scholarly journals Enhanced extended-range predictability of the 2018 late-winter Eurasian cold spell due to the stratosphere

2020 ◽  
Author(s):  
Lisa-Ann Kautz ◽  
Inna Polichtchouk ◽  
Thomas Birner ◽  
Hella Garny ◽  
Joaquim Pinto
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Causal Link ◽  
Late Winter ◽  
Cold Spell ◽  
Invariant State ◽  
Ensemble Forecasts ◽  
Probability Of Occurrence ◽  
Extended Range ◽  
Time Invariant

<p>A severe cold spell with surface temperatures reaching 10 K below climatology hit Eurasia during late February/early March 2018. This cold spell was associated with a Scandinavian blocking pattern followed by an extreme negative North Atlantic Oscillation (NAO) phase. Here we explore the predictability of this cold spell/NAO event using ensemble forecasts from the Subseasonal-to-Seasonal (S2S) archive. We find that this event was predicted with the observed strength roughly 10 days in advance. However, the probability of occurrence of the cold spell was doubled up to 25 days in advance, when a sudden stratospheric warming (SSW) occurred. Our results indicate that the amplitude of the cold spell was increased by the regime shift to the negative NAO phase at the end of February, which was likely favored by the SSW. We quantify the contribution of the SSW to the enhanced extended-range forecast skill for this particular event by running forecast ensembles in which the evolution of the stratosphere is nudged to a) the observed evolution, and b) a time invariant state. In the experiment with the observed stratospheric evolution nudged, the probability of occurrence of a strong cold spell is enhanced to 45%, while it is at its climatological value of 5% when the stratosphere is nudged to a time invariant state. These results showing enhanced predictability of surface extremes following SSWs extend previous observational evidence, which is mostly based on composite analyses, to a single event. Our results support that it is the subsequent evolution throughout the lower stratosphere following the SSW, rather than the occurrence of the SSW itself, that is crucial in coupling to large-scale tropospheric flow patterns. However, we caution that probabilistic gain in predictability alone is insufficient to conclude about a causal link between the SSW and the cold spell event.<br><br></p><p> </p>

Predictability of North Atlantic Tropical Cyclone Activity on Intraseasonal Time Scales

2010 ◽  
Vol 138 (12) ◽  
pp. 4362-4374 ◽  
Author(s):  
James I. Belanger ◽  
Judith A. Curry ◽  
Peter J. Webster
Keyword(s):  
Time Scales ◽  
North Atlantic ◽  
Large Scale ◽  
North Atlantic Ocean ◽  
Relative Vorticity ◽  
Vertical Shear ◽  
Forecast System ◽  
Ensemble Forecasts ◽  
Easterly Waves ◽  
The North

Abstract Recent work suggests that there may exist skill in forecasting tropical cyclones (TC) using dynamically based ensemble products, such as those obtained from the ECMWF Monthly Forecast System (ECMFS). The ECMFS features an ensemble of 51 coupled ocean–atmosphere simulations integrated to 32 days once per week. Predicted levels of TC activity in the North Atlantic Ocean with these monthly ensemble forecasts is compared with the observed variability during the months of June–October during 2008 and 2009. Results indicate that the forecast system can capture large-scale regions that have a higher or lower risk of TC activity and that it has skill above climatology for the Gulf of Mexico and the “Main Development Region” on intraseasonal time scales. Regional forecast skill is traced to the model’s ability to capture the large-scale evolution of deep-layer vertical shear, the frequency of easterly waves, and the variance in 850-hPa relative vorticity. The predictability of TC activity, along with the forecast utility of the ECMFS, is shown to be sensitive to the phase and intensity of the Madden–Julian oscillation at the time of model initialization.

scholarly journals Multi-model assessment of the late-winter tropospheric response to El Niño and La Niña

2021 ◽  
Author(s):  
Bianca Mezzina ◽  
Javier García-Serrano ◽  
Ileana Bladé ◽  
Froila M. Palmeiro ◽  
Lauriane Batté ◽  
...  
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Large Scale ◽  
Southern Oscillation ◽  
Late Winter ◽  
Model Assessment ◽  
Wave Source ◽  
Enso Events ◽  
The North ◽  
The North Atlantic

