scholarly journals Differences in the Sub-seasonal Predictability of Extreme Stratospheric Events

2022 ◽  
Author(s):  
Rachel Wai-Ying Wu ◽  
Zheng Wu ◽  
Daniela I. V. Domeisen
Keyword(s):  
Extreme Events ◽  
Weather Prediction ◽  
Polar Vortex ◽  
Wave Activity ◽  
Prediction System ◽  
Wave Amplification ◽  
Weather Forecasts ◽  
Surface Weather ◽  
Linear Behaviour ◽  
Strong Vortex

Abstract. Extreme stratospheric events such as sudden stratospheric warming and strong vortex events associated with an anomalously weak or strong polar vortex can have downward impacts on surface weather that can last for several weeks to months. Hence, successful predictions of these stratospheric events would be beneficial for extended range weather prediction. However, the predictability limit of extreme stratospheric events is most often limited to around 2 weeks or less. The predictability also strongly differs between events, and between event types. The reasons for the observed differences in the predictability, however, are not resolved. To better understand the predictability differences between events, we expand the definitions of extreme stratospheric events to wind deceleration and acceleration events, and conduct a systematic comparison of predictability between event types in the European Centre for Medium-Range Weather Forecasts (ECMWF) prediction system for the sub-seasonal predictions. We find that wind deceleration and acceleration events follow the same predictability behaviour, that is, events of stronger magnitude are less predictable in a close to linear relationship, to the same extent for both types of events. There are however deviations from this linear behaviour for very extreme events. The difficulties of the prediction system in predicting extremely strong anomalies can be traced to a poor predictability of extreme wave activity pulses in the lower stratosphere, which impacts the prediction of deceleration events, and interestingly, also acceleration events. Improvements in the understanding of the wave amplification that is associated with extremely strong wave activity pulses and accurately representing these processes in the model is expected to enhance the predictability of stratospheric extreme events and, by extension, their impacts on surface weather and climate.

Final Sudden Stratospheric Warmings and the memory of the stratosphere

2021 ◽  
Author(s):  
Alain Hauchecorne ◽  
Chantal Claud ◽  
Philippe Keckhut
Keyword(s):  
Zonal Wind ◽  
Planetary Wave ◽  
Middle Atmosphere ◽  
Temperature Anomaly ◽  
Polar Vortex ◽  
Wave Activity ◽  
Late Winter ◽  
Easterly Wind ◽  
Weather Forecasts ◽  
Stratospheric Circulation

<p>Sudden Stratospheric Warming (SSW) is the most spectacular dynamic event occurring in the middle atmosphere. It can lead to a warming of the winter polar stratosphere by a few tens of K in one to two weeks and a reversal of the stratospheric circulation from wintertime prevailing westerly winds to easterly winds similar to summer conditions. This strong modification of the stratospheric circulation has consequences for several applications, including the modification of the stratospheric infrasound guide. Depending on the date of the SSW, the westerly circulation can be re-established if the SSW occurs in mid-winter or the summer easterly circulation can be definitively established if the SSW occurs in late winter. In the latter case it is called Final Warming (FW). Each year, it is possible to define the date of the FW as the date of the final inversion of the zonal wind at 60°N - 10 hPa . If the FW is associated with a strong peak of planetary wave activity and a rapid increase in polar temperature, it is classified as dynamic FW. If the transition to the easterly wind is smooth without planetary wave activity, the FW is classified as radiative.</p><p>The analysis of the ERA5 database, which has recently been extended to 1950 (71 years of data), allowed a statistical analysis of the evolution of the stratosphere in winter. The main conclusions of this study will be presented :</p><p>- the state of the polar vortex in a given month is anticorrelated with its state 2 to 3 months earlier. The beginning of winter is anticorrelated with mid-winter and mid-winter is anticorrelated with the end of winter;</p><p>- dynamic FWs occur early in the season (March - early April) and are associated with a strong positive polar temperature anomaly, while radiative FWs occur later (late April - early May) without a polar temperature anomaly;</p><p>- the summer stratosphere (polar temperature and zonal wind) keeps the memory of its state in April-May at the time of FW at least until July .</p><p>These results could help to improve medium-range weather forecasts in the Northern Hemisphere due to the strong dynamic coupling between the troposphere and stratosphere during SSW events.</p>

scholarly journals SINGV – the Convective-Scale Numerical Weather Prediction System for Singapore

