Comparison of GEOS-5 AGCM planetary boundary layer depths computed with various definitions

McGrath-Spangler, E. L.; Molod, Andrea

doi:10.5194/acp-14-6717-2014

Cited by 46 publications

(37 citation statements)

References 25 publications

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“…2) differences among the three ensemble means are generally similar to the differences described in McGrath-Spangler and Molod (2014). Over land, Method 1 (K h : 2) estimates the greatest PBL depths in both seasons while Method 3 (bulk Ri) estimates lower depths due largely to a better representation of the shallow nighttime PBL.…”

Section: Impact On Model Climatesupporting

confidence: 62%

“…Therefore, the reduction in column dust is an improvement over northwestern Africa in DJF and the increase during JJA is a degradation. This is despite an indication from McGrath-Spangler and Molod (2014) that the bulk Richardson-number-based definition better represents the nocturnal PBL depth over the Sahara than the scalar-diffusivity-based ones. The amount of sea salt aerosol in the atmospheric column (Fig.…”

Section: Impact On Tracer Transportcontrasting

confidence: 42%

“…One way to quantify these processes is with the depth of the PBL. However, multiple PBL depth definitions exist and these estimated depths can vary substantially even when defined using the same atmospheric profile (Seidel et al, 2012;McGrath-Spangler and Molod, 2014). In the GEOS-5 AGCM, the PBL depth is used to calculate the turbulent length scale that is used to estimate the model turbulence at the next time step, making it important to properly estimate this depth and be cognizant of the process interactions affecting the simulated global weather and climate.…”

Section: Discussionmentioning

confidence: 99%

“…This definition is suitable for both convective and stable boundary layers and was shown by McGrath-Spangler and Molod (2014) to produce a more realistic diurnal cycle of PBL depth over many land areas. The bulk Richardson number (Ri b ) is given by…”

Section: Pbl Depth Definitionsmentioning

confidence: 99%

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Impact of planetary boundary layer turbulence on model climate and tracer transport

et al. 2015

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Abstract. Planetary boundary layer (PBL) processes are important for weather, climate, and tracer transport and concentration. One measure of the strength of these processes is the PBL depth. However, no single PBL depth definition exists and several studies have found that the estimated depth can vary substantially based on the definition used. In the Goddard Earth Observing System (GEOS-5) atmospheric general circulation model, the PBL depth is particularly important because it is used to calculate the turbulent length scale that is used in the estimation of turbulent mixing. This study analyzes the impact of using three different PBL depth definitions in this calculation. Two definitions are based on the scalar eddy diffusion coefficient and the third is based on the bulk Richardson number. Over land, the bulk Richardson number definition estimates shallower nocturnal PBLs than the other estimates while over water this definition generally produces deeper PBLs. The near-surface wind velocity, temperature, and specific humidity responses to the change in turbulence are spatially and temporally heterogeneous, resulting in changes to tracer transport and concentrations. Near-surface wind speed increases in the bulk Richardson number experiment cause Saharan dust increases on the order of 1 × 10 −4 kg m −2 downwind over the Atlantic Ocean. Carbon monoxide (CO) surface concentrations are modified over Africa during boreal summer, producing differences on the order of 20 ppb, due to the model's treatment of emissions from biomass burning. While differences in carbon dioxide (CO 2 ) are small in the time mean, instantaneous differences are on the order of 10 ppm and these are especially prevalent at high latitude during boreal winter. Understanding the sensitivity of trace gas and aerosol concentration estimates to PBL depth is important for studies seeking to calculate surface fluxes based on near-surface concentrations and for studies projecting future concentrations.

