The Monte Carlo Independent Column Approximation’s Conditional Random Noise: Impact on Simulated Climate

2005 ◽  
Vol 18 (22) ◽  
pp. 4715-4730 ◽  
Author(s):  
P. Räisänen ◽  
H. W. Barker ◽  
J. N. S. Cole
Keyword(s):  
Monte Carlo ◽  
Global Climate ◽  
Random Noise ◽  
Radiative Heating ◽  
Time Interval ◽  
Additional Time ◽  
Time Step ◽  
Order Of Magnitude ◽  
Independent Column ◽  
The Impact

Abstract The Monte Carlo Independent Column Approximation (McICA) method for computing domain-average radiative fluxes is unbiased with respect to the full ICA, but its flux estimates contain conditional random noise. Results for five experiments are used to assess the impact of McICA-related noise on simulations of global climate made by the NCAR Community Atmosphere Model (CAM). The experiment with the least noise (an order of magnitude below that of basic McICA) is taken as the reference. Two additional experiments help demonstrate how the impact of noise depends on the time interval between calls to the radiation code. Each experiment is an ensemble of seven 15-month simulations. Experiments with very high noise levels feature significant reductions to cloudiness in the lowermost model layer over tropical oceans as well as changes in highly related quantities. This bias appears immediately, stabilizes after a couple of model days, and appears to stem from nonlinear interactions between clouds and radiative heating. Outside the Tropics, insignificant differences prevail. When McICA sampling is confined to cloudy subcolumns and when, on average, 50% more samples, relative to basic McICA, are drawn for selected spectral intervals, McICA noise is much reduced and the results of the simulation are almost statistically indistinguishable from the reference. This is true both for mean fields and for the nature of fluctuations on scales ranging from 1 day to at least 30 days. While calling the radiation code once every 3 h instead of every hour allows the CAM additional time to incorporate McICA-related noise, the impact of noise is enhanced only slightly. In contrast, changing the radiative time step by itself produces effects that generally exceed the impact of McICA’s noise.

scholarly journals Impact of natural climate variability on runoff based on Monte Carlo method

2017 ◽  
Vol 10 (2) ◽  
pp. 344-359 ◽  
Author(s):  
Jie Yang ◽  
Jianxia Chang ◽  
Jun Yao ◽  
Yimin Wang ◽  
Qiang Huang ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Method ◽  
Climate Variability ◽  
Natural Condition ◽  
Global Climate ◽  
Test Method ◽  
Natural Climate Variability ◽  
Local Interference ◽  
Natural Climate ◽  
The Impact

Abstract Studying the impact of climate variability is important for the rational utilization of water resources, especially in the case of intensified global climate variability. Climate variability can be caused by natural climate variability or human-caused climate variability. The analysis of Jinghe River Basin (JRB) may not be comprehensive because few studies have concentrated on natural climate variability. Therefore, the primary goal is to explore the impact of natural climate variability on runoff. A modified Mann–Kendall test method was adopted to analyze the aberrance point to determine the natural condition period during which runoff was only influenced by natural climate variability. Then, the Monte Carlo method was employed to extract segments of monthly runoff in the natural condition period and combine them to construct a long series to reduce the instability. Results indicate that the percentage of runoff variability affected by natural climate variability is 30.52% at a confidence level of 95%. Next, a topography-based hydrological model and climate elasticity method were used to simulate runoff after the aberrance point without considering the impact caused by local interference. Through a comparison of the measured and simulated runoff, we discovered that local interference has the greatest impact on runoff in the JRB.

scholarly journals Analysis of Impact of Aral Sea Catastrophe on Anomaly Climate Variables and Hydrological Processes

2021 ◽  
pp. 65-74
Author(s):  
T. Berdimbetov ◽  
S. Nietullaeva ◽  
A. Yegizbayeva
Keyword(s):  
Climate Change ◽  
Global Climate ◽  
Aral Sea ◽  
Hydrological Processes ◽  
Time Interval ◽  
Climate Data ◽  
Ambient Temperatures ◽  
The Difference ◽  
Normal Trend ◽  
The Impact

Since 1960, water level began to decline considerably due to anthropogenic impact of the Aral Sea (AS), and it is continued to this day, which has led to dramatic changes in the climate around the AS, including ambient temperatures and sharp increases in evapotranspiration. Although, it isn't possible to see normal trend in this precipitation. Time series analysis of the FTI (First Time Interval 1901-1960) and STI (Second Time Interval, 1960-2015), highlighting climate change around the AS, based on Global Climate Data, suggests that there is a significant negative difference between precipitation and evapotranspiration during the drying of the AS. It is possible to see the logical compatibility of the air temperature and difference between precipitation and evapotranspiration observed around the AS, i.e. the temperature fluctuation trend is positive and contrary to the difference between precipitation and evapotranspiration negative trend, which means that the annual hydrological budget was reduced according to the time scale. In this article, determining the AS as the central point, we analyze the changes in the thermal and hydrological processes observed on the AS, as well as the impact to the environment of anomalous climate change observed on and around the sea like the drying out of the AS.

