Trace Water Vapor Research Articles

The influence of moisture on precipitation patterns across the Western Tibetan Plateau and its response to sea surface temperature warming

Abstract The distribution of water resources in sub-basins across the Western Tibetan Plateau (WTP) is of critical importance due to not only ecological vulnerability resulting from the extremely arid climatology but also the political sensitivities surrounding the international rivers. In this study, we utilize an advanced water vapor tracer (WVT) embedded in the widely used regional climate model – Weather and Research Forecast (WRF), to quantify moisture contributions from four main sources towards precipitation over the WTP region. We also analyze influences on other sub-basins in the TP for comparison purposes. We examine how changes in sea surface temperature (SST) during 2010s compared to 1980s have influenced precipitation patterns and moisture contributions over recent decades. Our findings indicate that terrestrial moisture sources contribute more than oceanic sources towards the endorheic TP region. Recycling processes originating from highlands area are revealed to play a greater role in contributing moisture over WTP compared to those from lowlands areas. Furthermore, our results demonstrate stronger agreements between wetting distribution patterns and distributions of liquid/solid hydrometeors rather than water vapor distribution itself, highlighting condensation/freezing as critical factors. Notably, we observe different responses within Amu Dayra basin compared to the main WTP when subjected to SST changes. This study focuses on delineating distinct roles of terrestrial and oceanic moisture sources in driving precipitation changes over WTP, while specifically emphasizing condensation process’ contribution to inner TP’s precipitation and highlighting moisture transport form oceans’ influence on precipitation patterns over Amu Dayra basin.

Understanding tropical cyclone persistence over land: A case study of Cyclone Gulab

Abstract Tropical Cyclone (TC) Gulab originated in the Bay of Bengal during the post-monsoon season of 2021. Following an unusual westward trajectory, TC Gulab made landfall on the east coast of India, traversed central India, and reintensified over the Arabian Sea into TC Shaheen. This study employed an online Eulerian water vapor tracer (WVT) tool embedded within the Weather Research and Forecasting (WRF) model to investigate the role of land in terms of soil moisture and Land Use Land Cover (LULC) in persistance of TC Gulab over central India. We quantified the contributions of sub-regions and dominant LULC types within the Indian subcontinent to the precipitation associated with TC Gulab. Our findings indicate that evapotranspiration across the entire Indian subcontinent contributed approximately 30% to the post-landfall precipitation associated with TC Gulab. The highest contribution originated from the northwestern region, followed by the northeast. Croplands, the dominant LULC type, were the primary contributors, followed by forests. Despite changing the dominant land cover from cropland to forest, the low-pressure system persisted over land while altering the spatial patterns of precipitation. Sensitivity experiments demonstrated a linear decrease in precipitation originating from land with decreasing soil moisture (SM). Notably, there is a disproportionate decline in total precipitation with decreasing SM. Further analysis separating atmospheric vapor sources into land and ocean contributions using WVT revealed a compensatory mechanism. The contribution of oceanic vapor to atmospheric vapor over land increased when SM decreased due to increase in the latent heat over ocean. However, the total atmospheric vapor remained low, ultimately leading to a lower total precipitation. Although SM plays a role, our results highlight the importance of oceanic and atmospheric processes in determining TC persistence over land. This study offers valuable insights into the dynamics of land-atmosphere interactions during low-pressure systems of TCs.

How does greening affect the surface water budget in the Loess Plateau?

Significant vegetation increase in the Loess Plateau (LP) of China could strongly affect the surface water budget. Through the WRF model with the Water Vapor Tracer (WVT) method tracking moisture within the LP, this study conducted three sets of experiments from 1999 to 2018 with GLASS Fractional Vegetation Cover (FVC) data. The results indicate that vegetation has a critical role in partitioning evapotranspiration (ET) into transpiration (Et), canopy evaporation (Ecan), and soil evaporation (Edir), thus regulating terrestrial internal convective precipitation (P). The local P response largely depends on external P (E_P), while the internal P (I_P) contribution remains minor. In summer, the total wet difference of I_P in the LP is about 0.03 mm/day, almost 5 times that of E_P. Greening also causes surface runoff reduction. Thus, in spring and summer, surface water storage (W) decreases due to the greater increase in ET than in P. In autumn, W increases by about 0.06 mm/day due to a large decrease in Ecan, implying confining the increased W to shallower soils, resulting in accelerated loss of deep soil moisture. The greening trend of 2000–2018 contributed to an increase in I_P, which could not offset increased ET and reduced E_P, leading to terrestrial water storage reduction.