<p>El Niño-Southern Oscillation (ENSO) is known to affect the Northern Hemisphere tropospheric circulation in late-winter (January–March), but whether El Niño and La Niña lead to symmetric impacts and with the same underlying dynamics remains unclear, particularly in the North Atlantic. Three state-of-the-art atmospheric models forced by symmetric anomalous sea surface temperature (SST) patterns, mimicking strong ENSO events, are used to robustly diagnose symmetries and asymmetries in the extra-tropical ENSO response. Asymmetries arise in the sea-level pressure (SLP) response over the North Pacific and North Atlantic, as the response to La Niña tends to be weaker and shifted westward with respect to that of El Niño. The difference in amplitude can be traced back to the distinct energy available for the two ENSO phases associated with the non-linear diabatic heating response to the total SST field. The longitudinal shift is embedded into the large-scale Rossby wave train triggered from the tropical Pacific, as its anomalies in the upper troposphere show a similar westward displacement in La Niña compared to El Niño. To fully explain this shift, the response in tropical convection and the related anomalous upper-level divergence have to be considered together with the climatological vorticity gradient of the subtropical jet, i.e. diagnosing the tropical Rossby wave source. In the North Atlantic, the ENSO-forced SLP signal is a well-known dipole between middle and high latitudes, different from the North Atlantic Oscillation, whose asymmetry is not indicative of distinct mechanisms driving the teleconnection for El Niño and La Niña.</p><p>The multi-model assessment, with 50 members for each experiment, contributes to the ERA4CS-funded MEDSCOPE project and includes: EC-EARTH/IFS (L91, 0.01hPa), CNRM/ARPEGE (L91, 0.01hPa), CMCC/CAM (L46, 0.3hPa).</p>

scholarly journals North Atlantic atmospheric regimes and winter extremes in the Iberian peninsula

2011 ◽  
Vol 11 (3) ◽  
pp. 971-980 ◽  
Author(s):  
M. J. OrtizBeviá ◽  
E. SánchezGómez ◽  
F. J. Alvarez-García
Keyword(s):  
Iberian Peninsula ◽  
North Atlantic ◽  
Extreme Events ◽  
Minimum Temperature ◽  
Large Scale ◽  
Extreme Values ◽  
Climatic Variability ◽  
Winter Season ◽  
Historical Period ◽  
Probability Of Occurrence

Abstract. In this study, we assess the relationships between North Atlantic scale atmospheric regimes and extremes of precipitation and minimum temperature in the Iberian peninsula for an extended (DJFM) winter season. As found in previous studies, large scale atmospheric regimes are well represented in climate simulations while the extreme atmospheric variability is not. The relationship between some of these atmospheric regimes and the probability of occurrence of extreme values in simulations of present day climatic variability is validated here with daily observations at 68 meteorological stations all over the Iberian peninsula. Therefore, the possible changes in the probability of occurrence of winter extremes of minimum temperature and precipitation are obtained by projecting the changes in the probability of occurrence of the winter atmospheric regimes. The trends in the frequency of the observed large scale patterns give an indication of what can be expected in the next decades. For the long term (in a century), the changes are obtained directly from the comparison of the frequencies of the atmospheric regimes in the scenario simulations with those of the historical period. The projections obtained in this way are tested for consistency with the results obtained by comparing the changes in the extremes threshold values in the scenario with those of the historical simulations. The results point to a future with less precipitation extreme events and less minimum temperature extreme events in winter in the westerly central part of the Iberian peninsula.

scholarly journals Enhanced extended‐range predictability of the 2018 late‐winter Eurasian cold spell due to the stratosphere

2020 ◽  
Vol 146 (727) ◽  
pp. 1040-1055 ◽  
Author(s):  
Lisa‐Ann Kautz ◽  
Inna Polichtchouk ◽  
Thomas Birner ◽  
Hella Garny ◽  
Joaquim G. Pinto
Keyword(s):  
Late Winter ◽  
Cold Spell ◽  
Extended Range

