scholarly journals Fifty-Seven-Year California Reanalysis Downscaling at 10 km (CaRD10). Part I: System Detail and Validation with Observations

2007 ◽  
Vol 20 (22) ◽  
pp. 5553-5571 ◽  
Author(s):  
Masao Kanamitsu ◽  
Hideki Kanamaru
Keyword(s):  
Time Scales ◽  
Large Scale ◽  
Global Analysis ◽  
Regional Climate ◽  
Regional Scale ◽  
Surface Wind ◽  
Lateral Boundary ◽  
Climate Change Research ◽  
Near Surface ◽  
Precipitation Analysis

Abstract For the purpose of producing datasets for regional-scale climate change research and application, the NCEP–NCAR reanalysis for the period 1948–2005 was dynamically downscaled to hourly, 10-km resolution over California using the Regional Spectral Model. This is Part I of a two-part paper, describing the details of the downscaling system and comparing the downscaled analysis [California Reanalysis Downscaling at 10 km (CaRD10)] against observation and global analysis. An extensive validation of the downscaled analysis was performed using station observations, Higgins gridded precipitation analysis, and Precipitation-Elevation Regression on Independent Slopes Model (PRISM) precipitation analysis. In general, the CaRD10 near-surface wind and temperature fit better to regional-scale station observations than the NCEP–NCAR reanalysis used to force the regional model, supporting the premise that the regional downscaling is a viable method to attain regional detail from large-scale analysis. This advantage of CaRD10 was found on all time scales, ranging from hourly to decadal scales (i.e., from diurnal variation to multidecadal trend). Dynamically downscaled analysis provides ways to study various regional climate phenomena of different time scales because all produced variables are dynamically, physically, and hydrologically consistent. However, the CaRD10 is not free from problems. It suffers from positive bias in precipitation for heavy precipitation events. The CaRD10 is inaccurate near the lateral boundary where regional detail is damped by the lateral boundary relaxation. It is important to understand these limitations before the downscaled analysis is used for research.

scholarly journals Dynamical Downscaling of Global Analysis and Simulation over the Northern Hemisphere

2008 ◽  
Vol 136 (7) ◽  
pp. 2796-2803 ◽  
Author(s):  
Hideki Kanamaru ◽  
Masao Kanamitsu
Keyword(s):  
Northern Hemisphere ◽  
Large Scale ◽  
Climate Model ◽  
Dynamical Downscaling ◽  
Global Analysis ◽  
Regional Climate ◽  
Regional Scale ◽  
Research Unit ◽  
Climatic Research Unit ◽  
Climate Analysis

Abstract As an extreme demonstration of regional climate model capability, a dynamical downscaling of the NCEP–NCAR reanalysis was successfully performed over the Northern Hemisphere. Its success is due to the use of the scale-selective bias-correction scheme, which maintains the large-scale analysis of the driving global reanalysis in the interior of the domain where lateral boundary forcing has very little control. The downscaled analysis was found to produce reasonable regional details by comparison against 0.5° gridded analysis from the Climatic Research Unit of the University of East Anglia. Comparisons with smaller-area regional downscaling runs in India, Europe, and Japan using the same downscaling system showed that there is no degradation of quality in downscaled climate analysis by expanding the domain from a regional scale to a hemispherical scale.

scholarly journals The Impact of Grid and Spectral Nudging on the Variance of the Near-Surface Wind Speed

2015 ◽  
Vol 54 (5) ◽  
pp. 1021-1038 ◽  
Author(s):  
Claire Louise Vincent ◽  
Andrea N. Hahmann
Keyword(s):  
Wind Speed ◽  
Large Scale ◽  
Climate Models ◽  
Regional Climate ◽  
Surface Wind ◽  
Ground Level ◽  
Near Surface ◽  
Spectral Nudging ◽  
Outer Domain ◽  
The Impact

AbstractGrid and spectral nudging are effective ways of preventing drift from large-scale weather patterns in regional climate models. However, the effect of nudging on the wind speed variance is unclear. In this study, the impact of grid and spectral nudging on near-surface and upper boundary layer wind variance in the Weather Research and Forecasting Model is analyzed. Simulations are run on nested domains with horizontal grid spacing of 15 and 5 km over the Baltic Sea region. For the 15-km domain, 36-h simulations initialized each day are compared with 11-day simulations with either grid or spectral nudging at and above 1150 m above ground level (AGL). Nested 5-km simulations are not nudged directly but inherit boundary conditions from the 15-km experiments. Spatial and temporal spectra show that grid nudging causes smoothing of the wind in the 15-km domain at all wavenumbers, both at 1150 m AGL and near the surface where nudging is not applied directly, while spectral nudging mainly affects longer wavenumbers. Maps of mesoscale variance show spatial smoothing for both grid and spectral nudging, although the effect is less pronounced for spectral nudging. On the inner, 5-km domain, an indirect smoothing impact of nudging is seen up to 200 km inward from the dominant inflow boundary at 1150 m AGL, but there is minimal smoothing from the nudging near the surface, indicating that nudging an outer domain is an appropriate configuration for wind-resource modeling.