Theoretical analysis of the initial nucleation characteristics of trace water vapor frosting on a cryogenic surface

In certain extreme conditions characterized by ultra-low water vapor content and ultra-low temperatures (e.g. cryogenic wind tunnel), trace water vapor frosting can also pose significant hazards. Considering the crucial role of initial nucleation on subsequent frosting processes, this study firstly investigated and compared the nucleation characteristics of frosting at different water vapor contents (0.1−1000 ppmv) from humid air to trace water vapor based on classical nucleation theory. The preferred nucleation phase diagrams and critical nucleation conditions were analyzed. Sensitivity of the nucleation mass transfer rate, as well as the frosting pathways were further identified. Results show that the nucleation characteristics of trace water vapor frosting (<100 ppmv) is significantly different from that of humid air frosting (>1000 ppmv). Trace water vapor frosting is more inclined towards desublimation nucleation due to its lower nucleation temperature and larger critical contact angle. The critical contact angles for 1000 ppmv, 100 ppmv and 0.1 ppmv are 49°, 75° and 120°, respectively. Furthermore, trace water vapor nucleation requires a greater subcooling degree, has a smaller critical nucleation radius, and is highly sensitive to surface contact angle and further-subcooling degree. At a surface contact angle of 120°, the nucleation subcooling degree of 0.1 ppmv is 2.9 K greater than that of 1000 ppmv. This study helps understanding the nucleation characteristics under different water vapor content conditions, which indicates that reducing subcooling degree and increasing contact angle are more effective anti-frosting methods than reducing water vapor content for trace water vapor frosting.

Ultra-Fast-Healing Glassy Hyperbranched Plastics Capable of Restoring 26.4 MPa Tensile Strength within One Minute at Room Temperature.

The growing concern regarding widespread plastic pollution has propelled the development of sustainable self-healing plastics. Although considerable efforts have been dedicated to fabricating self-healing plastics, achieving rapid healing at room temperature is extremely challenging. Herein, we have developed an ultra-fast-healing glassy polyurethane (UGPU) by designing a hyperbranched molecular structure with a high density of multiple hydrogen bonds (H-bonds) on compliant acyclic heterochains and introducing trace water to form water bridge across the fractured surfaces. The compliant acyclic heterochains allow the dense multiple hydrogen bonds to form a frozen network, enabling tensile strength of up to 70 MPa and storage modulus of 2.5 GPa. The hyperbranched structure can drive the reorganization of the H-bonding network through the high mobility of the branched chains and terminals, thereby leading to self-healing ability at room temperature. Intriguingly, the presence of trace water vapor facilitates the formation of activated layers and the rearrangement of networks across the fractured UGPU sections, thereby enabling ultra-fast self-healing at room temperature. Consequently, the restored tensile strength after healing for 1 minute achieves a historic-record of 26.4 MPa. Furthermore, the high transparency (>90 %) and ultra-fast healing property of UGPU make it an excellent candidate for advanced optical and structural materials.

Ultra‐Fast‐Healing Glassy Hyperbranched Plastics Capable of Restoring 26.4 MPa Tensile Strength within One Minute at Room Temperature

