scholarly journals The use of regression for assessing a seasonal forecast model experiment

2016 ◽  
Vol 7 (4) ◽  
pp. 851-861 ◽  
Author(s):  
Rasmus E. Benestad ◽  
Retish Senan ◽  
Yvan Orsolini
Keyword(s):  
Sea Ice ◽  
Forecast Model ◽  
Ocean Model ◽  
Seasonal Forecasts ◽  
Air Temperatures ◽  
Model Set ◽  
Set Up ◽  
Numerical Model Experiments ◽  
The Tropics

Abstract. We show how factorial regression can be used to analyse numerical model experiments, testing the effect of different model settings. We analysed results from a coupled atmosphere–ocean model to explore how the different choices in the experimental set-up influence the seasonal predictions. These choices included a representation of the sea ice and the height of top of the atmosphere, and the results suggested that the simulated monthly mean air temperatures poleward of the mid-latitudes were highly sensitivity to the specification of the top of the atmosphere, interpreted as the presence or absence of a stratosphere. The seasonal forecasts for the mid-latitudes to high latitudes were also sensitive to whether the model set-up included a dynamic or non-dynamic sea-ice representation, although this effect was somewhat less important than the role of the stratosphere. The air temperature in the tropics was insensitive to these choices.

scholarly journals The use of regression for assessing a seasonal forecast model experiment

2016 ◽  
Author(s):  
Rasmus E. Benestad ◽  
Retish Senan ◽  
Yvan Orsolini
Keyword(s):  
Sea Ice ◽  
Forecast Model ◽  
Seasonal Forecast ◽  
Ocean Model ◽  
Seasonal Forecasts ◽  
Model Set ◽  
Set Up ◽  
Numerical Model Experiments ◽  
The Tropics

Abstract. We demonstrate how factorial regression can be used to analyse numerical model experiments, testing the effect of different model settings. We analysed results from a coupled atmosphere-ocean model to explore how the different choices in the experimental set-up influence the seasonal predictions. These choices included a representation of the sea-ice and the choice of top of the atmosphere, and the results suggested that the simulated monthly mean temperatures poleward of the mid-latitudes are highly sensitivity to the specification of the top of the atmosphere, interpreted as the presence or absence of a stratosphere. The seasonal forecasts for the mid-to-high latitudes were also sensitive to whether the model set-up included a dynamic or non-dynamics sea-ice representation, although this effect was less important than the role of the stratosphere. The temperature in the tropics was insensitive to these choices.

Role of river stage in characterization of phreatic line

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Vikram Kumar ◽  
Srivastava Granthi
Keyword(s):  
Irrigation Planning ◽  
Content Type ◽  
Measured Distance ◽  
Model Set ◽  
Downstream Section ◽  
Large Water ◽  
Set Up ◽  
Observation Wells

Purpose The purpose of this study is to understand the basics of interactions of groundwater and surface water, which is needed for effective management of water resources. Design/methodology/approach The experimental setup was framed using curved flume and the straight flume, which simulates the model of river and groundwater storage, respectively. The model set up further consists, downstream, central and upstream sections where 14 observation wells, which are arranged at a measured distance from the canal side. Findings Exit gradient is higher at downstream when the average head differences between canal and river are 31.9 cm and 35.7 cm. Free seepage height is more in the downstream wells than upstream and central wells. At the downstream section, there is a greater chance of instability of the riverbank. Research limitations/implications Results will be used for better planning of hydraulic structural design. Practical implications Results will help in storing the large water and better irrigation planning for the water acute states and locations. Originality/value The originality is own developed physical model and its own first type to understand the basic of interaction and effects.

scholarly journals An Analytical Framework for Understanding Tropical Meridional Modes

2017 ◽  
Vol 30 (9) ◽  
pp. 3303-3323 ◽  
Author(s):  
Cristian Martinez-Villalobos ◽  
Daniel J. Vimont
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Ocean Model ◽  
Sea Surface ◽  
Transient Growth ◽  
Kelvin Wave ◽  
Wes Feedback ◽  
Meridional Mode ◽  
The Tropics