Multivariable modeling and control of an activated sludge process

1998 ◽  
Vol 37 (12) ◽  
pp. 149-156 ◽  
Author(s):  
Carl-Fredrik Lindberg
Keyword(s):  
Activated Sludge ◽  
Nitrate Concentration ◽  
State Space Model ◽  
Activated Sludge Process ◽  
Invariant State ◽  
Linear Quadratic ◽  
Modeling And Control ◽  
Space Model ◽  
And Control ◽  
Time Invariant

This paper contains two contributions. First it is shown, in a simulation study using the IAWQ model, that a linear multivariable time-invariant state-space model can be used to predict the ammonium and nitrate concentration in the last aerated zone in a pre-denitrifying activated sludge process. Secondly, using the estimated linear model, a multivariable linear quadratic (LQ) controller is designed and used to control the ammonium and nitrate concentration.

scholarly journals Subseasonal Forecasts of the Northern Queensland Floods of February 2019: Causes and Forecast Evaluation

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 758
Author(s):  
Wayne Yuan-Huai Tsai ◽  
Mong-Ming Lu ◽  
Chung-Hsiung Sui ◽  
Yin-Min Cho
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Austral Summer ◽  
Rainfall Event ◽  
Monsoon Depression ◽  
Forecast Skill ◽  
Sea Surface ◽  
Central Pacific ◽  
Percentile Rank ◽  
Extended Range

During the austral summer 2018/19, devastating floods occurred over northeast Australia that killed approximately 625,000 head of cattle and inundated over 3000 homes in Townsville. In this paper, the disastrous event was identified as a record-breaking subseasonal peak rainfall event (SPRE). The SPRE was mainly induced by an anomalously strong monsoon depression that was modulated by the convective phases of an MJO and an equatorial Rossby (ER) wave. The ER wave originated from an active equatorial deep convection associated with the El Niño warm sea surface temperatures near the dateline over the central Pacific. Based on the S2S Project Database, we analyzed the extended-range forecast skill of the SPRE from two different perspectives, the monsoon depression represented by an 850-hPa wind shear index and the 15-day accumulated precipitation characterized by the percentile rank (PR) and the ratio to the three-month seasonal (DJF) totals. The results of four S2S models of this study suggest that the monsoon depression can maintain the same level of skill as the short-range (3 days) forecast up to 8–10 days. For precipitation parameters, the conclusions are similar to the monsoon depression. For the 2019 northern Queensland SPRE, the model forecast was, in general, worse than the expectation derived from the hindcast analysis. The clear modulation of the ER wave that enhanced the SPRE monsoon depression circulation and precipitation is suspected as the main cause for the lower forecast skill. The analysis procedure proposed in this study can be applied to analyze the SPREs and their associated large-scale drivers in other regions.

scholarly journals Relationship between the Track and Structural Evolution of Hurricane Sandy (2012) Using a Regional Ensemble

2018 ◽  
Vol 146 (12) ◽  
pp. 4279-4302 ◽  
Author(s):  
Alex M. Kowaleski ◽  
Jenni L. Evans
Keyword(s):  
Large Scale ◽  
Wrf Model ◽  
Structural Evolution ◽  
Hurricane Sandy ◽  
Weather Research And Forecasting ◽  
Extratropical Transition ◽  
Ensemble Forecasts ◽  
High Predictability ◽  
Regression Mixture ◽  
The Relationship

