scholarly journals The Rain Is Askew: Two Idealized Models Relating Vertical Velocity and Precipitation Distributions in a Warming World

2016 ◽  
Vol 29 (18) ◽  
pp. 6445-6462 ◽  
Author(s):  
Angeline G. Pendergrass ◽  
Edwin P. Gerber
Keyword(s):  
Relative Humidity ◽  
Energy Budget ◽  
Vertical Velocity ◽  
Climate Models ◽  
Vertical Motion ◽  
Latent Heating ◽  
Asymmetric Impact ◽  
Precipitation Increase ◽  
Rain Events ◽  
Warming World

Abstract As the planet warms, climate models predict that rain will become heavier but less frequent and that the circulation will weaken. Here, two heuristic models relating moisture, vertical velocity, and rainfall distributions are developed—one in which the distribution of vertical velocity is prescribed and another in which it is predicted. These models are used to explore the response to warming and moistening as well as changes in circulation, atmospheric energy budget, and stability. Some key assumptions of the models include that relative humidity is fixed within and between climate states and that stability is constant within each climate state. The first model shows that an increase in skewness of the vertical velocity distribution is crucial for capturing salient characteristics of the changing distribution of rain, including the muted rate of mean precipitation increase relative to extremes and the decrease in the total number or area of rain events. The second model suggests that this increase in the skewness of the vertical velocity arises from the asymmetric impact of latent heating on vertical 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.

Mechanisms behind the precipitation increase in Norway

2021 ◽  
Author(s):  
Kjersti Konstali ◽  
Asgeir Sorteberg
Keyword(s):  
Relative Humidity ◽  
Interannual Variability ◽  
Vertical Velocity ◽  
Absolute Magnitude ◽  
Diagnostic Model ◽  
Positive Trend ◽  
Water Vapour Content ◽  
Near Surface ◽  
Precipitation Increase

<p>We use a dataset with observations of daily precipitation from 55 homogeneity tested stations in Norway over the period 1900-2019 available from MET-Norway. These observations show that precipitation in Norway has increased monotonically by 19% since 1900. Notably, over half of the overall increase was recorded within the decade of 1980-1990. To examine possible mechanisms behind the precipitation increase, we use a diagnostic model to separate the effects of changes in vertical velocity, temperature and relative humidity. We use vertical velocity, near-surface temperature and relative humidity from two reanalysis products, ECMWF’s ERA-20C and NOAA’s 20th Century Reanalysis. The model-based precipitation estimates capture the interannual variability as well as the long-term trend, but the absolute magnitude of precipitation is underestimated. Within our model, we find that the variability in vertical velocity chiefly determines the interannual variability and long-term trends. In fact, the trend in vertical velocities contributes with more than 75% of the total modelled trend in precipitation between 1900-2019, and more than 60% of the anomalies between 1980-1990. However, over the last decades (1979 to 2019), changes in temperature and relative humidity are the main contributors to the trend. Thus, different physical processes shape the trend at different times. We hypothesize that the strong precipitation increase in the 1980’s is linked to an unusual high number of low pressure systems reaching Norway from the North-Atlantic. In recent decades, direct effects of global warming (rising temperatures and hence increased water vapour content) are thought to be the main cause of the positive trend in precipitation over Norway. </p>

scholarly journals Can Climate Models Capture the Structure of Extratropical Cyclones?

2010 ◽  
Vol 23 (7) ◽  
pp. 1621-1635 ◽  
Author(s):  
Jennifer L. Catto ◽  
Len C. Shaffrey ◽  
Kevin I. Hodges
Keyword(s):  
Relative Humidity ◽  
Vertical Velocity ◽  
Climate Models ◽  
Potential Temperature ◽  
Three Dimensional ◽  
Conveyor Belt ◽  
Dimensional Structure ◽  
Extratropical Cyclones ◽  
Wind Fields ◽  
Wind Speeds

