Vertical Distribution Of Water Vapor Research Articles

Spatial-temporal variation of water vapor scale height and its impact factors in different climate zones of China

Water vapor scale height reflects the vertical distribution of water vapor in the atmosphere, which is a vital parameter in tropospheric zenith wet delay (ZWD) modeling and GNSS meteorology. This study accurately calculated the long-term water vapor scale height using 89 radiosonde stations in China, analyzed the characteristics in temporal ad spatial variations and explored the impacts factors of the water vapor scale height from the perspective of the climate zones. The numerical results indicate that the water vapor scale height in China exhibits annual and semiannual variations with a rising-then-decreasing trend across the four seasons. A relatively larger value for the water vapor scale height were observed in the subtropical monsoon climate and the temperate continental climate zone, in which the values are greater than 2.35 km, while the values in temperate monsoon climate and the alpine plateau climate zone are relatively small. In addition, the water vapor scale height in different climate zones shows different trends, with a downward trend appeared in the subtropical monsoon climate and the alpine plateau climate zone, while an upward trend was observed in the temperate monsoon climate and the temperate continental climate zone. Furthermore, a positive correlation between water vapor scale height and temperature, pressure, and atmospheric precipitable water was found in China, with a varied degree of correlation in different climate zones.

Retrievals of vertical distribution of Martian water vapor from combined day and night MGS TES nadir spectra

Vertical distribution of water vapor in the Martian lower atmosphere (0–40 km) is an important characteristic of the Martian water cycle. It reflects a complex interplay between various processes shaping the contemporary water cycle, including atmospheric transport, formation of water ice clouds, sublimation of surface frost, and possible interaction with the subsurface. Despite the growing dataset of water vapor observations, there is yet no comprehensive climatology of the vertical distribution of vapor. Limb and solar occultation observations that are typically used to retrieve vapor vertical distribution are much less numerous than nadir observations and are available for limited seasons and locations. We propose a new methodology to retrieve vertical distribution of water vapor in the Martian lower atmosphere using only nadir data. The methodology is based on the observation that infrared spectra collected over same location during different parts of day are sensitive to water vapor in different parts of the atmosphere. We validate our new methodology by applying it to infrared spectra simulated for realistic Mars environments created with Mars General Circulation Model (GCM). These tests show that vertical profiles of vapor can be recovered with accuracy ~20–40%, which is comparable to accuracy of limb and occultation observations. Importantly, the new retrieval algorithm can constrain near-surface (0–10 km) vapor abundances that cannot be observed by limb and occultation techniques. Application of this new methodology to a large dataset on Martian nadir spectra, such as the one collected by the Thermal Emission Spectrometer (TES) onboard Mars Global Surveyor (MGS) during its mission in 1999–2004, can result in the development of the detailed climatology of vapor vertical distribution on Mars. As an initial step toward this goal, we apply the new retrieval methodology to a subset of nadir spectra collected by MGS TES during one Martian year. The retrieved vapor profiles are qualitatively consistent with vapor distributions predicted by the GCM for different seasons. Differences between retrieved and simulated profiles can be interpreted as reflecting wetter Martian atmosphere and weaker atmospheric transport, during some seasons. Retrieved vapor distribution during southern summer suggests disruption of atmospheric vapor transport into southern extra-tropics following a global dust storm.

Water Vapor Vertical Distribution on Mars During Perihelion Season of MY 34 and MY 35 With ExoMars‐TGO/NOMAD Observations