scholarly journals Modelling Public Transport Accessibility with Monte Carlo Stochastic Simulations: A Case Study of Ostrava

2019 ◽  
Vol 11 (24) ◽  
pp. 7098 ◽  
Author(s):  
Jiri Horak ◽  
Jan Tesla ◽  
David Fojtik ◽  
Vit Vozenilek
Keyword(s):  
Monte Carlo ◽  
Public Transport ◽  
Simulation Models ◽  
Stochastic Simulations ◽  
Time Interval ◽  
Real World Data ◽  
Transport Modelling ◽  
Transport Accessibility ◽  
Commuting Time ◽  
The Impact

Activity-based micro-scale simulation models for transport modelling provide better evaluations of public transport accessibility, enabling researchers to overcome the shortage of reliable real-world data. Current simulation systems face simplifications of personal behaviour, zonal patterns, non-optimisation of public transport trips (choice of the fastest option only), and do not work with real targets and their characteristics. The new TRAMsim system uses a Monte Carlo approach, which evaluates all possible public transport and walking origin–destination (O–D) trips for k-nearest stops within a given time interval, and selects appropriate variants according to the expected scenarios and parameters derived from local surveys. For the city of Ostrava, Czechia, two commuting models were compared based on simulated movements to reach (a) randomly selected large employers and (b) proportionally selected employers using an appropriate distance–decay impedance function derived from various combinations of conditions. The validation of these models confirms the relevance of the proportional gravity-based model. Multidimensional evaluation of the potential accessibility of employers elucidates issues in several localities, including a high number of transfers, high total commuting time, low variety of accessible employers and high pedestrian mode usage. The transport accessibility evaluation based on synthetic trips offers an improved understanding of local situations and helps to assess the impact of planned changes.

scholarly journals Tests of Monte Carlo Independent Column Approximation in the ECHAM5 Atmospheric GCM

2007 ◽  
Vol 20 (19) ◽  
pp. 4995-5011 ◽  
Author(s):  
P. Räisänen ◽  
S. Järvenoja ◽  
H. Järvinen ◽  
M. Giorgetta ◽  
E. Roeckner ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Water Content ◽  
Beta Distribution ◽  
Cloud Fraction ◽  
Total Water Content ◽  
Subgrid Scale ◽  
Total Water ◽  
Distribution Scheme ◽  
Independent Column ◽  
The Impact

Abstract The Monte Carlo Independent Column Approximation (McICA) method for computing domain-average radiative fluxes allows a flexible treatment of unresolved cloud structure, and it is unbiased with respect to the full ICA, but its flux estimates contain conditional random noise. Here, tests of McICA in the ECHAM5 atmospheric GCM are reported. ECHAM5 provides an interesting test bed for McICA because it carries prognostic variables for the subgrid-scale probability distribution of total water content, which allows us to determine subgrid-scale cloud variability directly from the resolved-scale model variables. Three experiments with differing levels of radiative noise, each consisting of ten 6-yr runs, are performed to estimate the impact of McICA noise on simulated climate. In an experiment that attempted to deliberately maximize McICA noise, a systematic reduction in low cloud fraction occurred. For a more reasonable implementation of McICA, the impact of noise is very small, although statistically discernible. In terms of the impacts of noise, McICA appears to be a viable approach for use in ECHAM5. However, to improve the simulation of cloud radiative effects, realistic representation of both unresolved and resolved cloud structures is needed, which remains a challenging problem. Comparison of ECHAM5 data with a global cloud system–resolving model dataset and with International Satellite Cloud Climatology Project data suggested two problems related to unresolved cloud structures. First, ECHAM5 appears to underestimate subgrid-scale cloud variability. This problem seems partly related to the use of the beta distribution scheme for total water content in ECHAM5: in its current form, the scheme is unable to generate highly inhomogeneous clouds (relative standard deviation of condensate amount >1). Second, it appears that in ECHAM5, overcast cloud layers occur too frequently and partially cloudy layers too rarely. This problem is not unique to the beta distribution scheme; in fact, it is more pronounced when using an alternative, relative humidity–based cloud fraction scheme.

scholarly journals A comparative study of the response of non-drizzling stratocumulus to meteorological and aerosol perturbations

2012 ◽  
Vol 12 (10) ◽  
pp. 27111-27172
Author(s):  
J. L. Petters ◽  
H. Jiang ◽  
G. Feingold ◽  
D. L. Rossiter ◽  
D. Khelif ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Cloud Droplet ◽  
Radiative Heating ◽  
Radiative Properties ◽  
Liquid Water Path ◽  
Cloud Properties ◽  
Stratiform Clouds ◽  
Order Of Magnitude ◽  
Aerosol State ◽  
The Impact