A theoretical framework is developed for understanding the transient growth and propagation characteristics of thermodynamically coupled, meridional mode–like structures in the tropics. The model consists of a Gill–Matsuno-type steady atmosphere under the long-wave approximation coupled via a wind–evaporation–sea surface temperature (WES) feedback to a “slab” ocean model. When projected onto meridional basis functions for the atmosphere the system simplifies to a nonnormal set of equations that describes the evolution of individual sea surface temperature (SST) modes, with clean separation between equatorially symmetric and antisymmetric modes. The following major findings result from analysis of the system: 1) a transient growth process exists whereby specific SST modes propagate toward lower-order modes at the expense of the higher-order modes; 2) the same dynamical mechanisms govern the evolution of symmetric and antisymmetric SST modes except for the lowest-order wavenumber, where for symmetric structures the atmospheric Kelvin wave plays a critically different role in enhancing decay; and 3) the WES feedback is positive for all modes (with a maximum for the most equatorially confined antisymmetric structure) except for the most equatorially confined symmetric mode where the Kelvin wave generates a negative WES feedback. Taken together, these findings explain why equatorially antisymmetric “dipole”-like structures may dominate thermodynamically coupled ocean–atmosphere variability in the tropics. The role of nonnormality and the role of realistic mean states in meridional mode variability are discussed.

scholarly journals On the effect of sea-ice dynamics on oceanic thermohaline circulation

1995 ◽  
Vol 21 ◽  
pp. 361-368
Author(s):  
W. D. Hibler ◽  
Jinlun Zhang
Keyword(s):  
Sea Ice ◽  
Thermohaline Circulation ◽  
Ocean Model ◽  
Flat Bottom ◽  
Ice Dynamics ◽  
Surface Ocean ◽  
The North ◽  
Air Temperatures ◽  
Sea Ice Dynamics ◽  
Ocean Salinity

An idealized planetary flat-bottom geostrophic ice–ocean model is constructed with boundaries at latitudes 5° and 65° N and longitudes 50° W and 10° E in order to approximate the North Atlantic. The model is driven by fixed zonally averaged wind, surface air temperatures and surface ocean salinity. A dynamic thermodynamic sea-ice model is coupled to the ocean model. Only the thermodynamic insulating effects of the sea ice are considered, and no salt fluxes due to melting and freezing are included. Four equilibrium simulations of about 5000 years each are performed: two with interactive sea ice with and without ice dynamics, and two control simulations with either a fixed or no ice cover.In the two simulations including interactive sea ice, characteristic oscillations in the ice thickness and ocean temperature are found to occur. The oscillations are smaller when sea-ice dynamics are included. The dominant oscillation occurs at about a 5 year period, with the key feature being that the presence of sea ice tends to insulate the ocean and hence allows an oceanic warming. This warming in turn eventually causes a melt-back of the ice and a subsequent cool-down of the ocean. Oscillations at longer periods of about 20 years in the thermohaline circulation are also observed. These longer-period oscillations are particularly pronounced in the northward surface water transport.

scholarly journals Runoff Forecasting and Its Application in Reservoir Operation and Flood Warnings in Nepal

2014 ◽  
Vol 15 ◽  
pp. 23-29
Author(s):  
Anup Khanal ◽  
Netra Prasad Timalsina ◽  
Knut Alfredsen
Keyword(s):  
Reservoir Operation ◽  
Weather Forecast ◽  
Forecast Model ◽  
Developed Countries ◽  
Runoff Forecasting ◽  
Model Set ◽  
Runoff Forecast ◽  
Set Up ◽  
Hbv Model ◽  
Flood Warnings

