Vapor Column Research Articles

Why the Real Atmosphere Has More Energy than Climate Models: Implications for Ground-Based Telescopes

The calculation of Gibbs free energy via the statistical multifractal analysis of airborne observations indicates that the atmosphere is not at local thermodynamic equilibrium. Both climate models and meteorological analyses assume that it is. Satellite retrievals use spectroscopic data taken at equilibrium in laboratories, leading to apparent consistency that is to some degree faulty. Line shapes of radiatively active species, the rotational energy of molecular nitrogen and oxygen, and the translational energy of all molecules are involved, resulting in less energy in models than exists in the real atmosphere. The resulting formulation of turbulence is from the smallest scales up and has implications for astronomical observation by adaptive optics. Kolmogorov (isotropy) is not evident. The effect of temperature on the overhead water vapour column at ground-based telescopes is also open to the effects of climate change. The degree to which the dynamic operational temperature differs from that obtained by the use of local thermodynamic equilibrium assumptions needs to be established by observational measurements. Some of the considerations will apply to the atmospheres of exoplanets with regard to photochemistry and signatures of life.

Measurement of GPS Derived Precipitable Water Vapour (PWV) in Low and High Altitudes in Nepal

The study of Precipitable Water Vapour (PWV) using satellite data and ground-based observation is crucial for understanding hydrological processes, atmospheric circulation, and weather systems. It is considered the most prominent greenhouse gas in the Earth’s atmosphere. It is highly variable in both space and time across the Earth. Precipitable Water Vapor is a measure of the total amount of water vapour present in a vertical column of the atmosphere from the Earth’s surface to the top of it. This study investigates the potential atmospheric water vapour column at high (JMSM)and low(GRHI) to understand water vapour dynamics. To investigate precipitable water vapour, GNSS/GPS data were downloaded from UNAVCO SAGE. The downloaded data were processed and analyzed using GAMIT/GLOBK software which is a comprehensive GPS analysis package developed at the Massachusetts Institute of Technology (MIT), the Harvard-Smithsonian Center for Astrophysics (CfA), and the Scripps Institution of Oceanography (SIO). The main purpose of this software is to process data for Atmospheric science. This paper’s findings investigate the PWV amount in high and low altitudes over a year. Our finding shows that there is a significant difference in PWV levels between the two stations, with low-altitude areas exhibiting higher humidity and precipitation during the monsoon season, while high altitudes show reduced water vapour concentrations influenced by surrounding climatic variation.

Validation of millimetre and sub-millimetre atmospheric collision-induced absorption at Chajnantor

Due to the importance of a reference atmospheric radiative transfer model for both planning and calibrating ground-based observations at millimetre and sub-millimetre wavelengths, we have undertaken a validation campaign consisting of acquiring atmospheric spectra under different weather conditions, in different diurnal moments and seasons, with the Atacama Pathfinder EXperiment (APEX), due to the excellent stability of its receivers and the very high frequency resolution of its back-ends. As a result, a dataset consisting of 56 spectra within the 157.3-742.1 GHz frequency range, at kilohertz resolution (smoothed to sim 2-10 MHz for analysis), and spanning one order of magnitude (sim 0.35-3.5 mm) in precipitable water vapour columns, has been gathered from October 2020 to September 2022. These data are unique for their quality and completeness and, due to the proximity of APEX to the Atacama Large Millimeter/Submillimeter Array (ALMA), they provide an excellent opportunity to validate the atmospheric radiative transfer model currently installed in the ALMA software. The main issues addressed in the study are possible missing lines in the model, line shapes, vertical profiles of atmospheric physical parameters and molecular abundances, seasonal and diurnal variations, and collision-induced absorption (CIA), to which this paper is devoted, in its N$_2$-N$_2$ + N$_2$-O$_2$ + O$_2$-O$_2$ (dry) and N$_2$-H$_2$O + O$_2$-H$_2$O (`foreign' wet) mechanisms. All these CIA terms should remain unchanged in the above-mentioned ALMA atmospheric model as a result of this work.

