Challenges in Mesoscale Prediction of a Nocturnal Stratocumulus-Topped Marine Boundary Layer and Implications for Operational Forecasting

Abstract A numerical study using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) was performed to assess the impact of initial and boundary conditions, the parameterization of turbulence transfer and its coupling with cloud-driven radiation, and cloud microphysical processes on the accuracy of mesoscale predictions and forecasts of the cloud-capped marine boundary layer. Aircraft, buoy, and satellite data and the large eddy simulation (LES) results during the Dynamics and Chemistry of Marine Stratocumulus field experiment (DYCOMS II) in July 2001 were used in the assessment. Three of the tested input fields (Eta, NCEP, and ECMWF) show deficiencies, mainly in the thermodynamic structure of the lowest 1500 m of the marine atmosphere. On a positive note, the simulated marine-layer depth showed good agreement with aircraft observations using the Eta fields, while using the NCEP and ECMWF datasets underestimated the marine-layer depth by about 20%–30%. The predicted turbulence kinetic energy (inversion strength) was about 50% of that obtained from the LES results (aircraft observed). As a consequence of moisture overprediction, the predicted liquid water path was twice the observed by 1–2 g kg−1. The sensitivity tests have shown that the selections of turbulence and cloud microphysical schemes significantly influence the turbulence estimates and cloud parameters. Two of the tested turbulence schemes (Eta PBL and Burk–Thompson) did not exhibit the coupling with radiation. The significant differences in the simulated turbulence estimates appear to be a consequence of the use of water-conserving potential temperature variables. The microphysical parameterization, which uses the number concentration of cloud drops in the autoconversion process, simulates a realistic evolution of precipitable hydrometeors in the cloudy marine layer on the positive side, but on the other hand enhances the decoupling in the turbulence structure. This study can provide guidance to operational forecasters concerning accuracy issues of the commonly used large-scale analyses for model initialization, and optimal selection of model parameterizations in order to simulate and forecast the cloudy atmospheric boundary layer over the ocean.

Download Full-text

Characterization of a boreal convective boundary layer and its impact on atmospheric chemistry during HUMPPA-COPEC-2010

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-9335-2012 ◽

2012 ◽

Vol 12 (19) ◽

pp. 9335-9353 ◽

Cited By ~ 30

Author(s):

H. G. Ouwersloot ◽

J. Vilà-Guerau de Arellano ◽

A. C. Nölscher ◽

M. C. Krol ◽

L. N. Ganzeveld ◽

...

Keyword(s):

Boundary Layer ◽

Atmospheric Chemistry ◽

Convective Boundary Layer ◽

Large Scale ◽

Spatial Scales ◽

Potential Temperature ◽

Chemical Species ◽

Convective Boundary ◽

The Impact

Abstract. We studied the atmospheric boundary layer (ABL) dynamics and the impact on atmospheric chemistry during the HUMPPA-COPEC-2010 campaign. We used vertical profiles of potential temperature and specific moisture, obtained from 132 radio soundings, to determine the main boundary layer characteristics during the campaign. We propose a classification according to several main ABL prototypes. Further, we performed a case study of a single day, focusing on the convective boundary layer, to analyse the influence of the dynamics on the chemical evolution of the ABL. We used a mixed layer model, initialized and constrained by observations. In particular, we investigated the role of large scale atmospheric dynamics (subsidence and advection) on the ABL development and the evolution of chemical species concentrations. We find that, if the large scale forcings are taken into account, the ABL dynamics are represented satisfactorily. Subsequently, we studied the impact of mixing with a residual layer aloft during the morning transition on atmospheric chemistry. The time evolution of NOx and O3 concentrations, including morning peaks, can be explained and accurately simulated by incorporating the transition of the ABL dynamics from night to day. We demonstrate the importance of the ABL height evolution for the representation of atmospheric chemistry. Our findings underscore the need to couple the dynamics and chemistry at different spatial scales (from turbulence to mesoscale) in chemistry-transport models and in the interpretation of observational data.