Runoff forecasting is a very useful tool in hydrology to predict runoff based on a weather forecast. In developed countries, the method is also currently used for flood forecasting, and to predict runoff for hydropower reservoirs and water allocation for irrigation. But this is not the case in Nepal. The purpose of this paper is to demonstrate how to set up a system for runoff forecasting for a Nepalese catchment and illustrate how these procedures could be utilized in reservoir operation and flood warnings. This paper provides the necessary steps for implementing such a system in Nepal, including the selection of a meteorological forecast model, bias correction of the model output, HBV model set up, and runoff forecast simulation.DOI: http://dx.doi.org/10.3126/hn.v15i0.11288HYDRO Nepal JournalJournal of Water Energy and EnvironmentVolume: 15, 2014 JulyPage: 23-29

scholarly journals Evaluating the dominant components of warming in Pliocene climate simulations

2014 ◽  
Vol 10 (1) ◽  
pp. 79-90 ◽  
Author(s):  
D. J. Hill ◽  
A. M. Haywood ◽  
D. J. Lunt ◽  
S. J. Hunter ◽  
F. J. Bragg ◽  
...  
Keyword(s):  
Energy Balance ◽  
Sea Ice ◽  
High Latitude ◽  
Model Comparison ◽  
Climate Models ◽  
Climate Model ◽  
Clear Sky ◽  
Air Temperatures ◽  
Planetary Albedo ◽  
The Tropics

Abstract. The Pliocene Model Intercomparison Project (PlioMIP) is the first coordinated climate model comparison for a warmer palaeoclimate with atmospheric CO2 significantly higher than pre-industrial concentrations. The simulations of the mid-Pliocene warm period show global warming of between 1.8 and 3.6 °C above pre-industrial surface air temperatures, with significant polar amplification. Here we perform energy balance calculations on all eight of the coupled ocean–atmosphere simulations within PlioMIP Experiment 2 to evaluate the causes of the increased temperatures and differences between the models. In the tropics simulated warming is dominated by greenhouse gas increases, with the cloud component of planetary albedo enhancing the warming in most of the models, but by widely varying amounts. The responses to mid-Pliocene climate forcing in the Northern Hemisphere midlatitudes are substantially different between the climate models, with the only consistent response being a warming due to increased greenhouse gases. In the high latitudes all the energy balance components become important, but the dominant warming influence comes from the clear sky albedo, only partially offset by the increases in the cooling impact of cloud albedo. This demonstrates the importance of specified ice sheet and high latitude vegetation boundary conditions and simulated sea ice and snow albedo feedbacks. The largest components in the overall uncertainty are associated with clouds in the tropics and polar clear sky albedo, particularly in sea ice regions. These simulations show that albedo feedbacks, particularly those of sea ice and ice sheets, provide the most significant enhancements to high latitude warming in the Pliocene.

scholarly journals The Impact of a Low Bias in Snow Water Equivalent Initialization on CFS Seasonal Forecasts

2017 ◽  
Vol 30 (21) ◽  
pp. 8657-8671 ◽  
Author(s):  
Patrick D. Broxton ◽  
Xubin Zeng ◽  
Nicholas Dawson
Keyword(s):  
Lead Time ◽  
Snow Water Equivalent ◽  
Seasonal Prediction ◽  
Seasonal Forecasts ◽  
Near Surface ◽  
Air Temperatures ◽  
Forecast Lead Time ◽  
Snow Water ◽  
The Impact

Across much of the Northern Hemisphere, Climate Forecast System forecasts made earlier in the winter (e.g., on 1 January) are found to have more snow water equivalent (SWE) in April–June than forecasts made later (e.g., on 1 April); furthermore, later forecasts tend to predict earlier snowmelt than earlier forecasts. As a result, other forecasted model quantities (e.g., soil moisture in April–June) show systematic differences dependent on the forecast lead time. Notably, earlier forecasts predict much colder near-surface air temperatures in April–June than later forecasts. Although the later forecasts of temperature are more accurate, earlier forecasts of SWE are more realistic, suggesting that the improvement in temperature forecasts occurs for the wrong reasons. Thus, this study highlights the need to improve atmospheric processes in the model (e.g., radiative transfer, turbulence) that would cause cold biases when a more realistic amount of snow is on the ground. Furthermore, SWE differences in earlier versus later forecasts are found to much more strongly affect April–June temperature forecasts than the sea surface temperature differences over different regions, suggesting the major role of snowpack in seasonal prediction during the spring–summer transition over snowy regions.