Electromagnetically induced transparency using selective reflection radiation from a thin Rb vapor cell

We have investigated electromagnetically induced transparency (EIT) in the spectrum of selective reflection at the interface between Rb atomic vapor and a dielectric nanocell window made of technical sapphire. Two types of spectroscopic cells were used: a nanocell with atomic vapor column thicknesses ranging from 150 to 1200 nm, and a 50μm-thick microcell. We have compared electromagnetically induced transparency resonances in a Λ-type atomic system observed using selective reflection as the probe radiation and/or transmission radiation. It was demonstrated that for thicknesses below 1000 nm, the selective reflection technique is more advantageous. Notably, at a thickness of ∼150nm, electromagnetically induced transparency resonance is clearly observed using selective reflection, while it is nearly absent when using transmission radiation. This enables the realization of ∼150nm spatial resolution in mapping a strongly inhomogeneous magnetic field of 3.3 G/μm.

Features of Selective Reflection of High-Intensity Laser Radiation Using Rubidium Nanocell

The effect of selective reflection (SR) of laser radiation from the boundary of 87Rb D2-line atomic vapors and a dielectric window was studied using a nanocell (NC) with a vapor column thickness of ~300 nm. The formation of an SR with a spectral width of 25 MHz, located on atomic transitions, is demonstrated. This is a record narrowing of the 670 MHz Doppler width by a factor of 27 using single-pass geometry. The SR signal reaches several percent of the intensity of its forming radiation, and the SR amplitude’s linear dependence is maintained up to 100 mW/cm2, which is almost two orders of magnitude greater than the saturation intensity of optical processes when using centimeter-long cells with atomic vapors. Such a high saturation intensity value is achieved by using the nanocell.

Flow film boiling on a sphere in the mixed and forced convection regimes

Saturated flow film boiling on a sphere has been numerically studied in this work for both vertical and horizontal flow configurations. The simulations were performed using a numerical methodology developed by the authors for boiling flows on three-dimensional unstructured meshes. For interface capturing, the coupled level set and volume of fluid method is used. The interface evolution, vapour wake dynamics and heat transfer have been thoroughly investigated by varying the saturated liquid flow velocity, sphere diameter and wall superheat. The relative importance of both the buoyancy and the inertial forces is described in terms of the Froude number $(Fr)$ . The vapour bubble evolves periodically at low $Fr$ values, while a stable vapour column develops at high $Fr$ values. The interface evolution pattern obtained in the present work is in good agreement with the results of experimental studies available in the literature. For all the values of $Fr$ , a stable vapour column develops for a large-diameter sphere and releases vapour bubbles of varying sizes. Furthermore, for a large-diameter sphere, surface capillary waves are observed at the interface, similar to the observations of some of the experimental studies available in the literature. The flow in the liquid and vapour wakes appears to be strongly coupled. The heat transfer in the present work is estimated using the spatially and temporally averaged Nusselt numbers. Finally, an fast Fourier transform analysis of the space-averaged Nusselt number reveals a strong interaction among the different forces.

Electromagnetically induced transparency with magnetically induced ΔF=0,mF=0→mF=0 probe transition

Interest in magnetically induced (MI) transitions of alkali metal atoms is caused by the fact that their intensities can exceed the intensities of ‘regular’ atomic transitions in a wide magnetic field range (200–4000 G). The goal of this work was to form and study, for the first time, electromagnetically induced transparency (EIT) resonance in a strong magnetic field using probe radiation tuned to |Fg=F,mF=0⟩→|Fe=F,mF=0⟩ MI transition, which is forbidden in zero magnetic fields. Two narrow-band linearly polarized cw diode lasers were used to form EIT resonance on a Λ-type system of a Cs atomic D2 line in a strong transverse magnetic field (up to 1000 G). The resonance was formed in a Cs atomic vapor nanocell with an atomic vapor column thickness of 850 nm.

