Boundary Layer Dynamics in a Simple Model for Convectively Coupled Gravity Waves

Abstract A simplified model of intermediate complexity for convectively coupled gravity waves that incorporates the bulk dynamics of the atmospheric boundary layer is developed and analyzed. The model comprises equations for velocity, potential temperature, and moist entropy in the boundary layer as well as equations for the free tropospheric barotropic (vertically uniform) velocity and first two baroclinic modes of vertical structure. It is based on the multicloud model of Khouider and Majda coupled to the bulk boundary layer–shallow cumulus model of Stevens. The original multicloud model has a purely thermodynamic boundary layer and no barotropic velocity mode. Here, boundary layer horizontal velocity divergence is matched with barotropic convergence in the free troposphere and yields environmental downdrafts. Both environmental and convective downdrafts act to transport dry midtropospheric air into the boundary layer. Basic states in radiative–convective equilibrium are found and are shown to be consistent with observations of boundary layer and free troposphere climatology. The linear stability of these basic states, in the case without rotation, is then analyzed for a variety of tropospheric regimes. The inclusion of boundary layer dynamics—specifically, environmental downdrafts and entrainment of free tropospheric air—enhances the instability of both the synoptic-scale moist gravity waves and nonpropagating congestus modes in the multicloud model. The congestus mode has a preferred synoptic-scale wavelength, which is absent when a purely thermodynamic boundary layer is employed. The weak destabilization of a fast mesoscale wave, with a phase speed of 26 m s−1 and coupling to deep convection, is also discussed.

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Occurrence and growth of sub-50 nm aerosol particles in the Amazonian boundary layer

10.5194/acp-2021-765 ◽

2021 ◽

Author(s):

Marco A. Franco ◽

Florian Ditas ◽

Leslie Ann Kremper ◽

Luiz A. T. Machado ◽

Meinrat O. Andreae ◽

...

Keyword(s):

Boundary Layer ◽

Meteorological Data ◽

Cloud Condensation Nuclei ◽

Deep Convection ◽

Potential Temperature ◽

Meteorological Conditions ◽

Subsequent Growth ◽

Wet Season ◽

Particle Injection ◽

Continuous Growth

Abstract. New particle formation (NPF), referring to the nucleation of molecular clusters and their subsequent growth into the cloud condensation nuclei (CCN) size range, is a globally significant and climate-relevant source of atmospheric aerosols. Classical NPF exhibiting continuous growth from a few nanometers to the Aitken mode around 60–70 nm is widely observed in the planetary boundary layer (PBL) around the world, but not in central Amazonia. Here, classical NPF events are rarely observed in the PBL, but instead, NPF begins in the upper troposphere (UT), followed by downdraft injection of sub-50 nm (CN< 50) particles into the PBL and their subsequent growth. Central aspects of our understanding of these processes in the Amazon have remained enigmatic, however. Based on more than six years of aerosol and meteorological data from the Amazon Tall Tower Observatory (ATTO, Feb 2014 to Sep 2020), we analyzed the diurnal and seasonal patterns as well as meteorological conditions during 254 of such Amazonian growth events on 217 event days, which show a sudden occurrence of particles between 10 and 50 nm in the PBL, followed by their growth to CCN sizes. The occurrence of events was significantly higher during the wet season, with 88 % of all events from January to June, than during the dry season, with 12 % from July to December, probably due to differences in the condensation sink (CS), atmospheric aerosol load, and meteorological conditions. Across all events, a median growth rate (GR) of 5.2 nm h−1 and a median CS of 0.0011 s−1 were observed. The growth events were more frequent during the daytime (74 %) and showed higher GR (5.9 nm h−1) compared to nighttime events (4.0 nm h−1), emphasizing the role of photochemistry and PBL evolution in particle growth. About 70 % of the events showed a negative anomaly of the equivalent potential temperature (∆θ'e) – as a marker for downdrafts – and a low satellite brightness temperature (Tir) – as a marker for deep convective clouds – in good agreement with particle injection from the UT in the course of strong convective activity. About 30 % of the events, however, occurred in the absence of deep convection, partly under clear sky conditions, and with a positive ∆θ'e anomaly. Therefore, these events do not appear to be related to downdraft injection and suggest the existence of other currently unknown sources of the sub-50 nm particles.

