scholarly journals Regional Assessments of Low Clouds against Large-Scale Stability in CAM5 and CAM-CLUBB Using MODIS and ERA-Interim Reanalysis Data

2015 ◽  
Vol 28 (4) ◽  
pp. 1685-1706 ◽  
Author(s):  
Terence L. Kubar ◽  
Graeme L. Stephens ◽  
Matthew Lebsock ◽  
Vincent E. Larson ◽  
Peter A. Bogenschutz
Keyword(s):  
Large Scale ◽  
Reanalysis Data ◽  
Smooth Transition ◽  
Cloud Data ◽  
Low Clouds ◽  
Community Atmosphere Model ◽  
Northeastern Pacific ◽  
Low Cloud ◽  
Cloud Parameterization ◽  
Static Energy

Abstract Daily gridded cloud data from MODIS and ERA-Interim reanalysis have been assessed to examine variations of low cloud fraction (CF) and cloud-top height and their dependence on large-scale dynamics and a measure of stability. To assess the stratocumulus (Sc) to cumulus (Cu) transition (STCT), the observations are used to evaluate two versions of the NCAR Community Atmosphere Model version 5 (CAM5), both the base model and a version that has implemented a new subgrid low cloud parameterization, Cloud Layers Unified by Binormals (CLUBB). The ratio of moist static energy (MSE) at 700–1000 hPa (MSEtotal) is a skillful predictor of median CF of screened low cloud grids. Values of MSEtotal less than 1.00 represent either conditionally or absolutely unstable layers, and probability density functions of CF suggest a preponderance of either trade Cu (median CF < 0.4) or transitional Sc clouds (0.4 < CF < 0.9). With increased stability (MSEtotal > 1.00), an abundance of overcast or nearly overcast low clouds exists. While both MODIS and ERA-Interim indicate a fairly smooth transition between the low cloud regimes, CAM5-Base simulates an abrupt shift from trade Cu to Sc, with trade Cu covering both too much area and occurring over excessively strong stabilities. In contrast, CAM-CLUBB simulates a smoother trade Cu to Sc transition (CTST) as a function of MSEtotal, albeit with too extensive coverage of overcast Sc in the primary northeastern Pacific subsidence region. While the overall CF distribution in CAM-CLUBB is more realistic, too few transitional clouds are simulated for intermediate MSEtotal compared to observations.

scholarly journals Instantaneous Linkages between Clouds and Large-Scale Meteorology over the Southern Ocean in Observations and a Climate Model

2017 ◽  
Vol 30 (23) ◽  
pp. 9455-9474 ◽  
Author(s):  
Casey J. Wall ◽  
Dennis L. Hartmann ◽  
Po-Lun Ma
Keyword(s):  
Southern Ocean ◽  
Large Scale ◽  
Climate Models ◽  
Climate Model ◽  
Austral Summer ◽  
Vertical Motion ◽  
Cloud Properties ◽  
Low Clouds ◽  
Community Atmosphere Model ◽  
Low Cloud

Instantaneous, coincident, footprint-level satellite observations of cloud properties and radiation taken during austral summer over the Southern Ocean are used to study relationships between clouds and large-scale meteorology. Cloud properties are very sensitive to the strength of vertical motion in the midtroposphere, and low-cloud properties are sensitive to estimated inversion strength, low-level temperature advection, and sea surface temperature. These relationships are quantified. An index for the meteorological anomalies associated with midlatitude cyclones is presented, and it is used to reveal the sensitivity of clouds to the meteorology within the warm and cold sectors of cyclones. The observed relationships between clouds and meteorology are compared to those in the Community Atmosphere Model, version 5 (CAM5), using satellite simulators. Low clouds simulated by CAM5 are too few, are too bright, and contain too much ice. In the cold sector of cyclones, the low clouds are also too sensitive to variations in the meteorology. When CAM5 is coupled with an updated boundary layer parameterization known as Cloud Layers Unified by Binormals (CLUBB), bias in the ice content of low clouds is dramatically reduced. More generally, this study demonstrates that examining the instantaneous time scale is a powerful approach to understanding the physical processes that control clouds and how they are represented in climate models. Such an evaluation goes beyond the cloud climatology and exposes model bias under various meteorological conditions.

