scholarly journals Observed impact of meso-scale vertical motion on cloudiness

2021 ◽  
Author(s):  
Geet George ◽  
Bjorn Stevens ◽  
Sandrine Bony ◽  
Marcus Klingebiel ◽  
Raphaela Vogel
Keyword(s):  
North Atlantic ◽  
Vertical Velocity ◽  
Vertical Motion ◽  
Controlling Factors ◽  
Cumulus Cloud ◽  
Shallow Cumulus ◽  
Tropical North Atlantic ◽  
Simple Mass ◽  
Meso Scale

AbstractWe use estimates of meso-scale vertical velocity and co-located cloud measurements from the second Next-Generation Aircraft Remote Sensing for Validation campaign (NARVAL2) in the tropical North Atlantic to show the observed impact of meso-scale vertical motion on tropical clouds. Our results not only confirm previously untested hypotheses about the role of dynamics being non-negligible in determining cloudiness, but go further to show that at the meso-scale, the dynamics has a more dominant control on cloudiness variability than thermodynamics. A simple mass-flux estimate reveals that meso-scale vertical velocity at the sub-cloud layer top explains much of the variations in peak shallow cumulus cloud fraction. In contrast, we find that thermodynamic cloud-controlling factors, such as humidity and stability, are unable to explain the variations in cloudiness at the meso-scale. Thus, capturing the observed variability of cloudiness may require not only a consideration of thermodynamic factors, but also dynamic ones such as the meso-scale vertical velocity.

scholarly journals Role of Mixed Layer Dynamics in Tropical North Atlantic Interannual Sea Surface Temperature Variability

2016 ◽  
Vol 29 (22) ◽  
pp. 8083-8101 ◽  
Author(s):  
Allyson Rugg ◽  
Gregory R. Foltz ◽  
Renellys C. Perez
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Atlantic ◽  
Sea Surface ◽  
Shortwave Radiation ◽  
Thermocline Depth ◽  
Equatorial Atlantic ◽  
Tropical North Atlantic ◽  
Sst Anomalies

Abstract This study examines the causes of observed sea surface temperature (SST) anomalies in the tropical North Atlantic between 1982 and 2015. The emphasis is on the boreal winter and spring seasons, when tropical Atlantic SSTs project strongly onto the Atlantic meridional mode (AMM). Results from a composite analysis of satellite and reanalysis data show important forcing of SST anomalies by wind-driven changes in mixed layer depth and shortwave radiation between 5° and 10°N, in addition to the well-known positive wind–evaporation–SST and shortwave radiation–SST feedbacks between 5° and 20°N. Anomalous surface winds also drive pronounced thermocline depth anomalies of opposite signs in the eastern equatorial Atlantic and intertropical convergence zone (ITCZ; 2°–8°N). A major new finding is that there is strong event-to-event variability in the impact of thermocline depth on SST in the ITCZ region, in contrast to the more consistent relationship in the eastern equatorial Atlantic. Much stronger anomalies of meridional wind stress, thermocline depth, and vertical turbulent cooling are found in the ITCZ region during a negative AMM event in 2009 compared to a negative event in 2015 and a positive event in 2010, despite SST anomalies of similar magnitude in the early stages of each event. The larger anomalies in 2009 led to a much stronger and longer-lived event. Possible causes of the inconsistent relationship between thermocline depth and SST in the ITCZ region are discussed, including the preconditioning role of the winter cross-equatorial SST gradient.

The Role of Aerosols in the Evolution of Tropical North Atlantic Ocean Temperature Anomalies

Science ◽  
2009 ◽  
Vol 324 (5928) ◽  
pp. 778-781 ◽  
Author(s):  
A. T. Evan ◽  
D. J. Vimont ◽  
A. K. Heidinger ◽  
J. P. Kossin ◽  
R. Bennartz
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Ocean Temperature ◽  
Temperature Anomalies ◽  
Tropical North Atlantic

scholarly journals Teleconnection mechanisms of northeast Brazil droughts: modeling and empirical evidence

2008 ◽  
Vol 23 (2) ◽  
pp. 115-125 ◽  
Author(s):  
Fred Kucharski ◽  
Dierk Polzin ◽  
Stefan Hastenrath
Keyword(s):  
Numerical Modelling ◽  
North Atlantic ◽  
Wave Train ◽  
Vertical Motion ◽  
Equatorial Pacific ◽  
Intertropical Convergence Zone ◽  
Sea Surface ◽  
North Atlantic Subtropical High ◽  
The North ◽  
Tropical North Atlantic

Targeted numerical modelling experimaents are conducted to complement the previous empirical diagnostics of circulation mechanisms leading from sea surface temperature (SST) departures in the equatorial Pacific in January to anomalies in the March-April rainy season of Brazil's Nordeste. A weak interhemispheric northward directed SST gradient in the Atlantic favors a more southerly position of the hydrostatically controlled low pressure trough, embedded in which is the Intertropical Convergence Zone (ITCZ), which is the main rainbearing system for the Nordeste. In addition, anomalously warm waters in the equatorial Pacific in January tend to be followed by Nordeste drought. The underlying chain of causalities has been explored by empirical diagnostics and numerical modelling. During El Nino years, an upper-tropospheric wave train extends from the equatorial eastern Pacific to the tropical North Atlantic, affecting the patterns of upper-tropospheric topography and divergence, and hence of vertical motion over the Atlantic. This leads to a weaker meridional pressure gradient on the equatorward flank of the North Atlantic subtropical high, weaker North Atlantic tradewinds, an anomalously far northerly ITCZ position and thus Nordeste drought. The previous empirical diagnostics are overall supported by the modelling experiments.

