scholarly journals The Diurnal Cycle of Cloud-Top Height and Cloud Cover over the Southeastern Pacific as Observed by GOES-10

2013 ◽  
Vol 70 (8) ◽  
pp. 2393-2408 ◽  
Author(s):  
David Painemal ◽  
Patrick Minnis ◽  
Larry O'Neill
Keyword(s):  
Boundary Layer ◽  
Mixed Boundary ◽  
Phase Speed ◽  
Tropical Rainfall Measuring Mission ◽  
Sea Breeze ◽  
Air Entrainment ◽  
Liquid Water Path ◽  
Diurnal Cycles ◽  
Southeastern Pacific ◽  
Microwave Imager

Abstract The diurnal cycles in cloud-top height Htop and cloud fraction (CF) in the southeastern Pacific stratocumulus region were determined for October–November 2008 by analyzing data from Geostationary Operational Environmental Satellite-10 (GOES-10) according to a diurnal/semidiurnal harmonic fitting technique. The value of Htop was obtained by applying a formula based on a linear regression of the differences between GOES-10 cloud-top temperature and Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) satellite sea surface temperature, with a common 0.25° × 0.25° spatial resolution. A satellite liquid water path (LWP) climatology complemented this dataset. Southwestward transects of Htop and LWP anomalies reveal a coherent propagating signal from the coast in the afternoon, with a typical phase speed of 25 m s−1. This pattern is preceded by a subsidence wave that reaches its peak a few hours before the maximum in Htop and LWP anomalies. Coincident increases in LWP and Htop after the subsidence wave passes suggest that the boundary layer deepening promotes cloud thickening and increased LWP, which are likely maintained through a well-mixed boundary layer and sufficient moisture fluxes that can counteract the effect of dry air entrainment. The interference between the radiatively and subsidence wave–driven cycles gives rise to a semidiurnal cycle in Htop along the coast. While the semidiurnal amplitude is near 80 m close to the coast with a fraction of explained variance greater than 0.4, it decreases to 30 m offshore (80°W). Similar to Htop, CF also exhibits contrasting zonal differences, but with a smaller semidiurnal component. The phase of the semidiurnal harmonic resembles the subsidence propagation westward, and the noticeable land–sea breeze circulation at 26°S that extends 200 km offshore.

Reconciling and Validating the Cloud Thickness and Liquid Water Path Tendencies Proposed by R. Wood and J. J. van der Dussen et al.

2015 ◽  
Vol 72 (5) ◽  
pp. 2033-2040 ◽  
Author(s):  
Mohamed S. Ghonima ◽  
Joel R. Norris ◽  
Thijs Heus ◽  
Jan Kleissl
Keyword(s):  
Boundary Layer ◽  
Liquid Water ◽  
Mixed Boundary ◽  
Liquid Water Path ◽  
Water Path ◽  
Large Eddy ◽  
Heat And Moisture ◽  
Cloud Thickness ◽  
Detailed Derivation ◽  
Good Agreement

Abstract A detailed derivation of stratocumulus cloud thickness and liquid water path tendencies as a function of the well-mixed boundary layer mass, heat, and moisture budget equations is presented. The derivation corrects an error in the cloud thickness tendency equation derived by R. Wood to make it consistent with the liquid water path tendency equation derived by J. J. van der Dussen et al. The validity of the tendency equations is then tested against the output of large-eddy simulations of a typical stratocumulus-topped boundary layer case and is found to be in good agreement.

scholarly journals Meteorological and Aerosol Effects on Marine Stratocumulus

2016 ◽  
Vol 73 (2) ◽  
pp. 807-820 ◽  
Author(s):  
Zhe Li ◽  
Huiwen Xue ◽  
Jen-Ping Chen ◽  
Wei-Chyung Wang
Keyword(s):  
Precipitation Amount ◽  
Wrf Model ◽  
Cloud Fraction ◽  
Cloud Base ◽  
Liquid Water Path ◽  
Marine Stratocumulus ◽  
Diurnal Cycles ◽  
Microphysical Properties ◽  
Southeastern Pacific ◽  
Lower Cloud