Global Mapping of HCl on Mars by IRTF/iSHELL

Hydrogen chloride (HCl)—a key marker of the chlorine cycle on Mars—has been recently discovered in the Martian atmosphere by the ExoMars/TGO mission. In-orbit data indicate that this molecule appears in the atmosphere only in a limited time period and specifically in the southern summer season. A snapshot global mapping of HCl is indispensable to examine its sources and sinks, but such observations are not currently possible from any orbiters. Here, we present the first spatially resolved map of HCl obtained with the ground-based NASA InfraRed Telescope Facility. We find clear features of HCl, demonstrating that HCl is present close to the surface. HCl is detected in the equatorial region for the first time, revealing that HCl is widely distributed on Mars. However, the spatial distribution of HCl is not uniform, and it is enhanced in the southern polar region. Interestingly, this nonuniform spatial distribution of HCl column abundance is strikingly similar to that of water vapor column abundance. This highlights the important role of water vapor in the evolution of HCl through the atmosphere, as previously noted, and suggests its potential involvement in the atmospheric chlorine source processes.

Experimental study of pool boiling heat transfer on hybrid surface coupled micro-pin-finned

The performance of identical hydrophilic-hydrophobic coupled micro-pin-finned surfaces was evaluated using FC-72 as the working fluid in pool boiling experiments. Three hydrophilic and hydrophobic coupled rectangular copper column surfaces (HH4, HH9, and HH16) were constructed to analyze their boiling heat transfer properties. By integrating the micro-pin-finned surface (PF) and the smooth surface (SS), the impact of various subcoolings (0 K, 15 K, and 25 K) on the critical heat flux (CHF) was explored. Surface HH16 showed the greatest sensitivity to subcooling effects on CHF, followed by HH9 and HH4, respectively. For HH9, the CHF at ΔTsub = 0 K, 15 K, and 25 K, reached 69.6 W·cm−2, 84.2 W·cm−2, and 93.7 W·cm−2, respectively. In comparison to other surfaces (PF, HH4, HH16), the CHF of HH9 climbs by 19.32 %, 8.75 %, and 10.8 % at saturated boiling, respectively. A high-quality camera captured bubble dynamics during the experiments. The results reveal that the hydrophilic and hydrophobic coupled micro-pin-finned copper surface has a greater critical heat flux (CHF) than the standard rectangular micro-pin-finned surface, although heat transfer performance (HTC) drops marginally (both saturated and subcooled boiling). Visual monitoring demonstrates that these coupled surfaces effectively prevent bubble coalescence during subcooled boiling. Additionally, this novel surface design may serve as an effective strategy to reduce drying and delay the onset of boiling crises. The CHF improvement of the HH9 on SS surface was 313.06 %, significantly higher than the 246.17 % of PF on SS, marking a performance increase of 66.89 %. The influence mechanism of the Lattice width coefficient and the Vapor column spacing coefficient on CHF were analyzed. Fluid replenishment and bubble formation behavior were applied to clarify the strengthened heat transfer and CHF triggering mechanism on the surface of the hydrophilic and hydrophobic coupled rectangular micro-pin-finned copper column surface.

Verification of parameterizations for clear sky downwelling longwave irradiance in the Arctic

Abstract. Ground-based high resolution observations of downward longwave irradiance (DLI), surface air temperature, water vapor surface partial pressure and column amount, zenith sky infrared (IR) radiance in the atmospheric window, and all-sky camera images are regularly obtained at the Thule High Arctic Atmospheric Observatory (THAAO, 76.5° N, 68.8° W), northwestern Greenland. The datasets for the years 2017 and 2018 have been used to assess the performance of different empirical formulas used to infer clear sky DLI. An algorithm to identify clear sky observations has been developed, based on value, variability, and persistence of zenith sky IR radiance. Seventeen different formulas to estimate DLI have been tested against the THAAO dataset, using the originally determined coefficients. The formulas that combine information on total column water vapor and surface air temperature appear to perform better than others, with a mean bias with respect to the measured DLI smaller than 1 W m−2 and a root mean squared error (RMSE) around 6 W m−2. Unexpectedly, some formulas specifically developed for the Arctic are found to produce poor statistical results. This is attributed partly to limitations in the originally used dataset, which does not cover a whole year or is relative to very specific condition (i.e., the presence of an ice sheet). As expected, the bias displays a significant improvement when the coefficients of the different formulas are calculated using the THAAO dataset. The presence of 2 full years of data allows the determination and the applicability of the coefficients for singular years and the evaluation of results. The smallest values of the bias and RMSE reach 0.1 and 5 W m−2, respectively. Overall, the best results are found for formulas that use both surface parameters and total water vapor column content, and have been developed from global datasets. Conversely, formulas that express the atmospheric emissivity as a linear function of the logarithm of the column integrated water vapor appear to reproduce poorly the observations at THAAO.

