Atmospheric Saturation Research Articles

New characteristics of Meiyu precipitation changes in the middle and lower reaches of the Yangtze River since 2000

This study comprehensively analyzed the long-term changes of Meiyu in the middle and lower reaches of the Yangtze River with regard to precipitation, precipitation threshold, and interdecadal changes in atmospheric circulation. Results revealed obvious new features of Meiyu precipitation since 2000. (1) Meiyu precipitation shows a significant linear increase trend, with an average increment of 73.5 mm every 10 years. The increase in torrential rain is the most significant, accounting for 61% of the total precipitation increase, and its proportion has been increasing, while the proportions of light, moderate, and heavy rain in the total precipitation have been decreasing. (2) At the interdecadal scale, Meiyu precipitation and the local surface average temperature show opposite changes. Meiyu precipitation decreases by approximately 150 mm for every 1°C increase in the average temperature. This inverse correlation was not evident before 2000. (3) The saturated specific humidity in this area shows a significant increasing trend, indicating that precipitation in this area is caused by a higher threshold of atmospheric saturation and condensation, which may be a reason for the low Meiyu precipitation during high-temperature years. (4) The main atmospheric circulation in East Asia associated with Meiyu shows clear interdecadal changes, including the Western North Pacific Subtropical High and South Asian High having become significantly stronger and having extended westward and eastward, respectively, thereby facilitating the occurrence and persistence of Meiyu precipitation. The atmospheric circulation patterns associated with Meiyu, such as the Western North Pacific Subtropical High and South Asian High, have more significant impacts on Meiyu precipitation.

Different Mechanisms for the Northern and Southern Winter Fog Events over Eastern China

Northern and southern fog events are identified over eastern China across 40 winters from 1981 to 2021. By performing composite analysis on these events, this study reveals that the formation of fog events is controlled by both dynamic and thermodynamic processes. The fog events were induced by Rossby wave trains over the Eurasian continent, leading to the development of surface wind and pressure anomalies, which favor the formation of fog events. The Rossby wave trains in northern and southern fog events are characterized by their occurrence in northern and southern locations, respectively, with different strengths. The water vapor fluxes that contribute to the enhancement of the northern fog events originate from the Yellow Sea and the East China Sea, whereas the southern fog events are characterized by water vapor from the East China Sea and the South China Sea. In both northern and southern fog events, dew point depression and positive A and K index anomalies are found in northern and southern regions of eastern China, which are indicative of supersaturated air and the unstable atmospheric saturation from the low to the middle troposphere, thus providing favorable conditions for the establishment of fog events in northern and southern regions of eastern China.

Limnological dynamics of methane (CH4) and carbon dioxide (CO2) emissions from a tropical hypertrophic reservoir lake

ABSTRACT Methane (CH4) and carbon dioxide (CO2) emissions from tropical freshwater ecosystems have been understudied, particularly in terms of their interaction with limnological dynamics, their cycling, and the emission mechanisms of CH4. To help reduce that knowledge gap, this study addressed these processes in Valle de Bravo (VB), a tropical (19° 11. 65′ N) reservoir lake, that provides water supply to Mexico City metropolitan area. CH4 and CO2 concentrations and emissions from VB were measured during four field campaigns distributed along the annual limnological cycle of the reservoir. Dissolved CH4 concentration varied over four orders of magnitude (0.015–176.808 μmol L−1), and dissolved CO2 varied from below atmospheric saturation (15.062 μmol L−1) to 10 times that concentration (219.505 μmol L−1). CH4 fluxes ranged from 23.25 to 1220.80 μmol m−2 day−1, while CO2 fluxes ranged from −60.11 to 254.99 mmol m−2 day−1. Seasonal monitoring also allowed the assessment of the annual emissions as well as the greenhouse gas (GHG) storage during thermal stratification, which accounted for >58% of the total GHG annual emissions from VB. Overall, VB is a source of GHG, and its major contribution is the CH4 released during the autumn overturn.