Abstract This study investigates the effects of meteorological conditions and aerosols on marine stratocumulus in the southeastern Pacific using the Weather Research and Forecasting (WRF) Model. Two regimes with different temperature and moisture conditions in the finest model domain are investigated. The western regime is around 87°–79°W, while the eastern regime is around 79°–71°W. In both regimes, cloud fraction, liquid water path (LWP), cloud thickness, and precipitation show significant diurnal cycles. Cloud fraction can be 0.83 during the night and down to 0.29 during the day in the western regime. The diurnal cycles in the eastern regime have smaller amplitudes but are still very strong. Stratocumulus properties also differ in the two regimes. Compared to the western regime, the eastern regime has lower temperature, higher relative humidity, and a more coupled boundary layer, leading to higher cloud fraction (by 0.11) and lower cloud-base height. The eastern regime also has lower inversion height that causes lower cloud-top height and thinner clouds and, hence, lower LWP and less precipitation. Cloud microphysical properties are very sensitive to aerosols in both regimes. Increasing aerosols greatly increase cloud number concentration, decrease cloud effective radius, and suppress precipitation. Cloud macrophysical properties (cloud fraction, LWP) are not sensitive to aerosols in either regime, most notably in the eastern regime where precipitation amount is less. The changes in cloud fraction and LWP caused by changes in aerosol concentrations are smaller than the changes in the diurnal cycle and the spatial variability between the two regimes.

Rainfall Contributions from Precipitation Systems with Different Sizes, Convective Intensities, and Durations over the Tropics and Subtropics

2011 ◽  
Vol 12 (3) ◽  
pp. 394-412 ◽  
Author(s):  
Chuntao Liu
Keyword(s):  
Grid Point ◽  
Tropical Rainfall Measuring Mission ◽  
Life Cycles ◽  
Diurnal Variations ◽  
Diurnal Cycles ◽  
Brightness Temperatures ◽  
Seasonal And Diurnal Variations ◽  
Microwave Imager ◽  
Rain Events ◽  
The Tropics

Abstract The rainfall contributions from precipitation features (PFs) with full spectra of different sizes and convective intensities over the tropics and subtropics are summarized using 12 yr of version 6 Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) and Microwave Imager (TMI) observations. Regional, seasonal, and diurnal variations of the rainfall contributions from various PFs are shown, with the global distribution of the sizes, PR echo tops, maximum heights of 30 dBZ, and minimum TMI 85-GHz brightness temperatures of PFs above which contribute half of the rainfall in each 2° × 2° region. Though the results from radar and microwave observations generally agree with each other, some large differences exist over land. Seasonal variations of sizes and intensities of precipitation systems are found over the northeast Pacific, northern SPCZ, and some land areas in addition to the well-known monsoon regions. The diurnal cycles of rainfall over land and ocean are interpreted with the combinations of life cycles of various precipitation systems, using the diurnal variations of rainfall contributions from precipitation systems with different sizes and intensities. The long-duration rainfall events with more than four consecutive 3-h periods with rain at a grid point are identified from 11 yr of TRMM 3B42 products. These “12-h rain events” contribute a larger proportion of the total rainfall over ocean than over land. They are mostly correlated with precipitation systems with large sizes and intense convection. However, they can also be caused by some shallow persistent precipitation systems, such as those over the northeast slope of the Andes in Peru in spring and fall and over the west coast of India in summer.

scholarly journals Evaluation of Warm-Rain Microphysical Parameterizations in Mesoscale Simulations of the Cloudy Marine Boundary Layer

2016 ◽  
Vol 144 (6) ◽  
pp. 2137-2154 ◽  
Author(s):  
Kevin J. Nelson ◽  
David B. Mechem ◽  
Yefim L. Kogan
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Cloud Condensation Nuclei ◽  
Forecast Model ◽  
Horizontal Resolution ◽  
Naval Research ◽  
Liquid Water Path ◽  
Cloud Properties ◽  
Southeastern Pacific ◽  
Warm Rain

Abstract Several warm-rain microphysical parameterizations are evaluated in a regional forecast model setting (using the Naval Research Laboratory’s Coupled Ocean–Atmosphere Mesoscale Prediction System) by evaluating how accurately the model is able to represent the marine boundary layer (MBL). Cloud properties from a large suite of simulations using different parameterizations and concentrations of cloud condensation nuclei (CCN) are compared to ship-based observations from the Variability of the American Monsoon Systems (VAMOS) Ocean–Cloud–Atmosphere–Land Study—Regional Experiment (VOCALS-REx) field campaign conducted over the southeastern Pacific (SEP). As in previous studies, the simulations systematically underestimate liquid water path and MBL cloud depth. On the other hand, the simulations overestimate precipitation rates relative to those derived from the scanning C-band radar on board the ship. Most of the simulations exhibit a diurnal cycle, although details differ somewhat from a recent observational study. In addition to direct comparisons with the observations, the internal microphysical consistency of simulated MBL cloud properties is assessed by comparing simulation output to a number of observationally and theoretically derived scalings for precipitation and coalescence scavenging. Simulation results are broadly consistent with these scalings, suggesting COAMPS is behaving in a microphysically consistent fashion. However, microphysical consistency as defined in the analysis is highly dependent upon the horizontal resolution of the model. Excessive depletion of CCN from large coalescence processing rates suggests the importance of parameterizing a source term for CCN or imposing some form of fixed, climatological background CCN concentration.

