Implementation and evaluation of a double-plume convective parameterization in NCAR CAM5

AbstractPerformance of global climate models (GCMs) is strongly affected by their cumulus parameterizations (CP) used. Similar to the approach in GFDL AM4, a double-plume CP, which unifies the deep and shallow convection in one framework, is implemented and tested in NCAR Community Atmospheric Model version 5 (CAM5). Based on the University of Washington (UW) shallow convection scheme, an additional plume was added to represent the deep convection. The shallow and deep plumes share the same cloud model, but use different triggers, fractional mixing rates and closures. The scheme was tested in single column, short-term hindcast and AMIP simulations. Compared with the default combination of Zhang-McFarlane scheme and UW scheme in CAM5, the new scheme tends to produce a top-heavy mass flux profile during the active monsoon period in the single column simulations. The scheme increases the intensity of tropical precipitation, closer to TRMM observations. The new scheme increased subtropical marine boundary layer clouds and high clouds over the deep tropics, both in better agreement with observations. Sensitivity tests indicate that regime dependent fractional entrainment rates of the deep plume are desired to improve tropical precipitation distribution and upper troposphere temperature. This study suggests that a double-plume approach is a promising way to combine shallow and deep convections in a unified framework.

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The Double-ITCZ Bias in CMIP6 Models

10.5194/egusphere-egu2020-21375 ◽

2020 ◽

Author(s):

Baijun Tian

Keyword(s):

Climate Models ◽

Global Climate ◽

Coupled Model ◽

Global Climate Models ◽

Cmip5 Models ◽

Tropical Precipitation ◽

Double Itcz ◽

Intercomparison Project ◽

Fully Coupled

<p>The double-Intertropical Convergence Zone (ITCZ) bias is one of the most outstanding problems in climate models. This study seeks to examine the double-ITCZ bias in the latest state-of-the-art fully coupled global climate models that participated in Coupled Model Intercomparison Project (CMIP) Phase 6 (CMIP6) in comparison to their previous generations (CMIP3 and CMIP5 models). To that end, we have analyzed the long-term annual mean tropical precipitation distributions and several precipitation bias indices that quantify the double-ITCZ biases in 75 climate models including 24 CMIP3 models, 25 CMIP3 models, and 26 CMIP6 models. We find that the double-ITCZ bias and its big inter-model spread persist in CMIP6 models but the double-ITCZ bias is slightly reduced from CMIP3 or CMIP5 models to CMIP6 models.</p>

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An Analysis of Convectively Coupled Kelvin Waves in 20 WCRP CMIP3 Global Coupled Climate Models

Journal of Climate ◽

10.1175/2009jcli3422.1 ◽

2010 ◽

Vol 23 (11) ◽

pp. 3031-3056 ◽

Cited By ~ 48

Author(s):

Katherine H. Straub ◽

Patrick T. Haertel ◽

George N. Kiladis

Keyword(s):

Climate Models ◽

Global Climate ◽

Three Dimensional ◽

Kelvin Waves ◽

Global Climate Models ◽

Specific Humidity ◽

Tropospheric Temperature ◽

Wave Band ◽

Kelvin Wave ◽

Shallow Convection

Abstract Output from 20 coupled global climate models is analyzed to determine whether convectively coupled Kelvin waves exist in the models, and, if so, how their horizontal and vertical structures compare to observations. Model data are obtained from the World Climate Research Program’s (WCRP’s) Coupled Model Intercomparison Project phase 3 (CMIP3) multimodel dataset. Ten of the 20 models contain spectral peaks in precipitation in the Kelvin wave band, and, of these 10, only 5 contain wave activity distributions and three-dimensional wave structures that resemble the observations. Thus, the majority (75%) of the global climate models surveyed do not accurately represent convectively coupled Kelvin waves, one of the primary sources of submonthly zonally propagating variability in the tropics. The primary feature common to the five successful models is the convective parameterization. Three of the five models use the Tiedtke–Nordeng convective scheme, while the other two utilize the Pan and Randall scheme. The 15 models with less success at generating Kelvin waves predominantly contain convective schemes that are based on the concept of convective adjustment, although it appears that those schemes can be improved by the addition of convective “trigger” functions. Three-dimensional Kelvin wave structures in the five successful models resemble observations to a large degree, with vertically tilted temperature, specific humidity, and zonal wind anomalies. However, no model completely captures the observed signal, with most of the models being deficient in lower-tropospheric temperature and humidity signals near the location of maximum precipitation. These results suggest the need for improvements in the representations of shallow convection and convective downdrafts in global models.