Ambient aerosols increase stomatal transpiration and conductance of hydroponic sunflowers by extending the hydraulic system to the leaf surface

IntroductionMany atmospheric aerosols are hygroscopic and play an important role in cloud formation. Similarly, aerosols become sites of micro-condensation when they deposit to the upper and lower surfaces of leaves. Deposited salts, in particular can trigger condensation at humidities considerably below atmospheric saturation, according to their hygroscopicity and the relative humidity within the leaf boundary layer. Salt induced water potential gradients and the resulting dynamics of concentrated salt solutions can be expected to affect plant water relations.MethodsHydroponic sunflowers were grown in filtered (FA) and unfiltered, ambient air (AA). Sap flow was measured for 18 days and several indicators of incipient drought stress were studied.ResultsAt 2% difference in mean vapor pressure deficit (D), AA sunflowers had 49% higher mean transpiration rates, lower osmotic potential, higher proline concentrations, and different tracer transport patterns in the leaf compared to FA sunflowers. Aerosols increased plant conductance particularly at low D.DiscussionThe proposed mechanism is that thin aqueous films of salt solutions from deliquescent deposited aerosols enter into stomata and cause an extension of the hydraulic system. This hydraulic connection leads – parallel to stomatal water vapor transpiration – to wick-like stomatal loss of liquid water and to a higher impact of D on plant water loss. Due to ample water supply by hydroponic cultivation, AA plants thrived as well as FA plants, but under more challenging conditions, aerosol deposits may make plants more susceptible to drought stress.

Experimental study of pool boiling on hydrophilic and hydrophobic thin films deposited on copper surfaces using atmospheric cold plasma

Critical heat flux (CHF) is considered a safety constraint in various types of thermal systems. Enhancement of CHF threshold brings about noticeable improvements in safety measures and overall economic structures. In this study, SiO2-like hydrophilic and polymer-like SiOxCyHz hydrophobic thin films are deposited on copper surfaces using atmospheric pressure plasma enhanced chemical vapor deposition of Ar/HMDSO in the presence/non-presence of O2. Pool boiling experiments are performed on prepared surfaces under atmospheric saturation conditions. The aim is to investigate the effect of surface modifications on CHF and such other key parameters as the onset of nucleate boiling (ONB) as well as heat transfer coefficient (HTC). Scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDX), and contact angle measurement are employed to determine the morphology and composition of the thin films. Experimental results demonstrate that the hydrophilic films deposited on surfaces give rise to significant increases in CHF and HTC compared to bare surfaces. Also observed was a reduction of up to 53% in the ONB of the hydrophobic films deposited on copper surfaces.

Influence of Non-Uniform Atmospheric Saturation on Extreme Hourly Precipitation Cloud Microphysical Processes in a Heavy Rainfall Case in Zhengzhou

Influence of Non-Uniform Atmospheric Saturation on Extreme Hourly Precipitation Cloud Microphysical Processes in a Heavy Rainfall Case in Zhengzhou

Medusa–Aqua system: simultaneous measurement and evaluation of novel potential halogenated transient tracers HCFCs, HFCs, and PFCs in the ocean

Abstract. This study evaluates the potential usefulness of the halogenated compounds HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14, and PFC-116 as oceanographic transient tracers to better constrain ocean ventilation processes. We do this mainly in terms of four aspects of the characteristics of the potential tracers: input function (including atmospheric history and historical surface saturation), seawater solubility, feasibility of measurement, and stability in seawater; of these, atmospheric history and seawater solubility have been investigated in previous work. For the latter two aspects, we collected seawater samples and modified an established analytical technique for the Medusa–Aqua system to simultaneously measure these compounds. HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, and HFC-125 have been measured in depth profiles in the Mediterranean Sea for the first time and for reproducibility in the Baltic Sea. We found that the historical surface saturation of halogenated transient tracers in the Mediterranean Sea is estimated to have been nearly constant at 94 % based on historical data. Of the investigated compounds, HCFC-142b, HCFC-141b, and HFC-134a are found to currently be the most promising transient tracers in the ocean. The compounds that have the greatest potential as future tracers are PFC-14 and PFC-116, mainly hampered by the low solubility in seawater that creates challenging analytical conditions, i.e., low concentrations. HCFC-22 is found to be likely unstable in warm seawater, which compromises the potential as an oceanic transient tracer, although it is possibly useful in colder water. For the compounds HFC-125 and HFC-23, we were not able to fully evaluate their potential as tracers due to inconclusive results, especially regarding their solubility and stability in seawater, but also with regard to potential analytical challenges. On the other hand, HFC-125, HFC-23, and HCFC-22 might not need to be considered because there are alternative tracers with similar input histories that are better suited as transient tracers.