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Section: Impact On Model Climatesupporting

confidence: 62%

Section: Impact On Tracer Transportcontrasting

confidence: 42%

Section: Discussionmentioning

confidence: 99%

Section: Pbl Depth Definitionsmentioning

confidence: 99%

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Impact of planetary boundary layer turbulence on model climate and tracer transport

et al. 2015

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“…The key aim of the different sections of this review is to identify and discuss some of the critical issues in monitoring shallow ABL, and in particular to help the scientific community address NBL depth variability in detail. Within the ongoing scientific projects related to the boundary layer process studies at the SIRTA observatory, it has been clearly recognized that improvement in the z i retrieval algorithms by determining the z i lying below the full-overlap is an important step to improve numerical models dedicated to the boundary layer process studies in both regional [28][29][30][31] and global scales (e.g., [32]). In general, this is an important aspect for routine monitoring of z i using aerosol LiDAR measurements.…”

Section: Introductionmentioning

confidence: 99%

Monitoring Depth of Shallow Atmospheric Boundary Layer to Complement LiDAR Measurements Affected by Partial Overlap

Pal

2014

Remote Sensing

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Abstract:There is compelling evidence that the incomplete laser beam receiver field-of-view overlap (i.e., partial overlap) of ground-based vertically-pointing aerosol LiDAR restricts the observational range for detecting aerosol layer boundaries to a certain height above the LiDAR. This height varies from one to few hundreds of meters, depending on the transceiver geometry. The range, or height of full overlap, is defined as the minimum distance at which the laser beam is completely imaged onto the detector through the field stop in the receiver optics. Thus, the LiDAR signal below the height of full overlap remains erroneous. In effect, it is not possible to derive the atmospheric boundary layer (ABL) top (z i ) below the height of full overlap using lidar measurements alone. This problem makes determination of the nocturnal z i almost impossible, as the nocturnal z i is often lower than the minimum possible retrieved height due to incomplete overlap of lidar. Detailed studies of the nocturnal boundary layer or of variability of low z i would require changes in the LiDAR configuration such that a complete transceiver overlap could be achieved at a much lower height. Otherwise, improvements in the system configuration or deployment (e.g., scanning LiDAR) are needed. However, these improvements are challenging due to the instrument configuration and the need for Raman channel signal, eye-safe laser transmitter for scanning deployment, etc. This paper presents a brief review of some of the challenges and opportunities in overcoming the partial overlap of the LiDAR transceiver to determine z i below the height of full-overlap using complementary approaches to derive low z i . A comprehensive discussion focusing on four different techniques is presented. These are based on the combined (1) ceilometer and LiDAR; (2) tower-based trace gas (e.g., CO 2 ) concentration profiles and LiDAR measurements; (3) 222 Rn budget approach and LiDAR-derived results; and (4) encroachment model and LiDAR observations.

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Retracted: The impact of a boundary layer height formulation on the GEOS‐5 model climate

McGrath-Spangler

2016

JGR Atmospheres

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Planetary boundary layer (PBL) processes are important for the estimation of surface‐atmosphere exchanges that impact global climate. One way of characterizing the strength of these processes is the PBL depth. In the Goddard Earth Observing System (GEOS‐5) atmospheric general circulation model, the PBL depth is also used in calculating the turbulent length scale, which, in turn, is used in estimating the turbulence and vertical mixing within the model. Therefore, changing the PBL depth definition directly affects the model climate. This study evaluates the climatological model response of two long‐term simulations using different PBL depth definitions. The first definition is based on a bulk Richardson number; the second uses a combination of the same bulk Richardson number definition over land plus a definition based on the turbulent eddy diffusion coefficient over water. The two simulations produce different spatiotemporal patterns of temperature, specific humidity, and wind speed related to the differences in turbulence. The largest differences, as expected, are present over water. Due to differences in atmospheric stability, the relationship between the two PBL depth estimates differ among the majority of the oceans and off the west coasts of continents, affecting the climatic response. Due to its optimization of the climatic response while maintaining a realistic diurnal cycle of PBL depth, the mixed PBL depth configuration is preferred.

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Comparison of GEOS-5 AGCM planetary boundary layer depths computed with various definitions

Cited by 46 publications

References 25 publications

Impact of planetary boundary layer turbulence on model climate and tracer transport

Impact of planetary boundary layer turbulence on model climate and tracer transport

Monitoring Depth of Shallow Atmospheric Boundary Layer to Complement LiDAR Measurements Affected by Partial Overlap

Retracted: The impact of a boundary layer height formulation on the GEOS‐5 model climate

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