scholarly journals Dynamic Effects on the Tropical Cloud Radiative Forcing and Radiation Budget

2008 ◽  
Vol 21 (11) ◽  
pp. 2337-2351 ◽  
Author(s):  
Jian Yuan ◽  
Dennis L. Hartmann ◽  
Robert Wood
Keyword(s):  
Vertical Velocity ◽  
Radiative Forcing ◽  
Large Scale ◽  
Vertical Motion ◽  
Relative Magnitude ◽  
Radiation Budget ◽  
Upward Motion ◽  
West Pacific ◽  
Cloud Forcing ◽  
The Tropics

Abstract Vertical velocity is used to isolate the effect of large-scale dynamics on the observed radiation budget and cloud properties in the tropics, using the methodology suggested by Bony et al. Cloud and radiation budget quantities in the tropics show well-defined responses to the large-scale vertical motion at 500 hPa. For the tropics as a whole, the ratio of shortwave to longwave cloud forcing (hereafter N) is about 1.2 in regions of upward motion, and increases to about 1.9 in regions of strong subsidence. If the analysis is restricted to oceanic regions with SST > 28°C, N does not increase as much for subsiding motions, because the stratocumulus regions are eliminated, and the net cloud forcing decreases linearly from about near zero for zero vertical velocity to about −15 W m−2 for strongly subsiding motion. Increasingly negative cloud forcing with increasing upward motion is mostly related to an increasing abundance of high, thick clouds. Although a consistent dynamical effect on the annual cycle of about 1 W m−2 can be identified, the effect of the probability density function (PDF) of the large-scale vertical velocity on long-term trends in the tropical mean radiation budget is very small compared to the observed variations. Observed tropical mean changes can be as large as ±3 W m−2, while the dynamical components are generally smaller than ±0.5 W m−2. For relatively small regions in the east and west Pacific, changes in the relative magnitude of longwave and shortwave cloud forcing can be related to the PDF of vertical velocity. The east Pacific in 1987 and 1998 showed large reductions of N in association with an increase in the fraction of the area in the domain with upward motion, and concomitant increases in high cloud. For the west Pacific in 1998, a large increase in N was caused not so much by a change in the mean vertical motion, but rather by a shift from top- to bottom-heavy upward motion.

scholarly journals Relationship between Shortwave Cloud Radiative Forcing and Local Meteorological Variables Compared in Observations and Several Global Climate Models

2006 ◽  
Vol 19 (17) ◽  
pp. 4344-4359 ◽  
Author(s):  
Markus Stowasser ◽  
Kevin Hamilton
Keyword(s):  
Relative Humidity ◽  
Vertical Velocity ◽  
Radiative Forcing ◽  
Large Scale ◽  
Climate Models ◽  
Grid Point ◽  
Global Climate Models ◽  
Coupled Models ◽  
Cloud Radiative Forcing ◽  
Cloud Forcing

Abstract The relations between local monthly mean shortwave cloud radiative forcing and aspects of the resolved-scale meteorological fields are investigated in hindcast simulations performed with 12 of the global coupled models included in the model intercomparison conducted as part of the preparation for Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). In particular, the connection of the cloud forcing over tropical and subtropical ocean areas with resolved midtropospheric vertical velocity and with lower-level relative humidity are investigated and compared among the models. The model results are also compared with observational determinations of the same relationships using satellite data for the cloud forcing and global reanalysis products for the vertical velocity and humidity fields. In the analysis the geographical variability in the long-term mean among all grid points and the interannual variability of the monthly mean at each grid point are considered separately. The shortwave cloud radiative feedback (SWCRF) plays a crucial role in determining the predicted response to large-scale climate forcing (such as from increased greenhouse gas concentrations), and it is thus important to test how the cloud representations in current climate models respond to unforced variability. Overall there is considerable variation among the results for the various models, and all models show some substantial differences from the comparable observed results. The most notable deficiency is a weak representation of the cloud radiative response to variations in vertical velocity in cases of strong ascending or strong descending motions. While the models generally perform better in regimes with only modest upward or downward motions, even in these regimes there is considerable variation among the models in the dependence of SWCRF on vertical velocity. The largest differences between models and observations when SWCRF values are stratified by relative humidity are found in either very moist or very dry regimes. Thus, the largest errors in the model simulations of cloud forcing are prone to be in the western Pacific warm pool area, which is characterized by very moist strong upward currents, and in the rather dry regions where the flow is dominated by descending mean motions.