scholarly journals Enhanced Detectability of Added Value in Limited-Area Model Results Separated into Different Spatial Scales

2006 ◽  
Vol 134 (8) ◽  
pp. 2180-2190 ◽  
Author(s):  
Frauke Feser
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Spatial Scales ◽  
Regional Climate ◽  
Regional Scale ◽  
Regional Climate Models ◽  
Added Value ◽  
Limited Area ◽  
Near Surface ◽  
Pattern Correlation

Abstract Regional climate models (RCMs) are a widely used tool to describe regional-scale climate variability and change. However, the added value provided by such models is not well explored so far, and claims have been made that RCMs have little utility. Here, it is demonstrated that RCMs are indeed returning significant added value. Employing appropriate spatial filters, the scale-dependent skill of a state-of-the-art RCM (with and without nudging of large scales) is examined by comparing its skill with that of the global reanalyses driving the RCM. This skill is measured by pattern correlation coefficients of the global reanalyses or the RCM simulation and, as a reference, of an operational regional weather analysis. For the spatially smooth variable air pressure the RCM improves this aspect of the simulation for the medium scales if the RCM is driven with large-scale constraints, but not for the large scales. For the regionally more structured quantity near-surface temperature the added value is more obvious. The simulation of medium-scale 2-m temperature anomaly fields amounts to an increase of the mean pattern correlation coefficient up to 30%.

Ocean Salinity Aspects of the Ningaloo Niño

2021 ◽  
pp. 1
Author(s):  
Yaru Guo ◽  
Yuanlong Li ◽  
Fan Wang ◽  
Yuntao Wei
Keyword(s):  
Fresh Water ◽  
Large Scale ◽  
Southern Oscillation ◽  
Regional Climate ◽  
Ocean Model ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Surface Salinity ◽  
Near Surface ◽  
Ocean Salinity

AbstractNingaloo Niño – the interannually occurring warming episode in the southeast Indian Ocean (SEIO) – has strong signatures in ocean temperature and circulation and exerts profound impacts on regional climate and marine biosystems. Analysis of observational data and eddy-resolving regional ocean model simulations reveals that the Ningaloo Niño/Niña can also induce pronounced variability in ocean salinity, causing large-scale sea surface salinity (SSS) freshening of 0.15–0.20 psu in the SEIO during its warm phase. Model experiments are performed to understand the underlying processes. This SSS freshening is mutually caused by the increased local precipitation (~68%) and enhanced fresh-water transport of the Indonesian Throughflow (ITF; ~28%) during Ningaloo Niño events. The effects of other processes, such as local winds and evaporation, are secondary (~18%). The ITF enhances the southward fresh-water advection near the eastern boundary, which is critical in causing the strong freshening (> 0.20 psu) near the Western Australian coast. Owing to the strong modulation effect of the ITF, SSS near the coast bears a higher correlation with the El Niño-Southern Oscillation (0.57, 0.77, and 0.70 with Niño-3, Niño-4, and Niño-3.4 indices, respectively) than sea surface temperature (-0.27, -0.42, and -0.35) during 1993-2016. Yet, an idealized model experiment with artificial damping for salinity anomaly indicates that ocean salinity has limited impact on ocean near-surface stratification and thus minimal feedback effect on the warming of Ningaloo Niño.

scholarly journals Regional Climate Model Emulator based on Deep Learning: Concept and First Evaluation of a Novel Hybrid Downscaling Approach

2021 ◽  
Author(s):  
Antoine Doury ◽  
Samuel Somot ◽  
Sébastien Gadat ◽  
Aurélien Ribes ◽  
Lola Corre
Keyword(s):  
Climate Change ◽  
Network Architecture ◽  
Large Scale ◽  
Climate Models ◽  
Climate Model ◽  
Regional Climate ◽  
Regional Climate Models ◽  
Future Climate ◽  
Near Surface ◽  
The Way