scholarly journals Large Eddy Simulation of the Diurnal Cycle in Southeast Pacific Stratocumulus

2009 ◽  
Vol 66 (2) ◽  
pp. 432-449 ◽  
Author(s):  
Peter Caldwell ◽  
Christopher S. Bretherton
Keyword(s):  
Boundary Layer ◽  
Diurnal Cycle ◽  
Liquid Water ◽  
Cloud Base ◽  
Liquid Water Path ◽  
Water Path ◽  
Diurnal Cycles ◽  
Eddy Simulation ◽  
Droplet Concentration ◽  
Large Eddy

Abstract This paper describes a series of 6-day large eddy simulations of a deep, sometimes drizzling stratocumulus-topped boundary layer based on forcings from the East Pacific Investigation of Climate (EPIC) 2001 field campaign. The base simulation was found to reproduce the observed mean boundary layer properties quite well. The diurnal cycle of liquid water path was also well captured, although good agreement appears to result partially from compensating errors in the diurnal cycles of cloud base and cloud top due to overentrainment around midday. At all times of the day, entrainment is found to be proportional to the vertically integrated buoyancy flux. Model stratification matches observations well; turbulence profiles suggest that the boundary layer is always at least somewhat decoupled. Model drizzle appears to be too sensitive to liquid water path and subcloud evaporation appears to be too weak. Removing the diurnal cycle of subsidence had little effect on simulated liquid water path. Simulations with changed droplet concentration and drizzle susceptibility showed large liquid water path differences at night, but differences were quite small at midday. Droplet concentration also had a significant impact on entrainment, primarily through droplet sedimentation feedback rather than through drizzle processes.

scholarly journals Observations of the boundary layer, cloud, and aerosol variability in the southeast Pacific near-coastal marine stratocumulus during VOCALS-REx

2011 ◽  
Vol 11 (18) ◽  
pp. 9943-9959 ◽  
Author(s):  
X. Zheng ◽  
B. Albrecht ◽  
H. H. Jonsson ◽  
D. Khelif ◽  
G. Feingold ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Cloud Droplet ◽  
Radiosonde Data ◽  
Liquid Water Path ◽  
Southeastern Pacific ◽  
Coastal Marine ◽  
Cloud Liquid Water Path ◽  
Boundary Layer Cloud ◽  
Meso Scale

Abstract. Aircraft observations made off the coast of northern Chile in the Southeastern Pacific (20° S, 72° W; named Point Alpha) from 16 October to 13 November 2008 during the VAMOS Ocean-Cloud- Atmosphere-Land Study-Regional Experiment (VOCALS-REx), combined with meteorological reanalysis, satellite measurements, and radiosonde data, are used to investigate the boundary layer (BL) and aerosol-cloud-drizzle variations in this region. On days without predominately synoptic and meso-scale influences, the BL at Point Alpha was typical of a non-drizzling stratocumulus-topped BL. Entrainment rates calculated from the near cloud-top fluxes and turbulence in the BL at Point Alpha appeared to be weaker than those in the BL over the open ocean west of Point Alpha and the BL near the coast of the northeast Pacific. The cloud liquid water path (LWP) varied between 15 g m−2 and 160 g m−2. The BL had a depth of 1140 ± 120 m, was generally well-mixed and capped by a sharp inversion without predominately synoptic and meso-scale influences. The wind direction generally switched from southerly within the BL to northerly above the inversion. On days when a synoptic system and related mesoscale costal circulations affected conditions at Point Alpha (29 October–4 November), a moist layer above the inversion moved over Point Alpha, and the total-water mixing ratio above the inversion was larger than that within the BL. The accumulation mode aerosol varied from 250 to 700 cm−3 within the BL, and CCN at 0.2 % supersaturation within the BL ranged between 150 and 550 cm−3. The main aerosol source at Point Alpha was horizontal advection within the BL from south. The average cloud droplet number concentration ranged between 80 and 400 cm−3. While the mean LWP retrieved from GOES was in good agreement with the in situ measurements, the GOES-derived cloud droplet effective radius tended to be larger than that from the aircraft in situ observations near cloud top. The aerosol and cloud LWP relationship reveals that during the typical well-mixed BL days the cloud LWP increased with the CCN concentrations. On the other hand, meteorological factors and the decoupling processes have large influences on the cloud LWP variation as well.