Large-scale vertical motion and its influence on cloudiness

2020 ◽  
Author(s):  
Geet George ◽  
Bjorn Stevens ◽  
Sandrine Bony ◽  
Marcus Klingebiel
Keyword(s):  
Large Scale ◽  
Vertical Motion ◽  
Cumulus Clouds ◽  
Shallow Cumulus ◽  
Integrated Water Vapour ◽  
Thermodynamics And Dynamics ◽  
Lifting Condensation Level ◽  
The Impact ◽  
First Time

<p>This study uses measurements from the <em>Elucidating the Role of Clouds-Circulation Coupling in Climate</em>, EUREC<sup>4</sup>A and the second <em>Next-Generation Aircraft Remote Sensing for Validation</em>, NARVAL2 campaigns to investigate the influence of large-scale environmental conditions on cloudiness. For the first time, these campaigns provide divergence measurements, making it possible to explore the impact of large-scale vertical motions on clouds. We attempt to explain the cloudiness through the varying thermodynamics and dynamics in the different environments.  For most of the NARVAL2 case-studies, cloudiness is poorly related to thermodynamical factors such as sea-surface temperature and lower tropospheric stability. Factors such as integrated water vapour and pressure velocity (ω) at 500 hPa and 700 hPa can be used to distinguish between actively convecting and suppressed regions, but they are not useful in determining the variation in cloudiness among suppressed cases. We find that ω in the boundary layer (up to ∼2 km) has a more direct control on the low-level cloudiness in these regions, than that in the upper layers. We use a simplistic method to show that ω at the lifting condensation level can be used to determine the cloud cover of shallow cumulus clouds. Thus, we argue that cloud schemes in models should not rely only on thermodynamical information, but also on dynamical predictors.</p>

scholarly journals Spatial variation in N<sub>2</sub>-fixation rate and diazotroph activity in the Tropical Atlantic

2006 ◽  
Vol 3 (6) ◽  
pp. 1739-1761
Author(s):  
J. P. Montoya ◽  
M. Voss ◽  
D. G. Capone
Keyword(s):  
Spatial Variation ◽  
Water Column ◽  
North Atlantic ◽  
N2 Fixation ◽  
Substantial Contribution ◽  
Tropical Atlantic ◽  
Fixation Rate ◽  
Tropical North Atlantic ◽  
Insight Into

Abstract. A variety of N2-fixers occur in the tropical Atlantic and these diazotrophs make a substantial contribution to the nitrogen budget of the upper water column. A synthesis of previously published and novel rate measurements for the Tropical North Atlantic provides insight into the role of two different diazotroph groups in supporting N2 fixation in the tropical Atlantic. The overall rate of N2-fixation by the two groups of diazotrophs was similar in the eastern and western parts of the basin, but N2-fixation by \\textit{Trichodesmium} was strongly dominant in the western part of the basin while small diazotrophs played a much larger role to the east of 40° W. The reasons for this shift in dominance are unclear, as is the identity of the small organisms fixing N2 in the water column.

scholarly journals JOANNE: Joint dropsonde Observations of the Atmosphere in tropical North atlaNtic meso-scale Environments

2021 ◽  
Vol 13 (11) ◽  
pp. 5253-5272
Author(s):  
Geet George ◽  
Bjorn Stevens ◽  
Sandrine Bony ◽  
Robert Pincus ◽  
Chris Fairall ◽  
...  
Keyword(s):  
North Atlantic ◽  
Dynamic Environment ◽  
Sampling Strategy ◽  
Trade Wind ◽  
Mesoscale Circulation ◽  
Gridded Data ◽  
Post Processing ◽  
Tropical North Atlantic ◽  
Vertical Spacing ◽  
Meso Scale

Abstract. As part of the EUREC4A field campaign which took place over the tropical North Atlantic during January–February 2020, 1215 dropsondes from the HALO and WP-3D aircraft were deployed through 26 flights to characterize the thermodynamic and dynamic environment of clouds in the trade-wind regions. We present JOANNE (Joint dropsonde Observations of the Atmosphere in tropical North atlaNtic meso-scale Environments), the dataset that contains these dropsonde measurements and the products derived from them. Along with the raw measurement profiles and basic post-processing of pressure, temperature, relative humidity and horizontal winds, the dataset also includes a homogenized and gridded dataset with 10 m vertical spacing. The gridded data are used as a basis for deriving diagnostics of the area-averaged mesoscale circulation properties such as divergence, vorticity, vertical velocity and gradient terms, making use of sondes dropped at regular intervals along a circular flight path. A total of 85 such circles, ∼ 222 km in diameter, were flown during EUREC4A. We describe the sampling strategy for dropsonde measurements during EUREC4A, the quality control for the data, the methods of estimation of additional products from the measurements and the different post-processed levels of the dataset. The dataset is publicly available (https://doi.org/10.25326/246, George et al., 2021b) as is the software used to create it (https://doi.org/10.5281/zenodo.4746312, George, 2021).

