scholarly journals Investigation of the Diurnal Variation of Marine Boundary Layer Cloud Microphysical Properties at the Azores

2014 ◽  
Vol 27 (23) ◽  
pp. 8827-8835 ◽  
Author(s):  
Xiquan Dong ◽  
Baike Xi ◽  
Peng Wu
Keyword(s):  
Boundary Layer ◽  
Diurnal Variation ◽  
Marine Boundary Layer ◽  
Surface Wind ◽  
Number Concentration ◽  
Diurnal Variations ◽  
Cloud Layer ◽  
Entire Study ◽  
Microphysical Properties ◽  
Seasonal And Diurnal Variations

Abstract A new method has been developed to retrieve the nighttime marine boundary layer (MBL) cloud microphysical properties, which provides a complete 19-month dataset to investigate the diurnal variation of MBL cloud microphysical properties at the Azores. Compared to the corresponding daytime results presented in the authors' previous study over the Azores region, all nighttime monthly means of cloud liquid water path (LWP) exceed their daytime counterparts with an annual-mean LWP of 140 g m−2, which is ~30.9 g m−2 larger than daytime. Because the MBL clouds are primarily driven by convective instabilities caused by cloud-top longwave (LW) radiative cooling, more MBL clouds are well mixed and coupled with the surface during the night; thus, its cloud layer is deeper and its LWP is higher. During the day, the cloud layer is warmed by the absorption of solar radiation and partially offsets the cloud-top LW cooling, which makes the cloud layer thinner with less LWP. The seasonal and diurnal variations of cloud LWC and optical depth basically follow the variation of LWP. There are, however, no significant day–night differences and diurnal variations in cloud-droplet effective radius (re), number concentration (Nd), and corresponding surface measured cloud condensation nuclei (CCN) number concentration (NCCN) (at supersaturation S = 0.2%). Surface NCCN increases from around sunrise (0300–0600 LT) to late afternoon, which strongly correlates with surface wind speed (r = 0.76) from 0300 to 1900 LT. The trend in hourly-mean Nd is consistent with NCCN variation from 0000 to 0900 LT but not for afternoon and evening with an averaged ratio (Nd/NCCN) of 0.35 during the entire study period.

scholarly journals Investigation of Regional and Seasonal Variations in Marine Boundary Layer Cloud Properties from MODIS Observations

2008 ◽  
Vol 21 (19) ◽  
pp. 4955-4973 ◽  
Author(s):  
Michael P. Jensen ◽  
Andrew M. Vogelmann ◽  
William D. Collins ◽  
Guang J. Zhang ◽  
Edward P. Luke
Keyword(s):  
Boundary Layer ◽  
General Circulation ◽  
Climate Models ◽  
Marine Boundary Layer ◽  
General Circulation Models ◽  
Test Bed ◽  
Liquid Water Path ◽  
Microphysical Properties ◽  
Cloud Properties ◽  
Peak Versus

Abstract To aid in understanding the role that marine boundary layer (MBL) clouds play in climate and assist in improving their representations in general circulation models (GCMs), their long-term microphysical and macroscale characteristics are quantified using observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard the National Aeronautics and Space Administration’s (NASA’s) Terra satellite. Six years of MODIS pixel-level cloud products are used from oceanic study regions off the west coasts of California, Peru, the Canary Islands, Angola, and Australia where these cloud types are common. Characterizations are given for their organization (macroscale structure), the associated microphysical properties, and the seasonal dependencies of their variations for scales consistent with the size of a GCM grid box (300 km × 300 km). MBL mesoscale structure is quantified using effective cloud diameter CD, which is introduced here as a simplified measure of bulk cloud organization; it is straightforward to compute and provides descriptive information beyond that offered by cloud fraction. The interrelationships of these characteristics are explored while considering the influences of the MBL state, such as the occurrence of drizzle. Several commonalities emerge for the five study regions. MBL clouds contain the best natural examples of plane-parallel clouds, but overcast clouds occur in only about 25% of the scenes, which emphasizes the importance of representing broken MBL cloud fields in climate models (that are subgrid scale). During the peak months of cloud occurrence, mesoscale organization (larger CD) increases such that the fractions of scenes characterized as “overcast” and “clumped” increase at the expense of the “scattered” scenes. Cloud liquid water path and visible optical depth usually trend strongly with CD, with the largest values occurring for scenes that are drizzling. However, considerable interregional differences exist in these trends, suggesting that different regression functionalities exist for each region. For peak versus off-peak months, the fraction of drizzling scenes (as a function of CD) are similar for California and Angola, which suggests that a single probability distribution function might be used for their drizzle occurrence in climate models. The patterns are strikingly opposite for Peru and Australia; thus, the contrasts among regions may offer a test bed for model simulations of MBL drizzle occurrence.