Abstract Composites of wind speeds, equivalent potential temperature, mean sea level pressure, vertical velocity, and relative humidity have been produced for the 100 most intense extratropical cyclones in the Northern Hemisphere winter for the 40-yr ECMWF Re-Analysis (ERA-40) and the high resolution global environment model (HiGEM). Features of conceptual models of cyclone structure—the warm conveyor belt, cold conveyor belt, and dry intrusion—have been identified in the composites from ERA-40 and compared to HiGEM. Such features can be identified in the composite fields despite the smoothing that occurs in the compositing process. The surface features and the three-dimensional structure of the cyclones in HiGEM compare very well with those from ERA-40. The warm conveyor belt is identified in the temperature and wind fields as a mass of warm air undergoing moist isentropic uplift and is very similar in ERA-40 and HiGEM. The rate of ascent is lower in HiGEM, associated with a shallower slope of the moist isentropes in the warm sector. There are also differences in the relative humidity fields in the warm conveyor belt. In ERA-40, the high values of relative humidity are strongly associated with the moist isentropic uplift, whereas in HiGEM these are not so strongly associated. The cold conveyor belt is identified as rearward flowing air that undercuts the warm conveyor belt and produces a low-level jet, and is very similar in HiGEM and ERA-40. The dry intrusion is identified in the 500-hPa vertical velocity and relative humidity. The structure of the dry intrusion compares well between HiGEM and ERA-40 but the descent is weaker in HiGEM because of weaker along-isentrope flow behind the composite cyclone. HiGEM’s ability to represent the key features of extratropical cyclone structure can give confidence in future predictions from this model.

scholarly journals Sensitivity of the surface energy budget to drifting snow as simulated by MAR in coastal Adelie Land, Antarctica

2020 ◽  
Author(s):  
Louis Le Toumelin ◽  
Charles Amory ◽  
Vincent Favier ◽  
Christoph Kittel ◽  
Stefan Hofer ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Surface Energy ◽  
Energy Budget ◽  
Radiative Forcing ◽  
Climate Models ◽  
Surface Energy Budget ◽  
Near Surface ◽  
Surface Atmosphere ◽  
Drifting Snow ◽  
The Impact

Abstract. In order to understand the evolution of the climate of Antarctica, dominant processes that control surface and low-atmosphere meteorology need to be accurately captured in climate models. We used the regional climate model MAR (v3.11) at 10 km horizontal resolution, forced by ERA5 reanalysis over a 9-year period (2010–2018), to study the impact of drifting snow (designing here the wind-driven transport of snow particles below and above 2 m) on the near-surface atmosphere and surface in Adelie Land, East Antarctica. Two model runs were performed, respectively with and without drifting snow, and compared to half-hourly in situ observations at D17, a coastal and windy location of Adelie Land. We show that sublimation of drifting-snow particles in the atmosphere drives the difference between model runs and is responsible for significant impacts on the near-surface atmosphere. By cooling the low atmosphere and increasing its relative humidity, drifting snow also reduces sensible and latent heat exchanges at the surface (−5.9 W m−2 on average). Moreover, large and dense drifting-snow layers act as near-surface cloud by interacting with incoming radiative fluxes, enhancing incoming longwave radiations and reducing incoming shortwave radiations in summer (net radiative forcing: 5.9 W m−2). Even if drifting snow modifies these processes involved in surface-atmosphere interactions, the total surface energy budget is only slightly modified by introducing drifting snow, because of compensating effects in surface energy fluxes. The drifting-snow driven effects are not prominent near the surface but peak higher in the boundary layer (fifth vertical level, 38 m) where drifting snow sublimation is the most pronounced. Accounting for drifting snow in MAR generally improves the comparison at D17, more especially for the representation of relative humidity (mean bias reduced from −11.1 % to 2.9 %) and incoming longwave radiation (mean bias reduced from −7.6 W m−2 to −1.5 W m−2). Consequently, our results suggest that a detailed representation of drifting-snow processes is required in climate models to better capture the near–surface meteorology and surface–atmosphere interactions in coastal Adelie Land.

scholarly journals Sensitivity of the surface energy budget to drifting snow as simulated by MAR in coastal Adelie Land, Antarctica

2021 ◽  
Vol 15 (8) ◽  
pp. 3595-3614
Author(s):  
Louis Le Toumelin ◽  
Charles Amory ◽  
Vincent Favier ◽  
Christoph Kittel ◽  
Stefan Hofer ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Surface Energy ◽  
Energy Budget ◽  
Climate Models ◽  
Longwave Radiation ◽  
Surface Energy Budget ◽  
Near Surface ◽  
Surface Atmosphere ◽  
Drifting Snow ◽  
The Impact