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Modulation of Small-Scale Turbulence by Ducted Gravity Waves in the Nocturnal Boundary Layer

Journal of the Atmospheric Sciences ◽

10.1175/2007jas2359.1 ◽

2008 ◽

Vol 65 (4) ◽

pp. 1414-1427 ◽

Cited By ~ 28

Author(s):

Y. P. Meillier ◽

R. G. Frehlich ◽

R. M. Jones ◽

B. B. Balsley

Keyword(s):

Boundary Layer ◽

Gravity Waves ◽

Richardson Number ◽

Potential Temperature ◽

Nocturnal Boundary Layer ◽

Small Scale ◽

Temperature Structure ◽

Turbulence Measurements ◽

Gradient Richardson Number ◽

Scale Turbulence

Abstract Constant altitude measurements of temperature and velocity in the residual layer of the nocturnal boundary layer, collected by the Cooperative Institute for Research in Environmental Sciences (CIRES) Tethered Lifting System (TLS), exhibit fluctuations identified by previous work (Fritts et al.) as the signature of ducted gravity waves. The concurrent high-resolution TLS turbulence measurements (temperature structure constant C2T and turbulent kinetic energy dissipation rate ɛ) reveal the presence of patches of enhanced turbulence activity that are roughly synchronized with the troughs of the temperature and velocity fluctuations. To investigate the potentially dominant role ducted gravity waves might play on the modulation of atmospheric stability and therefore, on turbulence, time series of the wave-modulated gradient Richardson number (Ri) and of the vertical gradient of potential temperature ∂θ/∂z(t) are computed numerically and compared to the TLS small-scale turbulence measurements. The results of this study agree with the predictions of previous theoretical studies (i.e., wave-generated fluctuations of temperature and velocity modulate the gradient Richardson number), resulting in periodic enhancements of turbulence at Ri minima. The patches of turbulence observed in the TLS dataset are subsequently identified as convective instabilities generated locally within the unstable phase of the wave.

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Modulation of Internal Gravity Waves in a Multiscale Model for Deep Convection on Mesoscales

Journal of the Atmospheric Sciences ◽

10.1175/2010jas3269.1 ◽

2010 ◽

Vol 67 (8) ◽

pp. 2504-2519 ◽

Cited By ~ 7

Author(s):

Daniel Ruprecht ◽

Rupert Klein ◽

Andrew J. Majda

Keyword(s):

Gravity Waves ◽

Large Scale ◽

Energy Transport ◽

Deep Convection ◽

Potential Temperature ◽

Internal Gravity Waves ◽

Small Scale ◽

Closed Model ◽

Large Scale Flow ◽

Effective Stability

Abstract Starting from the conservation laws for mass, momentum, and energy together with a three-species bulk microphysics model, a model for the interaction of internal gravity waves and deep convective hot towers is derived using multiscale asymptotic techniques. From the leading-order equations, a closed model for the large-scale flow is obtained analytically by applying horizontal averages conditioned on the small-scale hot towers. No closure approximations are required besides adopting the asymptotic limit regime on which the analysis is based. The resulting model is an extension of the anelastic equations linearized about a constant background flow. Moist processes enter through the area fraction of saturated regions and through two additional dynamic equations describing the coupled evolution of the conditionally averaged small-scale vertical velocity and buoyancy. A two-way coupling between the large-scale dynamics and these small-scale quantities is obtained: moisture reduces the effective stability for the large-scale flow, and microscale up- and downdrafts define a large-scale averaged potential temperature source term. In turn, large-scale vertical velocities induce small-scale potential temperature fluctuations due to the discrepancy in effective stability between saturated and nonsaturated regions. The dispersion relation and group velocity of the system are analyzed and moisture is found to have several effects: (i) it reduces vertical energy transport by waves, (ii) it increases vertical wavenumbers but decreases the slope at which wave packets travel, (iii) it introduces a new lower horizontal cutoff wavenumber in addition to the well-known high wavenumber cutoff, and (iv) moisture can cause critical layers. Numerical examples reveal the effects of moisture on steady-state and time-dependent mountain waves in the present hot-tower regime.