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Aircraft measurements of aerosol and trace gas chemistry in the Eastern North Atlantic

10.5194/acp-2020-887 ◽

2020 ◽

Author(s):

Maria A. Zawadowicz ◽

Kaitlyn Suski ◽

Jiumeng Liu ◽

Mikhail Pekour ◽

Jerome Fast ◽

...

Keyword(s):

Mass Spectrometer ◽

North Atlantic ◽

Climate Models ◽

Marine Boundary Layer ◽

Global Climate ◽

Cloud Condensation Nuclei ◽

Proton Transfer Reaction ◽

Global Climate Models ◽

Aerosol Mass ◽

Eastern North Atlantic

Abstract. The Aerosol and Cloud Experiment in the Eastern North Atlantic (ACE-ENA) investigated properties of aerosols and subtropical marine boundary layer (MBL) clouds. Low subtropical marine clouds can have a large effect on Earth's radiative budget, but they are poorly represented in global climate models. In order to understand their radiative effects, it is imperative to understand the composition and sources of the MBL cloud condensation nuclei (CCN). The campaign consisted of two intensive operation periods (IOP) (June–July, 2017 and January–February, 2018) during which a fully instrumented G-1 aircraft was deployed from Lajes Field on Terceira Island in the Azores, Portugal. The G-1 conducted research flights in the vicinity of the Atmospheric Radiation Measurement (ARM) Eastern North Atlantic (ENA) atmospheric observatory on Graciosa Island. An Aerodyne HR-ToF Aerosol Mass Spectrometer (AMS) and Ionicon Proton-Transfer-Reaction Mass Spectrometer (PTR-MS) were deployed aboard the aircraft, characterizing chemistry of non-refractory aerosol and trace gases, respectively. The Eastern North Atlantic region was found to be very clean, with average non-refractory aerosol mass loading of 0.6 μg m−3 in the summer and 0.1 μg m

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Vertical Dependence of Horizontal Variation of Cloud Microphysics: Observations from the ACE-ENA field campaign and implications for warm rain simulation in climate models

10.5194/acp-2020-788 ◽

2020 ◽

Author(s):

Zhibo Zhang ◽

Qianqian Song ◽

David Mechem ◽

Vincent Larson ◽

Jian Wang ◽

...

Keyword(s):

Climate Models ◽

Marine Boundary Layer ◽

Global Climate ◽

Cloud Microphysics ◽

Global Climate Models ◽

Strong Positive Correlation ◽

Field Campaign ◽

Warm Rain ◽

Cloud Water Content ◽

Warm Rain Process

Abstract. In the current global climate models (GCM), the nonlinearity effect of subgrid cloud variations on the parameterization of warm rain process, e.g., the autoconversion rate, is often treated by multiplying the resolved-scale warm ran process rates by a so-called enhancement factor (EF). In this study, we investigate the subgrid-scale horizontal variations and covariation of cloud water content (qc) and cloud droplet number concentration (Nc) in marine boundary layer (MBL) clouds based on the in-situ measurements from a recent field campaign, and study the implications for the autoconversion rate EF in GCMs. Based on a few carefully selected cases from the field campaign, we found that in contrast to the enhancing effect of qc and Nc variations that tends to make EF > 1, the strong positive correlation between qc and Nc results in a suppressing effect that makes tends to make EF