Abstract. In order to understand the evolution of the climate of Antarctica, dominant processes that control surface and low-atmosphere meteorology need to be accurately captured in climate models. We used the regional climate model MAR (v3.11) at 10 km horizontal resolution, forced by ERA5 reanalysis over a 9-year period (2010–2018) to study the impact of drifting snow (designating here the wind-driven transport of snow particles below and above 2 m) on the near-surface atmosphere and surface in Adelie Land, East Antarctica. Two model runs were performed, one with and one without drifting snow, and compared to half-hourly in situ observations at D17, a coastal and windy location of Adelie Land. We show that sublimation of drifting-snow particles in the atmosphere drives the difference between model runs and is responsible for significant impacts on the near-surface atmosphere. By cooling the low atmosphere and increasing its relative humidity, drifting snow also reduces sensible and latent heat exchanges at the surface (−5.7 W m−2 on average). Moreover, large and dense drifting-snow layers act as near-surface cloud by interacting with incoming radiative fluxes, enhancing incoming longwave radiation and reducing incoming shortwave radiation in summer (net radiative forcing: 5.7 W m−2). Even if drifting snow modifies these processes involved in surface–atmosphere interactions, the total surface energy budget is only slightly modified by introducing drifting snow because of compensating effects in surface energy fluxes. The drifting-snow driven effects are not prominent near the surface but peak higher in the boundary layer (fourth vertical level, 12 m) where drifting-snow sublimation is the most pronounced. Accounting for drifting snow in MAR generally improves the comparison at D17, especially for the representation of relative humidity (mean bias reduced from −14.0 % to −0.7 %) and incoming longwave radiation (mean bias reduced from −20.4 W m−2 to −14.9 W m−2). Consequently, our results suggest that a detailed representation of drifting-snow processes is required in climate models to better capture the near-surface meteorology and surface–atmosphere interactions in coastal Adelie Land.

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 Dynamics of Cloud-Top Generating Cells in Winter Cyclones. Part I: Idealized Simulations in the Context of Field Observations

2016 ◽  
Vol 73 (4) ◽  
pp. 1507-1527 ◽  
Author(s):  
Jason M. Keeler ◽  
Brian F. Jewett ◽  
Robert M. Rauber ◽  
Greg M. McFarquhar ◽  
Roy M. Rasmussen ◽  
...  
Keyword(s):  
Vertical Velocity ◽  
Radiative Forcing ◽  
Initial Conditions ◽  
Vertical Wind Shear ◽  
Weather Research And Forecasting ◽  
Velocity Spectrum ◽  
Latent Heating ◽  
Heating Rates ◽  
Winter Storms ◽  
Radiation Parameterizations

Abstract This paper assesses the influence of radiative forcing and latent heating on the development and maintenance of cloud-top generating cells (GCs) in high-resolution idealized Weather Research and Forecasting Model simulations with initial conditions representative of the vertical structure of a cyclone observed during the Profiling of Winter Storms campaign. Simulated GC kinematics, structure, and ice mass are shown to compare well quantitatively with Wyoming Cloud Radar, cloud probe, and other observations. Sensitivity to radiative forcing was assessed in simulations with longwave-only (nighttime), longwave-and-shortwave (daytime), and no-radiation parameterizations. The domain-averaged longwave cooling rate exceeded 0.50 K h−1 near cloud top, with maxima greater than 2.00 K h−1 atop GCs. Shortwave warming was weaker by comparison, with domain-averaged values of 0.10–0.20 K h−1 and maxima of 0.50 K h−1 atop GCs. The stabilizing influence of cloud-top shortwave warming was evident in the daytime simulation’s vertical velocity spectrum, with 1% of the updrafts in the 6.0–8.0-km layer exceeding 1.20 m s−1, compared to 1.80 m s−1 for the nighttime simulation. GCs regenerate in simulations with radiative forcing after the initial instability is released but do not persist when radiation is not parameterized, demonstrating that radiative forcing is critical to GC maintenance under the thermodynamic and vertical wind shear conditions in this cyclone. GCs are characterized by high ice supersaturation (RHice > 150%) and latent heating rates frequently in excess of 2.00 K h−1 collocated with vertical velocity maxima. Ice precipitation mixing ratio maxima of greater than 0.15 g kg−1 were common within GCs in the daytime and nighttime simulations.

scholarly journals Effects of atmospheric dynamics and aerosols on the fraction of supercooled water clouds

2017 ◽  
Vol 17 (3) ◽  
pp. 1847-1863 ◽  
Author(s):  
Jiming Li ◽  
Qiaoyi Lv ◽  
Min Zhang ◽  
Tianhe Wang ◽  
Kazuaki Kawamoto ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Vertical Velocity ◽  
Meteorological Parameters ◽  
Temporal Correlation ◽  
Supercooled Liquid ◽  
Satellite Observation ◽  
Static Stability ◽  
Global Scale ◽  
Atmospheric Dynamics ◽  
Horizontal Wind