scholarly journals Low-Cloud Transitions across the Kuroshio Front in the East China Sea

2016 ◽  
Vol 29 (12) ◽  
pp. 4429-4443 ◽  
Author(s):  
Jing-Wu Liu ◽  
Shang-Ping Xie ◽  
Shuang Yang ◽  
Su-Ping Zhang
Keyword(s):  
East China Sea ◽  
Large Scale ◽  
East Asian Monsoon ◽  
East China ◽  
The East China Sea ◽  
Asian Monsoon Region ◽  
China Sea ◽  
Low Clouds ◽  
Low Cloud ◽  
Different Seasons

Abstract The East China Sea Kuroshio (ECSK) flows in the East Asian monsoon region where the background atmospheric circulation varies significantly with season. A sea surface temperature (SST) front associated with the ECSK becomes narrower and sharper from winter to spring. The present study investigates how low clouds respond to the ECSK front in different seasons by synthesizing spaceborne lidar and surface visual observations. The results reveal prominent cross-frontal transitions in low clouds, which exhibit distinct behavior between winter and spring. In winter, cloud responses are generally confined below 4 km by the strong background descending motion and feature a gradual cloud-top elevation from the cold to the warm flank of the front. The ice clouds on the cold flank of the ECSK front transform into liquid water clouds and rain on the warm flank. The springtime clouds, by contrast, are characterized by a sharp cross-frontal transition with deep clouds reaching up to 7 km over the ECSK. In both winter and spring, the low-cloud morphology exhibits a large transformation from the cold to the warm flank of the ECSK front, including increases in cloud-top height, a decline in smoothness of cloud top, and the transition from stratiform to convective clouds. All this along with the atmospheric soundings indicates that the decoupling of the marine atmospheric boundary layer (MABL) is more prevalent on the warm flank of the front. Thus, long-term observations reveal prominent cross-frontal low-cloud transitions in morphology associated with MABL decoupling that resemble a large-scale cloud-regime transition over the eastern subtropical Pacific.

scholarly journals Evaluating Low-Cloud Simulation from an Upgraded Multiscale Modeling Framework Model. Part III: Tropical and Subtropical Cloud Transitions over the Northern Pacific

2013 ◽  
Vol 26 (16) ◽  
pp. 5761-5781 ◽  
Author(s):  
Anning Cheng ◽  
Kuan-Man Xu
Keyword(s):  
Precipitable Water ◽  
Modeling Framework ◽  
Radiative Fluxes ◽  
Northern Summer ◽  
Community Atmosphere Model ◽  
Low Cloud ◽  
The Mean ◽  
Cloud Parameterization ◽  
Boundary Layer Cloud ◽  
Multiscale Modeling Framework

Abstract An analysis of simulated cloud regime transitions along a transect from the subtropical California coast to the tropics for the northern summer season (June–August) is presented in this study. The Community Atmosphere Model, version 5 (CAM5), superparameterized CAM (SPCAM), and an upgraded SPCAM with intermediately prognostic higher-order closure (SPCAM-IPHOC) are used to perform global simulations by imposing climatological sea surface temperature and sea ice distributions. The seasonal-mean properties are compared with recent observations of clouds, radiation, and precipitation and with multimodel intercomparison results. There are qualitative agreements in the characteristics of cloud regimes along the transect among the three models. CAM5 simulates precipitation and shortwave radiative fluxes well but the stratocumulus-to-cumulus transition occurs too close to the coast of California. SPCAM-IPHOC simulates longwave radiative fluxes and precipitable water well, but with systematic biases in shortwave radiative fluxes. The broad, stronger ascending band in SPCAM is related to the large biases in the convective region but the characteristics of the stratocumulus region are still more realistic and the transition occurs slightly farther away from the coast than in CAM5. Even though SPCAM-IPHOC produces the most realistic seasonal-mean transition, it underestimates the mean gradient in low-cloud cover (LCC) across the mean transition location because of an overestimate of LCC in the transition and convective regions that shifts the transition locations farther from the coast. Analysis of two decoupling measures shows consistency in the mean location and the histogram of decoupling locations with those of LCC transition. CAM5, however, lacks such a consistency, suggesting a need for further refinement of its boundary layer cloud parameterization.