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Regional modelling of aerosol interaction with deep convection and the effect on new particle formation over Amazonia

10.5194/egusphere-egu2020-6244 ◽

2020 ◽

Author(s):

Xuemei Wang ◽

Daniel Grosvenor ◽

Hamish Gordon ◽

Meinrat O. Andreae ◽

Ken Carslaw

Keyword(s):

Boundary Layer ◽

Cloud Condensation Nuclei ◽

Deep Convection ◽

Particle Formation ◽

Nucleation Mechanism ◽

Transport Processes ◽

Radiative Properties ◽

Free Troposphere ◽

New Particle Formation ◽

New Particles

It has been estimated that over 50% of the present-day global low-level cloud condensation nuclei (CCN) are formed from new particle formation (NPF), and that this process has a substantial effect on the radiative properties of shallow clouds (Gordon et al. 2017). In contrast, we have a very limited understanding of how NPF affects deep convective clouds. Deep clouds could interact strongly with NPF because they extend into the high free troposphere where most new particles are formed, and they are responsible for most of the vertical transport of the nucleating vapours. Andreae et al. (2018) hypothesised from ACRIDICON-CHUVA campaign that organic gas molecules are transported by deep convection to the upper troposphere where they are oxidised and produce new particles, which are then be entrained into the boundary layer and grow to CCN-relevent sizes.Here we study the interaction of deep convection and NPF using the United Kingdom Chemistry and Aerosols (UKCA) model coupled with the Cloud-AeroSol Interacting Microphyics (CASIM) embedded in the regional configuration of UK Met Office Hadley Centre Global Environment Model (HadGEM3). We simulate several days over a 1000 km region of the Amazon at 4 km resolution. We then compare the regional model, which resolves cloud up- and downdrafts, with the global model with parameterised convection and low resolution.Our simulations highlight three findings. Firstly, solely using a binary H2SO4-H2O nucleation mechanism strongly underestimates total aerosol concentrations compared to observations by a factor of 1.5-8 below 3 km over the Amazon. This points to the potential role of an additional nucleation mechanism, most likely involving biogenic compounds that occurs throughout more of the free troposphere. Secondly, deep convection transports insoluble gases such as DMS and monoterpenes vertically but not SO2&#160;or H2SO4. The time scale for DMS oxidation (~ 1 day) is much longer than for monoterpene (1-2 hours), which points to the importance of simulating biogenic nucleation over the Amazon in a cloud-resolving model, while lower-resolution global models may adequately capture DMS effects on H2SO4 nucleation. Finally, we also examine the Andreae et al (2018) hypothesis of aerosol supply to the boundary layer by quantifying cloud-free and cloudy up- and downdraft transport. The transport of newly formed aerosols into the boundary layer is 8 times greater in cloud-free regions than in the clouds, but these transport processes are of similar magnitude for large aerosols.

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Combined effects of surface conditions, boundary layer dynamics and chemistry on diurnal SOA-evolution

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-9331-2012 ◽

2012 ◽

Vol 12 (4) ◽

pp. 9331-9375 ◽

Cited By ~ 2

Author(s):

R. H. H. Janssen ◽

J. Vilà-Guerau de Arellano ◽

L. N. Ganzeveld ◽

P. Kabat ◽

J. L. Jimenez ◽

...