AbstractThe growing concern regarding widespread plastic pollution has propelled the development of sustainable self‐healing plastics. Although considerable efforts have been dedicated to fabricating self‐healing plastics, achieving rapid healing at room temperature is extremely challenging. Herein, we have developed an ultra‐fast‐healing glassy polyurethane (UGPU) by designing a hyperbranched molecular structure with a high density of multiple hydrogen bonds (H‐bonds) on compliant acyclic heterochains and introducing trace water to form water bridge across the fractured surfaces. The compliant acyclic heterochains allow the dense multiple hydrogen bonds to form a frozen network, enabling tensile strength of up to 70 MPa and storage modulus of 2.5 GPa. The hyperbranched structure can drive the reorganization of the H‐bonding network through the high mobility of the branched chains and terminals, thereby leading to self‐healing ability at room temperature. Intriguingly, the presence of trace water vapor facilitates the formation of activated layers and the rearrangement of networks across the fractured UGPU sections, thereby enabling ultra‐fast self‐healing at room temperature. Consequently, the restored tensile strength after healing for 1 minute achieves a historic‐record of 26.4 MPa. Furthermore, the high transparency (&gt;90 %) and ultra‐fast healing property of UGPU make it an excellent candidate for advanced optical and structural materials.

Simulation of the micro-gas desublimation crystallization during pressurization of cryogenic propellant

The desublimation crystallization of trace impurity gas at the temperature of liquid hydrogen and liquid oxygen is a common problem in cryogenic engineering, which usually leads to the failure of cryogenic liquid transportation. Liquid hydrogen and liquid oxygen are important aerospace propellants. In the pressurization process of cryogenic liquid propellant, a small amount of water vapor and other gases in the pressurized gas would appear desublimation and crystallization at low temperature. Inevitably, as the tail gas of hydrogen combustion, water vapor sometimes diffused into cryogenic liquid. This kind of desublimation crystallization was accompanied by heat and mass transfer, accompanied by gas-solid phase transition, moving boundary, random and extremely complicated crystallization growth process. It was of great engineering practical significance to study the heat and mass transfer mechanism and law of this complex desublimation phase change phenomenon for the progress and development of engineering technologies such as refrigeration, cryogenics and aerospace. In this paper, based on the homogeneous desublimation theory, the pressurization system of liquid oxygen tank with oxygen containing trace water vapor was taken as the research object, and the basic data of ice crystal formation and growth during pressurization, such as crystallization quantity, crystallization speed and size distribution, were calculated theoretically. It provided a theoretical basis for the experimental study of the real dynamic characteristics and laws of desublimation crystallization in the propulsion system. The research methods and conclusions in this paper also had some guiding significance for the use of liquid hydrogen in the storage, transportation and use of the hydrogen energy.

Moisture Recycling through Pumping by Mesoscale Convective Systems

Abstract Moisture recycling, the contribution of local evapotranspiration (ET) to precipitation, has been studied using bulk models assuming a well-mixed atmosphere. The latter is inconsistent with a climatologically stratified atmosphere that slants across latitudes. Reconciling the two views requires an understanding of overturning associated with different weather systems. In this study, we aim to better understand moisture recycling associated with mesoscale convective systems (MCSs). Using a convection-permitting WRF simulation equipped with water vapor tracers (WRF-WVT), we tag moisture from terrestrial ET in the U.S. Southern Great Plains during May 2015, when more than 20 MCS events occurred and produced significant precipitation and flooding. Water budget analysis reveals that approximately 76% of terrestrial ET is advected away from the region while the remaining 24% of terrestrial ET is “pumped” upward within the region, accounting for 12% of precipitation. Moisture recycling peaks during early night hours (1800–2400 LT) due to the mixing of the daytime accumulated ET by active convection. By focusing on five “diurnally driven” MCSs with less large-scale circulation influence than other MCSs during the same period, we find an upright pumping of terrestrial ET at the MCS initiation and development stages, which diverges into two branches during the MCS mature and decaying stages. One branch in the upper level advects the ET-sourced moisture downstream, while the other branch in the mid-to-upper level contributes to the trailing precipitation upstream. Overall, our analysis depicts a pumping mechanism associated with MCSs that mixes local ET vertically, highlighting its specific contributions to enhancing convective precipitation processes.