A Moist Static Energy Budget Analysis of Quasi-2-Day Waves Using Satellite and Reanalysis Data

2016 ◽  
Vol 73 (2) ◽  
pp. 743-759 ◽  
Author(s):  
Yukari Sumi ◽  
Hirohiko Masunaga
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Reanalysis Data ◽  
Convective Heating ◽  
Moist Static Energy ◽  
Wave Dynamics ◽  
Vertical Advection ◽  
Budget Analysis ◽  
Static Energy ◽  
Thermodynamic Processes

Abstract A moist static energy (MSE) budget analysis is applied to quasi-2-day waves to examine the effects of thermodynamic processes on the wave propagation mechanism. The 2-day waves are defined as westward inertia–gravity (WIG) modes identified with filtered geostationary infrared measurements, and the thermodynamic parameters and MSE budget variables computed from reanalysis data are composited with respect to the WIG peaks. The composite horizontal and vertical MSE structures are overall as theoretically expected from WIG wave dynamics. A prominent horizontal MSE advection is found to exist, although the wave dynamics is mainly regulated by vertical advection. The vertical advection decreases MSE around the times of the convective peak, plausibly resulting from the first baroclinic mode associated with deep convection. Normalized gross moist stability (NGMS) is used to examine the thermodynamic processes involving the large-scale dynamics and convective heating. NGMS gradually decreases to zero before deep convection and reaches a maximum after the convection peak, where low (high) NGMS leads (lags) deep convection. The decrease in NGMS toward zero before the occurrence of active convection suggests an increasingly efficient conversion from convective heating to large-scale dynamics as the wave comes in, while the increase afterward signifies that this linkage swiftly dies out after the peak.

scholarly journals Synoptic-scale controls of fog and low clouds in the Namib Desert

2019 ◽  
Author(s):  
Hendrik Andersen ◽  
Jan Cermak ◽  
Julia Fuchs ◽  
Peter Knippertz ◽  
Marco Gaetani ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Marine Boundary Layer ◽  
Synoptic Scale ◽  
Namib Desert ◽  
Sea Level Pressure ◽  
Mean Sea Level ◽  
Air Masses ◽  
Low Clouds ◽  
Low Cloud

Abstract. Fog is a defining characteristic of the climate of the Namib Desert and its water and nutrient input are important for local ecosystems. In part due to sparse observation data, the local mechanisms that lead to fog occurrence in the Namib are not yet fully understood, and to date, potential synoptic-scale controls have not been investigated. In this study, a recently established 14-year data set of satellite observations of fog and low clouds in the central Namib is analyzed in conjunction with reanalysis data to identify typical synoptic-scale conditions associated with fog and low-cloud occurrence in the central Namib during two seasons that characterize seasonal fog variability. It is found that during both seasons, mean sea level pressure and geopotential height at 500 hPa differ significantly between fog/low-cloud and clear days, with patterns indicating seasonally different synoptic-scale disturbances on fog and low-cloud days: cut-off lows during September, October, and November, and breaking Rossby waves during April, May, and June. These regularly occurring disturbances increase the probability of fog and low-cloud occurrence in the central Namib in two main ways: 1) an anomalously dry free troposphere in the coastal region of the Namib leads to stronger longwave cooling, especially over the ocean, facilitating low-cloud formation, and 2) local wind systems are modulated, leading to an onshore anomaly of marine boundary-layer air masses. This is consistent with air mass backtrajectories and a principal component analysis of spatial wind patterns that point to advected marine boundary- layer air masses on fog and low-cloud days, whereas subsiding continental air masses dominate on clear days. Large-scale free-tropospheric moisture transport into southern Africa seems to be a key factor modulating the onshore advection of marine boundary-layer air masses during April, May, and June, as the associated increase in greenhouse gas warming and thus surface heating is observed to contribute to a continental heat low anomaly. A statistical model is trained to discriminate between fog/low-cloud and clear days based on large-scale mean sea level pressure fields. The model accurately predicts fog and low-cloud days, illustrating the importance of large-scale pressure modulation and advective processes. It can be concluded that Namib-region fog is predominantly of advective nature, but also facilitated by increased radiative cooling. Seasonally different manifestations of synoptic-scale disturbances act to modify its day-to-day variability and the balance of mechanisms leading to its formation. The results are the basis for a new conceptual model on the synoptic-scale mechanisms that control fog and low clouds in the Namib Desert, and will guide future studies of coastal fog regimes.

