Transition Periods in the Diurnally-Varying Atmospheric Boundary Layer Over Land

Angevine, W. M.; Edwards, John M.; Lothon, Marie; LeMone, Margaret A.; Osborne, S.

doi:10.1007/s10546-020-00515-y

Cited by 39 publications

(24 citation statements)

References 109 publications

(132 reference statements)

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“…Angevine et al (2001) have shown that the most extreme day-to-day variations in the duration of the morning transition were found on days with cloud influence at Cabauw tower in the Netherlands. The daytime convective BL over Amazonia is generally cloud influenced and rarely cloud-free (Betts et al, 2009); therefore days with cloud influence during the morning transition stage are not excluded from the analysis.…”

Section: The Morning Transition Boundary Layer and Its Relation To The Afternoon Shdeep Convectionmentioning

confidence: 99%

Morning boundary layer conditions for shallow to deep convective cloud evolution during the dry season in the central Amazon

et al. 2021

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Abstract. Observations of the boundary layer (BL) processes are analyzed statistically for dry seasons of 2 years and in detail, as case studies, for 4 shallow convective days (ShCu) and 4 shallow-to-deep convective days (ShDeep) using a suite of ground-based measurements from the Observation and Modeling of the Green Ocean Amazon (GoAmazon 2014/5) Experiment. The BL stages in ShDeep days, from the nighttime to the cloudy mixing layer stage, are then described in comparison with ShCu days. Atmospheric thermodynamics and dynamics, environmental profiles, and surface turbulent fluxes were employed to compare these two distinct situations for each stage of the BL evolution. Particular attention is given to the morning transition stage, in which the BL changes from stable to unstable conditions in the early morning hours. Results show that the decrease in time duration of the morning transition on ShDeep days is associated with high humidity and well-established vertical wind shear patterns. Higher humidity since nighttime not only contributes to lowering the cloud base during the rapid growth of the BL but also contributes to the balance between radiative cooling and turbulent mixing during nighttime, resulting in higher sensible heat flux in the early morning. The sensible heat flux promotes rapid growth of the well-mixed layer, thus favoring the deeper BL starting from around 08:00 LST (UTC−4 h). Under these conditions, the time duration of morning transition is used to promote convection, having an important effect on the convective BL strength and leading to the formation of shallow cumulus clouds and their subsequent evolution into deep convective clouds. Statistical analysis was used to validate the conceptual model obtained from the case studies. Despite the case-to-case variability, the statistical analyses of the processes in the BL show that the described processes are very representative of cloud evolution during the dry season.

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Section: The Morning Transition Boundary Layer and Its Relation To The Afternoon Shdeep Convectionmentioning

confidence: 99%

Morning boundary layer conditions for shallow to deep convective cloud evolution during the dry season in the central Amazon

et al. 2021

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“…The increase in the number concentration between morning and noon is coincident with the time when surface sensible heat flux becomes positive, the nocturnal BL is eroded and the convective BL is rapidly built (Stull, 1988;Angevine et al, 2020; https://doi.org/10.5194/acp-2021-314 Preprint. Discussion started: 20 April 2021 c Author(s) 2021.…”

Section: Diurnalmentioning

confidence: 99%

How weather events modify aerosol particle size distributions in the Amazon boundary layer

Machado

Franco²,

Kremper

et al. 2021

Preprint

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Abstract. This study evaluates the effect of weather events on the aerosol particle size distribution (PSD) at the Amazon Tall Tower Observatory (ATTO). This research combines in-situ measurements of PSD and remote sensing data of lightning density, brightness temperature, cloud top height, cloud liquid water, and rain rate and vertical velocity. Measurements were obtained by a scanning mobility particle sizers (SMPS), the new generation of GOES satellites (GOES-16), the SIPAM S-band radar, and the LAP 3000 radar wind profiler recently installed at the ATTO-Campina site. The combined data allow exploring changes in PSD due to different meteorological processes. The average diurnal cycle shows a higher abundance of ultrafine particles (NUFP) in the early morning, which is coupled with lower concentrations in Aitken (NAIT) and accumulation (NACC) mode particles. From the early morning to the middle of the afternoon, an inverse behavior is observed, where NUFP decreases and NAIT and NACC increase, reflecting a typical particle growth process. Composite figures show an increase of NUFP before, during, and after lightning was detected by the satellite above ATTO. These findings strongly indicate a close relationship between vertical transport and deep convective clouds. Lightning density is connected with a large increase in NUFP, beginning approximately 100 minutes before the maximum lightning density and reaching peak values around 200 minutes later. In addition, the removal of NACC by convective transport was found. Both the increase in NUFP and the decrease in NACC appear in parallel with the increasing intensity of lightning activity. The NUFP increases exponentially with the thunderstorm intensity. In contrast, NAIT and NACC show a different behavior, decreasing from approximately 100 minutes before the maximum lightning activity and reaching a minimum at the time of maximum lightning activity. The effect of cloud top height, cloud liquid water, and rain rate shows the same behavior, but with different patterns among seasons. The convective processes do not occur continually but are modulated by gravity waves in the range of 1 to 5 hours, creating a complex mechanism of interaction with a succession of updrafts and downdrafts, clouds and clear sky situations. The radar wind profiler measured the vertical distribution of the vertical velocity. These profiles show that downdrafts are mainly located below 10 km, while aircraft observations during the ACRIDICON-CHUVA campaign had shown maximum concentrations of ultrafine particles mainly above 10 km. Our study opens new scientific questions to be evaluated in order to understand the intricate physical and chemical mechanisms involved in the production of new particles in Amazonia.

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“…The morning transition (MT) is of interest for weather and air quality forecast as it impacts the distribution of temperature, humidity, and pollutants in the developing CBL (e.g., Holtslag et al., 2013; Morbidelli et al., 2011). Nevertheless, it is difficult to investigate and understand since important drivers including advection, shear, and entrainment are typically simplified or neglected (Angevine et al., 2020; Bange et al., 2007; Wildmann et al., 2015).…”

Section: Introductionmentioning

confidence: 99%

Revealing the Morning Transition in the Mountain Boundary Layer Using Fiber‐Optic Distributed Temperature Sensing

Fritz

Lapo

Freundorfer

et al. 2021

Geophysical Research Letters

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In the morning, the nocturnal stable boundary layer, SBL, transitions into its daytime convective counterpart substantially impacting the distribution of temperature, humidity, and pollutants. Applying distributed temperature sensing (DTS) below a tethered balloon (2–200 m) and along a tower (0–11 m), for the first time we observed three morning transitions (MTs) in a mountain boundary layer with high temporal (<10 s) and spatial (<0.25 m) resolutions. We show that MTs are best derived from a change in static stability from synchronous DTS observations. Our findings confirm that the MT occurs at the SBL top and bottom simultaneously, and identify horizontal heat advection as a main driver aiding solar surface heating in this midrange mountain valley. We conclude that heterogenous land use and mountainous topography cause complex interactions between valley‐scale and local airflows leading to thermal signatures characterized by strong, small‐scale variability. Our study highlights DTS as a crucial tool for investigating complex thermodynamic processes.

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Transition Periods in the Diurnally-Varying Atmospheric Boundary Layer Over Land

Cited by 39 publications

References 109 publications

Morning boundary layer conditions for shallow to deep convective cloud evolution during the dry season in the central Amazon

Morning boundary layer conditions for shallow to deep convective cloud evolution during the dry season in the central Amazon

How weather events modify aerosol particle size distributions in the Amazon boundary layer

Revealing the Morning Transition in the Mountain Boundary Layer Using Fiber‐Optic Distributed Temperature Sensing

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