Contribution of Recycled and External Advected Moisture to Precipitation and Its Inter‐Annual Variation Over the Tibetan Plateau

AbstractIn this study, we performed a high‐resolution simulation using the Weather Research and Forecasting model, integrated with water vapor tracers, covering the years 2005–2019. Our objective was to obtain deeper insights into the spatiotemporal dynamics of external advected and local evaporative water vapor, and to elucidate their impact on precipitation patterns across the Tibetan Plateau (TP). Our findings underscore that a significant proportion of TP's precipitation originates from external advected water vapor, primarily entering through the western and southern boundaries. During summer, stronger zonal and meridional water vapor transport, driven by prevailing westerly winds and the Asian monsoon, significantly influences seasonal and spatial precipitation variations. Additionally, we observed that the inter‐annual variation of precipitation is intricately linked to changes in the net water vapor influx, modulated by alterations in atmospheric circulation. We also analyze the Precipitation Recycling Ratio (PRR) which refers to the proportion of precipitation originated from local evaporative water vapor to the total precipitation, revealing distinctive elevation‐dependent variations aligned with grassland distribution. Notably, PRR exhibits asynchronous shifts with precipitation at different timescales, potentially linked to soil moisture‐precipitation feedback at intra‐annual scales. Moreover, the investigation highlights that inter‐annual variations in PRR are primarily linked to the inflow and outflow of water vapor as well as wind strength at 500 hPa, particularly prominent during colder seasons, while thermal factors carry comparable weight to dynamical factors in warmer seasons.

Experimental study of frosting characteristics of trace water vapor under cryogenic wind tunnel conditions

In cryogenic wind tunnels, the working fluid mixed with trace amounts of water vapor may form frost on the test model, which could affect the testing results. To investigate the frosting phenomenon under trace water condition, an experimental system is built for visualizing the frosting process on a cryogenic surface. The effects of variable factors on frost formation are analyzed focusing on the growth characteristics of frost layer. Under trace water and cryogenic surface conditions, the water vapor desublimates into crystals without obvious condensation. As the surface temperature increases from −183 ℃ to −123 ℃, the frost becomes thicker and more porous due to the thinner outer boundary layer. When the water vapor content rises from 30 ppm to 500 ppm, the frost morphology transforms from a flat layer to frost clumps with visible dendritic structure. Additionally, the decrease in nitrogen flow temperature and the increases in ambient pressure and surface roughness of the cryogenic surface are conducive to the development of the branches on the frost crystal, which accelerate the growth of the frost layer. Furthermore, a dimensionless correlation is proposed for predicting the frost thickness under cryogenic and trace water conditions, with an overall error within ±20 %.

Determination of Ozone Concentration Levels in Urban Environments Using a Laser Spectroscopy System

In urban areas, there has been a recent rise in ground-level ozone. Given its toxicity to both humans and the environment, the investigation of ozone pollution demands attention and should not be overlooked. Therefore, we conducted a study on ozone concentration in three distinct locations within the city of Magurele, Romania. This investigation considered variations in both structure and location during the spring and summer seasons, specifically at a breathing level of 1.5 m above the ground. Our analysis aimed to explore the impact of different locations and meteorological variables on ozone levels. The three measurement points were strategically positioned in diverse settings: within the city, in a forest, and within an industrial area. For these measurements, we used a laser spectroscopy system to determine the system’s sensitivity and selectivity and the influence of humidity in the detection of ozone in ambient air, which is a mixture of trace gases and water vapor. During the March–August campaign, the mean values in the three measuring points were 24.45 ± 16.44 ppb, 11.96 ± 3.80 ppb, and 95.01 ± 37.11 ppb. The peak concentrations of ozone were observed during the summer season. A diurnal analysis revealed that the atmospheric ozone levels were higher in the latter part of the day compared to the earlier part. These measurements suggest that the atmospheric temperature plays a significant role in tropospheric ozone production. Additionally, meteorological variables such as wind speed and direction were found to influence the ozone concentration. Remarkably, despite substantial traffic, the ozone levels remained consistently low throughout the entire period within the forested area. This observation may suggest the remarkable ability of trees to mitigate pollution levels.