scholarly journals Building a cloud in the Southeast Atlantic: Understanding low-cloud controls based on satellite observations with machine learning

2018 ◽  
Author(s):  
Julia Fuchs ◽  
Jan Cermak ◽  
Hendrik Andersen
Keyword(s):  
Machine Learning ◽  
Large Scale ◽  
Cloud Droplet ◽  
Reanalysis Data ◽  
Cloud Fraction ◽  
Effective Radius ◽  
Gradient Boosting ◽  
Tropospheric Temperature ◽  
Aerosol Cloud ◽  
Low Cloud

Abstract. Understanding the processes that determine low-cloud properties and aerosol–cloud interactions (ACI) is crucial for the estimation of their radiative effects. However, the covariation of meteorology and aerosols complicates the determination of cloud-relevant influences and the quantification of the aerosol–cloud relation. This study identifies and analyzes sensitivities of cloud fraction and cloud droplet effective radius to their meteorological and aerosol environment in the atmospherically stable Southeast Atlantic during the biomass-burning season. The effect of geophysical parameters on clouds is investigated based on a machine learning technique, gradient boosting regression trees (GBRTs), using a combination of satellite and reanalysis data as well as trajectory modeling of air-mass origins. A comprehensive, multivariate analysis of important drivers of cloud occurrence and properties is performed and evaluated. The statistical model reveals marked subregional differences of relevant drivers and processes determining low clouds in the Southeast Atlantic. Cloud fraction is sensitive to changes of lower tropospheric stability in the oceanic, southwestern subregion, while in the northeastern subregion it is governed mostly by surface winds. In the pristine, oceanic subregion large-scale dynamics and aerosols seem to be more important for changes of cloud droplet effective radius than in the polluted, near-shore subregion, where free tropospheric temperature is more relevant. This study suggests the necessity to consider distinct ACI regimes in cloud studies in the Southeast Atlantic.

scholarly journals Albedo susceptibility of Northeastern Pacific stratocumulus: the role of covarying meteorological conditions

2021 ◽  
Author(s):  
Jianhao Zhang ◽  
Xiaoli Zhou ◽  
Graham Feingold
Keyword(s):  
Large Scale ◽  
Meteorological Factors ◽  
Meteorological Conditions ◽  
Radiative Properties ◽  
Liquid Water Path ◽  
Cloud Albedo ◽  
Low Clouds ◽  
Low Cloud ◽  
Ne Pacific

Abstract. Quantification of the radiative adjustment of marine low-clouds to aerosol perturbations, regionally and globally, remains the largest source of uncertainty in assessing current and future climate. An important step towards quantifying the role of aerosol in modifying cloud radiative properties is to quantify the susceptibility of cloud albedo and liquid water path (LWP) to perturbations in cloud droplet number concentration (Nd). We use 10 years of space-borne observations from the polar-orbiting Aqua satellite, to quantify the albedo susceptibility of marine low-clouds over the northeast (NE) Pacific stratocumulus region to Nd perturbations. Overall, we find a low-cloud brightening potential of 20.8 ± 0.96 W m−2 ln(Nd)−1, despite an overall negative LWP adjustment for non-precipitating marine stratocumulus, owing to the high occurrence (37% of the time) of thin non-precipitating clouds (LWP < 55 g m−2) that exhibit brightening. In addition, we identify two more susceptibility regimes, the entrainment-darkening regime (36% of the time), corresponding to negative LWP adjustment, and the precipitating-brightening regime (22% of the time), corresponding to precipitation suppression. The influence of large-scale meteorological conditions, obtained from the ERA5 reanalysis, on the albedo susceptibility is also examined. Over the NE Pacific, clear seasonal covariabilities among meteorological factors related to the large-scale circulation are found to play an important role in grouping favorable conditions for each susceptibility regime. Our results indicate that, for the NE Pacific stratocumulus deck, the strongest positively susceptible cloud states occur most frequently for low cloud top height (CTH), the highest lower-tropospheric stability (LTS), low sea-surface temperature (SST), and the lowest free-tropospheric relative humidity (RHft) conditions, whereas cloud states that exhibit negative LWP adjustment occur most frequently under high CTH and intermediate LTS, SST, and RHft conditions. The warm rain suppression driven cloud brightening is found to preferably occur either under unstable atmospheric conditions (low LTS) or high RHft conditions that co-occur with warm SST. Mutual information analyses reveal a dominating control of LWP, Nd and CTH (cloud state indicators) on low-cloud albedo susceptibility, rather than of the meteorological factors that drive these cloud states.

