying surface at lower levels. The characteristics of spatial distribution of the trend are well described by the two sets of reanalysis data in the middle and upper levels, but there are some deficiencies in depicting the trend in the lower levels.

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Identification of source-sink relationships in southern Africa by stable water isotopes analysis and Lagrangian moisture source diagnostics

10.5194/egusphere-egu2020-16042 ◽

2020 ◽

Author(s):

Marielle Geppert ◽

Stephan Pfahl ◽

Ulrich Struck ◽

Ingo Kirchner ◽

Elisha Shemang ◽

...

Keyword(s):

Isotopic Composition ◽

Southern Africa ◽

Specific Humidity ◽

Water Isotopes ◽

Stable Water Isotopes ◽

Moisture Source ◽

Moisture Sources ◽

Transport Patterns ◽

Isotope Measurements ◽

Water Isotope

Many palaeoclimate reconstructions are based on the fact that stable water isotopes are conserved in different highly resolved paleo-archives such as ice cores or calcium carbonates. Stable water isotopes are tracers of moisture in the atmosphere because they record information about evaporation and condensation processes during the transport of air parcels. These processes cause isotopic fractionation that leads to isotopic enrichment or depletion. The isotopic composition of precipitation is strongly correlated with altitude above sea level, distance to the coast and local surface air temperature. Knowledge on the source and transport of moisture is thus crucial for the interpretation of stable isotopes in precipitation and in palaeo-archives. Studies analysing the linkage between stable water isotope measurements and moisture sources in southern Africa are scarce. Yet, as changes in the transport pattern can influence precipitation patterns and amounts, in a semi-arid region like southern Africa that is threatened by droughts, this knowledge is of particular interest. Thus, the aims of this study are (1) to reveal the principal moisture source areas and transport routes of specific target areas in southern Africa, (2) to assess the influence of different transport patterns on the isotopic composition of precipitation and by this (3) to create a modern analogue for palaeoclimate studies in this region. About 200 water samples, mainly from headwaters of rivers, but also from precipitation events, springs and lakes, were collected throughout southern Africa and the stable water isotope composition (&#948;2H and &#948;18O) was analysed. To detect moisture sources for this set of isotope measurements, backward air parcel trajectories were calculated from the sample location, using the LAGRANTO tool based on ERA5 reanalysis data. Variations in specific humidity along the trajectories were then used to detect moisture uptake. The analysis reveals main transport patterns related to the Intertropical Convergence Zone and easterly winds as well as the effects of topographical forcing, which is, for example, very pronounced above Lesotho. The results provide detailed insights into the relationships between atmospheric circulation and &#948;2H and &#948;18O values of precipitation over southern Africa, which is a prerequisite for the interpretation of isotopic records that are used for palaeoclimatic reconstructions.

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Atmospheric Moisture Sources, Paths, and the Quantitative Importance to the Eastern Asian Monsoon Region

Journal of Hydrometeorology ◽

10.1175/jhm-d-15-0082.1 ◽

2016 ◽

Vol 17 (2) ◽

pp. 637-649 ◽

Cited By ~ 12

Author(s):

Lintao Li ◽

Albertus J. Dolman ◽

Zongxue Xu

Keyword(s):

Asian Monsoon ◽

Southwest Monsoon ◽

Particle Dispersion ◽

Transport Processes ◽

Specific Humidity ◽

Lagrangian Model ◽

Monsoon Region ◽

Asian Monsoon Region ◽

Moisture Source ◽

Moisture Sources

Abstract A Lagrangian model [Flexible Particle dispersion model (FLEXPART)] was used to calculate the back trajectories of air parcels residing over the East Asian monsoon region (EAM) for a 4-yr period (2009–12). To detect the moisture source–sink relationships to the EAM, the moisture budgets [evaporation minus precipitation (E − P)] were evaluated by diagnosing the changes of specific humidity along the trajectories. A circulation constraint method was proposed to define the moisture sources of the EAM, to quantify their importance, to depict the moisture transport processes, and to reveal the fate of the moisture from different sources. The results indicated that in winter the largest airmass inflow is through the dry westerlies, but they do not form net precipitation. The much smaller contribution of the tropical oceans is more relevant to winter precipitation. In summer, the main contribution was through the southwest monsoon, with a mean specific humidity of 9.8 g kg−1 when entering the EAM, providing more than 40% of the moisture to the EAM and making the southwest monsoon the most humid and abundant moisture source of the EAM. Local evaporation plays an important role as a moisture source for the EAM both in summer and winter.

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Modeling Insights into Precipitation Deuterium Excess as an Indicator of Raindrop Evaporation in Lanzhou, China

Water ◽

10.3390/w13020193 ◽

2021 ◽

Vol 13 (2) ◽

pp. 193

Author(s):

Fenli Chen ◽

Mingjun Zhang ◽

Athanassios A. Argiriou ◽

Shengjie Wang ◽

Qian Ma ◽

...

