scholarly journals The PreVOCA experiment: modeling the lower troposphere in the Southeast Pacific

2010 ◽  
Vol 10 (10) ◽  
pp. 4757-4774 ◽  
Author(s):  
M. C. Wyant ◽  
R. Wood ◽  
C. S. Bretherton ◽  
C. R. Mechoso ◽  
J. Bacmeister ◽  
...  
Keyword(s):  
Diurnal Cycle ◽  
Climate Models ◽  
Global Climate ◽  
Cloud Fraction ◽  
Atmospheric Modeling ◽  
Global Climate Models ◽  
Model Assessment ◽  
Regional Models ◽  
Study Region ◽  
Forecast Models

Abstract. The Preliminary VOCALS Model Assessment (PreVOCA) aims to assess contemporary atmospheric modeling of the subtropical South East Pacific, with a particular focus on the clouds and the marine boundary layer (MBL). Models results from fourteen modeling centers were collected including operational forecast models, regional models, and global climate models for the month of October 2006. Forecast models and global climate models produced daily forecasts, while most regional models were run continuously during the study period, initialized and forced at the boundaries with global model analyses. Results are compared in the region from 40° S to the equator and from 110° W to 70° W, corresponding to the Pacific coast of South America. Mean-monthly model surface winds agree well with QuikSCAT observed winds and models agree fairly well on mean weak large-scale subsidence in the region next to the coast. However they have greatly differing geographic patterns of mean cloud fraction with only a few models agreeing well with MODIS observations. Most models also underestimate the MBL depth by several hundred meters in the eastern part of the study region. The diurnal cycle of liquid water path is underestimated by most models at the 85° W 20° S stratus buoy site compared with satellite, consistent with previous modeling studies. The low cloud fraction is also underestimated during all parts of the diurnal cycle compared to surface-based climatologies. Most models qualitatively capture the MBL deepening around 15 October 2006 at the stratus buoy, associated with colder air at 700 hPa.

scholarly journals The PreVOCA experiment: modeling the lower troposphere in the Southeast Pacific

2009 ◽  
Vol 9 (6) ◽  
pp. 23909-23953 ◽  
Author(s):  
M. C. Wyant ◽  
R. Wood ◽  
C. S. Bretherton ◽  
C. R. Mechoso ◽  
J. Bacmeister ◽  
...  
Keyword(s):  
Diurnal Cycle ◽  
Climate Models ◽  
Global Climate ◽  
Cloud Fraction ◽  
Atmospheric Modeling ◽  
Global Climate Models ◽  
Model Assessment ◽  
Regional Models ◽  
Study Region ◽  
Forecast Models

Abstract. The Preliminary VOCALS Model Assessment (PreVOCA) aims to assess contemporary atmospheric modeling of the subtropical South East Pacific, with a particular focus on the clouds and the marine boundary layer (MBL). Models results from fourteen modeling centers were collected including operational forecast models, regional models, and global climate models for the month of October 2006. Forecast models and global climate models produced daily forecasts, while most regional models were run continuously during the study period, initialized and forced at the boundaries with global model analyses. Results are compared in the region from 40° S to the equator and from 110° W to 70° W, corresponding to the Pacific coast of South America. Mean-monthly model surface winds agree well with QuikSCAT observed winds and models agree fairly well on mean weak large-scale subsidence in the region next to the coast. However they have greatly differing mean geographic patterns of cloud fraction with only a few models agreeing well with MODIS observations. Most models also underestimate the MBL depth by several hundred meters in the eastern part of the study region. The diurnal cycle of liquid water path is underestimated by most models at the 85° W 20° S stratus buoy site compared with satellite, consistent with previous modeling studies. The low cloud fraction is also underestimated during all parts of the diurnal cycle compared to surface-based climatologies. Most models qualitatively capture the MBL deepening around 15 October 2006 at the stratus buoy, associated with colder air at 700 hPa.

Understanding the Roles of Convective Trigger Functions in the Diurnal Cycle of Precipitation in the NCAR CAM5

2021 ◽  
pp. 1-52
Author(s):  
Zeyu Cui ◽  
Guang J. Zhang ◽  
Yong Wang ◽  
Shaocheng Xie
Keyword(s):  
Great Plains ◽  
Diurnal Cycle ◽  
Climate Models ◽  
Global Climate ◽  
Convective Available Potential Energy ◽  
Global Climate Models ◽  
Peak Time ◽  
Entrainment Rate ◽  
Trigger Function ◽  
Diurnal Cycle Of Precipitation