Nucleate boiling heat transfer performance of different laser processed copper surfaces

ABSTRACTPresent study reports the nucleate pool boiling characteristics of micro structured copper surface developed by utilizing two different laser systems, namely, pulsed Nd:YAG laser and continuous wave laser. Tests are conducted at atmospheric pressure and saturation temperature by using water as pool liquid. Enhancement in heat transfer coefficients was observed over all laser processed surfaces. The maximum enhancement in heat transfer coefficient was found to be 136% and 93% for the micro structured surfaces developed by using continuous wave and pulsed laser, respectively, compared to the reference smooth surface. The enhancement in heat transfer performance of micro structured surfaces are due to the presence of surface pores, grooves and micro cavities generated due to laser melting process.

Large Spatial and Temporal Variability of Carbon Dioxide and Methane in a Eutrophic Lake

AbstractLakes are conduits of greenhouse gases to the atmosphere; however, most efflux estimates for individual lakes are based on extrapolations from a limited number of locations. Within‐lake variability in carbon dioxide (CO2) and methane (CH4) arises from differences in water sources, mixing, atmospheric exchange, and biogeochemical transformations, all of which vary across multiple temporal and spatial scales. We asked, how variable are CO2 and CH4 across the surface of a single lake, how do spatial patterns change seasonally, and how well does the typical sampling location represent the entire lake surface? During the 2016 ice‐free period, we mapped surface water concentrations of CO2 and CH4 approximately weekly in Lake Mendota (USA) and modeled diffusive gas exchange. During stratification, CO2 was generally lower than atmospheric saturation (mean 19.81 μM) and relatively homogenous (mean coefficient of variation 0.12), whereas CH4 was routinely extremely supersaturated (mean 0.29 μM) with greater spatial heterogeneity (mean coefficient of variation 0.65). During fall mixis, concentrations of both gases increased and became more spatially variable, but their spatial arrangements differed. In this system, samples collected from the lake center reasonably well represented the spatially weighted mean CO2 concentration but overestimated annual CO2 efflux by 21%. For CH4, the lake center underestimated annual diffusive efflux by only 8.6% but poorly represented lakewide concentrations and fluxes on any given day. Upscaling from a single site to the whole lake requires consideration of spatial variation to assess lakewide carbon dynamics due to heterogeneity in within‐lake processing, transport to the lake surface, and exchange with the atmosphere.

The last common ancestor of animals lacked the HIF pathway and respired in low-oxygen environments.

Animals have a carefully orchestrated relationship with oxygen. When exposed to low environmental oxygen concentrations, and during periods of increased energy expenditure, animals maintain cellular oxygen homeostasis by enhancing internal oxygen delivery, and by enabling the anaerobic production of ATP. These low-oxygen responses are thought to be controlled universally across animals by the hypoxia-inducible factor (HIF). We find, however, that sponge and ctenophore genomes lack key components of the HIF pathway. Since sponges and ctenophores are likely sister to all remaining animal phyla, the last common ancestor of extant animals likely lacked the HIF pathway as well. Laboratory experiments show that the marine sponge Tethya wilhelma maintains normal transcription under oxygen levels down to 0.25% of modern atmospheric saturation, the lowest levels we investigated, consistent with the predicted absence of HIF or any other HIF-like pathway. Thus, the last common ancestor of all living animals could have metabolized aerobically under very low environmental oxygen concentrations.

