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

2019 ◽  
Vol 19 (19) ◽  
pp. 12235-12260 ◽  
Author(s):  
Camille Risi ◽  
Joseph Galewsky ◽  
Gilles Reverdin ◽  
Florent Brient
Keyword(s):  
Water Vapor ◽  
Isotopic Composition ◽  
General Circulation ◽  
Model Simulation ◽  
Circulation Model ◽  
Horizontal Distribution ◽  
Mixing Processes ◽  
Horizontal Advection ◽  
Tropical Oceans ◽  
Stratocumulus Clouds

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 motivated by the hypothesis that the altitude from which the free tropospheric air originates (zorig) is an important factor: when the air mixing into the SCL is lower in altitude, it is generally moister, and thus it depletes the SCL more efficiently. We extend previous simple box models of the SCL by prescribing the shape of δD vertical profiles as a function of humidity profiles and by accounting for rain evaporation and horizontal advection effects. The model relies on the assumption that δD profiles are steeper than mixing lines, and that the SCL is at steady state, restricting its applications to timescales longer than daily. In the model, δD0 is expressed as a function of zorig, humidity and temperature profiles, surface conditions, a parameter describing the steepness of the δD vertical gradient, and a few parameters describing rain evaporation and horizontal advection effects. We show that δD0 does not depend on the intensity of entrainment, in contrast to several previous studies that had hoped that δD0 measurements could help estimate this 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. In turn, could δD0 measurements help estimate zorig and thus discriminate between different mixing processes? For such isotope-based estimates of zorig to be useful, we would need a precision of a few hundred meters in deep convective regions and smaller than 20 m in stratocumulus regions. To reach this target, we would need daily measurements of δD in the mid-troposphere and accurate measurements of δD0 (accuracy down to 0.1 ‰ in the case of stratocumulus clouds, which is currently difficult to obtain). We would also need information on the horizontal distribution of δD to account for horizontal advection effects, and full δD profiles to quantify the uncertainty associated with the assumed shape for δD profiles. Finally, rain evaporation is an issue in all regimes, even in stratocumulus clouds. Innovative techniques would need to be developed to quantify this effect from observations.

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.

scholarly journals Seasonality of moisture supplies to precipitation over the Third Pole: a stable water isotopic perspective

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Xiaoxin Yang ◽  
Tandong Yao
Keyword(s):  
Water Vapor ◽  
Isotopic Composition ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Potential Effect ◽  
Water Vapor Transport ◽  
The Tibetan Plateau ◽  
Physical Processes ◽  
Large Scale Atmospheric Circulation

Abstract This study integrated isotopic composition in precipitation at 50 stations on and around the Tibetan Plateau (TP) and demonstrated the distinct seasonality of isotopic composition in precipitation across the study period. The potential effect of water vapor isotopes on precipitation isotopes is studied by comparing the station precipitation data with extensive isotopic patterns in atmospheric water vapor, revealing the close linkage between the two. The analysis of contemporary water vapor transport and potential helps confirm the different mechanisms behind precipitation isotopic compositions in different areas, as the southern TP is more closely related to large-scale atmospheric circulation such as local Hadley and summer monsoon circulations during other seasons than winter, while the northern TP is subject to the westerly prevalence and advective moisture supply and precipitation processes. The new data presented in this manuscript also enrich the current dataset for the study of precipitation isotopes in this region and together provide a valuable database for verification of the isotope-integrated general circulation model and explanation of related physical processes.

scholarly journals Comparison of a global-climate model simulation to a cloud-system resolving model simulation for long-term thin stratocumulus clouds

2009 ◽  
Vol 9 (17) ◽  
pp. 6497-6520 ◽  
Author(s):  
S. S. Lee ◽  
J. E. Penner ◽  
M. Wang
Keyword(s):  
General Circulation ◽  
Climate Model ◽  
Model Simulation ◽  
Global Climate Model ◽  
Circulation Model ◽  
Radiation Budget ◽  
Cloud System ◽  
Cloud Base ◽  
Cumulus Clouds ◽  
Stratocumulus Clouds

Abstract. A case of thin, warm marine-boundary-layer (MBL) clouds is simulated by a cloud-system resolving model (CSRM) and is compared to the same case of clouds simulated by a general circulation model (GCM). In this study, the simulation by the CSRM adopts higher resolutions which are generally used in large-eddy simulations (LES) and more advanced microphysics as compared to those by the GCM, enabling the CSRM-simulation to act as a benchmark to assess the simulation by the GCM. Explicitly simulated interactions among the surface latent heat (LH) fluxes, buoyancy fluxes, and cloud-top entrainment lead to the deepening-warming decoupling and thereby the transition from stratiform clouds to cumulus clouds in the CSRM. However, in the simulation by the GCM, these interactions are not resolved and thus the transition to cumulus clouds is not simulated. This leads to substantial differences in liquid water content (LWC) and radiation between simulations by the CSRM and the GCM. When stratocumulus clouds are dominant prior to the transition to cumulus clouds, interactions between supersaturation and cloud droplet number concentration (CDNC) (controlling condensation) and those between rain evaporation and cloud-base instability (controlling cloud dynamics and thereby condensation) determine LWC and thus the radiation budget in the simulation by the CSRM. These interactions result in smaller condensation and thus smaller LWC and reflected solar radiation by clouds in the simulation by the CSRM than in the simulation by the GCM where these interactions are not resolved. The resolved interactions (associated with condensation and the transition to cumulus clouds) lead to better agreement between the CSRM-simulation and observation than that between the GCM-simulation and observation.