scholarly journals Evaluation of Forecasted Southeast Pacific Stratocumulus in the NCAR, GFDL, and ECMWF Models

2009 ◽  
Vol 22 (11) ◽  
pp. 2871-2889 ◽  
Author(s):  
Cécile Hannay ◽  
David L. Williamson ◽  
James J. Hack ◽  
Jeffrey T. Kiehl ◽  
Jerry G. Olson ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Diurnal Cycle ◽  
Mixed Boundary ◽  
Eddy Diffusivity ◽  
Atmospheric Model ◽  
Surface Energy Budget ◽  
Liquid Water Path ◽  
Community Atmosphere Model ◽  
Southeast Pacific ◽  
Pbl Scheme

Abstract Forecasts of southeast Pacific stratocumulus at 20°S and 85°W during the East Pacific Investigation of Climate (EPIC) cruise of October 2001 are examined with the ECMWF model, the Atmospheric Model (AM) from GFDL, the Community Atmosphere Model (CAM) from NCAR, and the CAM with a revised atmospheric boundary layer formulation from the University of Washington (CAM-UW). The forecasts are initialized from ECMWF analyses and each model is run for 3–5 days to determine the differences with the EPIC field observations. Observations during the EPIC cruise show a well-mixed boundary layer under a sharp inversion. The inversion height and the cloud layer have a strong and regular diurnal cycle. A key problem common to the models is that the planetary boundary layer (PBL) depth is too shallow when compared to EPIC observations. However, it is suggested that improved PBL depths are achieved with more physically realistic PBL schemes: at one end, CAM uses a dry and surface-driven PBL scheme and produces a very shallow PBL, while the ECWMF model uses an eddy-diffusivity/mass-flux approach and produces a deeper and better-mixed PBL. All the models produce a strong diurnal cycle in the liquid water path (LWP), but there are large differences in the amplitude and phase when compared to the EPIC observations. This, in turn, affects the radiative fluxes at the surface and the surface energy budget. This is particularly relevant for coupled simulations as this can lead to a large SST bias.

scholarly journals Observations of the boundary layer, cloud, and aerosol variability in the southeast Pacific coastal marine stratocumulus during VOCALS-REx

2011 ◽  
Vol 11 (5) ◽  
pp. 15417-15468
Author(s):  
X. Zheng ◽  
B. Albrecht ◽  
H. H. Jonsson ◽  
D. Khelif ◽  
G. Feingold ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Cloud Droplet ◽  
Number Concentration ◽  
The Other ◽  
Specific Humidity ◽  
Radiosonde Data ◽  
Liquid Water Path ◽  
Southeastern Pacific ◽  
Cloud Droplet Number Concentration

Abstract. Aircraft observations made off the coast of northern Chile in the Southeastern Pacific (20° S, 72° W; named Point Alpha) from 16 October to 13 November 2008 during the VAMOS Ocean-Cloud-Atmosphere-Land Study-Regional Experiment (VOCALS-REx), combined with meteorological reanalysis, satellite measurements, and radiosonde data, are used to investigate the boundary layer (BL) and aerosol-cloud-drizzle variations in this region. The BL at Point Alpha was typical of a non-drizzling stratocumulus-topped BL on days without predominately synoptic and meso-scale influences. The BL had a depth of 1140 ± 120 m, was well-mixed and capped by a sharp inversion. The wind direction generally switched from southerly within the BL to northerly above the inversion. The cloud liquid water path (LWP) varied between 15 g m−2 and 160 g m−2. From 29 October to 4 November, when a synoptic system affected conditions at Point Alpha, the cloud LWP was higher than on the other days by around 40 g m−2. On 1 and 2 November, a moist layer above the inversion moved over Point Alpha. The total-water specific humidity above the inversion was larger than that within the BL during these days. Entrainment rates (average of 1.5 ± 0.6 mm s−1) calculated from the near cloud-top fluxes and turbulence (vertical velocity variance) in the BL at Point Alpha appeared to be weaker than those in the BL over the open ocean west of Point Alpha and the BL near the coast of the northeast Pacific. The accumulation mode aerosol varied from 250 to 700 cm−3 within the BL, and CCN at 0.2 % supersaturation within the BL ranged between 150 and 550 cm−3. The main aerosol source at Point Alpha was horizontal advection within the BL from south. The average cloud droplet number concentration ranged between 80 and 400 cm−3, which was consistent with the satellite-derived values. The relationship of cloud droplet number concentration and CCN at 0.2 % supersaturation from 18 flights is Nd =4.6 × CCN0.71. While the mean LWP retrieved from GOES was in good agreement with the in situ measurements, the GOES-derived cloud droplet effective radius tended to be larger than that from the aircraft {in situ} observations near cloud top. The aerosol and cloud LWP relationship reveals that during the typical well-mixed BL days the cloud LWP increased with the CCN concentrations. On the other hand, meteorological factors and the decoupling processes have large influences on the cloud LWP variation as well.