Keyword(s):

Boundary Layer ◽

Atmospheric Boundary Layer ◽

Land Surface ◽

Large Scale ◽

Organic Aerosol ◽

Layer Growth ◽

Combined Effects ◽

Free Troposphere ◽

Surface Conditions ◽

Boundary Layer Dynamics

Abstract. We study the combined effects of land surface conditions, atmospheric boundary layer dynamics and chemistry on the diurnal evolution of biogenic secondary organic aerosol in the atmospheric boundary layer, using a model that contains the essentials of all these components. First, we evaluate the model for a case study in Hyytiälä, Finland, and find that it is able to well reproduce the observed dynamics and gas-phase chemistry. We show that the exchange of organic aerosol between the free troposphere and the boundary layer (entrainment) must be taken into account in order to explain the observed diurnal cycle in organic aerosol (OA) concentration. An examination of the budgets of organic aerosol and terpene concentration shows that the former is dominated by entrainment, while the latter is mainly driven by emission and chemical transformation. We systematically examine the role of the land surface, which governs both the surface energy balance partitioning and terpene-emissions, and the large-scale atmospheric process of vertical subsidence. Entrainment is especially important for the dilution of organic aerosol concentrations under conditions of dry soils and low terpene-emissions. Subsidence suppresses boundary layer growth while enhancing entrainment. Therefore it influences the relationship between organic aerosol and terpene-concentrations. Our findings indicate that the diurnal evolution of SOA in the boundary layer is the result of coupled effects of the land surface, dynamics of the atmospheric boundary layer, chemistry, and free troposphere conditions. This has potentially some consequences for the design of both field campaigns and large-scale modeling studies.

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Diurnal Cycle of Precipitation Observed in the Western Coastal Area of Sumatra Island: Offshore Preconditioning by Gravity Waves

Monthly Weather Review ◽

10.1175/mwr-d-16-0468.1 ◽

2017 ◽

Vol 145 (9) ◽

pp. 3745-3761 ◽

Cited By ~ 41

Author(s):

Satoru Yokoi ◽

Shuichi Mori ◽

Masaki Katsumata ◽

Biao Geng ◽

Kazuaki Yasunaga ◽

...

Keyword(s):

Gravity Waves ◽

Diurnal Cycle ◽

Coastal Area ◽

Potential Temperature ◽

Lower Troposphere ◽

Free Troposphere ◽

Sumatra Island ◽

Precipitation Zone ◽

Diurnal Cycle Of Precipitation ◽

Water Vapor Mixing Ratio

This study analyzes data obtained by intensive observation during a pilot field campaign of the Years of the Maritime Continent Project (Pre-YMC) to investigate the diurnal cycle of precipitation in the western coastal area of Sumatra Island. The diurnal cycle during the campaign period (November–December 2015) is found to have a number of similarities with statistical behavior of the diurnal cycle as revealed by previous studies, such as afternoon precipitation over land, nighttime offshore migration of the precipitation zone, and dependency on Madden–Julian oscillation (MJO) phase. Composite analyses of radiosonde soundings from the Research Vessel (R/V) Mirai, deployed about 50 km off the coast, demonstrate that the lower free troposphere starts cooling in late afternoon (a couple of hours earlier than the cooling in the boundary layer), making the lower troposphere more unstable just before precipitation starts to increase. As the nighttime offshore precipitation tends to be more vigorous on days when the cooling in the lower free troposphere is larger, it is possible that the destabilization due to the cooling contributes to the offshore migration of the precipitation zone via enhancement of convective activity. Comparison of potential temperature and water vapor mixing ratio tendencies suggests that this cooling is substantially due to vertical advection by an ascent motion, which is possibly a component of shallow gravity waves. These results support the idea that gravity waves emanating from convective systems over land play a significant role in the offshore migration of the precipitation zone.

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Free troposphere as the dominant source of CCN in the Equatorial Pacific boundary layer: long-range transport and teleconnections

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-1279-2013 ◽

2013 ◽

Vol 13 (1) ◽

pp. 1279-1326 ◽

Cited By ~ 2

Author(s):

A. D. Clarke ◽

S. Freitag ◽

R. M. C. Simpson ◽

J. G. Hudson ◽

S. G. Howell ◽

...