scholarly journals Comparison of a global-climate model simulation to a cloud-system resolving model simulation for long-term thin stratocumulus clouds

2009 ◽  
Vol 9 (3) ◽  
pp. 12283-12344 ◽  
Author(s):  
S. S. Lee ◽  
J. E. Penner ◽  
M. Wang
Keyword(s):  
General Circulation ◽  
Climate Model ◽  
Model Simulation ◽  
Global Climate Model ◽  
Circulation Model ◽  
Radiation Budget ◽  
Cloud System ◽  
Cloud Base ◽  
Cumulus Clouds ◽  
Stratocumulus Clouds

Abstract. A case of thin, warm marine-boundary-layer (MBL) clouds is simulated by a cloud-system resolving model (CSRM) and is compared to the same case of clouds simulated by a general circulation model (GCM). In this study, the simulation by the CSRM adopts higher resolutions and more advanced microphysics as compared to those by the GCM, enabling the CSRM-simulation to act as a benchmark to assess the simulation by the GCM. Explicitly simulated interactions among the surface latent heat (LH) fluxes, buoyancy fluxes, and cloud-top entrainment lead to the deepening-warming decoupling and thereby the transition from stratiform clouds to cumulus clouds in the CSRM. However, in the simulation by the GCM, these interactions are not resolved and thus the transition to cumulus clouds is not simulated. This leads to substantial differences in cloud mass and radiation between simulations by the CSRM and the GCM. When stratocumulus clouds are dominant prior to the transition to cumulus clouds, interactions between supersaturation and cloud droplet number concentration (CDNC) (controlling condensation) and those between rain evaporation and cloud-base instability (controlling cloud dynamics and thereby condensation) determine cloud mass and thus the radiation budget in the simulation by the CSRM. These interactions result in smaller condensation and thus smaller cloud mass and reflected solar radiation by clouds in the simulation by the CSRM than in the simulation by the GCM where these interactions are not resolved. The resolved interactions (associated with condensation and the transition to cumulus clouds) lead to better agreement between the CSRM-simulation and observation than that between the GCM-simulation and observation.

scholarly journals Simulation of the isotopic composition of stratospheric water vapour – Part 1: Description and evaluation of the EMAC model

2015 ◽  
Vol 15 (10) ◽  
pp. 5537-5555 ◽  
Author(s):  
R. Eichinger ◽  
P. Jöckel ◽  
S. Brinkop ◽  
M. Werner ◽  
S. Lossow
Keyword(s):  
Isotopic Composition ◽  
Water Vapour ◽  
General Circulation ◽  
Climate Model ◽  
Hydrological Cycle ◽  
Circulation Model ◽  
Isotope Ratios ◽  
Physical Fractionation ◽  
Water Isotopologues ◽  
Stratospheric Water Vapour

Abstract. This modelling study aims at an improved understanding of the processes that determine the water vapour budget in the stratosphere by means of the investigation of water isotope ratios. An additional (and separate from the actual) hydrological cycle has been introduced into the chemistry–climate model EMAC, including the water isotopologues HDO and H218O and their physical fractionation processes. Additionally an explicit computation of the contribution of methane oxidation to H2O and HDO has been incorporated. The model expansions allow detailed analyses of water vapour and its isotope ratio with respect to deuterium throughout the stratosphere and in the transition region to the troposphere. In order to assure the correct representation of the water isotopologues in the model's hydrological cycle, the expanded system has been evaluated in several steps. The physical fractionation effects have been evaluated by comparison of the simulated isotopic composition of precipitation with measurements from a ground-based network (GNIP) and with the results from the isotopologue-enabled general circulation model ECHAM5-wiso. The model's representation of the chemical HDO precursor CH3D in the stratosphere has been confirmed by a comparison with chemical transport models (1-D, CHEM2D) and measurements from radiosonde flights. Finally, the simulated stratospheric HDO and the isotopic composition of water vapour have been evaluated, with respect to retrievals from three different satellite instruments (MIPAS, ACE-FTS, SMR). Discrepancies in stratospheric water vapour isotope ratios between two of the three satellite retrievals can now partly be explained.

scholarly journals Wind forcing of salinity anomalies in the Denmark Strait overflow