scholarly journals Estimating Zonal Ekman Transport along Coastal Senegal during Passage of Hurricane Fred (2015) from August 30 to 31, 2015

2019 ◽  
Author(s):  
Abdou Lahat Dieng ◽  
Siny Ndoye ◽  
Gregory S. Jenkins ◽  
Saïdou Moustapha Sall ◽  
Amadou Thierno Gaye
Keyword(s):  
Forecast Model ◽  
Ocean Model ◽  
Coastal Communities ◽  
Ekman Transport ◽  
Southerly Wind ◽  
Wind Speeds ◽  
Meridional Winds ◽  
Observed Damage ◽  
Coastal Damage

We examine the role of zonal Ekman transport along the coast of Senegal on 30 August, 2015 when the tropical disturbance associated with Tropical Cyclone Fred was located to the west of Senegal causing considerable coastal damage to coastal areas south of Dakar, Senegal. Ten-meter winds from three Weather Research and Forecast model simulations were used to estimate zonal Ekman transport, with the largest values found during the 30 August. The simulations are in agreement with limited coastal observations showing increasing southerly wind speeds during 30 August but are overestimated relative to the 3 coastal stations. The strong meridional winds translate into increased zonal Ekman transport to the coast of Senegal on 30 August. The use of a coupled ocean model will improve the estimates of Ekman transport along the Guinea-Senegalese coast. The observed damage suggests that artificial and natural barriers (mangroves) should be strengthened to protect coastal communities in Senegal.

scholarly journals Evaluating the dominant components of warming in Pliocene climate simulations

2013 ◽  
Vol 9 (2) ◽  
pp. 1599-1625
Author(s):  
D. J. Hill ◽  
A. M. Haywood ◽  
D. J. Lunt ◽  
S. J. Hunter ◽  
F. J. Bragg ◽  
...  
Keyword(s):  
Energy Balance ◽  
Sea Ice ◽  
High Latitude ◽  
Model Comparison ◽  
Climate Models ◽  
Climate Model ◽  
Cloud Albedo ◽  
Clear Sky ◽  
Air Temperatures ◽  
The Tropics

Abstract. The Pliocene Model Intercomparison Project is the first coordinated climate model comparison for a warmer palaeoclimate with atmospheric CO2 significantly higher than pre-industrial concentrations. The simulations of the mid-Pliocene warm period show global warming of between 1.8 and 3.6 °C above pre-industrial surface air temperatures, with significant polar amplification. Here we perform energy balance calculations on all eight of the coupled ocean–atmosphere simulations within PlioMIP Experiment 2 to evaluate the causes of the increased temperatures and differences between the models. In the tropics simulated warming is dominated by greenhouse gas increases, with cloud albedo feedbacks enhancing the warming in most of the models, but by widely varying amounts. The responses to mid-Pliocene climate forcing in the Northern Hemisphere mid-latitudes are substantially different between the climate models, with the only consistent response being a warming due to increased greenhouse gases. In the high latitudes all the energy balance components become important, but the dominant warming influence comes from the clear sky albedo. This demonstrates the importance of specified ice sheet and high latitude vegetation boundary conditions and simulated sea ice and snow albedo feedbacks. The largest components in the overall uncertainty are associated with cloud albedo feedbacks in the tropics and polar clear sky albedo, particularly in sea ice regions. These simulations show that high latitude albedo feedbacks provide the most significant enhancements to Pliocene greenhouse warming.

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