AbstractThe water vapor in the Martian atmosphere plays a significant role in the planet's climate, being crucial in most of the chemical and radiative transfer processes. Despite its importance, the vertical distribution of H2O in the atmosphere has not still been characterized precisely enough. The recent ExoMars Trace Gas Orbiter mission, with its Nadir and Occultation for MArs Discovery instrument, has allowed us to measure the H2O vertical distribution with unprecedented resolution. Recent studies of vertical profiles have shown that high dust concentration in the atmosphere, in particular during dust storms, induces an efficient transport of the H2O to higher altitudes, from 40 km up to 80 km. We study the H2O vertical distribution in a subset of solar occultations during the perihelion of two Martian years (MYs), including the 2018 Global Dust Storm (GDS), in order to compare the same Martian season under GDS and non‐GDS conditions. We present our state‐of‐the‐art retrieval scheme, and we apply it to a combination of two diffraction orders, which permits sounding up to about 100 km. We confirm recent findings of H2O increasing at high altitudes during Ls = 190°–205° in MY 34, reaching abundances of about 150 ppmv at 80 km in both hemispheres not found during the same period of MY 35. We found a hygropause's steep rising during the GDS from 30 up to 80 km. Furthermore, strong supersaturation events have been identified at mesospheric altitudes even in presence of water ice layers retrieved by the IAA team.

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.

Mechanisms of the transport height of water vapor by tropical cyclones on heavy rainfall

The moisture transport by tropical cyclones is characterized by high intensity and altitude, which may affect the microphysical processes of heavy rainfall triggered by tropical cyclones. In this study, we used the Weather Research and Forecasting (WRF) model to conduct numerical simulations on a heavy rainfall event near the Yangtze River Delta induced by Super Typhoon Mangkhut (2018). The vertical distribution of water vapor was modified to highlight the impact of moisture transport at various heights. The results showed that the distribution and intensity of the rainfall event changed with the transport height of water vapor. Ensuring that the water vapor content in the column kept constant, the total amount of precipitation in the region was greatest when the transport occurred primarily at low levels, and smallest when the transport occurred primarily at mid-levels. Detailed analysis of cloud water, rainwater, and frozen hydrometeors showed that liquid- (ice-) phase processes were the dominant microphysical processes when the transport height is low (mid-to-low). The deposition and riming processes contributed to heavy precipitation when the transport height was at the mid-to-upper levels. Our findings underscore the influence of moisture transport with high intensities and altitudes by tropical cyclones on microphysical processes, ultimately leading to changes in the distribution and intensity of heavy rainfall. Therefore, when analyzing heavy precipitation events, particular attention should be given to the moisture transport at the mid-to-upper levels.

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.

A Two‐Martian Years Survey of the Water Vapor Saturation State on Mars Based on ACS NIR/TGO Occultations

AbstractOn Mars, condensation is the major factor constraining the vertical distribution of water vapor. Recent measurements of water and temperature profiles showed that water can be strongly supersaturated at and above the level where clouds form during the aphelion and perihelion seasons. Since 2018, the near‐infrared spectrometer (NIR) of the Atmospheric Chemistry Suite onboard the Trace Gas Orbiter has measured H2O and temperature profiles using solar occultation in the infrared from below 10 to 100 km of altitude. Here, we provide the first long‐term monitoring of the water saturation state. The survey spans 2 Martian years from Ls = 163° of MY34 to Ls = 170° of MY36. We found that water is often supersaturated above aerosol layers. In the aphelion season, the water mixing ratio above 40 km in the mid‐to‐high latitudes was below 3 ppmv and yet is found to be supersaturated. Around the perihelion, water is also supersaturated above 60 km with a mixing ratio of 30–50 ppmv. Stronger saturation is observed during the dusty season in MY35 compared to what was observed in MY34 during the Global Dust Storm and around the perihelion. Saturation varied between the evening and morning terminators in response to temperature modulation imparted by thermal tides. Although water vapor is more abundant in the evening, colder morning temperatures induce a daily peak of saturation. This data set establishes a new paradigm for water vapor on Mars, revealing that supersaturation is nearly ubiquitous, particularly during the dust season, thereby promoting water escape on an annual average.

Global Variations in Water Vapor and Saturation State Throughout the Mars Year 34 Dusty Season.