Abstract. Based on 8 years of (January 2008–December 2015) cloud phase information from the GCM-Oriented Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) Cloud Product (GOCCP), aerosol products from CALIPSO and meteorological parameters from the ERA-Interim products, the present study investigates the effects of atmospheric dynamics on the supercooled liquid cloud fraction (SCF) during nighttime under different aerosol loadings at global scale to better understand the conditions of supercooled liquid water gradually transforming to ice phase. Statistical results indicate that aerosols' effect on nucleation cannot fully explain all SCF changes, especially in those regions where aerosols' effect on nucleation is not a first-order influence (e.g., due to low ice nuclei aerosol frequency). By performing the temporal and spatial correlations between SCFs and different meteorological factors, this study presents specifically the relationship between SCF and different meteorological parameters under different aerosol loadings on a global scale. We find that the SCFs almost decrease with increasing of aerosol loading, and the SCF variation is closely related to the meteorological parameters but their temporal relationship is not stable and varies with the different regions, seasons and isotherm levels. Obviously negative temporal correlations between SCFs versus vertical velocity and relative humidity indicate that the higher vertical velocity and relative humidity the smaller SCFs. However, the patterns of temporal correlation for lower-tropospheric static stability, skin temperature and horizontal wind are relatively more complex than those of vertical velocity and humidity. For example, their close correlations are predominantly located in middle and high latitudes and vary with latitude or surface type. Although these statistical correlations have not been used to establish a certain causal relationship, our results may provide a unique point of view on the phase change of mixed-phase cloud and have potential implications for further improving the parameterization of the cloud phase and determining the climate feedbacks.

scholarly journals Transferability Intercomparison: An Opportunity for New Insight on the Global Water Cycle and Energy Budget

2007 ◽  
Vol 88 (3) ◽  
pp. 375-384 ◽  
Author(s):  
E. S. Takle ◽  
J. Roads ◽  
B. Rockel ◽  
W. J. Gutowski ◽  
R. W. Arritt ◽  
...  
Keyword(s):  
Energy Budget ◽  
Climate Models ◽  
Climate Model ◽  
Water Cycle ◽  
Regional Climate ◽  
Climate Conditions ◽  
Continental Scale ◽  
Global Water Cycle ◽  
Wide Range ◽  
Global Water

A new approach, called transferability intercomparisons, is described for advancing both understanding and modeling of the global water cycle and energy budget. Under this approach, individual regional climate models perform simulations with all modeling parameters and parameterizations held constant over a specific period on several prescribed domains representing different climatic regions. The transferability framework goes beyond previous regional climate model intercomparisons to provide a global method for testing and improving model parameterizations by constraining the simulations within analyzed boundaries for several domains. Transferability intercomparisons expose the limits of our current regional modeling capacity by examining model accuracy on a wide range of climate conditions and realizations. Intercomparison of these individual model experiments provides a means for evaluating strengths and weaknesses of models outside their “home domains” (domain of development and testing). Reference sites that are conducting coordinated measurements under the continental-scale experiments under the Global Energy and Water Cycle Experiment (GEWEX) Hydrometeorology Panel provide data for evaluation of model abilities to simulate specific features of the water and energy cycles. A systematic intercomparison across models and domains more clearly exposes collective biases in the modeling process. By isolating particular regions and processes, regional model transferability intercomparisons can more effectively explore the spatial and temporal heterogeneity of predictability. A general improvement of model ability to simulate diverse climates will provide more confidence that models used for future climate scenarios might be able to simulate conditions on a particular domain that are beyond the range of previously observed climates.

scholarly journals Climatological Increased Precipitation from July to August in the Western North Pacific Region Simulated by CMIP6 Models

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 664
Author(s):  
Xiao Dong ◽  
Renping Lin
Keyword(s):  
North Pacific ◽  
Western North Pacific ◽  
Vertical Motion ◽  
Atmospheric Model ◽  
Coupled Models ◽  
Model Simulations ◽  
Observational Analysis ◽  
Budget Analysis ◽  
Circulation Change ◽  
Precipitation Increase

In this study, the climatological precipitation increase from July to August over the western North Pacific (WNP) region was investigated through observations and simulations in the Coupled Model Intercomparison Project Phase 6 (CMIP6), atmospheric model simulations and historical experiments. Firstly, observational analysis showed that the precipitation increase is associated with a decrease in the local sea surface temperature (SST), indicating that the precipitation increase is not driven by the change in SST. In addition, the pattern of precipitation increase is similar to the vertical motion change at 500-hPa, suggesting that the precipitation increase is related to the circulation change. Moisture budget analysis further confirmed this relation. In addition to the observational analysis, the outputs from 26 CMIP6 models were further evaluated. Compared with atmospheric model simulations, air–sea coupled models largely improve the simulation of the climatological precipitation increase from July to August. Furthermore, model simulations confirmed that the bias in the precipitation increase is intimately associated with the circulation change bias. Thus, two factors are responsible for the bias of the precipitation increase from July to August in climate models: air–sea coupling processes and the performance in vertical motion change.

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