The Sensitivity of the Radiation Budget in a Climate Simulation to Neglecting the Effect of Small Ice Particles

2007 ◽  
Vol 20 (14) ◽  
pp. 3527-3541 ◽  
Author(s):  
Faisal S. Boudala ◽  
George A. Isaac ◽  
N. A. McFarlane ◽  
J. Li
Keyword(s):  
Radiative Forcing ◽  
Circulation Model ◽  
Longwave Radiation ◽  
Radiation Budget ◽  
Climate Simulation ◽  
Climate Modelling ◽  
Ir Radiation ◽  
Cloud Forcing ◽  
Ice Particles ◽  
The Tropics

Abstract The sensitivity of the atmospheric radiation budget to ignoring small ice particles (D ≤ 100 μm) in parameterization of the mean effective size of ice particles was investigated by using the Canadian Centre for Climate Modelling and Analysis (CCCma) third-generation general atmospheric circulation model (AGCM3). The results indicate that small ice particles play two crucial roles in the radiative transfer that influence the simulated climate. First, they inhibit the IR radiation from escaping to space and, second, they enhance the scattering of solar radiation. On average, these two effects tend to partially cancel each other out. However, based on AGCM simulations, the small ice crystals make clouds more opaque to IR radiation. Generally, 5-yr seasonally averaged GCM results suggest that the strongest anomalies in outgoing longwave radiation (OLR) are found in the Tropics, reaching 15 to 25 W m−2 in areas where cold high cirrus anvil clouds are prevalent. The global average change in net cloud radiative forcing was 2.4 W m−2 in June–August (JJA) and 1.7 W m−2 in December–February (DJF). The change in globally averaged 5-yr mean cloud forcing was close to 1.9 W m−2. When the small particles were included, the globally averaged 5-yr mean precipitation decreased by about 8%, but cloudiness increased only slightly (by 2%). The 5-yr averaged global mean surface (screen) temperature also increased slightly (about 0.2°C) when the small ice particles were included.

The Relation Between Large-Scale Vertical Motion and Weather in Summer

1958 ◽  
Vol 39 (10) ◽  
pp. 521-531 ◽  
Author(s):  
R. C. Curtis ◽  
H. A. Panofsky
Keyword(s):  
United States ◽  
Vertical Velocity ◽  
Large Scale ◽  
Vertical Motion ◽  
Convective Precipitation ◽  
Eastern United States ◽  
Fair Weather ◽  
Momentum Exchange ◽  
The Mean ◽  
Single Predictor

Large-scale vertical velocities are shown to be closely related to the probabilities of convective precipitation and fair weather in the eastern United States during July 1955. In the daytime the mean relative humidity of the 900 to 700 mb layer is better related to the probability of convective precipitation than the vertical velocity. At night, however, vertical velocity is the best single predictor of convective precipitation, with a modified Showalter Index being a very useful additional criterion. The large-scale vertical velocities that occur in normal summer synoptic situations appear to be produced by a diurnal variation in the momentum exchange between the ground and the air.

Using CloudSat observations to evaluate cloud top heights from convection parameterization

2017 ◽  
Vol 2 (2) ◽  
Author(s):  
Guang Jun Zhang ◽  
Mingcheng Wang
Keyword(s):  
Radiative Forcing ◽  
Model Simulation ◽  
Convective Cloud ◽  
Radiation Budget ◽  
Convective Clouds ◽  
Average Temperature ◽  
Community Atmosphere Model ◽  
Convection Parameterization ◽  
Cloud Ice ◽  
The Tropics

How high convective clouds can go is of great importance to climate. Cloud ice and liquid water that detrain near the top of convective cores are important for the formation of anvil clouds and thus impact cloud radiative forcing and the Earth’s radiation budget. This study uses CloudSat observations to evaluate convective cloud top heights in the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM5). Results show that convective cloud top heights in the tropics are much lower than observed by CloudSat, by more than 2 km on average. Temperature and moisture anomalies from climatological means are composited for convective clouds of different heights for both observations and model simulation. It is found that convective environment is warmer and moister, and the anomalies are larger for clouds of higher tops. For a given convective cloud top height, the corresponding atmosphere in CAM5 is more convectively unstable than what the CloudSat observations indicate, suggesting that there is too much entrainment into convective clouds in the model.