AbstractThe wrong diurnal cycle of precipitation is a common weakness of current global climate models (GCMs). To improve the simulation of the diurnal cycle of precipitation and understand what physical processes control it, we test a convective trigger function described in Xie et al. (2019) with additional optimizations in the NCAR Community Atmosphere Model version 5 (CAM5). The revised trigger function consists of three modifications: 1) replacing the Convective Available Potential Energy (CAPE) trigger with a dynamic CAPE (dCAPE) trigger, 2) allowing convection to originate above the top of planetary boundary layer (i.e., the unrestricted air parcel launch level - ULL), and 3) optimizing the entrainment rate and threshold value of the dynamic CAPE generation rate for convection onset based on observations. Results from 1°-resolution simulations show that the revised trigger can alleviate the long-standing GCM problem of too early maximum precipitation during the day and missing the nocturnal precipitation peak that is observed in many regions, including the US Southern Great Plains (SGP). The revised trigger also improves the simulation of the propagation of precipitation systems downstream of the Rockies and the Amazon region. A further composite analysis over the SGP unravels the mechanisms through which the revised trigger affects convection. Additional sensitivity tests show that both the peak time and the amplitude of the diurnal cycle of precipitation are sensitive to the entrainment rate and dCAPE threshold values.

scholarly journals Climate Model Assessment of Changes in Winter–Spring Streamflow Timing over North America

2018 ◽  
Vol 31 (14) ◽  
pp. 5581-5593 ◽  
Author(s):  
Jonghun Kam ◽  
Thomas R. Knutson ◽  
P. C. D. Milly
Keyword(s):  
United States ◽  
Climate Models ◽  
Climate Model ◽  
Global Climate ◽  
Internal Variability ◽  
Global Climate Models ◽  
Anthropogenic Influence ◽  
Model Assessment ◽  
The North ◽  
Streamflow Timing

Over regions where snowmelt runoff substantially contributes to winter–spring streamflows, warming can accelerate snowmelt and reduce dry-season streamflows. However, conclusive detection of changes and attribution to anthropogenic forcing is hindered by the brevity of observational records, model uncertainty, and uncertainty concerning internal variability. In this study, the detection/attribution of changes in midlatitude North American winter–spring streamflow timing is examined using nine global climate models under multiple forcing scenarios. Robustness across models, start/end dates for trends, and assumptions about internal variability are evaluated. Marginal evidence for an emerging detectable anthropogenic influence (according to four or five of nine models) is found in the north-central United States, where winter–spring streamflows have been starting earlier. Weaker indications of detectable anthropogenic influence (three of nine models) are found in the mountainous western United States/southwestern Canada and in the extreme northeastern United States/Canadian Maritimes. In the former region, a recent shift toward later streamflows has rendered the full-record trend toward earlier streamflows only marginally significant, with possible implications for previously published climate change detection findings for streamflow timing in this region. In the latter region, no forced model shows as large a shift toward earlier streamflow timing as the detectable observed shift. In other (including warm, snow free) regions, observed trends are typically not detectable, although in the U.S. central plains we find detectable delays in streamflow, which are inconsistent with forced model experiments.

scholarly journals Global warming and monsoon climate

MAUSAM ◽  
2021 ◽  
Vol 52 (1) ◽  
pp. 245-262
Author(s):  
M. LAL ◽  
SANJEEV K. SINGH
Keyword(s):  
Summer Monsoon ◽  
Climate Models ◽  
Asian Summer Monsoon ◽  
Global Climate ◽  
Indian Subcontinent ◽  
Monsoon Season ◽  
Global Climate Models ◽  
Sulfate Aerosols ◽  
Study Region ◽  
Near Surface

The response of the Asian summer monsoon to transient increases of greenhouse gases (GHGs) and sulfate aerosols in the Earth's atmosphere is examined using the data generated in numerical experiments with available coupled atmosphere-ocean global climate models (A-O GCMs). A comparison of observed and model-simulated trends in monthly mean near-surface temperature and rainfall over the region provides evidence of skill of the A-O GCMs in simulating the regional climatology. The potential role of the sulfate aerosols in obscuring the GHG- induced warming over the Indian subcontinent is discussed. Even though the simulated total seasonal rainfall over the Indian subcontinent during summer monsoon season is underestimated in most of the A-O GCMs, the year to year variability in simulated monsoon rainfall over the study region is found to be in fair agreement with the observed climatology.

scholarly journals Simulating the diurnal cycle of rainfall in global climate models: resolution versus parameterization

2011 ◽  
Vol 39 (1-2) ◽  
pp. 399-418 ◽  
Author(s):  
Paul A. Dirmeyer ◽  
Benjamin A. Cash ◽  
James L. Kinter ◽  
Thomas Jung ◽  
Lawrence Marx ◽  
...  
Keyword(s):  
Diurnal Cycle ◽  
Climate Models ◽  
Global Climate ◽  
Global Climate Models

scholarly journals Evaluation of Hemispheric Asymmetries in Marine Cloud Radiative Properties