Accurate determination of line intensity of H[formula omitted]O near 7181 cm−1 : SI-traceable measurement using primary trace-moisture standard in N[formula omitted] gas

The absorption spectra of trace water vapor in N2 gas with a mole fraction of 500 nmol/mol in the pressure range of 20 kPa to 140 kPa were obtained near 7181 cm−1 using wavelength-meter-controlled cavity ring-down spectroscopy (WMC-CRDS). The reference gas (water vapor in N2 gas) was produced using a generation system of primary measurement standards for trace moisture in gases, where the amount of water vapor was measured using a gravimetric method. The obtained spectra of H2O were analyzed using a multispectrum fitting technique with a speed-dependent asymmetric Voigt profile (SDAVP). The values of the line intensity were determined with traceability to the International System of Units (SI). We could achieve the expanded uncertainty below 2 % for the line intensities of the strong lines.

Primary measurement standards for trace moisture in multiple gases: extension of gas species to He and O2

The National Metrology Institute of Japan developed a multi-gas trace-moisture generator which was designed for generating trace water vapor (trace moisture) in multiple gases. Using this system, we previously developed primary measurement standards for trace moisture in N2 (10 nmol mol−1–5 μmol mol−1) and Ar (10 nmol mol−1–1 μmol mol−1). In this study, we have extended the target gas species; trace-moisture standards in He and O2 in the rage of 10 nmol mol−1 − 1 μmol mol−1 were developed. The relative expanded uncertainty (k = 2) of the trace-moisture standard in He was 0.74 %–5.7 %, and that in O2 was 0.78 %–8.9 %. In addition, we have improved stability of the flow rate of the diluent gas by controlling the temperature around the flow measurement/control systems and re-evaluated the uncertainty of the trace-moisture standards in N2 and Ar. The updated relative expanded uncertainty (k = 2) of the trace-moisture standard in N2 and Ar is 0.41 %–2.6 % and 0.73 %–2.6 %, respectively. The uncertainty budgets of the standards in these four gases are presented. The trace-moisture standard in N2 developed using the multi-gas trace-moisture generator was confirmed to be consistent with the standards realized by other generators, whose international comparability were already ensured. A commercial moisture analyzer (MA) based on the cavity ring-down spectroscopy (CRDS) was connected to the multi-gas trace-moisture generator as a device under test, and its performance was evaluated by comparing the readings with the standard values. The MA showed lower accuracy and stability in the measurement of moisture in He when it was used in the default setting, whereas it performed well in N2. This performance difference is related to the pressure-broadening coefficient of water, which depends on the gas species. We estimated the pressure-broadening coefficients of water by N2, Ar, He and O2 and discuss the gas-type dependence of the performance of CRDS-based MAs.

Real-time mass detection of trace water vapor frosting on a cryogenic surface based on quartz crystal Microbalance (QCM) sensor

Trace water vapor remaining in a large-scale cryogenic wind tunnel may form an extremely thin frost layer on the scaled model, significantly affecting the aerodynamic characteristics and degrading the data quality. Developing a high-precision detection method for trace water vapor frosting can be very helpful in revealing the underlying mechanisms. In this work, utilizing the relationship between deposited mass and frequency variation of Quartz Crystal Microbalance (QCM), an ultra-sensitive (nanogram level) mass sensor for cryogenic and flow conditions was developed. Furthermore, after investigating the effects of different parameters (flow velocity, pressure, temperature and mass) on frequency, the real-time mass detection of trace water vapor frosting under cryogenic and flow conditions was achieved for the first time. The results show that the effect of flow velocity or pressure on frequency is almost negligible compared to that of temperature or mass. Although temperature (from 290 K to 140 K) has a significant effect on frequency, by using the relationship between the measurement surface and the reference surface, the separate effect of mass on frequency can be obtained and the real-time mass detection is achieved. The calculated total deposited mass by trace water vapor frosting is about 4.64 μg/cm2 when the water vapor content, lowest surface temperature, pressure, velocity and frosting time are 186.5 ppb, 140 K, 0.1 MPa(G), 1.0 m/s, 160 min, respectively. This self-designed device and the analysis results of this work can be used as a reference for the quantitative measurement of trace water frosting as well as the phase change process of other trace substances in cryogenic and flow environments.