2019 ◽  
Vol 36 (3) ◽  
Author(s):  
Xiang-Yu Huang ◽  
Dale Barker ◽  
Stuart Webster ◽  
Anurag Dipankar ◽  
Adrian Lock ◽  
...  
Keyword(s):  
Numerical Weather Prediction ◽  
Weather Prediction ◽  
Extreme Rainfall ◽  
Prediction System ◽  
Local Data ◽  
Weather Forecasts ◽  
Numerical Weather ◽  
The United Kingdom ◽  
Convective Scale ◽  
The Impact

Extreme rainfall is one of the primary meteorological hazards in Singapore, as well as elsewhere in the deep tropics, and it can lead to significant local flooding. Since 2013, the Meteorological Service Singapore (MSS) and the United Kingdom Met Office (UKMO) have been collaborating to develop a convective-scale Numerical Weather Prediction (NWP) system, called SINGV. Its primary aim is to provide improved weather forecasts for Singapore and the surrounding region, with a focus on improved short-range prediction of localized heavy rainfall. This paper provides an overview of the SINGV development, the latest NWP capabilities at MSS and some key results of evaluation. The paper describes science advances relevant to the development of any km-scale NWP suitable for the deep tropics and provides some insights into the impact of local data assimilation and utility of ensemble predictions.

Predictability of the stratospheric polar vortex in the ECMWF S2S reforecasts

2021 ◽  
Author(s):  
Rachel Wai-Ying Wu ◽  
Daniela I.V. Domeisen
Keyword(s):  
Lead Time ◽  
Polar Vortex ◽  
Onset Date ◽  
Strong Wind ◽  
Sudden Stratospheric Warming ◽  
Stratospheric Polar Vortex ◽  
Zonal Winds ◽  
Surface Weather ◽  
Acceleration And Deceleration ◽  
Strong Vortex

<p>Extreme stratospheric events, e.g strong vortex events and sudden stratospheric warming (SSW) events, are often the main focus of stratospheric predictability studies. Other than strong vortex and SSW events, strong vortex acceleration and deceleration events are related but less studied events. A better understanding of the mechanisms of acceleration and deceleration events would also contribute to the understanding of SSWs and strong vortex events in the stratosphere. As SSWs tend to be less predictable than strong vortex events, it is hypothesized that the predictability of acceleration and deceleration events might differ as they are related to opposite mechanisms. We identify wind acceleration and deceleration events using the daily mean of the zonal mean zonal winds at 60°N and 10 hPa from the ERA-interim reanalysis for the winters of 1998/99-2018/19. Acceleration and deceleration events are defined as a wind change over a 10-day window above the 60th percentile of the magnitude of all identified events. To evaluate the predictability of the events, the ECMWF S2S hindcasts are verified against ERA-interim data. As expected, the predictability of the events increases with decreasing lead time (as the model initialisation date approaches the event onset date). We also find that all 4 types of events, namely acceleration, deceleration, strong vortex and SSW events, show the same predictability behavior, that is, that the predictability of an event is independent of its nature but dependent only on its magnitude. We discuss the difficulties of the model in predicting events associated with strong wind changes by investigating the heat flux-wind relationship in the model. A better understanding of the predictability and dynamical variability in the stratospheric polar vortex by the model could provide a better understanding of the mechanisms of stratospheric events, thus potentially also improving surface weather predictability.</p>

Gravity wave activity during the southern hemispheric sudden stratospheric warming 2019

2020 ◽  
Author(s):  
Andreas Dörnbrack ◽  
Tyler Mixa ◽  
Bernd Kaifler ◽  
Markus Rapp
Keyword(s):  
Weather Prediction ◽  
Polar Vortex ◽  
Numerical Weather Prediction Model ◽  
Wave Activity ◽  
Meteorological Conditions ◽  
Background Information ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Airborne Measurements