Keyword(s):

Arid Region ◽

Quantitative Methods ◽

Isotope Composition ◽

Sampling Site ◽

Western China ◽

Cloud Base ◽

Deuterium Excess ◽

Semi Arid Region ◽

Semi Arid

The deuterium excess in precipitation is an effective indicator to assess the existence of sub-cloud evaporation of raindrops. Based on the synchronous measurements of stable isotopes of hydrogen and oxygen (δ2H and δ18O) in precipitation for several sites in Lanzhou, western China, spanning for approximately four years, the variations of deuterium excess between the ground and the cloud base are evaluated by using a one-box Stewart model. The deuterium excess difference below the cloud base during summer (−17.82‰ in Anning, −11.76‰ in Yuzhong, −21.18‰ in Gaolan and −12.41‰ in Yongdeng) is greater than that in other seasons, and difference in winter is weak due to the low temperature. The variations of deuterium excess in precipitation due to below-cloud evaporation are examined for each sampling site and year. The results are useful to understand the modification of raindrop isotope composition below the cloud base at a city scale, and the quantitative methods provide a case study for a semi-arid region at the monsoon margin.

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Different trends between extreme and median surface aerosol extinction coefficients over China inferred from quality controlled visibility data

10.5194/acp-2017-335 ◽

2017 ◽

Author(s):

Jing Li ◽

Chengcai Li ◽

Chunsheng Zhao

Keyword(s):

Northwest China ◽

Positive Trend ◽

Median Surface ◽

Aerosol Extinction ◽

Significance Level ◽

The North ◽

Synoptic Conditions ◽

The Mean ◽

Mean Trend ◽

Year 2000

Abstract. Although the temporal changes of aerosol properties have been widely investigated, the majority focused on the averaged condition without much emphasis on the extremes. However, the latter can be more important in terms of human health and climate change. This study uses a previously validated, quality-controlled visibility dataset to investigate the long-term trends of extreme surface aerosol extinction coefficient (AEC) over China, and compare them with the median trends. Two methods are used to independently evaluate the trends, which arrive at consistent results. The sign of extreme and median trends are generally coherent, whereas their magnitudes show distinct spatial and temporal differences. In the 1980s, an overall positive trend is found throughout China with the extreme trend exceeding the mean trend, except for Northwest China and the North China Plain. In the 1990s, AEC over Northeast and Northwest China starts to decline while the rest of the country still exhibits an increase. The extreme trends continue to dominate in the south while it yields to the mean trend in the north. After year 2000, the extreme trend becomes weaker than the mean trend overall in terms of both the magnitude and significance level. The annual trend can be primarily attributed to winter and fall trends. The results suggest that the decadal changes of pollution in China may be governed by different mechanisms. Synoptic conditions that often result in extreme air quality changes might dominate in the 1980s, whereas emission increase might be the main factor for the 2000s.

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Influence of Below-Cloud Evaporation on Deuterium Excess in Precipitation of Arid Central Asia and Its Meteorological Controls

Journal of Hydrometeorology ◽

10.1175/jhm-d-15-0203.1 ◽

2016 ◽

Vol 17 (7) ◽

pp. 1973-1984 ◽

Cited By ~ 37

Author(s):

Shengjie Wang ◽

Mingjun Zhang ◽

Yanjun Che ◽

Xiaofan Zhu ◽

Xuemei Liu

Keyword(s):

Relative Humidity ◽

Central Asia ◽

Air Temperature ◽

Sampling Site ◽

Heavy Precipitation ◽

Cloud Base ◽

Deuterium Excess ◽

Arid Central Asia ◽

Observation Network ◽

The Difference

Abstract The deuterium excess is a second-order parameter linking water-stable oxygen and hydrogen isotopes and has been widely used in hydrological studies. The deuterium excess in precipitation is greatly influenced by below-cloud evaporation through unsaturated air, especially in an arid climate. Based on an observation network of isotopes in precipitation of arid central Asia, the difference in deuterium excess from cloud base to ground was calculated for each sampling site. The difference on the southern slope of the Tian Shan is generally larger than that on the northern slope, and the difference during the summer months is greater than that during the winter months. Generally, an increase of 1% in evaporation of raindrops causes deuterium excess to decrease by approximately 1‰. Under conditions of low air temperature, high relative humidity, heavy precipitation, and large raindrop diameter, a good linear correlation is exhibited between evaporation proportion and difference in deuterium excess, and a linear regression slope of <1‰ %−1 can be seen; in contrast, under conditions of high air temperature, low relative humidity, light precipitation, and small raindrop diameter, the linear relationship is relatively weak, and the slope is much larger than 1‰ %−1. A sensitivity analysis under different climate scenarios indicates that, if air temperature has increased by 5°C, deuterium excess difference decreases by 0.3‰–4.0‰ for each site; if relative humidity increases by 10%, deuterium excess difference increases by 1.1‰–10.3‰.