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Impacts of Vertical Structure of Convection in Global Warming: The Role of Shallow Convection

Journal of Climate ◽

10.1175/jcli-d-15-0563.1 ◽

2016 ◽

Vol 29 (12) ◽

pp. 4665-4684 ◽

Cited By ~ 6

Author(s):

Chao-An Chen ◽

Jia-Yuh Yu ◽

Chia Chou

Keyword(s):

Global Warming ◽

Climate Models ◽

Global Climate ◽

Deep Convection ◽

Atmospheric Stability ◽

Detailed Examination ◽

Global Climate Models ◽

Shallow Convection ◽

Tropical Circulation ◽

Heavy Structure

Abstract Global-warming-induced changes in regional tropical precipitation are usually associated with changes in the tropical circulation, which is a dynamic contribution. This study focuses on the mechanisms of the dynamic contribution that is related to the partition of shallow convection in tropical convection. To understand changes in tropical circulation and its associated mechanisms, 32 coupled global climate models from CMIP3 and CMIP5 were investigated. The study regions are convection zones with positive precipitation anomalies, where both enhanced and reduced ascending motions are found. Under global warming, an upward-shift structure of ascending motion is observed in the entire domain, implying a deepening of convection and a more stable atmosphere, which leads to a weakening of the tropical circulation. In a more detailed examination, areas with enhanced (weakened) ascending motion are associated with more (less) import of moist static energy by a climatologically bottom-heavy (top heavy) structure of vertical velocity, which is similar to a “rich get richer” mechanism. In a warmer climate, different climatological vertical profiles tend to induce different changes in atmospheric stability: the bottom-heavy (top heavy) structure brings a more (less) unstable condition and is favorable (unfavorable) to the strengthening of the convective circulation. The bottom-heavy structure is associated with shallow convection, while the top-heavy structure is usually related to deep convection. This study suggests a hypothesis and a possible linkage for projecting and understanding future circulation change from the current climate: shallow convection will tend to strengthen tropical circulation and enhance upward motion in a future warmer climate.

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Vertical dependence of horizontal variation of cloud microphysics: observations from the ACE-ENA field campaign and implications for warm-rain simulation in climate models

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-3103-2021 ◽

2021 ◽

Vol 21 (4) ◽

pp. 3103-3121

Author(s):

Zhibo Zhang ◽

Qianqian Song ◽

David B. Mechem ◽

Vincent E. Larson ◽

Jian Wang ◽

...

Keyword(s):

Climate Models ◽

Marine Boundary Layer ◽

Global Climate ◽

Cloud Microphysics ◽

Global Climate Models ◽

Strong Positive Correlation ◽

Field Campaign ◽

Warm Rain ◽

Cloud Water Content ◽

Warm Rain Process

Abstract. In the current global climate models (GCMs), the nonlinearity effect of subgrid cloud variations on the parameterization of warm-rain process, e.g., the autoconversion rate, is often treated by multiplying the resolved-scale warm-rain process rates by a so-called enhancement factor (EF). In this study, we investigate the subgrid-scale horizontal variations and covariation of cloud water content (qc) and cloud droplet number concentration (Nc) in marine boundary layer (MBL) clouds based on the in situ measurements from a recent field campaign and study the implications for the autoconversion rate EF in GCMs. Based on a few carefully selected cases from the field campaign, we found that in contrast to the enhancing effect of qc and Nc variations that tends to make EF > 1, the strong positive correlation between qc and Nc results in a suppressing effect that tends to make EF < 1. This effect is especially strong at cloud top, where the qc and Nc correlation can be as high as 0.95. We also found that the physically complete EF that accounts for the covariation of qc and Nc is significantly smaller than its counterpart that accounts only for the subgrid variation of qc, especially at cloud top. Although this study is based on limited cases, it suggests that the subgrid variations of Nc and its correlation with qc both need to be considered for an accurate simulation of the autoconversion process in GCMs.

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Optimal Geometric Characterization of Forced Zonal Mean Tropical Precipitation Changes.