scholarly journals Simulating observed cloud transitions in the northeast Pacific during CSET

2021 ◽  
Author(s):  
Peter N. Blossey ◽  
Christopher S. Bretherton ◽  
Johannes Mohrmann
Keyword(s):  
Boundary Layer ◽  
Case Studies ◽  
Mixed Boundary ◽  
Cloud Droplet ◽  
Liquid Water Path ◽  
Field Campaign ◽  
Large Eddy Simulation Model ◽  
Northeast Pacific ◽  
First Case ◽  
Large Eddy

AbstractThe goal of this study is to challenge a large eddy simulation model with a range of observations from a modern field campaign and to develop case studies useful to other modelers. The 2015 Cloud System Evolution in the Trades (CSET) field campaign provided a wealth of in situ and remote sensing observations of subtropical cloud transitions in the summertime Northeast Pacific. Two Lagrangian case studies based on these observations are used to validate the thermodynamic, radiative and microphysical properties of large eddy simulations (LES) of the stratocumulus to cumulus transition. The two cases contrast a relatively fast cloud transition in a clean, initially well-mixed boundary layer vs. a slower transition in an initially decoupled boundary layer with higher aerosol concentrations and stronger mean subsidence. For each case, simulations of two neighboring trajectories sample mesoscale variability and the coherence of the transition in adjacent air masses. In both cases, LES broadly reproduce satellite and aircraft observations of the transition. Simulations of the first case match observations more closely than for the second case, where simulations underestimate cloud cover early in the simulations and overestimate cloud top height later. For the first case, simulated cloud fraction and liquid water path increase if a larger cloud droplet number concentration is prescribed. In the second case, precipitation onset and inversion cloud breakup occurs earlier when the LES domain is chosen large enough to support strong mesoscale organization.

scholarly journals Leeside Boundary Layer Confluence and Afternoon Thunderstorms over Mayaguez, Puerto Rico

2013 ◽  
Vol 52 (2) ◽  
pp. 439-454 ◽  
Author(s):  
Mark R. Jury ◽  
Sen Chiao
Keyword(s):  
Boundary Layer ◽  
Puerto Rico ◽  
Wind Shear ◽  
Wrf Model ◽  
Sea Breeze ◽  
Shear Zones ◽  
Near Surface ◽  
Diurnal Cycles ◽  
High Resolution Models ◽  
Island Wake

AbstractThe midsummer boundary layer (BL) circulation and afternoon thunderstorm convection on the lee side of Puerto Rico is studied using observations and high-resolution models. Satellite infrared data help to identify cases on 5 and 14 June 2010 when midday surface temperatures show a 2°C gradient between land and sea and afternoon cloud-top temperatures <−60°C. Acoustic sounder profiles are analyzed for climatology, wind shear, turbulence, and diurnal cycles in the 40–300-m layer. Weather Research and Forecasting (WRF) model simulations indicate that sea-breeze flow is entrained into convective cells near Mayaguez, Puerto Rico. The simulated BL wind shear is too weak (0.5 × 10−2 s−1) in comparison with the acoustic sounder (2 × 10−2 s−1). Model 900-hPa winds are southeasterly and spread simulated convection too far north in comparison with radar. The pattern of near-surface winds in the island wake triggers afternoon thunderstorms near Mayaguez. A feature of the confluent circulation around Puerto Rico is opposing shear zones on the leeward corners of the island and a sea breeze of 5 m s−1 over the west coast during midday.

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