Abstract An ensemble of 72 Weather Research and Forecasting (WRF) Model simulations is evaluated to examine the relationship between the track of Hurricane Sandy (2012) and its structural evolution. Initial and boundary conditions are obtained from ECMWF and GEFS ensemble forecasts initialized at 0000 UTC 25 October. The 5-day WRF simulations are initialized at 0000 UTC 27 October, 48 h into the global model forecasts. Tracks and cyclone phase space (CPS) paths from the 72 simulations are partitioned into 6 clusters using regression mixture models; results from the 4 most populous track clusters are examined. The four analyzed clusters vary in mean landfall location from southern New Jersey to Maine. Extratropical transition timing is the clearest difference among clusters; more eastward clusters show later Sandy–midlatitude trough interaction, warm seclusion formation, and extratropical transition completion. However, the intercluster variability is much smaller when examined relative to the landfall time of each simulation. In each cluster, a short-lived warm seclusion forms and contracts through landfall while lower-tropospheric potential vorticity concentrates at small radii. Despite the large-scale similarity among the clusters, relevant intercluster differences in landfall-relative extratropical transition are observed. In the easternmost cluster the Sandy–trough interaction is least intense and the warm seclusion decays the most by landfall. In the second most eastward cluster Sandy retains the most intact warm seclusion at landfall because of a slightly later (relative to landfall) and weaker trough interaction compared to the two most westward clusters. Nevertheless, the remarkably similar large-scale evolution of Sandy among the four clusters indicates the high predictability of Sandy’s warm seclusion extratropical transition before landfall.

scholarly journals Atmospheric Conditions Associated with Labrador Sea Deep Convection: New Insights from a Case Study of the 2006/07 and 2007/08 Winters

2016 ◽  
Vol 29 (14) ◽  
pp. 5281-5297 ◽  
Author(s):  
Who M. Kim ◽  
Stephen Yeager ◽  
Ping Chang ◽  
Gokhan Danabasoglu
Keyword(s):  
North America ◽  
North Atlantic ◽  
Large Scale ◽  
Initial Conditions ◽  
Deep Convection ◽  
La Niña ◽  
Labrador Sea ◽  
Atmospheric Conditions ◽  
Circulation Anomaly ◽  
La Nina

Abstract Deep convection in the Labrador Sea (LS) resumed in the winter of 2007/08 under a moderately positive North Atlantic Oscillation (NAO) state. This is in sharp contrast with the previous winter with weak convection, despite a similar positive NAO state. This disparity is explored here by analyzing reanalysis data and forced-ocean simulations. It is found that the difference in deep convection is primarily due to differences in large-scale atmospheric conditions that are not accounted for by the conventional NAO definition. Specifically, the 2007/08 winter was characterized by an atmospheric circulation anomaly centered in the western North Atlantic, rather than the eastern North Atlantic that the conventional NAO emphasizes. This anomalous circulation was also accompanied by anomalously cold conditions over northern North America. The controlling influence of these atmospheric conditions on LS deep convection in the 2008 winter is confirmed by sensitivity experiments where surface forcing and/or initial conditions are modified. An extended analysis for the 1949–2009 period shows that about half of the winters with strong heat losses in the LS are associated with such a west-centered circulation anomaly and cold conditions over northern North America. These are found to be accompanied by La Niña–like conditions in the tropical Pacific, suggesting that the atmospheric response to La Niña may have a strong influence on LS deep convection.

On krylov matrices and controllability of n-dimensional linear time-invariant state equations

1996 ◽  
Vol 3 (1-2) ◽  
pp. 99-109
Author(s):  
Andrzej Maćkiewicz ◽  
Francisco López Almansa ◽  
José A. Inaudi
Keyword(s):  
Linear Time ◽  
Invariant State ◽  
State Equations ◽  
Linear Time Invariant ◽  
Time Invariant

Application of Supervisory Predictive Control Based on T-S Model in pH Neutralization Process

2014 ◽  
Vol 511-512 ◽  
pp. 867-870
Author(s):  
Su Zhen Li ◽  
Xiang Jie Liu ◽  
Gang Yuan
Keyword(s):  
Predictive Control ◽  
Linear Time ◽  
Control Performance ◽  
Invariant State ◽  
Linear Time Invariant ◽  
Neutralization Process ◽  
S Model ◽  
Time Invariant ◽  
Ph Neutralization ◽  
Ph Neutralization Process

T-S model is linearized at sampling points into the form of linear time-invariant state space , and using supervisory predictive control and muti-step predictive control strategy, which reduces amount of calculation and improves the control performance. Introduction

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