Amazon River influence on nitrogen fixation in the western tropical North Atlantic

2019 ◽  
Vol 77 (2) ◽  
pp. 191-213
Author(s):  
Joseph P. Montoya ◽  
Jason P. Landrum ◽  
Sarah C. Weber
Keyword(s):  
North Atlantic ◽  
Suspended Particle ◽  
Dominant Role ◽  
Amazon River ◽  
N Fixation ◽  
Particulate Nitrogen ◽  
Biological N Fixation ◽  
Relative Contribution ◽  
Tropical North Atlantic

We measured rates of N- and C-fixation with a direct tracer method in regions of the western tropical North Atlantic influenced by the Amazon River plume during the high flow period of 2010 (May–June 2010). We found distinct regional variations in N-fixation activity, with the lowest rates in the plume proper and the highest rates in the plume margins and in offshore waters. A comparison of our N- and C-fixation measurements showed that the relative contribution of N-fixation to total primary production increased from the plume core toward oceanic waters, and that most of the C-fixation in this system was supported by sources of nitrogen other than those derived from biological N-fixation, or diazotrophy. We complemented these rate experiments with measurements of the δ15N of suspended particles (δ15PN), which documented the important and often dominant role of diazotrophs in supplying nitrogen to particulate organic matter in the water column. These coupled measurements revealed that small phytoplankton contributed more new nitrogen to the particulate nitrogen pool than larger phytoplankton. We used a habitat classification method to assess the fac- tors that control diazotrophic activity and contribution to the suspended particle pool, both of which increased from the plume toward oceanic waters. Our findings provide an important constraint on the role of the Amazon plume in creating distinct niches and roles for diazotrophs in the nutrient and carbon budgets of the western tropical North Atlantic.

scholarly journals The boundary condition for vertical velocity and its interdependence with surface gas exchange

2017 ◽  
Vol 17 (13) ◽  
pp. 8177-8187 ◽  
Author(s):  
Andrew S. Kowalski
Keyword(s):  
Boundary Condition ◽  
Vertical Velocity ◽  
Molecular Diffusion ◽  
Classical Mechanics ◽  
Vertical Motion ◽  
Diffusive Transport ◽  
Eddy Diffusivities ◽  
Upward Transport ◽  
Definition Of

Abstract. The law of conservation of linear momentum is applied to surface gas exchanges, employing scale analysis to diagnose the vertical velocity (w) in the boundary layer. Net upward momentum in the surface layer is forced by evaporation (E) and defines non-zero vertical motion, with a magnitude defined by the ratio of E to the air density, as w = E/ρ. This is true even right down at the surface where the boundary condition is w|0 = E/ρ|0 (where w|0 and ρ|0 represent the vertical velocity and density of air at the surface). This Stefan flow velocity implies upward transport of a non-diffusive nature that is a general feature of the troposphere but is of particular importance at the surface, where it assists molecular diffusion with upward gas migration (of H2O, for example) but opposes that of downward-diffusing species like CO2 during daytime. The definition of flux–gradient relationships (eddy diffusivities) requires rectification to exclude non-diffusive transport, which does not depend on scalar gradients. At the microscopic scale, the role of non-diffusive transport in the process of evaporation from inside a narrow tube – with vapour transport into an overlying, horizontal airstream – was described long ago in classical mechanics and is routinely accounted for by chemical engineers, but has been neglected by scientists studying stomatal conductance. Correctly accounting for non-diffusive transport through stomata, which can appreciably reduce net CO2 transport and marginally boost that of water vapour, should improve characterisations of ecosystem and plant functioning.

scholarly journals Reconciling Differences Between Large‐Eddy Simulations and Doppler Lidar Observations of Continental Shallow Cumulus Cloud‐Base Vertical Velocity

2019 ◽  
Vol 46 (20) ◽  
pp. 11539-11547 ◽  
Author(s):  
Satoshi Endo ◽  
Damao Zhang ◽  
Andrew M. Vogelmann ◽  
Pavlos Kollias ◽  
Katia Lamer ◽  
...  
Keyword(s):  
Vertical Velocity ◽  
Large Eddy Simulations ◽  
Cloud Base ◽  
Doppler Lidar ◽  
Cumulus Cloud ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Lidar Observations
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