Sea surfacepCO2and O2dynamics in the partially ice-covered Arctic Ocean

Understanding the physical and biogeochemical processes that control CO2 and dissolved oxygen (DO) dynamics in the Arctic Ocean (AO) is crucial for predicting future air-sea CO2 fluxes and ocean acidification. Past studies have primarily been conducted on the AO continental shelves during low-ice periods and we lack information on gas dynamics in the deep AO basins where ice typically inhibits contact with the atmosphere. To study these gas dynamics, in situ time-series data have been collected in the Canada Basin during late summer to autumn of 2012. Partial pressure of CO2 (pCO2), DO concentration, temperature, salinity, and chlorophyll-a fluorescence (Chl-a) were measured in the upper ocean in a range of sea ice states by two drifting instrument systems. Although the two systems were on average only 222 km apart, they experienced considerably different ice cover and external forcings during the 40–50 day periods when data were collected. The pCO2 levels at both locations were well below atmospheric saturation whereas DO was almost always slightly supersaturated. Modeling results suggest that air-sea gas exchange, net community production (NCP), and horizontal gradients were the main sources of pCO2 and DO variability in the sparsely ice-covered AO. In areas more densely covered by sea ice, horizontal gradients were the dominant source of variability, with no significant NCP in the surface mixed layer. If the AO reaches equilibrium with atmospheric CO2 as ice cover continues to decrease, aragonite saturation will drop from a present mean of 1.00 ± 0.02 to 0.86 ± 0.01.

Gas exchange of CO2 and O2 in partially ice-covered regions of the Arctic Ocean investigated using in situ sensors

Sea surface CO2 dynamics are not well characterized in the Arctic Ocean (AO). Most data are from ship-based studies during the low-ice period (May-September) and obtained from near shore areas because of accessibility. More CO2 data are needed to improve models for predicting the future of the carbon cycle in the region and its relationship to ocean acidification. Air-sea gas exchange rates are complicated by the presence of ice. Consequently gas exchange rates have a larger uncertainty in the AO compared to other ocean regions. To provide more information about CO2 dynamics and gas exchange in the AO, in situ time-series data have been collected from the Canada Basin during late summer to autumn of 2012. Partial pressure of CO2 (pCO2), dissolved O2 (DO) concentration, temperature, and salinity were measured at ∼6-m depth under little ice and multi-year ice on two ice-tethered profilers (ITPs) for 40-50 days. The pCO2 levels were always below atmospheric saturation whereas DO was almost always slightly above saturation. Although the two ITPs were on an average only 222 km apart, one was further south and had 14 ± 12% ice cover; whereas the more northern ITP had 63 ± 16% ice cover. Consequently the two data sets differed significantly in external forcings. Modeled variability of CO2 and DO estimate that gas exchange would significantly alter sea surface pCO2 in the low ice cover record but minimally in the more extensively ice-covered region. If these conditions extended over the entire AO, the total uptake of atmospheric CO2 would be 28.6 Tg C yr-1 and 15.4 Tg C yr-1 under low and high ice-covered conditions, respectively.

Радиолокационная идентификация пустынных областей - источников насыщения пылью атмосферы

Радиолокационная идентификация пустынных областей - источников насыщения пылью атмосферы

Why does tropical convective available potential energy (CAPE) increase with warming?

AbstractRecent work has produced a theory for tropical convective available potential energy (CAPE) that highlights the Clausius‐Clapeyron (CC) scaling of the atmosphere's saturation deficit as a driver of increases in CAPE with warming. Here we test this so‐called “zero‐buoyancy” theory for CAPE by modulating the saturation deficit of cloud‐resolving simulations of radiative‐convective equilibrium in two ways: changing the sea surface temperature (SST) and changing the environmental relative humidity (RH). For earthlike and warmer SSTs, undilute parcel buoyancy in the lower troposphere is insensitive to increasing SST because of a countervailing CC scaling that balances the increase in the saturation deficit; however, buoyancy increases dramatically with SST in the upper troposphere. Conversely, in the RH experiment, undilute buoyancy throughout the troposphere increases monotonically with decreasing RH. We show that the zero‐buoyancy theory successfully predicts these contrasting behaviors, building confidence that it describes the fundamental physics of CAPE and its response to warming.