Keyword(s):

Boundary Layer ◽

Marine Boundary Layer ◽

Cloud Condensation Nuclei ◽

Large Fraction ◽

Deep Convection ◽

Equatorial Pacific ◽

Quasi Equilibrium ◽

Free Troposphere ◽

Low Carbon ◽

Mixing Ratios

Abstract. Airborne aerosol measurements in the central equatorial Pacific during PASE (Pacific Atmospheric Sulfur Experiment) revealed that cloud condensation nuclei (CCN) activated in marine boundary layer (MBL) clouds were dominated by entrainment from the free troposphere (FT). About 65% entered at sizes effective as CCN in MBL clouds, while 25% entered the MBL too small to activate but subsequently grew via gas to particle conversion. The remaining 10% were inferred to be sea-salt aerosol; there was no discernable nucleation in the MBL. FT aerosols at low carbon monoxide (CO) mixing ratios (< 63 ppbv) were small and relatively volatile with a number mode around 30–40 nm dry diameter and tended to be associated with cloud outflow from distant deep convection (3000 km or more). Higher CO concentrations were commonly associated with trajectories from South America and the Amazon region (ca. 10 000 km away) and occurred in layers indicative of combustion sources partially scavenged by precipitation. These had number mode near 60–80 nm diameter with a large fraction already CCN.2 (those activated at 0.2% supersaturation and representative of MBL clouds) before entrainment into the MBL. Flight averaged concentrations of CCN.2 were similar for measurements near the surface, below the inversion and above the inversion, confirming that subsidence of FT aerosol dominated MBL CCN.2. Concurrent flight-to-flight variations of CCN.2 at all altitudes below 3 km imply MBL CCN.2 concentrations were in quasi-equilibrium with the FT over a 2–3 day time scale. This extended FT transport over thousands of kilometers indicates teleconnections between MBL CCN and cloud-scavenged sources of both natural and/or residual combustion origin. The low aerosol scattering and mass in such layers results in poor detection by satellite and this source of CCN is not represented in most current models. The measurements confirm nucleation in the MBL was not evident during PASE and argue against the CLAW hypothesis being effective in this region during PASE.

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Influence of corona discharge on the ozone budget in the tropical free troposphere: a case study of deep convection during GABRIEL

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-8917-2014 ◽

2014 ◽

Vol 14 (17) ◽

pp. 8917-8931 ◽

Cited By ~ 12

Author(s):

H. Bozem ◽

H. Fischer ◽

C. Gurk ◽

C. L. Schiller ◽

U. Parchatka ◽

...

Keyword(s):

Boundary Layer ◽

Corona Discharge ◽

Deep Convection ◽

Convective Transport ◽

Free Troposphere ◽

Direct Production ◽

Model Calculations ◽

Mixing Ratios ◽

Outflow Region

Abstract. Convective redistribution of ozone and its precursors between the boundary layer (BL) and the free troposphere (FT) influences photochemistry, in particular in the middle and upper troposphere (UT). We present a case study of convective transport during the GABRIEL campaign over the tropical rain forest in Suriname in October 2005. During one measurement flight the inflow and outflow regions of a cumulonimbus cloud (Cb) have been characterized. We identified a distinct layer between 9 and 11 km altitude with enhanced mixing ratios of CO, O3, HOx, acetone and acetonitrile. The elevated O3 contradicts the expectation that convective transport brings low-ozone air from the boundary layer to the outflow region. Entrainment of ozone-rich air is estimated to account for 62% (range: 33–91%) of the observed O3. Ozone is enhanced by only 5–6% by photochemical production in the outflow due to enhanced NO from lightning, based on model calculations using observations including the first reported HOx measurements over the tropical rainforest. The "excess" ozone in the outflow is most probably due to direct production by corona discharge associated with lightning. We deduce a production rate of 5.12 × 1028 molecules O3 flash−1 (range: 9.89 × 1026–9.82 × 1028 molecules O3 flash−1), which is at the upper limit of the range reported previously.