Abstract. The impact of changes in aerosol and cloud droplet concentration (Na and Nd) on the radiative forcing of stratocumulus-topped boundary layers (STBLs) has been widely studied. How these impacts compare to those due to variations in meteorological context has not been investigated in a systematic fashion. In this study we examine the impact of observed variations in meteorological context and aerosol state on daytime, non-drizzling stratiform evolution, and determine how resulting changes in cloud properties compare. We perturb aerosol and meteorological properties within an observationally-constrained LES and determine the cloud response, focusing on changes in liquid water path (LWP), bulk optical depth (τ) and cloud radiative forcing (CRF). We find that realistic variations in meteorological context (i.e. jump properties) can elicit responses in τ and shortwave (SW) CRF that are on the same order of magnitude as, and at times larger than, those responses found due to similar changes in aerosol state (i.e Nd). Further, we find that one hour differences in the timing of SW radiative heating can lead to substantial changes in LWP and τ. Our results suggest that, for observational studies of aerosol influences on the radiative properties of stratiform clouds, consistency in meteorological context (the cloud top jump properties in particular) and time of observations from day-to-day must be carefully considered.

Numerical simulation of flow with large eddy simulation at Re = 3900

2019 ◽  
Vol 30 (5) ◽  
pp. 2397-2409 ◽  
Author(s):  
Niaz B. Khan ◽  
Zainah B. Ibrahim ◽  
Mian Ashfaq Ali ◽  
Mohammed Jameel ◽  
Muhammad Ijaz Khan ◽  
...  
Keyword(s):  
Time Interval ◽  
Turbulence Statistics ◽  
Time Step ◽  
Ansys Fluent ◽  
Content Type ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Recirculation Length ◽  
Icem Cfd ◽  
The Impact

Purpose Over the past few decades, the flow around circular cylinders has been one of the highly researched topics in the field of offshore engineering and fluid-structure interaction (FSI). In the current study, numerical simulations for flow around a fixed circular cylinder are performed at Reynolds number (Re) = 3900 with the LES method using the ICEM-CFD and ANSYS Fluent tool for meshing and analysis, respectively. Previously, similar studies have been conducted at the same Reynolds number, but there have been discrepancies in the results, particularly in calculating the recirculation length and angle of separation. In addition, the purpose of this study is to address the impact of time interval averaging to obtain the fully converged solution. Design/methodology/approach This study presents the LES method, using the ICEM-CFD and ANSYS fluent tool for meshing and analysis. Findings In the current study, turbulence statistics are sampled for 25, 50, 75 and 100 vortex-shedding cycles with the CFL value O (1). The recirculation length, angle of separation, hydrodynamic coefficients and the wake behind the cylinder are investigated up to ten diameters. The drag coefficient and Strouhal number are observed to be less sensitive, whereas the recirculation length appeared to be highly dependent on the average time statistics and the non-dimensional time step. Similarly, the mean streamwise and cross-flow velocity are observed to be sensitive to the average time statistics and non-dimensional time step in the wake region near the cylinder. Originality/value In the current investigation, turbulence statistics are sampled for 25, 50, 75 and 100 vortex-shedding cycles with the CFL value O (1), using large eddy simulation method at Re = 3900 around a circular cylinder. The impact of time interval averaging to obtain the fully converged mean flow field is addressed. No such consideration is yet published in the literature.

Impact of LULC Changes on LST in Rajshahi District of Bangladesh: A Remote Sensing Approach

2020 ◽  
Vol 3 (1) ◽  
pp. 11-23 ◽  
Author(s):  
Abdulla Al Kafy ◽  
Abdullah Al-Faisal ◽  
Mohammad Mahmudul Hasan ◽  
Md. Soumik Sikdar ◽  
Mohammad Hasib Hasan Khan ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Surface Temperature ◽  
Land Surface ◽  
Agricultural Land ◽  
Global Climate ◽  
Urban Expansion ◽  
Water Bodies ◽  
Landsat 8 ◽  
Lulc Changes ◽  
The Impact

Urbanization has been contributing more in global climate warming, with more than 50% of the population living in cities. Rapid population growth and change in land use / land cover (LULC) are closely linked. The transformation of LULC due to rapid urban expansion significantly affects the functions of biodiversity and ecosystems, as well as local and regional climates. Improper planning and uncontrolled management of LULC changes profoundly contribute to the rise of urban land surface temperature (LST). This study evaluates the impact of LULC changes on LST for 1997, 2007 and 2017 in the Rajshahi district (Bangladesh) using multi-temporal and multi-spectral Landsat 8 OLI and Landsat 5 TM satellite data sets. The analysis of LULC changes exposed a remarkable increase in the built-up areas and a significant decrease in the vegetation and agricultural land. The built-up area was increased almost double in last 20 years in the study area. The distribution of changes in LST shows that built-up areas recorded the highest temperature followed by bare land, vegetation and agricultural land and water bodies. The LULC-LST profiles also revealed the highest temperature in built-up areas and the lowest temperature in water bodies. In the last 20 years, LST was increased about 13ºC. The study demonstrates decrease in vegetation cover and increase in non-evaporating surfaces with significantly increases the surface temperature in the study area. Remote-sensing techniques were found one of the suitable techniques for rapid analysis of urban expansions and to identify the impact of urbanization on LST.

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