To understand the evolving martian water cycle, a global perspective of the combined vertical and horizontal distribution of water is needed in relation to supersaturation and water loss and how it varies spatially and temporally. The global vertical water vapor distribution is investigated through an analysis that unifies water, temperature and dust retrievals from several instruments on multiple spacecraft throughout Mars Year (MY) 34 with a global circulation model. During the dusty season of MY 34, northern polar latitudes are largely absent of water vapor below 20km with variations above this altitude due to transport from mid-latitudes during a global dust storm, the downwelling branch of circulation during perihelion season and the intense MY 34 southern summer regional dust storm. Evidence is found of supersaturated water vapor breaking into the northern winter polar vortex. Supersaturation above around 60km is found for most of the time period, with lower altitudes showing more diurnal variation in the saturation state of the atmosphere. Discrete layers of supersaturated water are found across all latitudes. The global dust storm and southern summer regional dust storm forced water vapor at all latitudes in a supersaturated state to 60-90km where it is more likely to escape from the atmosphere. The reanalysis data set provides a constrained global perspective of the water cycle in which to investigate the horizontal and vertical transport of water throughout the atmosphere, of critical importance to understand how water is exchanged between different reservoirs and escapes the atmosphere.

Global Vertical Distribution of Water Vapor on Mars: Results From 3.5Years of ExoMars-TGO/NOMAD Science Operations.

We present water vapor vertical distributions on Mars retrieved from 3.5years of solar occultation measurements by Nadir and Occultation for Mars Discovery onboard the ExoMars Trace Gas Orbiter, which reveal a strong contrast between aphelion and perihelion water climates. In equinox periods, most of water vapor is confined into the low-middle latitudes. In aphelion periods, water vapor sublimated from the northern polar cap is confined into very low altitudes-water vapor mixing ratios observed at the 0-5km lower boundary of measurement decrease by an order of magnitude at the approximate altitudes of 15 and 30km for the latitudes higher than 50°N and 30-50°N, respectively. The vertical confinement of water vapor at northern middle latitudes around aphelion is more pronounced in the morning terminators than evening, perhaps controlled by the diurnal cycle of cloud formation. Water vapor is also observed over the low latitude regions in the aphelion southern hemisphere (0-30°S) mostly below 10-20km, which suggests north-south transport of water still occurs. In perihelion periods, water vapor sublimated from the southern polar cap directly reaches high altitudes (>80km) over high southern latitudes, suggesting more effective transport by the meridional circulation without condensation. We show that heating during perihelion, sporadic global dust storms, and regional dust storms occurring annually around 330° of solar longitude (L S) are the main events to supply water vapor to the upper atmosphere above 70km.

Vertical distribution of water vapour for Martian northern hemisphere summer in Mars Year 28 from Mars Climate Sounder

We present, for the first time, retrievals of the vertical distribution of water vapour from Mars Climate Sounder (MCS) aboard Mars Reconnaissance Orbiter (MRO), an original goal of the mission compromised by channel filter performance issues. To work around this problem a two-stage retrieval has been developed and was applied to MCS observations for MY28 NH summer (Ls=111–173°, 26 September 2006 to 27 January 2007). Retrievals were consistent with observations by other instruments for both column abundances (e.g., peak NH summer column abundance of 70 pr. μm compared with 50 pr. μm in the literature) and vertical profiles. Other key results are nightside vertical profiles of water vapour (retrieved for the first time) and interaction of atmospheric water vapour with the aphelion cloud belt. Seasonal changes in the hygropause (a proxy for condensation level) are reflected in changes in the cloud belt. During late northern summer, when the hygropause level is high at the equator and tropics, the cloudbase is higher (increasing by ≈10 km from 25 to 35 km) and the belt is weaker.

Water Vapor on Mars: A Refined Climatology and Constraints on the Near‐Surface Concentration Enabled by Synergistic Retrievals