The Role of Mesoscale Cellular Convective Cloud Morphologies in Low Cloud Feedbacks 

2021 ◽  
Author(s):  
Isabel L. McCoy ◽  
Daniel T. McCoy ◽  
Robert Wood ◽  
Paquita Zuidema ◽  
Frida A.-M. Bender
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Global Climate ◽  
Convective Cloud ◽  
Static Stability ◽  
Reanalysis Data ◽  
Global Climate Models ◽  
Liquid Water Path ◽  
Radiative Impacts ◽  
Low Cloud

&lt;p&gt;Mesoscale cellular convective (MCC) clouds occur in large-scale patterns over the ocean, are prevalent in sub-tropical cloud regions and mid-latitudes, and have important radiative impacts on the climate system. On average, closed MCC clouds have higher albedos than open or disorganized MCC clouds for the same cloud fraction which suggests differences in micro- and macro-physical characteristics between MCC morphologies. Marine cold air outbreaks (MCAOs) influence the development of open MCC clouds and the transition from closed to open MCC clouds in the mid-latitudes. A MCAO index, M, combines atmospheric surface forcing and static stability and can be used to examine global MCC morphology dependencies. MCC cloud morphology occurrence is also expected to shift with sea surface temperature (SST) changes as the climate warms. Analysis of MCC identifications (derived from a neural network classifier applied to MODIS satellite collection 6 liquid water path retrievals) and ECMWF ERA5 reanalysis data shows that closed MCC cloud occurrence shifts to open or disorganized MCC within an M-SST space. Global climate models (GCMs) predict that M will change regionally in strength as SSTs increase. Based on our derived MCC-M-SST relationship in the current climate, closed MCC occurrence frequency is expected to increase with a weakening of M but decrease with an increase in SSTs. This results in a shift to cloud morphologies with lower albedos. Cloud controlling factor analysis is used to estimate the resulting low cloud morphology feedback which is found to be spatially varied and between &amp;#177;0.15 W m&lt;sup&gt;-2&lt;/sup&gt; K&lt;sup&gt;-1&lt;/sup&gt;. Because the morphology feedback is estimated to be positive in the extra-tropics and is not currently represented in GCMs, this implies a higher climate sensitivity than GCMs currently estimate.&lt;/p&gt;

scholarly journals Comparing ERA-Interim clouds with satellite observations using a simplified satellite simulator

2018 ◽  
Author(s):  
Martin Stengel ◽  
Cornelia Schlundt ◽  
Stefan Stapelberg ◽  
Oliver Sus ◽  
Salomon Eliasson ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Reanalysis Data ◽  
Cloud Fraction ◽  
Satellite Observations ◽  
Vertical Position ◽  
Polar Regions ◽  
Cloud Properties ◽  
Low Clouds ◽  
Low Cloud ◽  
Cloud Optical Thickness

