Fractal nature of the planetary boundary layer depth in the trade‐wind cumulus regime

Abstract The adjustment of the trade wind atmospheric boundary layer to an abrupt sea surface warming is investigated using a large-eddy simulation (LES) and two simple bulk models: a mixed-layer model (MLM), and a model based on the mixing-line hypothesis (XLM). The near-surface temperature adjusts in a few hours, faster than can be expected from the characteristic time scales associated with the physical processes at play. The near-surface humidity adjusts more slowly, with a time scale of about a day, and it exhibits an initial decrease before increasing to its equilibrium value. An analysis of the MLM suggests that the initial tendency of humidity and temperature results from the difference in Bowen ratios between the equilibrium and the perturbation. An analysis of the three linear modes of the XLM shows that the fastest-decaying mode adjusts the subcloud-layer buoyancy, with a constructive interaction of all of the physical processes. The second-fastest-decaying mode is an adjustment of the boundary layer thermodynamical structure and the slowest mode adjusts the boundary layer depth. Approximate analytical expressions of the time scales characterizing these linear modes are derived both for the MLM and the XLM. The MLM exhibits no scale separation between the fastest and second-fastest time scales and a scale separation between these and the slowest time scale only in the case of a shallow well-mixed boundary layer. The XLM exhibits a scale separation between the buoyancy adjustment of the subcloud layer and the overall thermodynamic adjustment, while conserving the scale separation with the slower adjustment of the boundary layer depth.

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Evaluating daytime planetary boundary-layer height estimations resolved by both active and passive remote sensing instruments during the CHEESEHEAD19 field campaign

10.5194/amt-2021-363 ◽

2021 ◽

Author(s):

James B. Duncan Jr. ◽

Laura Bianco ◽

Bianca Adler ◽

Tyler Bell ◽

Irina V. Djalalova ◽

...

Keyword(s):

Remote Sensing ◽

Boundary Layer ◽

Planetary Boundary Layer ◽

Spectral Resolution ◽

High Spectral Resolution ◽

Layer Depth ◽

Field Campaign ◽

Atmospheric Modelling ◽

Microwave Radiometers ◽

Wind Profilers

Abstract. During the Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors 2019 (CHEESEHEAD19) field campaign, held in the summer of 2019 in northern Wisconsin, U.S.A., active and passive ground-based remote sensing instruments were deployed to understand the response of the planetary boundary layer to heterogeneous land surface forcing. These instruments include Radar Wind Profilers, Microwave Radiometers, Atmospheric Emitted Radiance Interferometers, Ceilometers, High Spectral Resolution Lidars, Doppler Lidars, and Collaborative Lower Atmospheric Modelling Profiling Systems that combine several of these instruments. In this study, these ground-based remote sensing instruments are used to estimate the height of the daytime planetary boundary layer, and their performance is compared against independent boundary-layer depth estimates obtained from radiosondes launched as part of the field campaign. The impact of clouds (in particular boundary layer clouds) on boundary-layer depth is also investigated. We found that while overall all instruments are able to provide reasonable boundary-layer depth estimates, each of them shows strengths and weaknesses under certain conditions. For example, Radar Wind Profilers perform well during cloud free conditions, and Microwave Radiometers and Atmospheric Emitted Radiance Interferometers have a very good agreement during all conditions, but are limited by the smoothness of the retrieved thermodynamic profiles. The estimates from Ceilometers and High Spectral Resolution Lidars can be hindered by the presence of elevated aerosol layers or clouds, and the multi-instrument retrieval from the Collaborative Lower Atmospheric Modelling Profiling Systems can be constricted to a limited height range in low aerosol conditions.

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Lagrangian simulation of the passive tracer in the convective planetary boundary layer

Proceeding of THMT-15. Proceedings of the Eighth International Symposium On Turbulence Heat and Mass Transfer ◽

10.1615/ichmt.2015.thmt-15.1460 ◽

2015 ◽

Author(s):

Boris B. Ilyushin ◽

I.V Mitin ◽

Dmitrii Ph. Sikovsky

Keyword(s):

Boundary Layer ◽

Planetary Boundary Layer ◽

Passive Tracer ◽

Lagrangian Simulation ◽

Convective Planetary Boundary Layer

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Sensitivity of an Idealized Tropical Cyclone to the Configuration of the Global Forecast System–Eddy Diffusivity Mass Flux Planetary Boundary Layer Scheme

Atmosphere ◽

10.3390/atmos12020284 ◽

2021 ◽

Vol 12 (2) ◽

pp. 284

Author(s):

Evan A. Kalina ◽

Mrinal K. Biswas ◽

Jun A. Zhang ◽

Kathryn M. Newman

Keyword(s):

Boundary Layer ◽

Planetary Boundary Layer ◽

Weather Prediction ◽

Intensity Change ◽

Rapid Intensification ◽

Forecast System ◽

Stability Functions ◽

Non Local ◽

The Stability ◽

Heat And Moisture

The intensity and structure of simulated tropical cyclones (TCs) are known to be sensitive to the planetary boundary layer (PBL) parameterization in numerical weather prediction models. In this paper, we use an idealized version of the Hurricane Weather Research and Forecast system (HWRF) with constant sea-surface temperature (SST) to examine how the configuration of the PBL scheme used in the operational HWRF affects TC intensity change (including rapid intensification) and structure. The configuration changes explored in this study include disabling non-local vertical mixing, changing the coefficients in the stability functions for momentum and heat, and directly modifying the Prandtl number (Pr), which controls the ratio of momentum to heat and moisture exchange in the PBL. Relative to the control simulation, disabling non-local mixing produced a ~15% larger storm that intensified more gradually, while changing the coefficient values used in the stability functions had little effect. Varying Pr within the PBL had the greatest impact, with the largest Pr (~1.6 versus ~0.8) associated with more rapid intensification (~38 versus 29 m s−1 per day) but a 5–10 m s−1 weaker intensity after the initial period of strengthening. This seemingly paradoxical result is likely due to a decrease in the radius of maximum wind (~15 versus 20 km), but smaller enthalpy fluxes, in simulated storms with larger Pr. These results underscore the importance of measuring the vertical eddy diffusivities of momentum, heat, and moisture under high-wind, open-ocean conditions to reduce uncertainty in Pr in the TC PBL.

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