AbstractWith the utilization of a novel synergistic approach, we constrain the vertical distribution of water vapor on Mars with measurements from nadir‐pointing instruments. Water vapor column abundances were retrieved simultaneously with PFS (sensing the thermal infrared range) and SPICAM (sensing the near‐infrared range) on Mars Express, yielding distinct yet complementary sensitivity to different parts of the atmospheric column. We show that by exploiting a spectral synergy retrieval approach, we obtain more accurate water vapor column abundances compared to when only one instrument is used, providing a new and highly robust reference climatology from Mars Express. We present a composite global data set covering all seasons and latitudes, assembled from colocated observations sampled from seven Martian years. The synergy also offers a way to study the vertical partitioning of water, which has remained out of the scope of nadir observations made by single instruments covering a single spectral interval. Special attention is given to the north polar region, with extra focus on the sublimation of the seasonal polar cap during the late spring and summer seasons. Column abundances from the Mars Climate Database were found to be significantly higher than synergistically retrieved values, especially in the summer Northern Hemisphere. Deviations between synergy and model in both magnitude and meridional variation of the vertical confinement were also discovered, suggesting that certain aspects of the transport and dynamics of water vapor are not fully captured by current models.

Martian atmospheric water vapor abundances in MY26-30 from Mars Express PFS/LW observations

I report on retrievals of water vapor abundances in the Martian atmosphere using observations by Planetary Fourier Spectrometer Long Wavelength channel (PFS/LW) aboard the Mars Express (MEx) spacecraft. PFS/LW observations used in this work cover almost 4 Martian Years from Ls ~ 331° in MY26 (January 2004) to Ls ~ 209° in MY30 (December 2010). Vapor abundances were retrieved from nadir spectra collected over a range of latitudes, seasons and local hours. Most of the retrieved abundances correspond to daytime observations at local hours from 8 to 17 h. The spatial and temporal coverage of retrieved abundances varies significantly between years of observations, with the best coverage in MY27 and MY29. The average annual water vapor cycle observed by PFS/LW is qualitatively similar to the cycle observed by the Thermal Emission Spectrometer (TES) onboard Mars Global Surveyor (MGS), however the PFS/LW abundances are systematically lower. The likely reason for this difference is the difference in the respective water vapor absorption models. Comparison between PFS/LW abundances for time periods with low atmospheric dust opacity between different years of observations does not show significant interannual variability. PFS/LW abundances are significantly lower than the abundances retrieved from observations by Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on Mars Reconnaissance Orbiter (MRO) in MY29. The difference is likely due to the differences in retrieval models for different spectral regions used by CRISM and PFS/LW to retrieve water vapor abundances and due to different environmental parameters used in the retrievals. PFS/LW abundances are generally similar to abundances retrieved by the SPICAM IR instrument, except in the polar regions during summer. The difference likely arises because of non-uniform vertical distribution of water vapor in the summer polar atmospheres and different sensitivities of the two instruments to vertical distribution of vapor. The PFS/LW observed systematic longitudinal dependence of scaled vapor abundances in the northern tropics with two maxima at longitudes ~30–60°E and ~ 240–270°E. This longitudinal dependence resembles a standing wave forced in the local atmospheric flow by topography and surface thermo-physical properties. The longitudinal non-uniformity of water vapor possibly shows a seasonal dependence increasing around solstices and decreasing around equinoxes. During northern spring in the Northern Polar Region (NPR) PFS/LW observed an increase of vapor near the edge of the seasonal cap interpreted as a buildup of vapor by repeated cycles of water ice freezing and sublimation at the cap edge. Similar, but weaker and longitudinally non-uniform increase in vapor near the edge of the seasonal cap is observed in the Southern Polar Region (SPR) during spring. Tentative signs of water vapor diurnal variability were observed in the PFS/LW data over northern mid-latitudes during late spring and early summer, potentially reflecting vapor exchange between the regolith and the atmosphere.

Water Vapor Vertical Distribution Measurement with Ground-Based Lidar

Water Vapor Vertical Distribution Measurement with Ground-Based Lidar

Annual Appearance of Hydrogen Chloride on Mars and a Striking Similarity With the Water Vapor Vertical Distribution Observed by TGO/NOMAD

AbstractHydrogen chloride (HCl) was recently discovered in the atmosphere of Mars by two spectrometers onboard the ExoMars Trace Gas Orbiter. The reported detection made in Martian Year 34 was transient, present several months after the global dust storm during the southern summer season. Here, we present the full data set of vertically resolved HCl detections obtained by the NOMAD instrument, which covers also Martian year 35. We show that the particular increase of HCl abundances in the southern summer season is annually repeated, and that the formation of HCl is independent from a global dust storm event. We also find that the vertical distribution of HCl is strikingly similar to that of water vapor, which suggests that the uptake by water ice clouds plays an important role. The observed rapid decrease of HCl abundances at the end of the southern summer would require a strong sink independent of photochemical loss.