Download Full-text

The Effects of Environmental Wind Shear Direction on Tropical Cyclone Boundary Layer Thermodynamics and Intensity Change from Multiple Observational Datasets

Monthly Weather Review ◽

10.1175/mwr-d-21-0022.1 ◽

2021 ◽

Author(s):

Joshua B. Wadler ◽

Joseph J. Cione ◽

Jun A. Zhang ◽

Evan A. Kalina ◽

John Kaplan

Keyword(s):

Boundary Layer ◽

Tropical Cyclone ◽

Wind Shear ◽

Large Scale ◽

Deep Layer ◽

Potential Temperature ◽

Intensity Change ◽

Asymmetric Distribution ◽

Shear Direction ◽

The Impact

AbstractThe relationship between deep-layer environmental wind shear direction and tropical cyclone (TC) boundary layer thermodynamic structures is explored in multiple independent databases. Analyses derived from the tropical cyclone buoy database (TCBD) show that when TCs experience northerly-component shear, the 10-m equivalent potential temperature (θe) tends to be more symmetric than when shear has a southerly component. The primary asymmetry in θe in TCs experiencing southerly-component shear is radially outwards from twice the radius of maximum wind speed, with the left-of-shear quadrants having lower θe by 4–6 K than the right-of-shear quadrants. As with the TCBD, an asymmetric (symmetric) distribution of 10-m θe for TCs experiencing southerly-component (northerly-component) shear was found using composite observations from dropsondes. These analyses show that differences in the degree of symmetry near the sea surface extend through the depth of the boundary layer. Additionally, mean dropsonde profiles illustrate that TCs experiencing northerly-component shear are more potentially unstable between 500 m and 1000 m altitude, signaling a more favorable environment for the development of surface-based convection in rainband regions.Analyses from the Statistical Hurricane Intensity Prediction Scheme (SHIPS) Database show that subsequent strengthening (weakening) for TCs in the Atlantic Basin preferentially occurs in northerly-component (southerly-component) deep-layer environmental wind shear environments which further illustrates that the asymmetric distribution of boundary layer thermodynamics is unfavorable for TC intensification. These differences emphasize the impact of deep-layer wind shear direction on TC intensity changes which likely result from the superposition of large-scale advection with the shear-relative asymmetries in TC structure.

Download Full-text

Characterization of a boreal convective boundary layer and its impact on atmospheric chemistry during HUMPPA-COPEC-2010

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-13619-2012 ◽

2012 ◽

Vol 12 (6) ◽

pp. 13619-13665 ◽

Cited By ~ 2

Author(s):

H. G. Ouwersloot ◽

J. Vilà-Guerau de Arellano ◽

A. C. Nölscher ◽

M. C. Krol ◽

L. N. Ganzeveld ◽

...

Keyword(s):

Boundary Layer ◽

Atmospheric Chemistry ◽

Convective Boundary Layer ◽

Large Scale ◽

Spatial Scales ◽

Potential Temperature ◽

Chemical Species ◽

Convective Boundary ◽

Systematic Analysis ◽

The Impact

Abstract. We studied the atmospheric boundary layer (ABL) dynamics and the impact on atmospheric chemistry during the HUMPPA-COPEC-2010 campaign. We used vertical profiles of potential temperature and specific moisture, obtained from 132 radio soundings, to determine the main boundary layer characteristics during the campaign. We propose a classification according to several main ABL prototypes. Further, we performed a case study of a single day characterized as a convective boundary layer to analyse the influence of the dynamics on the chemical evolution of the ABL, using a systematic analysis that can easily be extended to other periods during HUMPPA-COPEC-2010. We used a mixed layer model, initialized and constrained by observations. In particular, we investigated the role of large scale atmospheric dynamics (subsidence and advection) on the ABL development and the evolution of chemical species concentrations. We find that, if the large scale forcings are taken into account, the ABL dynamics are represented satisfactorily. Subsequently, we studied the impact of mixing with a residual layer aloft during the morning transition on atmospheric chemistry. The time evolution of NOx and O3 concentrations, including morning peaks, can be explained and accurately simulated by incorporating the transition of the ABL dynamics from night to day. We demonstrate the importance of the ABL height evolution for the representation of atmospheric chemistry. Our findings underscore the need to couple the dynamics and chemistry at different spatial scales (from turbulence to mesoscale) in chemistry-transport models and in the interpretation of observational data.