scholarly journals Technical Note: On the use of nudging for aerosol–climate model intercomparison studies

2014 ◽  
Vol 14 (16) ◽  
pp. 8631-8645 ◽  
Author(s):  
K. Zhang ◽  
H. Wan ◽  
X. Liu ◽  
S. J. Ghan ◽  
G. J. Kooperman ◽  
...  
Keyword(s):  
Large Scale ◽  
Climate Model ◽  
Cloud Amount ◽  
Temperature Fields ◽  
Specific Humidity ◽  
Radiation Budget ◽  
Anthropogenic Aerosols ◽  
Cloud Forcing ◽  
Free Running ◽  
The Impact

Abstract. Nudging as an assimilation technique has seen increased use in recent years in the development and evaluation of climate models. Constraining the simulated wind and temperature fields using global weather reanalysis facilitates more straightforward comparison between simulation and observation, and reduces uncertainties associated with natural variabilities of the large-scale circulation. On the other hand, the forcing introduced by nudging can be strong enough to change the basic characteristics of the model climate. In the paper we show that for the Community Atmosphere Model version 5 (CAM5), due to the systematic temperature bias in the standard model and the sensitivity of simulated ice formation to anthropogenic aerosol concentration, nudging towards reanalysis results in substantial reductions in the ice cloud amount and the impact of anthropogenic aerosols on long-wave cloud forcing. In order to reduce discrepancies between the nudged and unconstrained simulations, and meanwhile take the advantages of nudging, two alternative experimentation methods are evaluated. The first one constrains only the horizontal winds. The second method nudges both winds and temperature, but replaces the long-term climatology of the reanalysis by that of the model. Results show that both methods lead to substantially improved agreement with the free-running model in terms of the top-of-atmosphere radiation budget and cloud ice amount. The wind-only nudging is more convenient to apply, and provides higher correlations of the wind fields, geopotential height and specific humidity between simulation and reanalysis. Results from both CAM5 and a second aerosol–climate model ECHAM6-HAM2 also indicate that compared to the wind-and-temperature nudging, constraining only winds leads to better agreement with the free-running model in terms of the estimated shortwave cloud forcing and the simulated convective activities. This suggests nudging the horizontal winds but not temperature is a good strategy for the investigation of aerosol indirect effects since it provides well-constrained meteorology without strongly perturbing the model's mean climate.

scholarly journals The Madden–Julian Oscillation’s Impacts on Worldwide Tropical Cyclone Activity

2014 ◽  
Vol 27 (6) ◽  
pp. 2317-2330 ◽  
Author(s):  
Philip J. Klotzbach
Keyword(s):  
Tropical Cyclone ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Vertical Motion ◽  
Tropical Cyclone Activity ◽  
Cyclone Activity ◽  
Sea Level Pressure ◽  
Tropical Cyclone Frequency ◽  
The Tropics ◽  
Cyclone Frequency

Abstract The 30–60-day Madden–Julian oscillation (MJO) has been documented in previous research to impact tropical cyclone (TC) activity for various tropical cyclone basins around the globe. The MJO modulates large-scale convective activity throughout the tropics, and concomitantly modulates other fields known to impact tropical cyclone activity such as vertical wind shear, midlevel moisture, vertical motion, and sea level pressure. The Atlantic basin typically shows the smallest modulations in most large-scale fields of any tropical cyclone basins; however, it still experiences significant modulations in tropical cyclone activity. The convectively enhanced phases of the MJO and the phases immediately following them are typically associated with above-average tropical cyclone frequency for each of the global TC basins, while the convectively suppressed phases of the MJO are typically associated with below-average tropical cyclone frequency. The number of rapid intensification periods are also shown to increase when the convectively enhanced phase of the MJO is impacting a particular tropical cyclone basin.