Boiling mechanism of biphilic surfaces based on Helmholtz instability and Taylor instability

This study demonstrated that combination hydrophilic copper and hydrophobic nano-silver surfaces simultaneously enhanced the critical heat flux (CHF) and heat transfer coefficient (HTC) in pool boiling heat transfer (BHT) with deionized water as the employed working fluid. To further investigate the influence of geometric factors on heat transfer, this study designed three patterns denoted as squares/stripes/networks, ranging from 50 μm to 3000 μm. The effects of pattern size d, spacing p, and pitch ratio p/d on heat transfer results were obtained. Based on bubble visualization, the study further analyzed the reasons for inflection points in the boiling curve and the mechanisms caused by porous hydrophobic coating. Finally, the study proposed a numerical model suitable for predicting CHF of biphilic surfaces based on Helmholtz instability and Taylor instability. The model began with vapor columns escaping toward far-field and the fluid supplied to the heating surface. Concrete model derivation and adjustments are categorized according to the relationship between pattern size and bubble detachment diameter. For surfaces where the bubble detachment diameter exceeds the pattern size, this study originated from the perspective of Helmholtz instability on the vapor column surface. The resulting model is anticipated to quantitatively solve for the former and modulate the wavelength of Taylor instability on biphilic surfaces. Regarding surfaces with bubble detachment diameters smaller than the pattern size, this research begins with the existence time of the micro-liquid layer. The derived model validates the predominant role of p/d in the CHF values on micron-scale biphilic surfaces.

Atmospheric dependence of the direct, diffuse, and global clear-sky conversion ratios between solar photosynthetic active irradiance and photon flux

The ratio of the global solar photosynthetic active radiation (PAR) photon flux (in μmol/m2s) to global solar PAR irradiance (in W/m2) is of interest to convert one into another. This ratio is usually considered as a constant value close to its extraterrestrial value, 4.55μmol/J. However, this ratio depends on the spectral composition of solar radiation at ground level and it is different for the diffuse and beam components of solar irradiance. Under clear-sky conditions, the three PAR ratios (global, beam and diffuse) are determined by the local atmospheric composition and the relative air mass. In this work, the SMARTS spectral irradiance model with MERRA-2 atmospheric inputs is used to evaluate the dependence of these ratios under clear-sky conditions with air mass, aerosol optical depth (AOD), precipitable water vapor and ozone column. The accuracy of the SMARTS beam spectral irradiance is previously assessed using local spectroradiometer measurements. The clear-sky ratios for the diffuse and direct components increase with increasing air mass, while the global ratio shows only a weak air mass dependence. The clear-sky ratios can be modeled with simple bi-variate linear models in air mass and AOD. These results can be used in similar climatic regions to convert PAR flux to PAR irradiance and vice versa with increased accuracy for the global, direct, and diffuse radiation under cloud-free conditions.

Shock induced variable density flows in the vacuum microchannel: I. medium laser fluence

Laser-matter interactions with metal target cause plasma explosion and shock accelerated variable density flow instabilities in the Semiconfined Configuration (SCC). Their study gives deeper insight into the flow instabilities present in all microchannel devices. Blast wave motion along the SCC microchanel causes the Kelvin–Helmholtz (KH) instability and formation of vortex filaments for the critical Reynolds number. Appearing in all shear layers—it affects the fluid transport efficiency. Shear layer acceleration causes a Raleigh-Taylor instability (RTI). Oriented bubble growth by discrete merging indicates anisotropic RTI mixing. Similar RTI flame instability appears in the conversion of chemical energy into electricity affecting microcombustion efficiency. Another case of anisotropic RTI is the flow boiling for cooling of chips and microelectronic devices. The RTI boiling which appears for the critical heat flux is based on rising surface vapor columns (oriented bubble growth) with liquid counterflow (spike prominences) for the critical wavelength at density interface. The RT bubble merging graph trees determine turbulent mixing which affects the heat transfer rates. Bottom-wall turbulent flow in the SCC microchannel causes streaks of the low momentum fluid and formation of hairpin vortex packets with lattice organization. This makes possible to quantify parameters responsible for the evolution of hairpin vortex packets in the microchannel devices. Appearing from the low to the high Reynolds numbers they affect the transport properties, control of the fluid motion, enhancement of mixing, or the separation of fluids. Fluid particle ejecta—thin supersonic jets - evolve into long needle-like jets which start spiraling, helical pairing and swirling in the field of thermal gradients. Such instabilities appear in the microcombustion flame instability and in the space micropropulsion systems. Oscillating and spiral flames appear in the presence of thermal gradient in the microchannel, due to the combined effects of thermal gradient fields and the mixture flow rates.