Revisiting Biophysical Impacts of Greening on Precipitation Over the Loess Plateau of China Using WRF With Water Vapor Tracers

AbstractThe Loess Plateau of China has witnessed a remarkable greening trend due to vegetation restoration in recent decades. However, the precipitation response to greening remains unclear, and the hydrological effect of greening is controversial. Here, we revisited biophysical effects of greening on precipitation over the plateau during 2002–2015 using the state‐of‐the‐art water vapor tracer embedded in a regional coupled model. We find that greening can promote the growing season precipitation (0.45 mm·day−1), with 15% and 85% of the precipitation increment resulting from increases in the local evapotranspiration and the water vapor inflow from outside the plateau, respectively. As a consequence, the enhanced precipitation can compensate for the terrestrial water loss driven by the increased evapotranspiration, leading to a slight increase in the water yield. This study highlights the dominant role of the nonlocal effect in precipitation responses to greening in this region.

The Contribution of Subtropical Moisture Within an Atmospheric River on Moisture Flux, Cloud Structure, and Precipitation Over the Salmon River Mountains of Idaho Using Moisture Tracers

AbstractThe impact of an atmospheric river (AR) on the flux of subtropical moisture across Idaho's Salmon River Mountains and precipitation over the mountains is evaluated using the Weather, Research, and Forecasting model with water vapor tracers (WRF‐WVT). The AR impacted Idaho between 17 and 19 January 2017 during the Seeded and Natural Orographic Wintertime Clouds: The Idaho Experiment (SNOWIE) campaign. WRF‐WVT is configured to isolate the subtropical moisture contribution to the AR, the moisture flux, and precipitation. Subtropical water vapor advected by the AR into Idaho is tagged and tracked in three‐dimensional space throughout the run. This allows the contribution of the subtropical moisture to the vertical distribution of water vapor and the precipitation to be directly calculated. The simulated cloud structure is compared with airborne radar data collected during two SNOWIE intensive operation periods. This study found that more than 70% of the moisture flux and more than 80% of the precipitation across the Idaho Mountains during SNOWIE IOP 4 could be attributed to subtropical moisture within the AR. Nearly all of the moisture flux in the upper cloud and 50% of the moisture in the lower cloud was attributable to the subtropical moisture. The subtropical moisture contribution within the AR to precipitation ranged from 35% in northern Idaho to more than 90% in southern Idaho. Across the entire period of impact of the AR, more than 60% of precipitation in Idaho was attributable to the subtropical moisture within the AR, with this percentage increasing toward the south across the state.

Mechanisms of trace water vapor desublimation over airfoil in transonic cryogenic wind tunnels

Cryogenic wind tunnels can provide a larger operating Reynolds number compared to conventional ones. However, the internationally known “moisture contamination problem” resulting from the residual trace water vapor desublimation in the cryogenic wind tunnel may affect the accuracy of the aerodynamic data. Due to extreme difficulties in experiments, the detailed trace water desublimation characteristics remain unrevealed. An Euler–Euler two-phase flow model based on classical nucleation theory and a droplet growth model were established to predict the trace water vapor spontaneous desublimation in the nitrogen flow over airfoil in a transonic cryogenic wind tunnel. The proposed model was validated by experimental data obtained from the literature and showed good agreements. The verified model was applied to 0.152-m National Advisory Committee for Aeronautics 0012 airfoil in a Langley 0.3-m transonic cryogenic wind tunnel under a series of operating conditions. The simulated results reveal that the water vapor desublimation process in a transonic cryogenic wind tunnel can be divided into two patterns by a critical region. In pattern I, over the upper critical total temperature, the water vapor desublimates quickly during the rapid expansion of gas flow over the airfoil surface. In pattern II, below the lower critical total temperature, the water vapor is sufficiently supercooled and desublimates completely into small ice particles in the free-stream flow. For pattern I, the desublimation characteristics were analyzed in detail, and the influences of the desublimation process on the aerodynamic data were quantitatively evaluated, which can provide theoretical guidance for the practical operation of transonic cryogenic wind tunnels.