Abstract Providing reliable information on climate change at local scale remains a challenge of first importance for impact studies and policymakers. Here, we propose a novel hybrid downscaling method combining the strengths of both empirical statistical downscaling methods and Regional Climate Models (RCMs). The aim of this tool is to enlarge the size of high-resolution RCM simulation ensembles at low cost.We build a statistical RCM-emulator by estimating the downscaling function included in the RCM. This framework allows us to learn the relationship between large-scale predictors and a local surface variable of interest over the RCM domain in present and future climate. Furthermore, the emulator relies on a neural network architecture, which grants computational efficiency. The RCM-emulator developed in this study is trained to produce daily maps of the near-surface temperature at the RCM resolution (12km). The emulator demonstrates an excellent ability to reproduce the complex spatial structure and daily variability simulated by the RCM and in particular the way the RCM refines locally the low-resolution climate patterns. Training in future climate appears to be a key feature of our emulator. Moreover, there is a huge computational benefit in running the emulator rather than the RCM, since training the emulator takes about 2 hours on GPU, and the prediction is nearly instantaneous. However, further work is needed to improve the way the RCM-emulator reproduces some of the temperature extremes, the intensity of climate change, and to extend the proposed methodology to different regions, GCMs, RCMs, and variables of interest.

Role of dynamic and thermodynamic processes for the propagation of organized convection in a large-scale flow

2020 ◽  
Author(s):  
Hyunju Jung ◽  
Ann Kristin Naumann ◽  
Bjorn Stevens
Keyword(s):  
Dynamic Process ◽  
Large Scale ◽  
Surface Wind ◽  
Propagation Speed ◽  
Background Wind ◽  
Near Surface ◽  
Large Scale Flow ◽  
Model Setup ◽  
Self Aggregation ◽  
Organized Convection

<p>Convective self-aggregation in radiative convective equilibrium has been studied due to its similarities to organized convection in the tropics. As tropical atmospheric phenomena are embedded in a large-scale flow, we impose a background wind to the model setup using convection-permitting simulation to analyze the interaction of convective self-aggregation with the background wind. The simulations show that when imposing a background wind, the convective cluster propagates in the direction of the imposed wind but slows down compared to what pure advection would suggest, and eventually becomes stationary. The dynamic process dominates slowing down the propagation speed of the cluster because the surface momentum flux acts as a drag on the near-surface wind, terminating the propagation. The thermodynamic process through the wind-induce surface feedback contributes to only 6% of the propagation speed of the convective cluster and is strongly modified by the dynamic process.</p>

scholarly journals Evaluation of Arctic sea-ice drift and its dependency on near-surface wind and sea-ice concentration and thickness in the coupled regional climate model HIRHAM-NAOSIM

2019 ◽  
Author(s):  
Xiaoyong Yu ◽  
Annette Rinke ◽  
Wolfgang Dorn ◽  
Gunnar Spreen ◽  
Christof Lüpkes ◽  
...  
Keyword(s):  
Wind Speed ◽  
Sea Ice ◽  
Climate Model ◽  
Regional Climate ◽  
Surface Wind ◽  
Arctic Sea Ice ◽  
Near Surface ◽  
Drift Speed ◽  
Ice Drift ◽  
Sea Ice Drift

Abstract. We examine the simulated Arctic sea-ice drift speed for the period 2003–2014 in the coupled Arctic regional climate model HIRHAM-NAOSIM 2.0. In particular, we evaluate the dependency of the drift speed on the near-surface wind speed and sea-ice conditions. Considering the seasonal cycle of Arctic basin averaged drift speed, the model reproduces the summer-autumn drift speed well, but significantly overestimates the winter-spring drift speed, compared to satellite-derived observations. Also, the model does not capture the observed seasonal phase lag between drift and wind speed, but the simulated drift speed is more in phase with near-surface wind. The model calculates a realistic negative relationship between drift speed and ice thickness and between drift speed and ice concentration during summer-autumn when concentration is relatively low, but the correlation is weaker than observed. A daily grid-scale diagnostic indicates that the model reproduces the observed positive relationship between drift and wind speed. The strongest impact of wind changes on drift speed occurs for high and moderate wind speeds, with a low impact for calm conditions. The correlation under low-wind conditions is overestimated in the simulations, compared to observation/reanalysis. A sensitivity experiment demonstrates the significant effects of sea-ice form drag included by an improved parameterization of the transfer coefficients for momentum and heat over sea ice. However, this does not improve the agreement of the modelled drift speed/wind speed ratio with observations based on reanalysis for wind and remote sensing for sea ice drift. An improvement might be possible, among others, by tuning the open parameters of the parameterization in future.

