WATER VAPOR DISTRIBUTION IN THE SUB-CLOUD TRADE WIND AIR

1962 ◽  
Author(s):  
ANDREW F. BUNKER
Keyword(s):  
Water Vapor ◽  
Trade Wind ◽  
Vapor Distribution

scholarly journals The vertical structure and spatial variability of lower-tropospheric water vapor and clouds in the trades

2020 ◽  
Vol 20 (10) ◽  
pp. 6129-6145
Author(s):  
Ann Kristin Naumann ◽  
Christoph Kiemle
Keyword(s):  
Water Vapor ◽  
Cloud Fraction ◽  
Airborne Lidar ◽  
Cloud Base ◽  
Trade Wind ◽  
Model Resolution ◽  
Grid Spacing ◽  
Model Bias ◽  
Shallow Cumulus ◽  
Vapor Distribution

Abstract. Horizontal and vertical variability of water vapor is omnipresent in the tropics, but its interaction with cloudiness poses challenges for weather and climate models. In this study we compare airborne lidar measurements from a summer and a winter field campaign in the tropical Atlantic with high-resolution simulations to analyze the water vapor distributions in the trade wind regime, its covariation with cloudiness, and their representation in simulations. Across model grid spacing from 300 m to 2.5 km, the simulations show good skill in reproducing the water vapor distribution in the trades as measured by the lidar. An exception to this is a pronounced moist model bias at the top of the shallow cumulus layer in the dry winter season which is accompanied by a humidity gradient that is too weak at the inversion near the cloud top. The model's underestimation of water vapor variability in the cloud and subcloud layer occurs in both seasons but is less pronounced than the moist model bias at the inversion. Despite the model's insensitivity to resolution from hecto- to kilometer scale for the distribution of water vapor, cloud fraction decreases strongly with increasing model resolution and is not converged at hectometer grid spacing. The observed cloud deepening with increasing water vapor path is captured well across model resolution, but the concurrent transition from cloud-free to low cloud fraction is better represented at hectometer resolution. In particular, in the wet summer season the simulations with kilometer-scale resolution overestimate the observed cloud fraction near the inversion but lack condensate near the observed cloud base. This illustrates how a model's ability to properly capture the water vapor distribution does not necessarily translate into an adequate representation of shallow cumulus clouds that live at the tail of the water vapor distribution.

scholarly journals The vertical Structure and spatial Variability of lower tropospheric Water Vapor and Clouds in the Trades

2019 ◽  
Author(s):  
Ann Kristin Naumann ◽  
Christoph Kiemle
Keyword(s):  
Water Vapor ◽  
Winter Season ◽  
Cloud Fraction ◽  
Airborne Lidar ◽  
Cloud Base ◽  
Trade Wind ◽  
Model Resolution ◽  
Grid Spacing ◽  
Shallow Cumulus ◽  
Vapor Distribution

Abstract. Horizontal and vertical variability of water vapor is omnipresent in the tropics but its interaction with cloudiness poses challenges for weather and climate models. In this study we compare airborne lidar measurements from a summer and a winter field campaign in the tropical Atlantic with high-resolution simulations to analyse the water vapor distributions in the trade wind regime, its covariation with cloudiness and their representation in simulations. Across model grid spacing from 300 m to 2.5 km, the simulations show good skill in reproducing the water vapor distribution in the trades as measured by the lidar. An exception to this is a pronounced moist model bias at the top of the shallow cumulus layer in the dry winter season which is accompanied by a too weak humidity inversion at the cloud top. The model's underestimation of water vapor variability in the cloud and subcloud layer occurs in both seasons but is less pronounced. Despite the model's insensitivity to resolution from hecto- to kilometer scale for the distribution of water vapor, cloud fraction decreases strongly with increasing model resolution and is not converged at hectometer grid spacing. The observed cloud deepening with increasing water vapor path is captured well across model resolution but the concurrent transition from cloud-free to low cloud fraction is better represented at hectometer resolution. In particular, in the wet summer season the simulations with kilometer-scale resolution overestimate the observed cloud fraction near the inversion but lack condensate near the observed cloud base. This illustrates how a model's ability to properly capture the water vapor distribution does not need to translate into an adequate representation of shallow cumulus clouds that live at the tail of the water vapor distribution.