Constructing 3D model of air pollution of Moscow and recommendations at the choice of gas resistant plant variety for landscaping areas of Moscow

A consequence of the rapid growth in production is the intensive during recent decades an atmosphere saturation of cities by gaseous and waste dust. A necessary tool for monitoring the state of the air basin is the monitoring of ambient air, the results of which are extremely important and necessary for the sustainable development of the environment. The best means to work with a wide variety of data are geo-information systems. Among the components of the biosphere's living matter the most important factor of neutralization of the gaseous toxicants is the vegetation, especially trees and bushes.

Methane and nitrous oxide emissions from a subtropical estuary (the Brisbane River estuary, Australia)

Methane (CH4) and nitrous oxide (N2O) are two key greenhouse gases. Their global atmospheric budgeting is, however, flout with challenges partly due to lack of adequate field studies determining the source strengths. Knowledge and data limitations exist for subtropical and tropical regions especially in the southern latitudes. Surface water methane and nitrous oxide concentrations were measured in a subtropical estuarine system in the southern latitudes in an extensive field study from 2010 to 2012 and water–air fluxes estimated using models considering the effects of both wind and flow induced turbulence. The estuary was found to be a strong net source of both CH4 and N2O all-year-round. Dissolved N2O concentrations ranged between 9.1±0.4 to 45.3±1.3nM or 135 to 435% of atmospheric saturation level, while CH4 concentrations varied between 31.1±3.7 to 578.4±58.8nM or 1210 to 26,430% of atmospheric saturation level. These results compare well with measurements from tropical estuarine systems. There was strong spatial variability with both CH4 and N2O concentrations increasing upstream the estuary. Strong temporal variability was also observed but there were no clear seasonal patterns. The degree of N2O saturation significantly increased with NOx concentrations (r2=0.55). The estimated water–air fluxes varied between 0.1 and 3.4mgN2Om−2d−1 and 0.3 to 27.9mgCH4m−2d−1. Total emissions (CO2-e) were N2O (64%) dominated, highlighting the need for reduced nitrogen inputs into the estuary. Choice of the model(s) for estimation of the gas transfer velocity had a big bearing on the estimated total emissions.

Evaluation of MODIS surrogates for meteorological humidity data in east Africa

Satellite remote-sensing technology has shown promising results in characterizing the environment in which plants and animals thrive. Scientists, biologists, and epidemiologists are adopting remotely sensed imagery to compensate for the paucity of weather information measured by weather stations. With measured humidity from three stations as baselines, our study reveals that normalized difference vegetation index (NDVI) and atmospheric saturation deficit at the 780 hPa pressure level (DMODIS), both of which were derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor, were significantly correlated with station saturation deficits (Dstn) (|r| = 0.42–0.63, p < 0.001). These metrics have the potential to estimate saturation deficits over east Africa. Four to nine days of lags were found in the NDVI responding to Dstn. For the daily estimation of Dstn, DMODIS yielded better performance than the NDVI. However, both of them poorly explained variation in daily Dstn using simple regression models (adj. R2 = 0.17–0.39). When the estimation temporal scale was changed to 16 days, performance was similar, and both were better than daily estimations. For Dstn estimation at coarser geographic scales, given that many factors such as soil, vegetation, slope, aspect, and wind speed might complicate NDVI response lags and model construction, DMODIS is preferable as a proxy to saturation deficit over ground due to its simple relationship with Dstn.