<p>At the end of the austral winter 2019, a sudden stratospheric warming led to an early breakdown of the polar vortex. The meteorological conditions during this event are documented and analysed by means of operational analyses of the Intgrated Forecast System (IFS) of the ECMWF and ERA5 data. Especially, we focus on the decline of stratospheric wave activity over the southern tip of South America. For this region, ground-based and airborne measurements are employed to compare selected diagnostics with fields from the ECMWF's numerical weather prediction model IFS. Furthmore, the meteorological conditions for one selected research flight during the SOUTHTRAC campaign are presented. This part serves as background information for a case study presented by Tyler Mixa.</p>

scholarly journals The Gridding of MOS

2009 ◽  
Vol 24 (2) ◽  
pp. 520-529 ◽  
Author(s):  
Bob Glahn ◽  
Kathryn Gilbert ◽  
Rebecca Cosgrove ◽  
David P. Ruth ◽  
Kari Sheets
Keyword(s):  
United States ◽  
Prediction Models ◽  
Weather Prediction ◽  
Correction Method ◽  
Maximum Temperature ◽  
Weather Variables ◽  
Weather Forecasts ◽  
Surface Weather ◽  
Model Output Statistics ◽  
Numerical Weather Prediction Models

Abstract Model output statistics (MOS) guidance forecasts have been produced at stations and provided to National Weather Service forecasters and private entities for over three decades. As the numerical weather prediction models became more accurate, MOS followed that trend. Up until a few years ago, the MOS produced at observation locations met the basic need for guidance. With the advent of the Interactive Forecast Preparation System and the National Digital Forecast Database, gridded MOS forecasts became needed as guidance for forecasters. One method of providing such grids is to objectively analyze the MOS forecasts for points. A basic successive correction method has been extended to analyze MOS forecasts and surface weather variables. This method is being applied to MOS forecasts to provide guidance for producing grids of sensible weather elements such as temperature, clouds, and snow amount. Guidance forecasts have been implemented for the conterminous United States for most weather elements contained in routine weather forecasts. This paper describes the method applied to daytime maximum temperature over the conterminous United States and gives example results.

scholarly journals The Relevance of the Location of Blocking Highs for Stratospheric Variability in a Changing Climate

2015 ◽  
Vol 28 (2) ◽  
pp. 531-549 ◽  
Author(s):  
Blanca Ayarzagüena ◽  
Yvan J. Orsolini ◽  
Ulrike Langematz ◽  
Janna Abalichin ◽  
Anne Kubin
Keyword(s):  
Atmospheric Chemistry ◽  
Polar Vortex ◽  
Wave Activity ◽  
Northwestern Pacific ◽  
Atlantic Sector ◽  
The Past ◽  
The Pacific ◽  
Transient Simulations ◽  
Strong Vortex ◽  
Stratospheric Variability

Abstract Previous research shows that blocking highs (BHs) influence wintertime polar stratospheric variability through the modulation of the climatological planetary waves (PWs) depending on the BH location. BHs over the Euro-Atlantic sector tend to enhance the upward PW propagation, and those over the northwestern Pacific Ocean tend to reduce it. Future changes are examined in the response of the wave activity flux to the BH location and their relationship with wintertime stratospheric variability in transient simulations of ECHAM/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC). After it is verified that EMAC can reproduce qualitatively well the geographical dependence of the BH influence on PW activity injection, it is shown that this dependence does not change in the future. However, an eastward shift of the pattern of the BH influence on PW propagation over the Pacific, a farther eastward extension of the pattern over the Atlantic Ocean, and an intensification of the wavenumber-1 component of the interaction between climatological and anomalous waves are detected. Changes in the upper-tropospheric jet and an intensification of the wavenumber-1 climatological wave due to a strengthening of the Aleutian low agree with these variations. The spatial distribution of future BHs preceding extreme polar vortex events is also affected by the slight modifications in the wave activity pattern. Hence, future BHs preceding strong vortex events tend to be more concentrated over the Pacific than in the past, where BHs interfere negatively with wavenumber-1 climatological waves. Future BHs prior to major stratospheric warmings are located in a broader area than in the past, predominantly over an extended Euro-Atlantic sector.

scholarly journals Wave Activity Events and the Variability of the Stratospheric Polar Vortex

2014 ◽  
Vol 27 (20) ◽  
pp. 7796-7806 ◽  
Author(s):  
Abraham Solomon
Keyword(s):  
Polar Vortex ◽  
Wave Activity ◽  
Stratospheric Polar Vortex ◽  
Weather Forecasts ◽  
Planetary Scale ◽  
Intraseasonal Variations ◽  
Medium Range ◽  
Polar Stratosphere ◽  
Hemisphere Winter ◽  
Wave Induced

