Comments on: ‘The Neutral, Barotropic Planetary Boundary Layer, Capped by a Low-Level Inversion’ by G. D. Hess, Boundary-Layer Meteorology (2004) 110, pp. 319–355

2006 ◽  
Vol 119 (1) ◽  
pp. 171-179 ◽  
Author(s):  
Juan Carlos Bergmann
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Low Level ◽  
Boundary Layer Meteorology ◽  
Level Inversion

scholarly journals Impacts of Modifications to a Local Planetary Boundary Layer Scheme on Forecasts of the Great Plains Low-Level Jet Environment

2018 ◽  
Vol 33 (5) ◽  
pp. 1109-1120 ◽  
Author(s):  
David E. Jahn ◽  
William A. Gallus
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Planetary Boundary Layer ◽  
Great Plains ◽  
Potential Temperature ◽  
Specific Humidity ◽  
Low Level ◽  
Stable Conditions ◽  
Pbl Scheme ◽  
Low Level Jet

Abstract The Great Plains low-level jet (LLJ) is influential in the initiation and evolution of nocturnal convection through the northward advection of heat and moisture, as well as convergence in the region of the LLJ nose. However, accurate numerical model forecasts of LLJs remain a challenge, related to the performance of the planetary boundary layer (PBL) scheme in the stable boundary layer. Evaluated here using a series of LLJ cases from the Plains Elevated Convection at Night (PECAN) program are modifications to a commonly used local PBL scheme, Mellor–Yamada–Nakanishi–Niino (MYNN), available in the Weather Research and Forecasting (WRF) Model. WRF forecast mean absolute error (MAE) and bias are calculated relative to PECAN rawinsonde observations. The first MYNN modification invokes a new set of constants for the scheme closure equations that, in the vicinity of the LLJ, decreases forecast MAEs of wind speed, potential temperature, and specific humidity more than 19%. For comparison, the Yonsei University (YSU) scheme results in wind speed MAEs 22% lower but specific humidity MAEs 17% greater than in the original MYNN scheme. The second MYNN modification, which incorporates the effects of potential kinetic energy and uses a nonzero mixing length in stable conditions as dependent on bulk shear, reduces wind speed MAEs 66% for levels below the LLJ, but increases MAEs at higher levels. Finally, Rapid Refresh analyses, which are often used for forecast verification, are evaluated here and found to exhibit a relatively large average wind speed bias of 3 m s−1 in the region below the LLJ, but with relatively small potential temperature and specific humidity biases.

scholarly journals Evaluation of Planetary Boundary Layer Parameterizations in Tropical Cyclones by Comparison of In Situ Observations and High-Resolution Simulations of Hurricane Isabel (2003). Part II: Inner-Core Boundary Layer and Eyewall Structure

2009 ◽  
Vol 137 (11) ◽  
pp. 3675-3698 ◽  
Author(s):  
David S. Nolan ◽  
Daniel P. Stern ◽  
Jun A. Zhang
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Boundary Layers ◽  
Planetary Boundary Layer ◽  
Inner Core ◽  
Model Simulation ◽  
Low Level ◽  
Pbl Parameterization ◽  
Hurricane Isabel

Abstract This is the second of a two-part study of the representation of the planetary boundary layer (PBL) in high-resolution Weather Research and Forecast Model (WRF) simulations of Hurricane Isabel (2003). The Yonsei University (YSU) PBL parameterization and the Mellor–Yamada–Janjić (MYJ) PBL parameterization are evaluated by direct comparison to in situ data obtained by research aircraft. The numerical model, simulation design, details of the PBL schemes, and the representation of the boundary layer in the outer-core were presented in Part I. This part presents a detailed study of the inner-core PBL, including its axisymmetric and asymmetric structures, and comparisons to analyses of dropsonde data from previous studies. Although neither PBL scheme was designed specifically for hurricane conditions, their simulated boundary layers are reasonably good representations of the observed boundary layer. Both schemes reproduce certain unique features of the hurricane boundary layer, such as the separate depths of the well-mixed layer and the inflow layer, and the pronounced wind speed maxima near the top of the inflow layer. Modification of the original YSU and MYJ schemes to have ocean roughness lengths more in agreement with recent studies considerably improves the results of both schemes. Even with these improvements, the MYJ consistently produces larger frictional tendencies in the boundary layer than the YSU scheme, leading to a stronger low-level inflow and a stronger azimuthal wind maximum at the top of the boundary layer. For both schemes, differences in the low-level asymmetries between the simulated and observed wind fields appear to be related to eyewall asymmetries forced by environmental wind shear. The effects of varying horizontal and vertical resolutions are also considered. Increasing the vertical resolution in the PBL results in minor improvements in the inner-core structures. Increasing the horizontal resolution around the eyewall also leads to improved boundary layers, as well as an improvement of the vertical structure of the inner-core wind field. A summary and discussion of the results of both Parts I and II is provided.

Characteristics of Nocturnal Low-Level Jets Observed in the North Florida Area

2009 ◽  
Vol 137 (8) ◽  
pp. 2605-2621 ◽  
Author(s):  
Anandakumar Karipot ◽  
Monique Y. Leclerc ◽  
Gengsheng Zhang
Keyword(s):  
Boundary Layer ◽  
Interannual Variability ◽  
Planetary Boundary Layer ◽  
Hilbert Huang Transform ◽  
Low Level ◽  
The North ◽  
Low Level Jets ◽  
Regional Reanalysis ◽  
Sodar Measurements ◽  
Jet Characteristics

Abstract The seasonal and interannual variability of the nocturnal low-level jets over the north Florida region are investigated using sodar measurements spanning 540 nights. On average, jets are present in 62% of the nocturnal periods examined. The observed jet speeds range between 3 and 21 m s−1 and heights are between 80 and 700 m. Observations show that the low-level jet occurs more frequently (70% of the nocturnal periods) during the colder months November–February in contrast with the warmer months June–August (∼47%). The presence of southerly jets dominates the summer months, whereas northerly jets are more frequent during winter. Colder months frequently exhibit jets with speeds exceeding 14 m s−1, often associated with the passage of frontal systems. The interannual variability observed using the North American Regional Reanalysis (NARR) wind profile data during a 4-yr period shows only minimal differences in jet characteristics. A comparison of jet heights with NARR planetary boundary layer heights suggests that jets at the north Florida location frequently occur within the planetary boundary layer. The occurrence and speed of observed low-level jets are linked to both the land–ocean temperature contrast and to the strength and orientation of surface pressure gradients over the region. A high occurrence of large-amplitude oscillations with approximately a 24-h period near the jet height is shown using the Hilbert–Huang transform analysis, suggesting that inertial oscillations are one possible cause of jet formation in north Florida.

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

Atmosphere ◽  
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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