scholarly journals Aerosol particle characteristics measured in the United Arab Emirates and their response to mixing in the boundary layer

2021 ◽  
Author(s):  
Jutta Kesti ◽  
John Backman ◽  
Ewan James O'Connor ◽  
Anne Hirsikko ◽  
Eija Asmi ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Aerosol Particle ◽  
United Arab Emirates ◽  
Wind Direction ◽  
Aerosol Particles ◽  
Surface Wind ◽  
Number Concentration ◽  
Particle Properties ◽  
Boundary Layer Height

Abstract. Aerosol particles play an important in role in the microphysics of clouds and hence on their likelihood to precipitate. In the changing climate already dry areas such as the United Arab Emirates (UAE) are predicted to become even drier. Comprehensive observations of the daily and seasonal variation in aerosol particle properties in such locations are required reducing the uncertainty in such predictions. We analyse observations from a one-year measurement campaign at a background location in the United Arab Emirates to investigate the properties of aerosol particles in this region, study the impact of boundary layer mixing on background aerosol particle properties measured at the surface and study the temporal evolution of the aerosol particle cloud formation potential in the region. We used in-situ aerosol particle measurements to characterise the aerosol particle composition, size, number and cloud condensation nuclei (CCN) properties, in-situ SO2 measurements as an anthropogenic signature and a long-range scanning Doppler lidar to provide vertical profiles of the horizontal wind and turbulent properties to monitor the evolution of the boundary layer. Anthropogenic sulphate dominated the aerosol particle mass composition in this location. There was a clear diurnal cycle in the surface wind direction, which had a strong impact on aerosol particle total number concentration, SO2 concentration and black carbon mass concentration. Local sources were the predominant source of black carbon, as concentrations clearly depended on the presence of turbulent mixing, with much higher values during calm nights. The measured concentrations of SO2, instead, were highly dependent on the surface wind direction as well as on the depth of the boundary layer when entrainment from the advected elevated layers occurred. The wind direction at the surface or of the elevated layer suggests that the cities of Dubai, Abu Dhabi and other coastal conurbations were the remote sources of SO2. We observed new aerosol particle formation events almost every day (on four days out of five on average). Calm nights had the highest CCN number concentrations and lowest κ values and activation fractions. We did not observe any clear dependence of CCN number concentration and κ parameter on the height of the daytime boundary layer, whereas the activation fraction did show a slight increase with increasing boundary layer height, due to the change in the shape of the aerosol particle size distribution where the relative portion of larger aerosol particles increased with increasing boundary layer height. We believe that this indicates that size is more important than chemistry for aerosol particle CCN activation at this site. The combination of instrumentation used in this campaign enabled us to identify periods when anthropogenic pollution from remote sources that had been transported in elevated layers was present, and had been mixed down to the surface in the growing boundary layer.

Exploring microphysical properties of marine boundary layer clouds through network analysis

2021 ◽  
Author(s):  
Lucile Ricard ◽  
Athanasios Nenes ◽  
Jakob Runge ◽  
Paraskevi Georgakaki
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Network Analysis ◽  
Marine Boundary Layer ◽  
Large Eddy Simulations ◽  
Dynamical Structure ◽  
Boundary Layer Clouds ◽  
Microphysical Properties ◽  
Spatial Coverage ◽  
Large Eddy