Multi‐Annual Monitoring of the Water Vapor Vertical Distribution on Mars by SPICAM on Mars Express

AbstractThe distribution of water vapor with altitude has long remained a missing piece of the observational data set of water vapor on Mars. In this study, we present the first multi‐annual survey of water vapor profile covering the altitude range from 0 to 100 km based on the SPICAM/Mars Express occultation measurements. During the aphelion season, water remains confined below 40–60 km for all Martian years observed. The highest altitude where water vapor can be spotted is between 70 and 90 km during the southern summer (Ls = 240–300°; perihelion season), approaching the transition between the middle and upper atmosphere. In this season, years without a global dust storm (GDS) show a significant moistening of the upper atmosphere (∼100 ppmv) in the southern hemisphere, confirming a seasonal impact on the hydrogen escape rate. The two observed GDS, in MY28 and MY34, show a substantial disparity in water vapor response. The storm in MY28, which coincides with the southern summer solstice, creates the largest excess of water in both hemispheres at >80 km. This climatology of water vapor will supply a robust statistical basis to address the long‐term escape processes of water from Mars.

Validation of Water Vapor Vertical Distributions Retrieved from MAX-DOAS over Beijing, China

Water vapor vertical profiles are important in numerical weather prediction, moisture transport, and vertical flux calculation. This study presents the Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) retrieval algorithm for water vapor vertical profiles and the retrieved results are validated with corresponding independent datasets under clear sky. The retrieved Vertical Column Densities (VCDs) and surface concentrations are validated with the Aerosol Robotic Network (AERONET) and National Climatic Data Centre (NCDC) datasets, achieving good correlation coefficients (R) of 0.922 and 0.876, respectively. The retrieved vertical profiles agree well with weekly balloon-borne radiosonde measurements. Furthermore, the retrieved water vapor concentrations at different altitudes (100–2000 m) are validated with the corresponding European Centre for Medium-range Weather Forecasts (ECMWF) ERA-interim datasets, achieving a correlation coefficient (R) varying from 0.695 to 0.857. The total error budgets for the surface concentrations and VCDs are 31% and 38%, respectively. Finally, the retrieval performance of the MAX-DOAS algorithm under different aerosol loads is evaluated. High aerosol loads obstruct the retrieval of surface concentrations and VCDs, with surface concentrations more liable to severe interference from such aerosol loads. To summarize, the feasibility of detecting water vapor profiles using MAX-DOAS under clear sky is confirmed in this work.

Total column water vapor retrieval for Global Ozone Monitoring Experience-2 (GOME-2) visible blue observations

Abstract. We present a new total column water vapor (TCWV) retrieval algorithm in the visible blue spectral band for the Global Ozone Monitoring Experience 2 (GOME-2) instruments on board the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Metop satellites. The blue band algorithm allows the retrieval of water vapor from sensors which do not cover longer wavelengths, such as the Ozone Monitoring Instrument (OMI) and the Copernicus atmospheric composition missions Sentinel-5 Precursor (S5P), Sentinel-4 (S4) and Sentinel-5 (S5). The blue band algorithm uses the differential optical absorption spectroscopic (DOAS) technique to retrieve water vapor slant columns. The measured water vapor slant columns are converted to vertical columns using air mass factors (AMFs). The new algorithm has an iterative optimization module to dynamically find the optimal a priori water vapor profile. This makes it better suited for climate studies than usual satellite retrievals with static a priori or vertical profile information from the chemistry transport model (CTM). The dynamic a priori algorithm makes use of the fact that the vertical distribution of water vapor is strongly correlated to the total column. The new algorithm is applied to GOME-2A and GOME-2B observations to retrieve TCWV. The data set is validated by comparing it to the operational product retrieved in the red spectral band, sun photometer and radiosonde measurements. Water vapor columns retrieved in the blue band are in good agreement with the other data sets, indicating that the new algorithm derives precise results and can be used for the current and forthcoming Copernicus Sentinel missions S4 and S5.