scholarly journals Spaceborne differential absorption radar water vapor retrieval capabilities in tropical and subtropical boundary layer cloud regimes

2021 ◽  
Vol 14 (10) ◽  
pp. 6443-6468
Author(s):  
Richard J. Roy ◽  
Matthew Lebsock ◽  
Marcin J. Kurowski
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Trade Wind ◽  
Retrieval Algorithm ◽  
Line Center ◽  
Vertical Resolution ◽  
Horizontal Integration ◽  
Differential Absorption ◽  
Near Surface ◽  
Cloud Regimes

Abstract. Differential absorption radar (DAR) near the 183 GHz water vapor absorption line is an emerging measurement technique for humidity profiling inside of clouds and precipitation with high vertical resolution, as well as for measuring integrated water vapor (IWV) in clear-air regions. For radar transmit frequencies on the water line flank away from the highly attenuating line center, the DAR system becomes most sensitive to water vapor in the planetary boundary layer (PBL), which is a region of the atmosphere that is poorly resolved in the vertical by existing spaceborne humidity and temperature profiling instruments. In this work, we present a high-fidelity, end-to-end simulation framework for notional spaceborne DAR instruments that feature realistically achievable radar performance metrics and apply this simulator to assess DAR's PBL humidity observation capabilities. Both the assumed instrument parameters and radar retrieval algorithm leverage recent technology and algorithm development for an existing airborne DAR instrument. To showcase the capabilities of DAR for humidity observations in a variety of relevant PBL settings, we implement the instrument simulator in the context of large eddy simulations (LESs) of five different cloud regimes throughout the trade-wind subtropical-to-tropical cloud transition. Three distinct DAR humidity observations are investigated: IWV between the top of the atmosphere and the first detected cloud bin or Earth's surface; in-cloud water vapor profiles with 200 meter vertical resolution; and IWV between the last detected cloud bin and the Earth's surface, which can provide a precise measurement of the sub-cloud humidity. We provide a thorough assessment of the systematic and random errors for all three measurement products for each LES case and analyze the humidity precision scaling with along-track measurement integration. While retrieval performance depends greatly on the specific cloud regime, we find generally that for a radar with cross-track scanning capability, in-cloud profiles with 200 m vertical resolution and 10 %–20 % uncertainty can be retrieved for horizontal integration distances of 100–200 km. Furthermore, column IWV can be retrieved with 10 % uncertainty for 10–20 km of horizontal integration. Finally, we provide some example science applications of the simulated DAR observations, including estimating near-surface relative humidity using the cloud-to-surface column IWV and inferring in-cloud temperature profiles from the DAR water vapor profiles by assuming a fully saturated environment.

scholarly journals Mountain waves modulate the water vapor distribution in the UTLS

2017 ◽  
Author(s):  
Romy Heller ◽  
Christiane Voigt ◽  
Stuart Beaton ◽  
Andreas Dörnbrack ◽  
Stefan Kaufmann ◽  
...  
Keyword(s):  
Water Vapor ◽  
New Zealand ◽  
Vertical Transport ◽  
Vapor Transport ◽  
Water Vapor Transport ◽  
Mountain Wave ◽  
Mountain Waves ◽  
Wave Event ◽  
Transport And Mixing ◽  
Vapor Distribution