<p>Aerosol-cloud interactions remain the largest uncertainty in assessments of anthropogenic climate forcing, while the complexity of these interactions require methods that enable abstractions and simplifications that allow their improved treatment in climate models. Marine boundary layer clouds are an important component of the climate system as their large albedo and spatial coverage strongly affect the planetary radiative balance. High resolution simulations of clouds provide an unprecedented understanding of the structure and behavior of these clouds in the marine atmosphere, but the amount of data is often too large and complex to be useful in climate simulations. Data reduction and inference methods provide a way that to reduce the complexity and dimensionality of datasets generated from high-resolution Large Eddy Simulations.</p><p>In this study we use network analysis, (the δ-Maps method) to study the complex interaction between liquid water, droplet number and vertical velocity in Large Eddy Simulations of Marine Boundary Layer clouds. δ-Maps identifies domains that are spatially contiguous and possibly overlapping and characterizes their connections and temporal interactions. The objective is to better understand microphysical properties of marine boundary layer clouds, and how they are impacted by the variability in aerosols. Here we will capture the dynamical structure of the cloud fields predicted by the MIMICA Large Eddy Simulation (LES) model. The networks inferred from the different simulation fields are compared between them (intra-comparisons) using perturbations in initial conditions and aerosol, using a set of four metrics. The networks are then evaluated for their differences, quantifying how much variability is inherent in the LES simulations versus the robust changes induced by the aerosol fields. </p>

Diurnal variations and source apportionment of ozone at the summit of Mount Huang, a rural site in Eastern China

2020 ◽  
Author(s):  
Jinhui Gao
Keyword(s):  
Boundary Layer ◽  
Diurnal Variation ◽  
Source Apportionment ◽  
Southern China ◽  
Eastern China ◽  
Vertical Mixing ◽  
Diurnal Variations ◽  
Rural Site ◽  
Positive Contribution ◽  
Negative Contribution

<p>Comprehensive measurements were conducted at the summit of Mount (Mt.) Huang, a rural site located in eastern China during the summer of 2011. They observed that ozone showed pronounced diurnal variations with high concentrations at night and low values during daytime. The Weather Research and Forecasting with Chemistry (WRF-Chem) model was applied to simulate the ozone concentrations at Mt. Huang in June 2011. With processes analysis and online ozone tagging method we coupled into the model system, the causes of this diurnal pattern and the contributions from different source regions were investigated. Our results showed that boundary layer diurnal cycle played an important role in driving the ozone diurnal variation. Further analysis showed that the negative contribution of vertical mixing was significant, resulting in the ozone decrease during the daytime. In contrast, ozone increased at night owing to the significant positive contribution of advection. This shifting of major factor between vertical mixing and advection formed this diurnal variation. Ozone source apportionment results indicated that approximately half was provided by inflow effect of ozone from outside the model domain (O<sub>3-INFLOW</sub>) and the other half was formed by ozone precursors (O<sub>3-PBL</sub>) emitted in eastern, central, and southern China. In the O<sub>3-PBL</sub>, 3.0% of the ozone was from Mt. Huang reflecting the small local contribution (O<sub>3-LOC</sub>) and the non-local contributions (O<sub>3-NLOC</sub>) accounted for 41.6%, in which ozone from the southerly regions contributed significantly, for example, 9.9% of the ozone originating from Jiangxi, representing the highest geographical contributor. Because the origin and variation of O<sub>3-NLOC</sub> was highly related to the diurnal movements in boundary layer, the similar diurnal patterns between O<sub>3-NLOC</sub> and total ozone both indicated the direct influence of O<sub>3-NLOC</sub> and the importance of boundary layer diurnal variations in the formation of such distinct diurnal ozone variations at Mt. Huang.</p>

scholarly journals Numerical Simulations of Spatial Distributions and Diurnal Variations of Low-Level Jets in China during Early Summer

2014 ◽  
Vol 27 (15) ◽  
pp. 5747-5767 ◽  
Author(s):  
Yu Du ◽  
Qinghong Zhang ◽  
Yi-leng Chen ◽  
Yangyang Zhao ◽  
Xu Wang
Keyword(s):  
Boundary Layer ◽  
Diurnal Variation ◽  
Tarim Basin ◽  
Southern China ◽  
Early Summer ◽  
Northeastern China ◽  
Diurnal Variations ◽  
Spatial Distributions ◽  
Model Data ◽  
Low Level Jets