Visualized experimental study on steady-state performance of a loop heat pipe under elevated acceleration fields

In this article, an experimental investigation was carried out to explore the steady-state operational behavior of a newly designed nickel-water dual compensation chamber loop heat pipe (DCCLHP) under elevated acceleration fields. Glass windows were fabricated and embedded on a condenser and two compensation chambers (CCs) for the purpose of visual observation of vapor and liquid distribution. The steady-state operational behaviors and any new phenomena were discussed. The heat load from 30 W to 110 W and the acceleration magnitude from 1 g to 13 g as well as four different acceleration directions were taken into account. Experimental results indicate that: (i) as the heat load increases, the steady-state operational temperature of the DCCLHP increases, while thermal resistance may increase or decrease, also depending on both the acceleration direction and magnitude. (ii) The thermal resistance at both direction A and D is significantly larger than that at both direction B and C. The minimum thermal resistance with 0.78 K/W at 11 g with 70 W and operational temperature with 72.7 °C at 3 g with 30 W are achieved at direction C. (iii) as the acceleration magnitude increases, both operational temperature and thermal resistance tend to decrease for both direction B and C, whereas an opposite tendency is observed for both direction A and D. (iv) both the vapor column and liquid column alternatively distribute in the condenser channel that could increase or decrease the loop pressure drop. Inclined vapor–liquid interface and different liquid amount in both CCs are formed at different accelerations. Stratified flow or annular flow could lead to the film condensation heat transfer in the condensation channel.

Characterization and Absolute Calibration of the Far-infrared Field Integral Line Spectrometer for SOFIA

We present the characterization and definitive flux calibration of the Far-infrared Field Integral Line Spectrometer (FIFI-LS) instrument on board SOFIA. The work is based on measurements made in the laboratory with an internal calibrator and on observations of planets, moons, and asteroids as absolute flux calibrators made during the entire lifetime of the instrument. We describe the techniques used to derive flat fields, water vapor column estimates, detector linearity, spectral and spatial resolutions, and absolute flux calibration. Two sets of responses are presented, before and after the entrance filter window was changed in 2018 to improve the sensitivity at 52 μm, a wavelength range previously not covered by PACS on Herschel. The relative spectral response of each detector and the illumination pattern of the arrays of the FIFI-LS arrays are derived using the internal calibrator before each observational series. The linearity of the array response is estimated by considering observations of bright sources. We find that the deviation from the linearity of the FIFI-LS arrays affects the flux estimations by less than 1%. The flux calibration accuracy is estimated to be 15% or better across the entire wavelength range of the instrument. The limited availability of sky calibrators during each observational series is the major limiting factor of the flux calibration accuracy.

Thermal Sounding of the Martian Atmosphere Using the ACS TIRVIM FT-IR Spectrometer on Board ExoMars TGO: Method for Solving the Inverse Problem