10.21203/rs.3.rs-697786/v1 ◽

2021 ◽

Author(s):

Aaron Donohoe ◽

Alyssa R Atwood ◽

David S Battisti

Keyword(s):

Last Glacial Maximum ◽

Climate Models ◽

Global Climate ◽

Glacial Maximum ◽

Global Climate Models ◽

Last Glacial ◽

Tropical Precipitation ◽

Precipitation Changes ◽

The Last Glacial Maximum ◽

The Last Glacial

Abstract The zonal and annual mean tropical precipitation response to paleoclimate and anthropogenic forcing scenarios ranging from the Last Glacial Maximum (LGM), CO2 quadrupling (4XCO2 ), mid-Holocene, North Atlantic freshwater hosing and volcanic forcing is analyzed in an ensemble of global climate models. Zonally averaged tropical precipitation changes are characterized in terms of three geometric manipulations of the climatological precipitation (hereafter, modes): meridional shifts, intensifications, and meridional contractions. We employ an optimization procedure that quantifies the magnitude and robustness (across different models) of changes in each mode in response to each forcing type. Additionally, the fraction of precipitation changes that are explained by the modes (in isolation and combined) is quantified. Shifts are generally less than 1º latitude in magnitude and explain a small fraction (<10%) of tropical precipitation changes. Contractions and intensifications are strongly anti-correlated across all simulations with a robust intensification and contraction of precipitation under global warming and a robust reduction and expansion under global cooling during the Last Glacial Maximum. The near constant scaling between contractions and intensifications across all simulations is used to define a joint contraction/intensification (CI) mode of tropical precipitation. The CI mode explains nearly 50% of the precipitation change under 4XCO2 and LGM forcing by optimizing a single parameter. These results suggest the shifting mode that has been extensively used to interpret paleo-rainfall reconstructions is of limited use for characterizing forced zonal mean precipitation changes and advocates for a reinterpretation of past precipitation changes to account for the CI mode

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A New Perspective on Coastally Trapped Disturbances Using Data from the Satellite Era

Bulletin of the American Meteorological Society ◽

10.1175/bams-d-18-0002.1 ◽

2019 ◽

Vol 100 (4) ◽

pp. 631-651 ◽

Cited By ~ 4

Author(s):

Timothy W. Juliano ◽

Zachary J. Lebo ◽

Gregory Thompson ◽

David A. Rahn

Keyword(s):

Climate Models ◽

Marine Boundary Layer ◽

Global Climate ◽

Warm Season ◽

Cloud Droplet ◽

Global Climate Models ◽

Spatial Inhomogeneity ◽

Radiation Budget ◽

Stratiform Clouds ◽

New Perspective

Abstract The ability of global climate models to simulate accurately marine stratiform clouds continues to challenge the atmospheric science community. These cloud types, which account for a large uncertainty in Earth’s radiation budget, are generally difficult to characterize due to their shallowness and spatial inhomogeneity. Previous work investigating marine boundary layer (MBL) clouds off the California coast has focused on clouds that form under the typical northerly flow regime during the boreal warm season. From about June through September, however, these northerly winds may reverse and become southerly as part of a coastally trapped disturbance (CTD). As the flow surges northward, it is accompanied by a broad cloud deck. Because these events are difficult to forecast, in situ observations of CTDs are few and far between, and little is known about their cloud physical properties. A climatological perspective of 23 CTD events—spanning the years from 2004 to 2016—is presented using several data products, including model reanalyses, buoys, and satellites. For the first time, satellite retrievals suggest that CTD cloud decks may play a unique role in the radiation budget due to a combination of aerosol sources that enhance cloud droplet number concentration and reduce cloud droplet effective radius. This particular type of cloud regime should therefore be treated differently than that which is more commonly found in the summertime months over the northeast Pacific Ocean. The potential influence of a coherent wind stress cycle on sea surface temperatures and sea salt aerosol is also explored.

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