2017 ◽  
Vol 30 (11) ◽  
pp. 4131-4147 ◽  
Author(s):  
Frida A.-M. Bender ◽  
Anders Engström ◽  
Robert Wood ◽  
Robert J. Charlson
Keyword(s):  
Hemispheric Asymmetry ◽  
Climate Models ◽  
Global Climate ◽  
Cloud Amount ◽  
Cloud Fraction ◽  
Global Climate Models ◽  
Radiative Properties ◽  
Contributing Factors ◽  
Cloud Albedo ◽  
Clear Sky

Abstract The hemispheric symmetry of albedo and its contributing factors in satellite observations and global climate models is evaluated. The analysis is performed on the annual mean time scale, on which a bimodality in the joint distribution of albedo and cloud fraction is evident, resulting from tropical and subtropical clouds and midlatitude clouds, respectively. Hemispheric albedo symmetry is not found in individual ocean-only latitude bands; comparing the Northern and Southern Hemisphere (NH and SH), regional mean albedo is higher in the NH tropics and lower in the NH subtropics and midlatitudes than in the SH counterparts. This follows the hemispheric asymmetry of cloud fraction. In midlatitudes and tropics the hemispheric asymmetry in cloud albedo also contributes to the asymmetry in total albedo, whereas in the subtropics the cloud albedo is more hemispherically symmetric. According to the observations, cloud contributions to compensation for higher clear-sky albedo in the NH come primarily from cloud albedo in midlatitudes and cloud amount in the subtropics. Current-generation climate models diverge in their representation of these relationships, but common features of the model–data comparison include weaker-than-observed asymmetry in cloud fraction and cloud albedo in the tropics, weaker or reversed cloud fraction asymmetry in the subtropics, and agreement with observed cloud albedo asymmetry in the midlatitudes. Models on average reproduce the NH–SH asymmetry in total albedo over the 60°S–60°N ocean but show higher occurrence of brighter clouds in the SH compared to observations. The albedo bias in both hemispheres is reinforced by overestimated clear-sky albedo in the models.

scholarly journals Ice Fog: The Current State of Knowledge and Future Challenges

2017 ◽  
Vol 58 ◽  
pp. 4.1-4.24 ◽  
Author(s):  
Ismail Gultepe ◽  
Andrew J. Heymsfield ◽  
Martin Gallagher ◽  
Luisa Ickes ◽  
Darrel Baumgardner
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Weather Forecast ◽  
Global Climate Models ◽  
Ice Clouds ◽  
Microphysical Properties ◽  
Ice Fog ◽  
Future Challenges ◽  
Forecast Models ◽  
Microphysical Processes

Abstract Ice fog is a natural, outdoor cloud laboratory that provides an excellent opportunity to study ice microphysical processes. Ice crystals in fog are formed through similar pathways as those in elevated clouds; that is, cloud condensation or ice nuclei are activated in an atmosphere supersaturated with respect to liquid water or ice. The primary differences between surface and elevated ice clouds are related to the sources of water vapor, the cooling mechanisms and dynamical processes leading to supersaturation, and the microphysical characteristics of the nuclei that affect ice fog crystal physical properties. As with any fog, its presence can be a hazard for ground or airborne traffic because of poor visibility and icing. In addition, ice fog plays a role in climate change by modulating the heat and moisture budgets. Ice fog wintertime occurrence in many parts of the world can have a significant impact on the environment. Global climate models need to accurately account for the temporal and spatial microphysical and optical properties of ice fog, as do weather forecast models. The primary handicap is the lack of adequate information on nucleation processes and microphysical algorithms that accurately represent glaciation of supercooled water fog. This chapter summarizes the current understanding of ice fog formation and evolution; discusses operating principles, limitations, and uncertainties associated with the instruments used to measure ice fog microphysical properties; describes the prediction of ice fog by the numerical forecast models and physical parameterizations used in climate models; identifies the outstanding questions to be resolved; and lists recommended actions to address and solve these questions.

Extreme Events in High Resolution CMCC Regional and Global Climate Models

2011 ◽  
Author(s):  
Enrico Scoccimarro ◽  
Silvio Gualdi ◽  
Antonella Sanna ◽  
Edoardo Bucchignani ◽  
Myriam Montesarchio
Keyword(s):  
High Resolution ◽  
Extreme Events ◽  
Climate Models ◽  
Global Climate ◽  
Global Climate Models
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