An Approach for Assimilating FY4 Lightning and Cloud Top Height Data Using 3DVAR

The vertical distribution of water vapor affects the intensity of the updraft, downdraft and cold pool in convection, so how to adjust lightning proxy-humidity in the vertical direction is very important for convective scale numerical weather prediction (NWP). In this study, a data assimilation approach is presented that uses information from FengYun4 (FY4) lightning data with cloud top height (CTH) data. Specifically, the FY4 CTH is used to locate the upper boundary of the relative humidity adjustment. This method can effectively determine the vertical distribution of water vapor and obtain accurate pseudo-observations. Two severe convection events with different characteristics were studied to evaluate the data assimilation approach for short-term precipitation forecast. For comparison, two other relative humidity adjustment schemes with different vertical ranges were performed. One scheme adjusted the relative humidity between two isothermal layers and introduced the smallest water vapor increments compared with the other two data assimilation experiments and showed a slight improvement on precipitation forecast. The other scheme adjusted the relative humidity between the lifting condensation level (LCL) and a fixed height and introduced the maximum water vapor increments and exhibited better precipitation forecast based on Equitable Threat Scores (ETSs). The adjustment between LCL and CTH introduced appropriate amounts of water vapor and was adaptable for various convection developments and effectively avoided producing spurious convection in the particular case. Assimilation of FY4 lightning and CTH data improves the short-term precipitation forecast and provides the best forecast skill in a particular forecast period.

Method for retrieval of atmospheric water vapor using OH airglow for correction of astronomical observations

Context. Water vapor in the atmosphere undergoes quick spatial and temporal variations. This has a serious impact on ground-based astronomical observations from the visible band to the infrared band resulting from water vapor attenuation and emission. Aims. We seek to show how the sky spectrum of an astronomical observation can be used to determine the amount of precipitable water vapor (PWV) along the line of sight toward the science target. Methods. In this work, we discuss a method to retrieve the PWV from the OH(8-3) band airglow spectrum. We analyzed the influences of the pressure and temperature of the atmosphere and the different water vapor vertical distributions on the PWV retrieval method in detail. Meanwhile, the accuracy of the method was analyzed via Monte Carlo simulations. To further verify the method of PWV retrieval, we carried out cross comparisons between the PWV retrieved from OH airglow and PWV from the standard star spectra of UVES using equivalent widths of telluric absorption lines observed from 2000 to 2016 at Cerro Paranal in Chile. Results. The Monte Carlo tests and the comparison between the two different methods prove the availability the PWV retrieval method from OH airglow. These results show that using OH airglow spectra in astronomical observations, PWVs along the same line of sight as the astronomical observations can be retrieved in real time. Conclusions. We provide a quick and economical method for retrieving the water vapor along the same line of sight of astronomical observation in the real time. This is especially helpful to correcting the effect of water vapor on astronomical observations.

SOIR/VEx observations of water vapor at the terminator in the Venus mesosphere

The Solar Occultation in the InfraRed (SOIR) instrument onboard Venus Express sounded the Venus mesosphere and lower thermosphere using solar occultation geometry between April 2006 and December 2014. The observations were all taken at the terminator. This paper reports on the water vapor vertical distribution above the clouds and geo-temporal variations, observed across the whole Venus Express mission. Water vapor profiles are sampled between 80 and 125 km from both the morning and evening side of the terminator. Calculations of the water vapor volume mixing ratio agree with those from previous studies, having an average atmospheric profile that varies between 0.56 ppmv and 2.45 ppmv. No significant variations were observed in observations taken between the morning and evening terminator. Short term variations of several Earth days dominate the data set, varying by up to a factor 18 over a 24 h period, from ~10 ppmv to ~0.55 ppmv at an altitude of ~111 km. Similar to previous trace gas observations by SOIR (HCl, HF and SO2), no significant spatial or long term trends are observed.