Download Full-text

Spatio-temporal variability of the atmospheric boundary layer depth over the Paris agglomeration: An assessment of the impact of the urban heat island intensity

Atmospheric Environment ◽

10.1016/j.atmosenv.2012.09.046 ◽

2012 ◽

Vol 63 ◽

pp. 261-275 ◽

Cited By ~ 70

Author(s):

S. Pal ◽

I. Xueref-Remy ◽

L. Ammoura ◽

P. Chazette ◽

F. Gibert ◽

...

Keyword(s):

Boundary Layer ◽

Atmospheric Boundary Layer ◽

Urban Heat Island ◽

Temporal Variability ◽

Urban Heat Island Intensity ◽

Heat Island ◽

Layer Depth ◽

Urban Heat ◽

Spatio Temporal ◽

The Impact

Download Full-text

Contrasting characteristics of open- and closed- cellular stratocumulus cloud in the Eastern North Atlantic

10.5194/acp-2021-63 ◽

2021 ◽

Author(s):

Michael P. Jensen ◽

Virendra P. Ghate ◽

Dié Wang ◽

Diana K. Apoznanski ◽

Mary J. Bartholomew ◽

...

Keyword(s):

Boundary Layer ◽

North Atlantic ◽

Large Scale ◽

Marine Boundary Layer ◽

Open Cell ◽

Cold Air ◽

Closed Cell ◽

Boundary Layer Cloud ◽

Eastern North Atlantic ◽

Layer Cloud

Abstract. Extensive regions of marine boundary layer cloud impact the radiative balance through their significant shortwave albedo while having little impact on outgoing longwave radiation. Despite this importance, these cloud systems remain poorly represented in large-scale models due to difficulty in representing the processes that drive their lifecycle and coverage. In particular, the mesoscale organization, and cellular structure of marine boundary clouds has important implications for the subsequent cloud feedbacks. In this study, we use long-term (2013–2018) observations from the Atmospheric Radiation Measurement (ARM) Facility's Eastern North Atlantic (ENA) site on Graciosa Island, Azores, Portugal to identify cloud cases with open- or closed-cellular organization. More than 500 hours of each organization type are identified. The ARM observations are combined with reanalysis and satellite products to quantify the cloud, precipitation, aerosol, thermodynamic and large-scale synoptic characteristics associated with these cloud types. Our analysis shows that both cloud organization populations occur during similar sea surface temperature conditions, but the open-cell cases are distinguished by stronger cold-air advection and large-scale subsidence compared to the closed-cell cases, consistent with their formation during cold-air outbreaks. We also find that the open-cell cases were associated with deeper boundary layers, stronger low-level winds, and higher-rain rates compared to their closed-cell counterparts. Finally, raindrops with diameters larger than one millimeter were routinely recorded at the surface during both populations, with a higher number of large drops during the open-cellular cases. The similarities and differences noted herein provide important insights into the environmental and cloud characteristics during varying marine boundary layer cloud mesoscale organization and will be useful for the evaluation of model simulations for ENA marine clouds.

Download Full-text

Ensemble forecasting with a stochastic convective parametrization based on equilibrium statistics

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-30457-2011 ◽

2011 ◽

Vol 11 (11) ◽

pp. 30457-30485 ◽

Cited By ~ 3

Author(s):

P. Groenemeijer ◽

G. C. Craig

Keyword(s):