Abstract The detailed spatial distributions and diurnal variations of low-level jets (LLJs) during early summer (May–July) in China are documented using 2006–11 hourly model data from the Weather Research and Forecasting (WRF) Model with a 9-km horizontal resolution. It was found that LLJs frequently occur in the following regions of China: the Tarim basin, northeastern China, the Tibetan Plateau (TP), and southern China. The LLJs over China are classified into two types: boundary layer jets (BLJs, below 1 km) and synoptic-system-related LLJs (SLLJs, within 1–4 km). The LLJs in the Tarim basin and the TP are mainly BLJs. The SLLJs over southern China and northeastern China are associated with the mei-yu front and northeast cold vortex (NECV), respectively. The BLJs in all regions show pronounced diurnal variations with maximum occurrences at nighttime or in the early morning, whereas diurnal variations of SLLJs vary, depending on the location. From the analysis of model data, the diurnal variation of BLJs is mainly caused by inertial oscillation at nighttime and vertical mixing in the boundary layer during daytime. Over northeastern China, SLLJ occurrences show little diurnal variation. Over southern China, two diurnal modes of SLLJs, propagation and stationary, exist and have seasonal variations, which is generally consistent with diurnal variations of precipitation.

scholarly journals Concentrations of OH and HO<sub>2</sub> radicals during NAMBLEX: measurements and steady state analysis

2005 ◽  
Vol 5 (6) ◽  
pp. 12403-12464 ◽  
Author(s):  
S. C. Smith ◽  
J. D. Lee ◽  
W. J. Bloss ◽  
G. P. Johnson ◽  
D. E. Heard
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Detection Limit ◽  
Diurnal Variation ◽  
Marine Boundary Layer ◽  
Chemical Conversion ◽  
Early Morning ◽  
Research Station ◽  
Solar Noon ◽  
Mean Concentration

Abstract. OH and HO2 concentrations were measured simultaneously at the Mace Head Atmospheric Research Station in the summer of 2002 during the NAMBLEX (North Atlantic Marine Boundary Layer EXperiment) field campaign. OH was measured by laser-induced fluorescence employing the FAGE (Fluorescence Assay by Gas Expansion) technique, with a mean daytime detection limit of 2.7×105 molecule cm−3 (5 min acquisition period; signal-to-noise ratio = 1). HO2 was detected as OH following its chemical conversion through addition of NO, with a mean detection limit of 4.4×106 molecule cm−3. The diurnal variation of OH was measured on 24 days, and that of HO2 on 17 days. The local solar noon OH concentrations ranged between (3–8)×106 molecule cm−3, with a 24 h mean concentration of 9.1×105 molecule cm−3. The local solar noon HO2 concentrations were (0.9–2.1)×108 molecule cm−3 (3.5–8.2 pptv), with a 24 h mean concentration of 4.2×107 molecule cm−3. HO2 radicals in the range (2–3)×107 molecule cm−3 were observed at night. During NAMBLEX, a comprehensive suite of supporting measurements enabled a detailed study of the behaviour of HOx radicals under primarily clean marine conditions. Case study periods highlight the typical radical levels observed under different conditions. Steady state expressions are used to calculate OH and HO2 concentrations and to evaluate the effect of different free-radical sources and sinks. The diurnally averaged calculated to measured OH ratio was 1.04±0.36, but the ratio displays a distinct diurnal variation, being less than 1 during the early morning and late afternoon/evening, and greater than 1 in the middle of the day. For HO2 there was an overprediction, with the agreement between calculated and measured concentrations improved by including reaction with measured IO and BrO radicals and uptake to aerosols. Increasing the concentration of IO radicals included in the calculations to above that measured by a DOAS instrument with an absorption path located mainly over the ocean, reflecting the domination of the inter-tidal region as an iodine source at Mace Head, led to further improvement. The results are compared with previous measurements at Mace Head, and elsewhere in the remote marine boundary layer.

scholarly journals Turbulence in The Marine Boundary Layer and Air Motions Below Stratocumulus Clouds at the ARM Eastern North Atlantic Site

2021 ◽  
Author(s):  
Virendra P. Ghate ◽  
Maria P. Cadeddu ◽  
Xue Zheng ◽  
Ewan O’Connor
Keyword(s):  
Boundary Layer ◽  
North Atlantic ◽  
Vertical Velocity ◽  
Marine Boundary Layer ◽  
Cloud Layer ◽  
Similar Amount ◽  
Marine Stratocumulus ◽  
Stratocumulus Clouds ◽  
Eastern North Atlantic ◽  
Rain Rates