Atmospheric Heating Source Over the Tibetan Plateau and Its Regional Climate Impact

2019 ◽  
Author(s):  
Guoxiong Wu ◽  
Anmin Duan ◽  
Yimin Liu
Keyword(s):  
Large Scale ◽  
Asian Summer Monsoon ◽  
Global Climate ◽  
Regional Climate ◽  
Climate Impact ◽  
Climate Dynamics ◽  
The Tibetan Plateau ◽  
Near Surface ◽  
Heating Source ◽  
Asian Summer

With an average elevation of 4 kilometers, a combined area of more than 2.5 million square kilometers, and a variety of complicated landscapes, the Tibetan Plateau (TP) constitutes the highest and largest terrain on earth. The Tibetan and Iranian Plateau (TIP) form a dynamically coupled system that exerts a tremendous impact on the regional and global climate. The TIP’s geographic location in the subtropics of central and eastern Asia, along with its altitude, size, and steep terrain on the southern and eastern slopes, make this climate impact particularly unique. In winter, the TIP reacts to the impinging subtropical westerly flow, producing a strong negative mountain torque and forming a prominent stationary circulation dipole with a huge anticyclone circulation to its north and cyclone circulation to its south in the tropics. A specific winter climate pattern over Asia is thus formed. Due to its high elevation, the total mass of the air column over the TP is much smaller than over the neighboring regions, as the solar radiation heating in this region is more efficient. The atmospheric heating source (AHS) over the TP is negative in winter and strongly positive in summer. On this elevated terrain there is also a large number of intersecting isentropic surfaces in the lower troposphere. Along its sloping surfaces, the cooling in winter causes the near-surface air to slide downward and diverge toward its surroundings, whereas the surface heating of the slope in summer results in near-surface air ascent, causing the surrounding air to converge toward the plateau. More significantly, due to its huge size, the surface-sensible heating of the TIP produces a large-scale surface cyclonic circulation and works as an immense sensible-heat-driven air pump (SHAP), which transports abundant water vapor from ocean to land to support the Asian continental monsoon. In addition, the plateau’s heating produces a subtropical monsoonal meridional circulation and creates a large-scale air ascent background in subtropical Asia. Therefore, the Asian monsoon is the consequence of the seasonal change not only in land-sea thermal contrast but also in the thermal forcing of large-scale mountains. Since the 1980s, the near surface atmospheric warming amplitude over the TP has grown much larger than the global mean, and the changes in climate and AHS over the TP have already influenced the water resources, ecosystem services, mountain hazards, and livelihoods across and around the TP. Understanding the climate effect of the TP’s AHS is not only a key issue for climate dynamics, but can also help us to recognize the thermal forcing of other large-scale topographies, such as the Rockies and Andes Mountains, on the global climate in the framework of land-air-sea interaction. This article will introduce the effect of the TP’s AHS on the regional climate, with emphasis on the East Asian summer monsoon (EASM) and South Asian summer monsoon (SASM), in terms of the climatology, intra-seasonal oscillation, interannual variability, and decadal change. Controversies, challenges, and future perspectives on this topic will also be presented. Its informative content can be used as a professional reference for research scientists and professionals in the fields of meteorology, climate dynamics, environmental science, geography and geology, hydrology, and paleo-climatology. Most material presented here can also be helpful for non-specialists.

Assessing reasons for skilful predictions of winter windstorms over the Atlantic/European region

2020 ◽  
Author(s):  
Lisa Degenhardt ◽  
Gregor Leckebusch ◽  
Adam Scaife
Keyword(s):  
Large Scale ◽  
Surface Wind ◽  
Forecast Model ◽  
Surface Wind Speed ◽  
Seasonal Forecast ◽  
Forecast Skill ◽  
Seasonal Forecasts ◽  
Financial Industry ◽  
Near Surface ◽  
Skill Scores

<p>Severe Atlantic winter storms are affecting densely populated regions of Europe (e.g. UK, France, Germany, etc.). Consequently, different parts of the society, financial industry (e.g., insurance) and last but not least the general public are interested in skilful forecasts for the upcoming storm season (usually December to March). To allow for a best possible use of steadily improved seasonal forecasts, the understanding which factors contribute to realise forecast skill is essential and will allow for an assessment whether to expect a forecast to be skilful or not.</p><p>This study analyses the predictability of the seasonal forecast model of the UK MetOffice, the GloSea5. Windstorm events are identified and tracked following Leckebusch et al. (2008) via the exceedance of the 98<sup>th</sup> percentile of the near surface wind speed.</p><p>Seasonal predictability of windstorm frequency in comparison to observations (based e.g., on ERA5 reanalysis) are calculated and different statistical methods (skill scores) are compared.</p><p>Large scale patterns (e.g., NAO, AO, EAWR, etc.) and dynamical factors (e.g., Eady Growth Rate) are analysed and their predictability is assessed in comparison to storm frequency forecast skill. This will lead to an idea how the forecast skill of windstorms is depending on the forecast skill of forcing factors conditional to the phase of large-scale variability modes. Thus, we deduce information, which factors are most important to generate seasonal forecast skill for severe extra-tropical windstorms.</p><p>The results can be used to get a better understanding of the resulting skill for the upcoming windstorm season.</p>

Sign in / Sign up

Export Citation Format

Share Document