This paper presents a method for solving the inverse problem of thermal sounding using calibrated data from the ACS TIRVIM experiment on board the ExoMars Trace Gas Orbiter. The 1.7–17 µm range TIRVIM Fourier spectrometer as part of the ACS instrument complex aboard the ExoMars TGO operates in the nadir and solar occultation modes in orbit around Mars. The main scientific goal of TIRVIM in the nadir observation mode is the long-term constant monitoring of the thermal structure of the Martian atmosphere and the general content of aerosols and water vapor from measurements in the range of 5–16.7 µm (600–2000 cm–1). To process the TIRVIM nadir measurements, an algorithm was developed, allowing the retrieval of the vertical temperature profile from the surface to 60 km, the surface temperature, and the general content of dust and water ice in the atmosphere from the TIRVIM spectrum in the range of 600–1250 cm–1, as well as the water vapor column abundance according to measurements in the range of 1250–1830 cm–1. The processing method widely uses the achievements of previous similar experiments, taking into account the features of the TIRVIM spectra. Using the developed method 2.28 × 106 spectra obtained by TIRVIM in nadir by regular measurements, were processed with retrieval of the thermal structure up to 60 km altitude and the aerosol content in the atmosphere as well as additional 2.3 × 105 specially averaged TIRVIM spectra, were processed with retrieval of the water vapor column abundancein the Martian atmosphere.

A numerical investigation of the thermal–hydraulic performance during subcooled flow boiling in MMCs with different manifolds

Thermal management of high-heat-flux electronics has been a critical bottleneck for integrated circuit miniaturization and increased power density, and manifold microchannel (MMC) heat sinks are expected to be an efficient near-junction thermal solution. A numerical investigation based a self-developed solver has been conducted to explore the effects of manifold geometries on the thermal–hydraulic performance of MMC heat sinks during subcooled flow boiling, and phase, pressure, and mass distribution among microchannels are analyzed combined with temperature distribution. Heat flux makes little difference on the mass maldistribution among microchannels of MMCs regardless of single-phase and flow boiling, and flow patterns in the outlet manifolds of Z-type MMCs changes from bubbly flow, slug flow to vapor columns with segmented bubbles with increasing heat fluxes. As for the effect of manifold numbers, both the maximum temperature and the pressure drop decrease with increasing manifold numbers, and a relatively uniform distribution of mass and void fraction has been found for all cases of HU-type MMCs regardless of heat fluxes with the best thermal–hydraulic performance at N = 10. However, the thermal performance of Z-type MMCs would improve firstly and then flatten out with increasing manifold number, while the pressure drop presents an opposite trend. The differences in thermal–hydraulic performance are attributed to the longer flow path in Z-type manifolds, and the increasing manifold number presents a higher manifold pressure drop and thus would worsen the mass maldistribution. As for tapered manifolds, a tapered ratio of 0.33 could provide a slightly lower base temperature than the original case with a pressure drop decreased by over 25 %, and the pressure drop fluctuation at high heat fluxes could be suppressed by 70 % with significantly improved flow boiling stability. This work can serve as a basis for the further optimization of subcooled flow boiling in MMC heat sinks, and the results indicate that both an even mass distribution among microchannels and a desirable inlet/outlet port ratio for improved flow field are of great importance for the manifold design applied in MMC heat sinks for two-phase heat dissipation.

Evaluation of cloud-type impact on performance of the GL model version 1.2 for estimation of solar irradiance

ABSTRACT This work evaluates the quality of the satellite-based GLobal radiation model version 1.2 (GL1.2) estimates for four cloud classes. The GL1.2 calculates the global solar irradiance at ground level using images from a single visible band channel (VIS) of the Geostationary Operational Environmental Satellite – GOES (GOES-East). The model´s performance was assessed by comparing hourly mean GL1.2 values with ground-based hourly measurements from the Brazilian National Institute of Meteorology (INMET, 354 automatic weather stations), for the entire year 2017. A satellite-based cloud classifier was adopted to discriminate the datasets according to prevailing cloud conditions (cumulus, stratus, cirrus and multilayer), but the clear sky behaviour was presented. The results were analysed for the five Brazilian regions. In the first analysis, we selected days with a predominance for five stations. It was found that the diurnal cycle was well reproduced. Then the regional investigation for the cloud types reveals that the best results are found for the Center West region over multilayer cloud (mean bias error, MBEannual = -2 ± 91 Wm−2 and root mean squared error, RMSE = 91 Wm−2), while the worst ones are in the North over cumulus fields (MBEannual = 101.5 ± 136.4 Wm−2). When considering all cloud types, the MBEannual is lower than 5 Wm−2 for the Northeast, Southeast and South regions, but it reaches 101 Wm−2 in the North. It is noteworthy that winter has the highest MBE in all classes analysed in the North, as well as cirrus situations in other regions. Although the inhomogeneities of cumulus and the semitransparent cirrus clouds tend to propagate errors to the model, the quality of GL1.2 data has a high degree of agreement with the observations. Improvements including an updated monthly minimum reflectance (R min) and water vapour column (H2Ovapour), and a better spatial resolution of the Advanced Baseline Imager (ABI) of GOES-16 (ABI/GOES-16) VIS imagery will allow refinement, especially for cumulus clouds.