AbstractMarine stratocumulus clouds are intimately coupled to the turbulence in the boundary layer and drizzle is known to be ubiquitous within them. Six years of data collected at the Atmospheric Radiation Measurement (ARM)’s Eastern North Atlantic site are utilized to characterize turbulence in the marine boundary layer and air motions below stratocumulus clouds. Profiles of variance of vertical velocity binned by wind direction (wdir) yielded that the boundary layer measurements are affected by the island when the wdir is between 90° and 310° (measured clockwise from North where air is coming from). Data collected during the marine conditions (wdir<90 or wdir>310) showed that the variance of vertical velocity was higher during the winter months than during the summer months due to higher cloudiness, wind speeds, and surface fluxes. During marine conditions the variance of vertical velocity and cloud fraction exhibited a distinct diurnal cycle with higher values during the nighttime than during the daytime. Detailed analysis of 32 cases of drizzling marine stratocumulus clouds showed that for a similar amount of radiative cooling at the cloud top, within the sub-cloud layer 1) drizzle increasingly falls within downdrafts with increasing rain rates, 2) the strength of the downdrafts increases with increasing rain rates, and 3) the correlation between vertical air motion and rain rate is highest in the middle of the sub-cloud layer. The results presented herein have implications for climatological and model evaluation studies conducted at the ENA site, along with efforts of accurately representing drizzle-turbulence interactions in a range of atmospheric models.

scholarly journals Aerosol particle characteristics measured in the United Arab Emirates and their response to mixing in the boundary layer

2022 ◽  
Vol 22 (1) ◽  
pp. 481-503
Author(s):  
Jutta Kesti ◽  
John Backman ◽  
Ewan J. O'Connor ◽  
Anne Hirsikko ◽  
Eija Asmi ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Aerosol Particle ◽  
United Arab Emirates ◽  
Wind Direction ◽  
Aerosol Particles ◽  
Surface Wind ◽  
Number Concentration ◽  
Particle Properties ◽  
Boundary Layer Height

Abstract. Aerosol particles play an important role in the microphysics of clouds and hence in their likelihood to precipitate. In the changing climate already-dry areas such as the United Arab Emirates (UAE) are predicted to become even drier. Comprehensive observations of the daily and seasonal variation in aerosol particle properties in such locations are required, reducing the uncertainty in such predictions. We analyse observations from a 1-year measurement campaign at a background location in the United Arab Emirates to investigate the properties of aerosol particles in this region, study the impact of boundary layer mixing on background aerosol particle properties measured at the surface, and study the temporal evolution of the aerosol particle cloud formation potential in the region. We used in situ aerosol particle measurements to characterise the aerosol particle composition, size, number, and cloud condensation nuclei (CCN) properties; in situ SO2 measurements as an anthropogenic signature; and a long-range scanning Doppler lidar to provide vertical profiles of the horizontal wind and turbulent properties to monitor the evolution of the boundary layer. Anthropogenic sulfate dominated the aerosol particle mass composition in this location. There was a clear diurnal cycle in the surface wind direction, which had a strong impact on aerosol particle total number concentration, SO2 concentration, and black carbon mass concentration. Local sources were the predominant source of black carbon as concentrations clearly depended on the presence of turbulent mixing, with much higher values during calm nights. The measured concentrations of SO2, instead, were highly dependent on the surface wind direction as well as on the depth of the boundary layer when entrainment from the advected elevated layers occurred. The wind direction at the surface or of the elevated layer suggests that the oil refineries and the cities of Dubai and Abu Dhabi and other coastal conurbations were the remote sources of SO2. We observed new-aerosol-particle formation events almost every day (on 4 d out of 5 on average). Calm nights had the highest CCN number concentrations and lowest κ values and activation fractions. We did not observe any clear dependence of CCN number concentration and κ parameter on the height of the daytime boundary layer, whereas the activation fraction did show a slight increase with increasing boundary layer height due to the change in the shape of the aerosol particle size distribution where the relative portion of larger aerosol particles increased with increasing boundary layer height. We believe that this indicates that size is more important than chemistry for aerosol particle CCN activation at this site. The combination of instrumentation used in this campaign enabled us to identify periods when anthropogenic pollution from remote sources that had been transported in elevated layers was present and had been mixed down to the surface in the growing boundary layer.

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