Reproducibility by Climate Models of Cloud Radiative Forcing Associated with Tropical Convection

2012 ◽  
Vol 25 (4) ◽  
pp. 1247-1262 ◽  
Author(s):  
Hiroki Ichikawa ◽  
Hirohiko Masunaga ◽  
Yoko Tsushima ◽  
Hiroshi Kanzawa
Keyword(s):  
Radiative Forcing ◽  
Large Scale ◽  
Climate Models ◽  
Deep Convection ◽  
Coupled Model ◽  
Vertical Motion ◽  
Reanalysis Data ◽  
Cloud Radiative Forcing ◽  
Tropical Oceans ◽  
Suppression Mechanism

Abstract In this study, cloud radiative forcing (CRF) associated with convective activity over tropical oceans is analyzed for monthly mean data from twentieth-century simulations of 18 climate models participating in phase 3 of the Coupled Model Intercomparison Project (CMIP3) in comparison with observational and reanalysis data. The analysis is focused on the warm oceanic regions with sea surface temperatures (SSTs) above 27°C to exclude the regions with cold SSTs typically covered by low stratus clouds. CRF is evaluated for different regimes sorted by pressure-coordinated vertical motion at 500 hPa (ω500) as an index of large-scale circulation. The warm oceanic regions cover the regime of vertical motion ranging from strong ascent to weak descent. The most notable feature found in this study is a systematic underestimation by most models of the ratio of longwave cloud radiative forcing (LWCRF) to shortwave cloud radiative forcing (SWCRF) over the weak vertical motion regime defined as −10 < ω500 < 20 hPa day−1. The underestimation of the ratio corresponds to the underestimation of LWCRF and the overestimation of SWCRF. Clouds in models seem to be lower in the amount of high clouds but more reflective than those in the observations in this regime. In the weak vertical motion regime, the lower free troposphere is dry. In the large-scale environment condition, the reproducibility of LWCRF is high in models adopting the scheme where the relative humidity–based suppression for deep convection occurrence is implemented. Models adopting the Zhang and McFarlane scheme show good performance without such a suppression mechanism.

scholarly journals Vertical Structure of Spiral Shocks in a Corrugated Galactic Disc

1983 ◽  
Vol 100 ◽  
pp. 145-146
Author(s):  
A. H. Nelson ◽  
T. Matsuda ◽  
T. Johns
Keyword(s):  
Density Profile ◽  
Vertical Velocity ◽  
Gas Flow ◽  
Vertical Structure ◽  
Vertical Motion ◽  
Shock Structure ◽  
Galactic Disc ◽  
Gaussian Density ◽  
Abundant Evidence ◽  
Steady Shock

Numerical calculations of spiral shocks in the gas discs of galaxies (1,2,3) usually assume that the disc is flat, i.e. the gas motion is purely horizontal. However there is abundant evidence that the discs of galaxies are warped and corrugated (4,5,6) and it is therefore of interest to consider the effect of the consequent vertical motion on the structure of spiral shocks. If one uses the tightly wound spiral approximation to calculate the gas flow in a vertical cut around a circular orbit (i.e the ⊝ -z plane, see Nelson & Matsuda (7) for details), then for a gas disc with Gaussian density profile in the z-direction and initially zero vertical velocity a doubly periodic spiral potential modulation produces the steady shock structure shown in Fig. 1. The shock structure is independent of z, and only a very small vertical motion appears with anti-symmetry about the mid-plane.

scholarly journals Global climatology and trends in convective environments from ERA5 and rawinsonde data

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Mateusz Taszarek ◽  
John T. Allen ◽  
Mattia Marchio ◽  
Harold E. Brooks
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Global Climate ◽  
Convective Available Potential Energy ◽  
Global Climate Models ◽  
Convective Precipitation ◽  
The Past ◽  
The Tropics ◽  
Rawinsonde Data

AbstractGlobally, thunderstorms are responsible for a significant fraction of rainfall, and in the mid-latitudes often produce extreme weather, including large hail, tornadoes and damaging winds. Despite this importance, how the global frequency of thunderstorms and their accompanying hazards has changed over the past 4 decades remains unclear. Large-scale diagnostics applied to global climate models have suggested that the frequency of thunderstorms and their intensity is likely to increase in the future. Here, we show that according to ERA5 convective available potential energy (CAPE) and convective precipitation (CP) have decreased over the tropics and subtropics with simultaneous increases in 0–6 km wind shear (BS06). Conversely, rawinsonde observations paint a different picture across the mid-latitudes with increasing CAPE and significant decreases to BS06. Differing trends and disagreement between ERA5 and rawinsondes observed over some regions suggest that results should be interpreted with caution, especially for CAPE and CP across tropics where uncertainty is the highest and reliable long-term rawinsonde observations are missing.

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