Effective adsorption of Ultra-dilute CO2 over Polyethyleneimine-based adsorbent for H2 purification

Ultrahigh-purity hydrogen (6 N grade) suitable for hydrogen fuel cells requires the removal of CO2 impurity from commercial hydrogen feed. In this study, CO2 adsorption over a series of potential solid adsorbents was assessed at both high (0.1–1 bar) and low (hundreds of part-per-million) concentrations. With a distinct trend at higher concentrations (0.1–1 bar), PEI/S showed a remarkable CO2 capacity of 0.86 mmol/g at concentration as low as hundred part-per-million and outperformed the other adsorbents. The impacts of polyethylenimine (PEI) loading, adsorption temperature, co-existing H2O, and regenerability were investigated systematically. Adsorption isotherms of PEI/S at various loadings were represented with the Langmuir–Freundlich model, while adsorption kinetics were simulated and fitted with the AFO model. The effectiveness of PEI/S for CO2 removal was further investigated in dynamic fixed-bed breakthrough experiments. The co-presence of trace water vapor in the feed stream showed negligible inhibition on CO2 adsorption. In addition, multiple cycles of adsorption–desorption tests demonstrated the excellent regenerability of the PEI/S adsorbents. This study gave a comprehensive evaluation and demonstration of supported polyethylenimine as a potential TSA adsorbent for adsorptive removal of trace CO2 for ultrahigh purity H2 production.

First metrological validation of TwOGaSt, a new, absolute dTDLAS-trace-hygrometer, using the primary, coulometric, trace water vapour generator at PTB

Abstract We report the first realization of a TwOGaSt, a trace water optical gas standard (OGS) based on direct tunable diode laser absorption spectroscopy (dTDLAS). The TwOGaSt (Trace water Optical Gas Standard) hygrometer is equipped with a fiber-coupled DFB-laser emitting at 1.37 µm, a 36 m multi-pass astigmatic Herriott gas cell and a room-temperature InGaAs photo detector. TwOGaSt is capable of directly measuring absolute H2O concentration without any previous calibration of the spectrometer with reference gas mixtures. Water vapour amount fraction (= concentration) results delivered by TwOGaSt covering the concentration range from 10 to 350 µmol/mol (µmol/mol = ppm) were demonstrated and showed an optimum precision of 0.023 µmol/mol at a time resolution of 2 s. Further, we demonstrate the first metrological validation of this new OGS for absolute “calibration free” trace H2O amount fraction measurements in N2 and air, by comparing it with the primary coulometric trace water standard (CSFG) of PTB. The TwOGaSt results were in excellent agreement with the CSFG, PTB’s primary trace water vapor standard [1]. The relative standard uncertainty of the laser-hygrometer was determined to be is 1.2 %. This demonstrates that after SEALDH [2] and HAI [3], we now realized with TwOGaSt a laser-based, calibration-free, first-principles, optical gas standard (OGS) for the trace water vapor range, which is highly relevant for the upper troposphere and lower stratosphere (UT/LS) i. e. below 100 µmol/mol down to 4 µmol/mol (the tropopause H2O minimum).

Amazonian Moisture Recycling Revisited Using WRF With Water Vapor Tracers

AbstractPrevious studies have estimated that 25%–35% of Amazonian precipitation comes from evapotranspiration (ET) within the basin. However, due to simplifying assumptions of traditional models, these studies primarily focus on large spatial and temporal scales. This study is the first to analyze the moisture of Amazonian origin at the annual to daily timescale in four different subregions of the Amazon. We analyze the sources, sinks and stores of moisture that originates as Amazonian ET. To do this, we use the Weather Research and Forecast (WRF) regional meteorological model with the added capability of water vapor tracers to track this moisture. Moisture of Amazonian origin shows strong annual and semi‐annual signals, with contrasting behavior between the northern and southern parts of the basin. The tracers reveal a strong diurnal cycle of Amazonian water vapor which had not been previously reported. This signal is related to the diurnal cycle of ET, convective precipitation and advected moisture. ET's contribution to atmospheric moisture increases from early morning into the afternoon. Some of this moisture is rained out through convective storms in the early evening. Later in the night and following morning, strong winds associated with the South American Low Level Jet advect moisture downwind. The beating pattern becomes apparent when visualizing the Amazonian water vapor as an animation.