Seasonal vertical water vapor distribution at the Mars Phoenix Lander site

Using a combination of orbital and surface observations, we constrain the seasonal vertical distribution of water vapor in the planetary boundary layer in the lowest scale-height of the Martian atmosphere at the Phoenix Mars Lander location (68°N, 234°E). Previous observations have shown significant discrepancies regarding the vapor distribution in the boundary layer, drawing conflicting conclusions as to whether water is uniformly mixed below the cloud condensation height, or whether water is mostly confined in the near surface layer. We conclude that the uniformly well-mixed assumption for water vapor up to the cloud condensation level is not always compatible with observational constraints, particularly when peak near-surface water vapor abundances are observed during Ls = 110°–120°. The uniformly well-mixed assumption leads to an over-estimation of the total water vapor column abundances between Ls = 80°–120°, and an under-estimation of the total water vapor column abundances between Ls = 120°–150°. The overestimation of vapor in the column is particularly evident during peak surface water vapor pressures (∼Ls = 110°–120°), suggesting a concentration of water vapor at the surface that actively participates in subsurface exchange. Using both TECP and column vapor abundance as constraints for the vertical vapor distribution, the maximum height of the well-mixed vapor layer ranges between ∼3.5–13.5 km, all of which falls below the cloud condensation height for the corresponding season. From Ls = 120° to 150°, the maximum height of the well-mixed layer stays fairly consistent at a mean height of ∼7 km. These results are particularly important for providing insight into the seasonal transport of water and the role of regolith-atmospheric exchange.

Influence of smooth heater size on critical heat flux and heat transfer coefficient of saturated pool boiling heat transfer

In order to study the influence of smooth heater size on the performance of pool boiling heat transfer, saturated boiling experiments of FC-72 were conducted on eight sized smooth silicon chips (the test surfaces are denoted as S5 ∼ S30, and their dimensionless dimensions are in the range of Lh/Lc = 7 ∼ 42). The bubble dynamics during boiling were observed with a high-speed camera. The results indicated that in natural convection regime, the heat transfer coefficient decreases with increasing heater size at a given heat flux. Besides, the larger surfaces enter into the nucleate boiling regime earlier. In a fully developed nucleate boiling regime, S5 surface displays the optimal heat transfer performance. The reality is that no vapor columns are produced even in the high heat flux range due to its small bubble departure diameter and high bubble departure frequency. For S8 ∼ S15 surfaces, the wall temperatures increase continuously with the increase of heat flux, while S20 ∼ S30 surfaces present a trend of first keeping constant and then increasing. The active nucleation site densities on S15 ∼ S30 surfaces follow the law of Na = 0.45q2 in the whole nucleate boiling regime. By contrast, for S5 ∼ S12 surfaces, the nucleation site densities abide by this law only in a fully developed nucleate boiling regime. In addition, the departure diameter and departure frequency of bubbles increase with the increase of heat flux for all surfaces. It is observed that with the increase of smooth heater size, CHF presents a changing trend of first increasing (in range of Lh ≤ λD, λD is the most dangerous Taylor wavelength), then decreasing (in range of λD < Lh ≤ 3λD) and finally leveling off (in range of Lh > 3λD). Accordingly, the CHF value maximizes at the heater size Lh = λD. In the segment of decreased CHF, the decline rate of CHF in range of λD < Lh ≤ 2λD is larger than that in range of 2λD < Lh ≤ 3λD. Meanwhile, the influencing mechanisms of heater size on CHF were explained by consideration into bubble patterns and behavior.