Ocean Science ◽  
2011 ◽  
Vol 7 (6) ◽  
pp. 821-834 ◽  
Author(s):  
S. Hall ◽  
S. R. Dye ◽  
K. J. Heywood ◽  
M. R. Wadley
Keyword(s):  
General Circulation ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Mixing Processes ◽  
East Greenland ◽  
The North ◽  
East Greenland Current ◽  
Denmark Strait ◽  
Salinity Anomaly

Abstract. The overflow of dense water from the Nordic Seas to the North Atlantic through Denmark Strait is an important part of the global thermohaline circulation. The salinity of the overflow plume has been measured by an array of current meters across the continental slope off the coast of Angmagssalik, southeast Greenland since September 1998. During 2004 the salinity of the overflow plume changed dramatically; the entire width of the array (70 km) freshened between January 2004 and July 2004, with a significant negative salinity anomaly of about 0.06 in May. The event in May represents a fresh anomaly of over 3 standard deviations from the mean since recording began in 1998. The OCCAM 1/12° Ocean General Circulation Model not only reproduces the 2004 freshening event (r=0.96, p<0.01), but also correlates well with salinity observations over a previous 6 year period (r=0.54, p<0.01), despite the inevitable limitations of a z-coordinate model in representing the mixing processes at and downstream of the Denmark Strait sill. Consequently the physical processes causing the 2004 anomaly and prior variability in salinity are investigated using the model output. Our results reject the hypotheses that the anomaly is caused by processes occurring between the overflow sill and the moorings, or by an increase in upstream net freshwater input. Instead, we show that the 2004 salinity anomaly is caused by an increase in volume flux of low salinity water, with a potential density greater than 27.60 kg m−3, flowing towards the Denmark Strait sill in the East Greenland Current. This is caused by an increase in southward wind stress upstream of the sill at around 75° N 20° W four and a half months earlier, and an associated strengthening of the East Greenland Current.

scholarly journals A Multivariate Empirical Orthogonal Function Method to Construct Nitrate Maps in the Southern Ocean

2018 ◽  
Vol 35 (7) ◽  
pp. 1505-1519 ◽  
Author(s):  
Yu-Chiao Liang ◽  
Matthew R. Mazloff ◽  
Isabella Rosso ◽  
Shih-Wei Fang ◽  
Jin-Yi Yu
Keyword(s):  
Southern Ocean ◽  
General Circulation ◽  
Model Simulation ◽  
Potential Temperature ◽  
Circulation Model ◽  
Empirical Orthogonal Functions ◽  
Cluster Method ◽  
Sampling Strategies ◽  
Data Sampling ◽  
Mean Square Errors

AbstractThe ability to construct nitrate maps in the Southern Ocean (SO) from sparse observations is important for marine biogeochemistry research, as it offers a geographical estimate of biological productivity. The goal of this study is to infer the skill of constructed SO nitrate maps using varying data sampling strategies. The mapping method uses multivariate empirical orthogonal functions (MEOFs) constructed from nitrate, salinity, and potential temperature (N-S-T) fields from a biogeochemical general circulation model simulation Synthetic N-S-T datasets are created by sampling modeled N-S-T fields in specific regions, determined either by random selection or by selecting regions over a certain threshold of nitrate temporal variances. The first 500 MEOF modes, determined by their capability to reconstruct the original N-S-T fields, are projected onto these synthetic N-S-T data to construct time-varying nitrate maps. Normalized root-mean-square errors (NRMSEs) are calculated between the constructed nitrate maps and the original modeled fields for different sampling strategies. The sampling strategy according to nitrate variances is shown to yield maps with lower NRMSEs than mapping adopting random sampling. A k-means cluster method that considers the N-S-T combined variances to identify key regions to insert data is most effective in reducing the mapping errors. These findings are further quantified by a series of mapping error analyses that also address the significance of data sampling density. The results provide a sampling framework to prioritize the deployment of biogeochemical Argo floats for constructing nitrate maps.

scholarly journals Coherent Lagrangian swirls among submesoscale motions

2018 ◽  
Vol 116 (37) ◽  
pp. 18251-18256 ◽  
Author(s):  
F. J. Beron-Vera ◽  
A. Hadjighasem ◽  
Q. Xia ◽  
M. J. Olascoaga ◽  
G. Haller
Keyword(s):  
Nonlinear Dynamics ◽  
General Circulation ◽  
Satellite Altimetry ◽  
Model Simulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Surface Flow ◽  
Flow Data ◽  
Ocean General Circulation ◽  
Coherence Detection

The emergence of coherent Lagrangian swirls (CLSs) among submesoscale motions in the ocean is illustrated. This is done by applying recent nonlinear dynamics tools for Lagrangian coherence detection on a surface flow realization produced by a data-assimilative submesoscale-permitting ocean general circulation model simulation of the Gulf of Mexico. Both mesoscale and submesoscale CLSs are extracted. These extractions prove the relevance of coherent Lagrangian eddies detected in satellite-altimetry–based geostrophic flow data for the arguably more realistic ageostrophic multiscale flow.

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