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Do Undiluted Convective Plumes Exist in the Upper Tropical Troposphere?

Journal of the Atmospheric Sciences ◽

10.1175/2009jas3184.1 ◽

2010 ◽

Vol 67 (2) ◽

pp. 468-484 ◽

Cited By ~ 98

Author(s):

David M. Romps ◽

Zhiming Kuang

Keyword(s):

Kinetic Energy ◽

Deep Convection ◽

Potential Temperature ◽

Specific Humidity ◽

Heat Of Fusion ◽

Cloud Base ◽

Base Temperature ◽

Neutral Buoyancy ◽

Environmental Air ◽

Ice Phase

Abstract Using a passive tracer, entrainment is studied in cloud-resolving simulations of deep convection in radiative–convective equilibrium. It is found that the convective flux of undiluted parcels decays with height exponentially, indicating a constant probability per vertical distance of mixing with environmental air. This probability per distance is sufficiently large that undiluted updrafts are negligible above a height of 4–5 km and virtually absent above 10 km. These results are shown to be independent of the horizontal grid size within the range of 3.2 km to 100 m. Plumes that do reach the tropopause are found to be highly diluted. An equivalent potential temperature is defined that is exactly conserved for all reversible adiabatic transformations, including those with ice. Using this conserved variable, it is shown that the latent heat of fusion (from both freezing and deposition) causes only a small increase in the level of neutral buoyancy near the tropopause. In fact, when taken to sufficiently low pressures, a parcel with an ice phase ends up colder than it would without an ice phase. Nevertheless, the contribution from fusion to a parcel’s kinetic energy is quite large. Using an ensemble of tracers, information is encoded in parcels at the cloud base and decoded where the parcel is observed in the free troposphere. Using this technique, clouds at the tropopause are diagnosed for their cloud-base temperature, specific humidity, and vertical velocity. Using these as the initial values for a Lagrangian parcel model, it is shown that fusion provides the kinetic energy required for diluted parcels to reach the tropopause.

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Observed Variability of Cloud Frequency and Cloud-Base Height within 3600 m above the Surface over the Contiguous United States

Journal of Climate ◽

10.1175/jcli-d-16-0559.1 ◽

2017 ◽

Vol 30 (10) ◽

pp. 3725-3742 ◽

Cited By ~ 9

Author(s):

Ning An ◽

Kaicun Wang ◽

Chunlüe Zhou ◽

Rachel T. Pinker

Keyword(s):

United States ◽

Surface Air Temperature ◽

Cloud Amount ◽

Early Morning ◽

Cloud Base ◽

Positive Trend ◽

Diurnal Cycles ◽

Geographic Distributions ◽

Eastern Half ◽

Cloud Base Height

Abstract The geographic and temporal variability of the surface–3600-m cloud frequency and cloud-base height over the contiguous United States for a 5-yr period (2008–12) and the interannual variations for a 16-yr period (2000–15) are described using information from the Automated Surface Observing System (ASOS) observations. Clouds were separated into four categories by the cloud amount reported by ASOS: few (FEW), scattered (SCT), broken (BKN), and overcast (OVC). The geographic distributions and seasonal and diurnal cycles of the four categories of surface–3600-m cloud frequency have different patterns. Cloud frequency of FEW, SCT, and BKN peaks just after noon, whereas the frequency of OVC peaks in the early morning. However, the geographic distributions and seasonal and diurnal cycles of the four categories of the surface–3600-m cloud-base height are similar. The diurnal cycles of the cloud-base height within the surface–3600-m level present a minimum in the morning and peak in the late afternoon or early evening. Cloud frequency and cloud-base height within this range are closely related to surface air temperature and humidity conditions. From 2000 to 2015, the cloud frequency in the contiguous United States showed a positive trend of 0.28% yr−1 while the cloud-base height showed a negative trend of −4 m yr−1 for the surface–3600-m level, accompanied with a positive trend of precipitation days (0.14 days yr−1). Moreover, the increase of cloud frequency and the decrease of cloud-base height were most obvious in winter in the eastern half of the contiguous United States.