Abstract During Northern Hemisphere winter, polar stratospheric winds and temperatures exhibit significant variability that is due to the vertical propagation of planetary-scale waves. The most dramatic intraseasonal variations in temperature are associated with sudden stratospheric warmings (SSWs), which are wave-breaking events that occur approximately every other year. This paper will introduce the concept of wave activity events (WAEs), which are periods of enhanced pseudomomentum density in the polar stratosphere that occur every year. It will be demonstrated that all SSWs are associated with WAEs; furthermore, minor warmings and many final warmings in the polar spring are also WAEs, and therefore a better understanding of these more frequent wave events can provide additional insights into stratospheric wave-induced variability. Employing the Interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim) for 1979–2011, 119 WAEs are identified and their life cycle is compared with that of the 23 SSWs observed during this period.

Probability and deterministic amount of precipitation on the multi-model ensemble

2020 ◽  
Author(s):  
Juwon Kim ◽  
Hae-Jin Kong ◽  
Hyuncheol Shin
Keyword(s):  
Data Assimilation ◽  
Weather Prediction ◽  
Extreme Weather ◽  
Extreme Weather Events ◽  
Ensemble Prediction ◽  
Prediction System ◽  
Model Ensemble ◽  
Post Processing ◽  
Weather Forecasts ◽  
The Impact

<p>Multi-model ensemble using statistical post-processing is one of the methods to provide the impact of uncertainties of the Numerical Weather Prediction (NWP) models, with low cost and better accuracy for extreme weather forecasts. Extreme weather events such as heat/cold waves, windstorms, and heavy rainfall result in severe damage in human life and properties. However, the performance of the NWP models, particularly, heavy rain forecast is still low due to the intermittent and non-Gaussian properties. The light rain tends to be overestimated and the strong rain tends to be underestimated averagely on the NWP models. Thus the multi-model ensemble using statistical post-processing is activated to correct the discrepancies between the observation and the model intensity of precipitation.<br>The aim of this study is to provide the improvement of precipitation forecasts in probabilistic and deterministic aspects using a multi-model ensemble method with more weights on the less error and without any bias correction. Six types of models, namely, Local Data assimilation and Prediction System (LDPS), Local ENsemble System (LENS), Global Data assimilation and Prediction System (GDPS), Ensemble Prediction System-Global (EPSG) of Korea Meteorological Administration (KMA), the single and ensemble models of European Centre for Medium-Range Weather Forecasts (ECMWF), are used to blend. The preliminary results of the multi-model ensemble show similar results to the ECMWF ensemble mean in deterministic for 3-hourly accumulated precipitation over the East Asia and the middle of the performance among individual models in probabilistic over the South Korea. More details of the methodology, results, and improvements will be discussed in the presentation.</p>

scholarly journals Climatology and trends in the forcing of the stratospheric zonal-mean flow

2011 ◽  
Vol 11 (4) ◽  
pp. 11649-11690 ◽  
Author(s):  
E. Monier ◽  
B. C. Weare
Keyword(s):  
Planetary Wave ◽  
Polar Vortex ◽  
Wave Activity ◽  
Mean Flow ◽  
Flux Divergence ◽  
Temporal Shift ◽  
Weather Forecasts ◽  
Wave Forcing ◽  
Long Term Changes

Abstract. The momentum budget of the Transformed Eulerian-Mean (TEM) equation is calculated using the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40). This study outlines the considerable contribution of unresolved waves, dominated by gravity waves, to the forcing of the zonal-mean flow. A trend analysis, from 1980 to 2001, shows that the onset and break down of the Northern Hemisphere (NH) stratospheric polar night jet has a tendency to occur later. This temporal shift is associated with long-term changes in the planetary wave activity that are mainly due to synoptic waves. In the Southern Hemisphere (SH), the polar vortex shows a tendency to persist further into the SH summertime. This is associated with a statistically significant decrease in the intensity of the stationary EP flux divergence over the 1980–2001 period. Ozone depletion is well known for strengthening westerly winds through the thermal wind balance, which in turn causes a reduction in wave activity in high latitudes. This study suggests that the decrease in planetary wave activity provides an important feedback to the zonal wind as it delays the breakdown of the polar vortex. Finally, we identify long-term changes in the Brewer-Dobson circulation that, this study suggests, are largely caused by trends in the planetary wave activity during winter and by trends in the gravity wave forcing otherwise.

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