Abstract. An evaluation of the ERA-Interim clouds using satellite observations is presented. To facilitate such an evaluation in a proper way, a simplified satellite simulator has been developed and applied to six-hourly ERA-Interim reanalysis data covering the period 1982 to 2014. The simulator converts modelled cloud fields, for example those of the ERA-Interim reanalysis, to simulated cloud fields by accounting for specific characteristics of passive imaging satellite sensors such as the Advanced Very High Resolution Radiometer (AVHRR), which form the basis of many long-term observational datasets of cloud properties. It is attempted to keep the simulated cloud fields close to the original modelled cloud fields to allow a quality assessment of the latter based on comparisons of the simulated clouds fields with the observations. Applying the simulator to ERA-Interim data, this study firstly focuses on spatial distribution and frequency of clouds (total cloud fraction) and on their vertical position, using cloud top pressure to express the cloud fraction of high, mid-level and low clouds. Furthermore, the cloud-top thermodynamic phase is investigated. All comparisons incorporate knowledge of systematic uncertainties in the satellite observations and are further stratified by accounting for the limited sensitivity of the observations to clouds with very low cloud optical thickness (COT). The comparisons show that ERA-Interim has generally too low cloud fraction – nearly everywhere on the globe except in the polar regions. This underestimation is caused by a lack of mid-level and/or low clouds – for which the comparisons only show a minor sensitivity to cloud optical thickness thresholds applied. The amount of ERA-Interim high clouds, being higher than in the observations, agrees to the observations within their estimated uncertainties. Removing the optically very thin clouds (COT 

scholarly journals Boundary Layer and Cloud Structure Controls on Tropical Low Cloud Cover Using A-Train Satellite Data and ECMWF Analyses

2011 ◽  
Vol 24 (1) ◽  
pp. 194-215 ◽  
Author(s):  
Terence L. Kubar ◽  
Duane E. Waliser ◽  
J-L. Li
Keyword(s):  
Boundary Layer ◽  
Cross Section ◽  
Large Scale ◽  
Layer Structure ◽  
Deep Convection ◽  
Static Stability ◽  
Boundary Layer Stability ◽  
Middle Point ◽  
Cloud Data ◽  
Low Cloud

Abstract The Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), CloudSat radar, and the Moderate Resolution Imaging Spectroradiometer (MODIS) cloud data on the A-Train constellation complemented with the European Centre for Medium-Range Forecasts (ECMWF) analyses are used to investigate the cloud and boundary layer structure across a 10° wide cross section starting at 5°S near the international date line and extending to 35°N near the California coast from March 2008 to February 2009. The mean large-scale inversion height and low-level cloud tops, which correspond very closely to each other, are very shallow (∼500 m) over cold SSTs and high static stability near California and deepen southwestward (to a maximum of ∼1.5–2.0 km) along the cross section as SSTs rise. Deep convection near the ITCZ occurs at a surface temperature close to 298 K. While the boundary layer relative humidity (RH) is nearly constant where a boundary layer is well defined, it drops sharply near cloud top in stratocumulus regions, corresponding with strong thermal inversions and water vapor decrease, such that the maximum (−∂RH/∂z) marks the boundary layer cloud top very well. The magnitude correlates well with low cloud frequency during March–May (MAM), June–August (JJA), and September–November (SON) (r 2 = 0.85, 0.88, and 0.86, respectively). Also, CALIPSO and MODIS isolated low cloud frequency generally agree quite well, but CloudSat senses only slightly more than one-third of the low clouds as observed by the other sensors, as many clouds are shallower than 1 km and thus cannot be discerned with CloudSat due to contamination from the strong signal from surface clutter. Mean tropospheric ω between 300 and 700 hPa is examined from the ECMWF Year of Tropical Convection (YOTC) analysis dataset, and during JJA and SON, strong rising motion in the middle troposphere is confined to a range of 2-m surface temperatures between 297 and 300 K, consistent with previous studies that show a narrow range of SSTs over which deep ascent occurs. During December–February (DJF), large-scale ascending motion extends to colder SSTs and high boundary layer stability. A slightly different boundary layer stability metric is derived, the difference of moist static energy (MSE) at the middle point of the inversion (or at 700 hPa if no inversion exists) and the surface, referred to as ΔMSE. The utility of ΔMSE is its prediction of isolated uniform low cloud frequency, with very high r 2 values of 0.93 and 0.88, respectively, for the MODIS and joint lidar plus radar product during JJA but significantly lower values during DJF (0.46 and 0.40), with much scatter. To quantify the importance of free tropospheric dynamics in modulating the ΔMSE–low cloud relationships, the frequency as a function of ΔMSE of rising motion profiles (ω &lt; −0.05 Pa s−1) is added to the observed low cloud frequency for a maximum hypothetical low cloud frequency. Doing this greatly reduces the interseasonal differences and holds promise for using ΔMSE for parameterization schemes and examining low cloud feedbacks.

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