Large Scale ◽

Mesoscale Model ◽

Initial Conditions ◽

Deep Convection ◽

Horizontal Resolution ◽

Ensemble Forecasting ◽

Total Variance ◽

Ensemble Prediction ◽

Ensemble Prediction System ◽

The Impact

Abstract. The stochastic Plant-Craig scheme for deep convection was implemented in the COSMO mesoscale model and used for ensemble forecasting. Ensembles consisting of 100 48 h forecasts at 7 km horizontal resolution were generated for a 2000 × 2000 km domain covering central Europe. Forecasts were made for seven case studies and characterized by different large-scale meteorological environments. Each 100 member ensemble consisted of 10 groups of 10 members, with each group driven by boundary and initial conditions from a selected member from the global ECMWF Ensemble Prediction System. The precipitation variability within and among these groups of members was computed, and it was found that the relative contribution to the ensemble variance introduced by the stochastic convection scheme was substantial, amounting to as much as 76% of the total variance in the ensemble in one of the studied cases. The impact of the scheme was not confined to the grid scale, and typically contributed 25–50% of the total variance even after the precipitation fields had been smoothed to a resolution of 35 km. The variability of precipitation introduced by the scheme was approximately proportional to the total amount of convection that occurred, while the variability due to large-scale conditions changed from case to case, being highest in cases exhibiting strong mid-tropospheric flow and pronounced meso- to synoptic scale vorticity extrema. The stochastic scheme was thus found to be an important source of variability in precipitation cases of weak large-scale flow lacking strong vorticity extrema, but high convective activity.

Download Full-text

Contrasting characteristics of open- and closed-cellular stratocumulus cloud in the eastern North Atlantic

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-14557-2021 ◽

2021 ◽

Vol 21 (19) ◽

pp. 14557-14571

Author(s):

Michael P. Jensen ◽

Virendra P. Ghate ◽

Dié Wang ◽

Diana K. Apoznanski ◽

Mary J. Bartholomew ◽

...

Keyword(s):

Boundary Layer ◽

North Atlantic ◽

Large Scale ◽

Marine Boundary Layer ◽

Open Cell ◽

Cold Air ◽

Closed Cell ◽

Boundary Layer Cloud ◽

Eastern North Atlantic ◽

Layer Cloud

Abstract. Extensive regions of marine boundary layer cloud impact the radiative balance through their significant shortwave albedo while having little impact on outgoing longwave radiation. Despite this importance, these cloud systems remain poorly represented in large-scale models due to difficulty in representing the processes that drive their life cycle and coverage. In particular, the mesoscale organization and cellular structure of marine boundary clouds have important implications for the subsequent cloud feedbacks. In this study, we use long-term (2013–2018) observations from the Atmospheric Radiation Measurement (ARM) Facility's Eastern North Atlantic (ENA) site on Graciosa Island, Azores, Portugal, to identify cloud cases with open- or closed-cellular organization. More than 500 h of each organization type are identified. The ARM observations are combined with reanalysis and satellite products to quantify the cloud, precipitation, aerosol, thermodynamic, and large-scale synoptic characteristics associated with these cloud types. Our analysis shows that both cloud organization populations occur during similar sea surface temperature conditions, but the open-cell cases are distinguished by stronger cold-air advection and large-scale subsidence compared to the closed-cell cases, consistent with their formation during cold-air outbreaks. We also find that the open-cell cases were associated with deeper boundary layers, stronger low-level winds, and higher rain rates compared to their closed-cell counterparts. Finally, raindrops with diameters larger than 1 mm were routinely recorded at the surface during both populations, with a higher number of large drops during the open-cellular cases. The similarities and differences noted herein provide important insights into the environmental and cloud characteristics during varying marine boundary layer cloud mesoscale organization and will be useful for the evaluation of model simulations for ENA marine clouds.

Download Full-text

Large-Scale Structure of the June–July 1996 Marine Boundary Layer along California and Oregon

Monthly Weather Review ◽

10.1175/1520-0493(2000)128<1632:lssotj>2.0.co;2 ◽

2000 ◽

Vol 128 (6) ◽

pp. 1632-1652 ◽

Cited By ~ 57

Author(s):

C. E. Dorman ◽

T. Holt ◽

D. P. Rogers ◽

K. Edwards

Keyword(s):

Boundary Layer ◽

Large Scale ◽

Marine Boundary Layer ◽

Large Scale Structure ◽

Scale Structure ◽

June July

Download Full-text

How is the marine atmospheric boundary layer turbulence organized in the trades ?