Abstract. The water vapor distribution in the upper troposphere/lower stratosphere region (UTLS) has a strong impact on the atmospheric radiation budget. Transport and mixing processes on different scales mainly determine the water vapor concentration in the UTLS. Here, we investigate the effect of mountain waves on the vertical transport and mixing of water vapor. For this purpose we analyse measurements of water vapor and meteorological parameters recorded by the DLR Falcon and NSF/NCAR GV research aircraft taken during the Deep Propagating Gravity Wave Experiment (DEEPWAVE) in New Zealand. By combining different methods, we develop a new approach to quantify location, direction and irreversibility of the water vapor transport during a strong mountain wave event on 4 July 2014. A large positive vertical water vapor flux is detected above the Southern Alps extending from the troposphere to the stratosphere in the altitude range between 7.7 and 13.0 km. Wavelet analysis for the 8.9 km altitude level shows that the enhanced upward water vapor transport above the mountains is caused by mountain waves with horizontal wavelengths between 22 and 60 km. A downward transport of water vapor with 22 km wavelength is observed in the lee-side of the mountain ridge. While it is a priori not clear whether the observed fluxes are irreversible, low Richardson numbers derived from dropsonde data indicate enhanced turbulence in the tropopause region related to the mountain wave event. Together with the analysis of the water vapor to ozone correlation we find indications for vertical transport followed by irreversible mixing of water vapor. For our case study, we further estimate greater than 1 W m−2 radiative forcing by the increased water vapor concentrations in the UTLS above the Southern Alps of New Zealand resulting from mountain waves relative to unperturbed conditions. Hence, mountain waves have a great potential to affect the water vapor distribution in the UTLS. Our regional study may motivate further investigations of the global effects of mountain waves on the UTLS water vapor distributions and its radiative effects.

scholarly journals Controls on the water vapor isotopic composition near the surface of tropical oceans and role of boundary layer mixing processes

2019 ◽  
Author(s):  
Camille Risi ◽  
Joseph Galewsky ◽  
Gilles Reverdin ◽  
Florent Brient
Keyword(s):  
Water Vapor ◽  
Isotopic Composition ◽  
General Circulation ◽  
Model Simulation ◽  
Circulation Model ◽  
Sea Surface ◽  
Trade Wind ◽  
Mixing Processes ◽  
Tropical Oceans ◽  
Air Mixing

Abstract. Understanding what controls the water vapor isotopic composition of the sub-cloud layer (SCL) over tropical oceans (δD0) is a first step towards understanding the water vapor isotopic composition everywhere in the troposphere. We propose an analytical model to predict δD0 as a function of sea surface conditions, humidity and temperature profiles, and the altitude from which the free tropospheric air originates (zorig). To do so, we extend previous studies by (1) prescribing the shape of δD0 vertical profiles, and (2) linking δD0 to zorig. The model relies on the hypotheses that δD0 profiles are steeper than mixing lines and no clouds are precipitating. We show that δD0 does not depend on the intensity of entrainment, dampening hope that δD0 measurements could help constrain this long-searched quantity. Based on an isotope-enabled general circulation model simulation, we show that δD0 variations are mainly controlled by mid-tropospheric depletion and rain evaporation in ascending regions, and by sea surface temperature and zorig in subsiding regions. When the air mixing into the SCL is lower in altitude, it is moister, and thus it depletes more efficiently the SCL. In turn, could δD0 measurements help estimate zorig and thus discriminate between different mixing processes? Estimates that are accurate enough to be useful would be difficult to achieve in practice, requiring measuring daily δD profiles, and measuring δD0 with an accuracy of 0.1 ‰ and 0.4 ‰ in trade-wind cumulus and strato-cumulus clouds respectively.

Assessment of single-frequency observations in GNSS Tropospheric Tomography

2020 ◽  
Author(s):  
Robert Weber ◽  
Zohreh Adavi ◽  
Marcus Franz Glaner
Keyword(s):  
Water Vapor ◽  
Low Cost ◽  
Temporal Structure ◽  
Single Frequency ◽  
Dual Frequency ◽  
Alternative Approach ◽  
Spatio Temporal ◽  
Gnss Network ◽  
Vapor Distribution ◽  
Reconstructed Model

<p>Water vapor is one of the most variable components in the Earth’s atmosphere, which has a significant role in the formation of clouds, rain and snow, air pollution and acid rain. Therefore, increasing the accuracy of estimated water vapor can lead to more accurate predictions of severe weather, upcoming storms, and reducing natural hazards. In recent years, GNSS has turned out to be a valuable tool for remotely sensing the atmosphere. GNSS tomography is one of the most valuable tools to reconstruct the Spatio-temporal structure of the troposphere. However, locating dual-frequency receivers with a sufficient spatial resolution for GNSS tomography of a few tens of kilometers is not economically feasible. Therefore, in this research, the feasibility of using single-frequency receivers in GNSS tomography as a possible alternative approach has been investigated. The accuracy of the reconstructed model of water-vapor distribution using low-cost receivers is verified using radiosonde measurements in the area of the EPOSA (Echtzeit Positionierung Austria) GNSS network, which is mostly located in the east part of Austria for the period DoYs 233-246 in 2019.</p>