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Convective Bursts, Downdraft Cooling, and Boundary Layer Recovery in a Sheared Tropical Storm

Monthly Weather Review ◽

10.1175/mwr-d-12-00135.1 ◽

2013 ◽

Vol 141 (3) ◽

pp. 1048-1060 ◽

Cited By ~ 47

Author(s):

John Molinari ◽

Jaclyn Frank ◽

David Vollaro

Keyword(s):

Boundary Layer ◽

Deep Convection ◽

Potential Temperature ◽

Tangential Velocity ◽

Vertical Wind Shear ◽

Surface Heat ◽

Tropical Storm ◽

Convective Bursts ◽

Moisture Fluxes ◽

Heat And Moisture

Abstract Tropical Storm Edouard (2002) experienced episodic outbreaks of convection downshear within the storm core in the presence of 11–15 m s−1 of ambient vertical wind shear. These outbreaks lasted 2–6 h and were followed by long periods with no deep convection. Flights from U.S. Air Force reconnaissance aircraft within the boundary layer were used to investigate the cause of one such oscillation. Low equivalent potential temperature θe air filled the boundary layer as convection ceased, creating a 4–6-K deficit in θe within the convective region. Soundings within 110 km of the center were supportive of convective downdrafts, with midlevel relative humidity below 15% and large downdraft CAPE. Deep convection ceased within 75 km of the center for more than 8 h. Tangential velocity reached hurricane force locally during the convective outbreak, then became nearly symmetric after convection stopped, arguably as a result of axisymmetrization, and the storm weakened. Nevertheless, the corresponding lack of convective downdrafts during this period allowed surface heat and moisture fluxes to produce substantial increases in boundary layer entropy. A new burst of convection followed. Consistent with recent papers it is argued that tropical cyclone intensification and decay can be understood as a competition between surface heat and moisture fluxes (“fuel”) and low-entropy downdrafts into the boundary layer (“antifuel”).

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Influence of corona discharge on the ozone budget in the tropical free troposphere: a case study of deep convection during GABRIEL

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-5233-2014 ◽

2014 ◽

Vol 14 (4) ◽

pp. 5233-5270 ◽

Cited By ~ 1

Author(s):

H. Bozem ◽

H. Fischer ◽

C. Gurk ◽

C. L. Schiller ◽

U. Parchatka ◽

...

Keyword(s):

Boundary Layer ◽

Corona Discharge ◽

Deep Convection ◽

Convective Transport ◽

Free Troposphere ◽

Direct Production ◽

Model Calculations ◽

Mixing Ratios ◽

Steady State Model

Abstract. Convective redistribution of ozone and its precursors between the boundary layer (BL) and the free troposphere (FT) influences photochemistry, in particular that of the middle and upper troposphere (UT). We present a case study of convective transport during the GABRIEL campaign over the tropical rain forest in Suriname in October 2005. During a measurement flight on 12 October the inflow and outflow regions of a cumulonimbus cloud (Cb) have been characterized, providing evidence of convective transport. We identified a distinct layer between 9 and 11 km altitude with enhanced mixing ratios of CO, O3, HOx, acetone and acetonitrile. The elevated O3 contradicts the expectation that convective transport brings low ozone air from the boundary layer to the outflow region. The enhanced mixing ratio of ozone in the outflow was mainly of dynamical origin. Entrainment of ozone rich air at the outflow level into the convective outflow accounts for 62% (range: 33–91%) of the observed O3. Ozone is enhanced by only 5–6% by photochemical production in the outflow due to enhanced NO from lightning, based on steady state model calculations, using in-situ observations including the first reported HOx measurements over the tropical rainforest. The "excess" ozone in the outflow is most probably due to direct production by corona discharge associated with lightning. We deduce a production rate of 5.12 × 1028 molecules O3 flash−1 (range: 9.89 × 1026–9.82 × 1028 molecules O3 flash−1), which is at the upper limit of the range of the values reported previously.

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