10.5194/egusphere-egu21-12339 ◽

2021 ◽

Author(s):

Pierre-Etienne Brilouet ◽

Marie Lothon ◽

Sandrine Bony

Keyword(s):

Boundary Layer ◽

Atmospheric Boundary Layer ◽

Vertical Velocity ◽

Large Scale ◽

Layer Structure ◽

Potential Temperature ◽

Surface Wind ◽

Cloud Amount ◽

Velocity Spectrum ◽

Marine Atmospheric Boundary Layer

Tradewind clouds can exhibit a wide diversity of mesoscale organizations, and the turbulence of marine atmospheric boundary layer (MABL) can exhibit coherent structures and mesoscale circulations. One of the objectives of the EUREC4A (Elucidating the role of cloud-circulation coupling in climate) field experiment was to better understand the tight interplay between the mesoscale organization of clouds, boundary-layer processes, and the large-scale environment.During the experiment, that took place East of Barbados over the Western Tropical Atlantic Ocean in Jan-Feb 2020, the French ATR-42 research aircraft was devoted to the characterization of the cloud amount and of the subcoud layer structure. During its 17 research flights, it sampled a large diversity of large scale conditions and cloud patterns. Multiple sensors onboard the aircraft measured high-frequency fluctuations of potential temperature, water vapour mixing ratio and wind , allowing for an extensive characterization of the turbulence within the subcloud layer. A quality-controled and calibrated turbulence dataset was produced on the basis of these measurements, which is now available on the EUREC4A AERIS data portal.The MABL turbulent structure is studied using this dataset, through a spectral analysis of the vertical velocity. Vertical profiles of characteristic length scales reveal a non-isotropic structure with a stretching of the eddies along the mean wind. The organization strength of the turbulent field is also explored by defining a diagnostic based on the shape of the vertical velocity spectrum. The structure and the degree of organization of the subcloud layer are characterized for different types of mesoscale convective pattern and as a function of the large-scale environment, including near-surface wind and lower-tropospheric stability conditions.&#160;

Download Full-text

Dynamics of Aeolian Sand Streamers and Airflow Turbulence over a Beach Surface

10.5194/egusphere-egu21-5481 ◽

2021 ◽

Author(s):

Andreas Baas

Keyword(s):

Boundary Layer ◽

Turbulent Boundary Layer ◽

Temporal Variability ◽

Large Scale ◽

Sonic Anemometer ◽

Dynamic Structure ◽

Sand Transport ◽

Video Imagery ◽

Spatio Temporal ◽

The Impact

Sand transport by wind over granular beds displays dynamic structure and organisation in the form of streamers (aka &#8216;sand snakes&#8217;) that appear, meander and intertwine, and then dissipate as they are advected downwind. These patterns of saltating grain populations are thought to be initiated and controlled by coherent flow structures in the turbulent boundary layer wind that scrape over the bed surface raking up sand into entrainment. Streamer behaviour is thus fundamental to understanding sand transport dynamics, in particular its strong spatio-temporal variability, and is equally relevant to granular transport in other geophysical flows (fluvial, submarine).This paper presents findings on streamer dynamics and associated wind turbulence observed in a field experiment on a beach, with measurements from 30Hz video-imagery using Large-Scale Particle Image Velocimetry (LS-PIV), combined with 50Hz wind measurements from 3D sonic anemometry and co-located sand transport rate monitoring using an array of laser particle counters (&#8216;Wenglors&#8217;), all taking place over an area of ~10 m2 and over periods of several minutes. The video imagery was used to identify when and where streamers advected past the sonic anemometer and laser sensors so that relationships could be detected between the passage of turbulence structures in the airflow and the length- and time-scales, propagation speeds, and sand transport intensities of associated streamers. The findings form the basis for a phenomenological model of streamer dynamics under turbulent boundary layer flows that predicts the impact of spatio-temporal variability on local measurement of sand transport.

Download Full-text