Nucleate Boiling of n-Pentane in a Horizontal Confined Space

An experimental study was carried out on n-pentane nucleate boiling at atmospheric pressure and saturation temperature for different gap sizes. The boiling was investigated in a confined space delimited by two horizontal discs, a heated surface and an adiabatic surface, for distances varying between 0.1 mm and 13 mm. Tests were carried out on heated surfaces of 12 mm and 20 mm diameter. The effects of the gap size on the partial boiling curve and the diameter of the heated surface were studied. A dimensionless analysis was carried out and a correlation to describe the phenomenon of confined nucleate boiling is presented.

Mars atmospheric CO2 condensation above the north and south poles as revealed by radio occultation, climate sounder, and laser ranging observations

We study the condensation of CO2 in Mars' atmosphere using temperature profiles retrieved from radio occultation measurements from Mars Global Surveyor (MGS) as well as the climate sounding instrument onboard the Mars Reconnaissance Orbiter (MRO), and detection of reflective clouds by the MGS Mars Orbiter Laser Altimeter (MOLA). We find 11 events in 1999 where MGS temperature profiles indicate CO2 condensation and MOLA simultaneously detects reflective clouds. We thus provide causal evidence that MOLA non‐ground returns are associated with CO2 condensation, which strongly indicates their nature being CO2 clouds. The MGS and MRO temperature profiles together reveal the seasonal expansion and shrinking of the area and the vertical extent of atmospheric saturation. The occurrence rate of atmospheric saturation is maximized at high latitudes in the middle of winter. The atmospheric saturation in the northern polar region exhibits more intense seasonal variation than in the southern polar region. In particular, a shrinking of saturation area and thickness from LS ∼ 270° to ∼300° in 2007 is found; this is probably related to a planet‐encircling dust storm. Furthermore, we integrate the condensation area and the condensation occurrence rate to estimate cumulative masses of CO2 condensates deposited onto the northern and southern seasonal polar caps. The precipitation flux is approximated by the particle settling flux which is estimated using the impulse responses of MOLA filter channels. With our approach, the total atmospheric condensation mass can be estimated from these observational data sets with average particle size as the only free parameter. By comparison with the seasonal polar cap masses inferred from the time‐varying gravity of Mars, our estimates indicate that the average condensate particle radius is 8–22 μm in the northern hemisphere and 4–13 μm in the southern hemisphere. Our multi‐instrument data analysis provides new constraints on modeling the global climate of Mars.

Environmental controls on water use efficiency during severe drought in an Ozark Forest in Missouri, USA

AbstractTo accurately predict ecosystem responses induced by climate warming at local‐to‐global scales, models are in need of more precise knowledge of response during periods of environmental stress such as drought. In this paper, we studied environmental control of canopy‐level water use efficiency (WUE) during drought at an eddy flux site in an oak‐hickory forest in central Missouri, USA. Two consecutive severe droughts in the summers of 2006 and 2007 afforded coverage of a broad range of environmental conditions. We stratified data to obtain subranges that minimized cross‐correlations among putative WUE‐controlling factors. Our results showed that WUE was subject to control by atmospheric saturation deficit (ASD), soil water potential (SWP) and the ratio of diffuse to total photosynthetically active radiation (If/It). Generally, WUE was found to scale with 1/(ASD)0.5, consistent with predictions from stomatal optimization theory. In contrast, SWP and If/It were related to WUE in a linear fashion. ASD was better correlated with WUE than either of the other two factors. It was also observed that the relationship between WUE and any single controlling factor was subject to influence of the other two. One such example was an opposite response of WUE to SWP between low and high ASD values, suggesting a breakdown of stomatal optimality under severe environmental stresses and a shift from optimal stomatal regulation to nonstomatal regulation at leaf scale. We have demonstrated that different data handling (stratified vs. nonstratified) or selection (hourly vs. daily) could lead to different conclusions on the relationship between WUE and its controls. For this reason, we recommend modelers to be cautious when applying WUE‐response formulas at environmental conditions or at time scales different from those at which they are derived.