Dynamics and Chemistry of Marine Stratocumulus-DYCOMS-II (original) (raw)
Related papers
Modelling marine stratocumulus and its radiative properties
2010
Research to improve the representation of clouds and their radiative properties in climate models has been carried out over many years, and tropical boundary layer clouds which cover large regions have been identified as the largest contributor to the uncertainty. Many of these clouds arise in the subtropics at the eastern edge of subtropical anticyclones, where marine air is cooled by coastal upwelling of cold water from the deep ocean to form semipermanent cloud decks which have a large influence on the global climate. The southeast Pacific has the largest and most persistent stratocumulus deck in the world, where the winds drive intense coastal upwelling so that sea surface temperatures are colder along the Chilean and Peruvian coasts than at any comparable latitude, and the cool moist boundary layer has a strong inversion with the warm dry air aloft.
Thermodynamic and Aerosol Controls in Southeast Pacific Stratocumulus
Journal of the Atmospheric Sciences, 2012
A near-large-eddy simulation approach with size-revolving (bin) microphysics is employed to evaluate the relative sensitivity of southeast Pacific marine boundary layer cloud properties to thermodynamic and aerosol parameters. Simulations are based on a heavily drizzling cloud system observed by the NOAA ship Ronald H. Brown during the Variability of the American Monsoon Systems (VAMOS) Ocean–Cloud–Atmosphere–Land Study—Regional Experiment (VOCALS-Rex) field campaign. A suite of numerical experiments examines the sensitivity of drizzle to variations in boundary layer depth and cloud condensation nuclei (CCN) concentration in a manner consistent with the variability of those parameters observed during VOCALS-Rex. All four simulations produce cellular structures and turbulence characteristics of a circulation driven predominantly in a bottom-up fashion. The cloud and subcloud layers are coupled by strong convective updrafts that provide moisture to the cloud layer. Distributions of re...
Meteorological and Aerosol Effects on Marine Stratocumulus
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 878-798W, while the eastern regime is around 798-718W. 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.
Dynamics and Chemistry of Marine Stratocumulus (DYCOMS) Experiment
Bulletin of the American Meteorological Society, 1988
A combined atmospheric chemistry-meteorology experiment, the Dynamics and Chemistry of the Marine Stratocumulus (DYCOMS), was carried out during the summer of 1985 over the eastern Pacific Ocean using the NCAR Electra aircraft. The objectives were to 1) study the budgets of several trace reactive species in a relatively pristine, steady-state, horizontally homogeneous, well-mixed boundary layer capped by a strong inversion
Observations of marine stratocumulus in SE Pacific during the PACS 2003 cruise
Geophysical Research Letters, 2004
1] In November 2003, the NOAA Environmental Technology Laboratory (ETL) conducted measurements of Marine Boundary Layer (MBL) stratocumulus clouds, thermodynamic structure, surface fluxes and meteorology in the southeastern Pacific stratocumulus region. The observations were part of a field program to replace the WHOI Ocean Reference Station buoy at 20 S Latitude 85 W Longitude. During the cruise the MBL structure was characterized by a strong capping inversion, periods with well mixed conditions and marine stratus, clear sky periods and periods with moderate vertical gradients of potential temperature and mixing ratio that overlap with periods of small cloud fractional coverage, decoupled layers and low cloud base shallow cumuli clouds. The lifting condensation level (LCL) showed strong variability consistent with the variability of the MBL. Clouds with thickness more that 250 m had drizzle below the cloud base especially during nighttime. Large periods of clear skies were observed at the buoy location, especially just after the solar flux maximum. The aerosol size distribution measurements generally exhibited a bimodal structure. However, abrupt changes in the aerosol size distribution were also recorded, corresponding either with the presence of drizzle (and a depletion of the accumulation mode) or the presence of clear skies (and an increase in the Aitken mode). The stratocumulus observed during the 5-day station at the buoy location revealed a far more complex picture from the one captured during the East Pacific Investigation of Climate (EPIC) cruise to this same location in 2001.
Journal of Applied Meteorology and Climatology, 2014
Stratocumulus (Sc) clouds occur frequently over the cold waters of the southeastern Pacific Ocean. Data collected during two Pan American Climate Study research cruises in the tropical eastern Pacific illuminate many aspects of this Sc-topped marine boundary layer (MBL). Here the focus is on understanding gaps in detectable wind-profiler reflectivities during two boreal autumn cruises. After rigorous quality control that included applying the Riddle threshold of minimum signal-to-noise ratio (SNR) detectability, there are many instances with no measurable atmospheric signals through a depth of up to several hundred meters, often lasting for an hour or more. Rain gauge data from the autumn 2004 cruise are used to calibrate the profiler, which allows SNR to be converted to both equivalent reflectivity and the structure-function parameter of the index of refraction . Profiles of statistics from the two profiler modes (resolutions) highlight the wide range of during a 24-h period and bound the atmosphere’s when low-mode gaps are not mirrored in the high-mode data. Considering the gaps in terms of allows them to be understood as indications of reduced “top down” buoyancy processes and/or reduced turbulent intensity, both of which have been demonstrated by previous researchers to be associated with decoupling within the Sc-topped MBL. A decoupling index calculated from surface and ceilometer data strongly suggests that decoupled conditions were common and that the MBL was coupled when gaps in profiler reflectivity were unlikely. Further study of data from other cruises may lead to a method of using profiler reflectivity as an indicator of decoupled conditions.
Understanding wind profiler observations of the stratocumulus-topped marine boundary layer
2011
Clouds directly affect Earth's energy budget by changing the planet's albedo and the balance of incoming and outgoing radiation. Of particular interest are marine stratocumulus (Sc), which play an important role in this balance by typically cooling the planet. To better understand Sc and their effects, and to improve modeling, their thickness needs to be more precisely determined. While Sc cloud bottoms can be measured effectively by ceilometers, the tops prove to be more difficult. Wind profiler data are often suggested as an aid in identifying the top of the marine boundary layer (MBL), which coincides with the top of Sc, but interpretation of profiler data is often difficult. This project focuses on analyzing and understanding profiler data acquired over the eastern Pacific Ocean, with the assistance of both ceilometer and radiosonde data. Data were acquired during a Pan American Climate Study (PACS) research cruise off the west coast of South America in fall 2004. Monthly averages from the International Satellite Cloud Climatology Project (ISCCP) were used to identify days when the ship was likely under Sc. On 13 of those days, wind profiler data showed a layer of high reflectivity at 1-1.5km. The ceilometer cloud base heights never surpassed the layer's height, and the sonde relative humidity decreased sharply across the layer, indicating the inversion that caps the MBL. Further research can improve precision for finding the tops of Sc and help make algorithms that find the MBL top.