Regional Assimilation System for Transformed Retrievals from Satellite High-Resolution Infrared Data

2020 ◽  
Vol 59 (7) ◽  
pp. 1171-1193
Author(s):  
Paolo Antonelli ◽  
Tiziana Cherubini ◽  
Steven Businger ◽  
Siebren de Haan ◽  
Paolo Scaccia ◽  
...  
Keyword(s):  
Temperature Field ◽  
Water Vapor ◽  
North Pacific Ocean ◽  
A Priori ◽  
Satellite Sensors ◽  
Forecasting System ◽  
Cycling System ◽  
Priori Information ◽  
The Impact ◽  
Vapor Distribution

AbstractSatellite retrievals strive to exploit the information contained in thousands of channels provided by hyperspectral sensors and show promise in providing a gain in computational efficiency over current radiance assimilation methods by transferring computationally expensive radiative transfer calculations to retrieval providers. This paper describes the implementation of a new approach based on the transformation proposed in 2008 by Migliorini et al., which reduces the impact of the a priori information in the retrievals and generates transformed retrievals (TRs) whose assimilation does not require knowledge of the hyperspectral instruments characteristics. Significantly, the results confirm both the viability of Migliorini’s approach and the possibility of assimilating data from different hyperspectral satellite sensors regardless of the instrument characteristics. The Weather Research and Forecasting (WRF) Model’s Data Assimilation (WRFDA) 3-h cycling system was tested over the central North Pacific Ocean, and the results show that the assimilation of TRs has a greater impact in the characterization of the water vapor distribution than on the temperature field. These results are consistent with the knowledge that temperature field is well constrained by the initial and boundary conditions of the Global Forecast System (GFS), whereas the water vapor distribution is less well constrained in the GFS. While some preliminary results on the comparison between the assimilation with and without TRs in the forecasting system are presented in this paper, additional work remains to explore the impact of the new assimilation approach on forecasts and will be provided in a follow-up publication.

Data validation and mesoscale assimilation of Himawari-8 optimal cloud analysis products

2020 ◽  
Author(s):  
Michiko Otsuka ◽  
Hiromu Seko ◽  
Masahiro Hayashi ◽  
Ko Koizumi
Keyword(s):  
Water Vapor ◽  
Initial Conditions ◽  
Effective Radius ◽  
Data Sets ◽  
Spatiotemporal Resolution ◽  
Cloud Properties ◽  
Nonhydrostatic Model ◽  
Vapor Distribution ◽  
Data Assimilation System ◽  
Cloud Analysis

AbstractHimawari-8 optimal cloud analysis (OCA), which employs all 16 channels of the Advanced Himawari Imager, provides cloud properties such as cloud phase, top pressure, optical thickness, effective radius, and water path. By using OCA, the water vapor distribution can be inferred with high spatiotemporal resolution and with a wide coverage, including over the ocean, which can be useful for improving initial states for prediction of the torrential rainfalls that occur frequently in Japan. OCA products were first evaluated by comparing them with different kinds of data sets (surface, sonde, and ceilometer observations) and with model outputs, to determine their data characteristics. Overall, OCA data were consistent with observations of water clouds with moderate optical thicknesses at low to mid levels. Next, pseudo-relative humidity data were derived from the OCA products, and utilized in assimilation experiments of a few heavy rainfall cases, conducted with the Japan Meteorological Agency’s nonhydrostatic model-based Variational Data Assimilation System. Assimilation of OCA pseudo-relative humidities caused there to be significant differences in the initial conditions of water vapor fields compared to the control, especially where OCA clouds were detected, and their influence lasted relatively long in terms of forecast hours. Impacts of assimilation on other variables, such as wind speed, were also seen. When the OCA data successfully represented low-level inflows from over the ocean, they positively impacted precipitation forecasts at extended forecast times.

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