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Trends in Tropospheric Humidity from 1970 to 2008 over China from a Homogenized Radiosonde Dataset

Journal of Climate ◽

10.1175/jcli-d-11-00557.1 ◽

2012 ◽

Vol 25 (13) ◽

pp. 4549-4567 ◽

Cited By ~ 42

Author(s):

Tianbao Zhao ◽

Aiguo Dai ◽

Junhong Wang

Keyword(s):

Spatial Coherence ◽

Vertical Motion ◽

Precipitable Water ◽

Northern China ◽

Northwest China ◽

Specific Humidity ◽

Radiosonde Data ◽

Clapeyron Equation ◽

Dipole Pattern ◽

Highly Correlated

Abstract Radiosonde humidity data provide the longest record for assessing changes in atmospheric water vapor, but they often contain large discontinuities because of changes in instrumentation and observational practices. In this study, the variations and trends in tropospheric humidity (up to 300 hPa) over China are analyzed using a newly homogenized radiosonde dataset. It is shown that the homogenization removes the large shifts in the original records of dewpoint depression (DPD) resulting from sonde changes in recent years in China, and it improves the DPD’s correlation with precipitation and the spatial coherence of the DPD trend from 1970 to 2008. The homogenized DPD data, together with homogenized temperature, are used to compute the precipitable water (PW), whose correlation with the PW from ground-based global positioning system (GPS) measurements at three collocated stations is also improved after the homogenization. During 1970–2008 when the record is relatively complete, tropospheric specific humidity after the homogenization shows upward trends, with surface–300-hPa PW increasing by about 2%–5% decade−1 over most of China and by more than 5% decade−1 over northern China in winter. The PW variations and changes are highly correlated with those in lower–midtropospheric mean temperature (r = 0.83), with a dPW/dT slope of ~7.6% K−1, which is slightly higher than the 7% K−1 implied by Clausius–Clapeyron equation with a constant relative humidity (RH). The radiosonde data show only small variations and weak trends in tropospheric RH over China. An empirical orthogonal function (EOF) analysis of the PW reveals several types of variability over China, with the first EOF (31.4% variance) representing an upward PW trend over most of China (mainly since 1987). The second EOF (12.0% variance) shows a dipole pattern between Southeast and Northwest China and it is associated with a similar dipole pattern in atmospheric vertical motion. This mode exhibits mostly multiyear variations that are significantly correlated with Pacific decadal oscillation (PDO) and ENSO indices.

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Lagrangian detection of precipitation moisture sources for an arid region in northeast Greenland: relations to the North Atlantic Oscillation, sea ice cover, and temporal trends from 1979 to 2017

Weather and Climate Dynamics ◽

10.5194/wcd-2-1-2021 ◽

2021 ◽

Vol 2 (1) ◽

pp. 1-17

Author(s):

Lilian Schuster ◽

Fabien Maussion ◽

Lukas Langhamer ◽

Gina E. Moseley

Keyword(s):

Sea Ice ◽

North Atlantic Oscillation ◽

North Atlantic ◽

Arid Region ◽

Study Region ◽

Moisture Source ◽

Moisture Sources ◽

The North ◽

The North Atlantic ◽

The North Atlantic Oscillation

Abstract. Temperature in northeast Greenland is expected to rise at a faster rate than the global average as a consequence of anthropogenic climate change. Associated with this temperature rise, precipitation is also expected to increase as a result of increased evaporation from a warmer and ice-free Arctic Ocean. In recent years, numerous palaeoclimate projects have begun working in the region with the aim of improving our understanding of how this highly sensitive region responds to a warmer world. However, a lack of meteorological stations within the area makes it difficult to place the palaeoclimate records in the context of present-day climate. This study aims to improve our understanding of precipitation and moisture source dynamics over a small arid region located at 80∘ N in northeast Greenland. The origin of water vapour for precipitation over the study region is detected by a Lagrangian moisture source diagnostic, which is applied to reanalysis data from the European Centre for Medium-Range Weather Forecasts (ERA-Interim) from 1979 to 2017. While precipitation amounts are relatively constant during the year, the regional moisture sources display a strong seasonality. The most dominant winter moisture sources are the North Atlantic above 45∘ N and the ice-free Atlantic sector of the Arctic Ocean, while in summer the patterns shift towards local and north Eurasian continental sources. During the positive phases of the North Atlantic Oscillation (NAO), evaporation and moisture transport from the Norwegian Sea are stronger, resulting in larger and more variable precipitation amounts. Testing the hypothesis that retreating sea ice will lead to an increase in moisture supply remains challenging based on our data. However, we found that moisture sources are increasing in the case of retreating sea ice for some regions, in particular in October to December. Although the annual mean surface temperature in the study region has increased by 0.7 ∘C per decade (95 % confidence interval [0.4, 1.0] ∘C per decade) according to ERA-Interim data, we do not detect any change in the amount of precipitation with the exception of autumn where precipitation increases by 8.2 [0.8, 15.5] mm per decade over the period. This increase is consistent with future predicted Arctic precipitation change. Moisture source trends for other months and regions were non-existent or small.

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