Please join us for the first webinar of the monthly series of webinars hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project.
Date: Thursday, April 30, 2020, 10:30 am | (UTC-04:00) Eastern Time (US & Canada) | 1 hr Title: On the Subseasonal-to-seasonal Variability of Extra-tropics Speaker: Cristiana Stan, George Mason University, USA
Abstract Recent advancements in understanding the subseasonal-to-seasonal (S2S) variability outside of the tropics will be discussed. I will introduce the multi-channel singular spectral analysis (MSSA) method used to isolate the S2S variability in the extra-tropics, present the oscillatory modes dominating the extra-tropics on these time scales and their relationship with tropical and stratospheric variability, and discuss the implications of midlatitude oscillatory modes for the predictability at Week 3&4.
The S2S variability of the extra-tropics is dominated by three propagating oscillations with broad-band spectra centered at 120, 45, and 28 days are found. The first oscillatory mode is referred to as the midlatitude seasonal oscillation (MLSO), and the other two are referred to as midlatitude intraseasonal oscillation 1 and 2 (MLISO 1 and MLISO2). When combined, the oscillations explain up to 30% of the natural variability of the extra-tropics on the intra-seasonal to seasonal time scales. These oscillations share some features with the circumglobal wave guide and in some phases of their lifecycles they project onto the canonical teleconnection patterns.
MLSO and MLISO-1 are related to the intraseasonal convective activity of the tropics and MLISO-1 shows some connection with the stratospheric variability associated with QBO.
When used as predictors in a simple linear regression model with 2-meter temperature as predictand, the mid-latitude oscillations extend the potential predictability of dependent variable to about 20 days.
To participate send and email to subseasonal_to_seasonal_prediction_mjo_tel
Please join us for the May Webinar of the monthly series of webinars hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project.
Date: Thursday, May 28, 2020, 10:30am | (UTC-04:00) Eastern Time (US & Canada) | 1hr Title: Non-normal optimal growth of the Pacific-North American pattern Speaker: Stephanie Henderson, University of Wisconsin-Madison, USA
Abstract The Pacific-North American (PNA) pattern has been previously linked to tropical variability including the Madden-Julian Oscillation (MJO) and the El Niño-Southern Oscillation (ENSO), as well as internal extratropical variability. However, many questions remain regarding how these various relationships act, both together and individually, to yield observed PNA variability. The role of tropical heating and the extratropical circulation on PNA pattern growth is examined using linear inverse modeling (LIM). Optimal PNA growth is found to occur via the non-normal interference between the modes strongly coupled to sea surface temperatures (SST), including ENSO, and the modes internal to the atmosphere, such as the MJO. PNA growth beyond this interference is also examined through the development of an “internal atmospheric” LIM that excludes the modes strongly coupled to SST, such as ENSO, while retaining MJO variability. Optimal PNA growth in the internal atmospheric LIM is driven by MJO Indian Ocean heating with suppressed heating over the tropical western Pacific, and a retrograding northeast Pacific streamfunction anomaly. The separate contributions of tropical heating and the extratropical circulation on PNA growth are also investigated.
Importantly, the non-normal PNA growth highlights the difficulty in partitioning PNA variance into contributions from different phenomena and should be considered in attribution studies.
To participate send and email to subseasonal_to_seasonal_prediction_mjo_tel
Please join us for the June webinar of the monthly series of webinars hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project.
Title: MJO Teleconnections to the Euro-Atlantic sector Speaker: Robert Lee, National Centre for Atmospheric Science and Department of Meteorology, University of Reading, UK
Abstract The teleconnection from the Madden-Julian Oscillation (MJO) provides a source of subseasonal variability and predictability to the North Atlantic-European (NAE) region. The El Niño-Southern Oscillation (ENSO) modulates the seasonal mean state, through which the MJO and its teleconnection pattern propagates; however, its impact on this teleconnection to the NAE region has not been investigated. In this webinar I will present evidence of a robust dependence of the teleconnections from the MJO to NAE weather regimes on the phase of ENSO. I will demonstrate that the MJO to NAO+ regime tropospheric teleconnection is strongly enhanced during El Niño years, via enhanced Rossby wave activity, and inactive during La Niña. Conversely the MJO to NAO− regime stratospheric teleconnection is enhanced during La Niña years, and inactive during El Niño. This dependence on the background state has strong implications for subseasonal predictability, including interannual variations in subseasonal predictive skill. I will go on to show statistical analysis of the MJO-NAE teleconnections using a larger set of 29 patterns, known as the Grosswetterlagen (GWL), to represent the European weather. Since the GWL patterns are smaller in spatial scale, they capture more synoptic detail. These findings demonstrate how the MJO can modify the preferred evolution of the NAE atmospheric flow.
To participate send and email to subseasonal_to_seasonal_prediction_mjo_tel.
After a month of hiatus, we are resuming the monthly series of webinars hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project. Please join us for the August webinar.
Title: Impact of MJO propagation and background flow variability on the evolution of the MJO mid-latitude teleconnection
Speaker: Prof. Edmund Chang, School of Marine and Atmospheric Sciences, Stony Brook University
Date: Thursday, August 27, 2020 Time: 1pm EDT | 5pm UTC
Abstract The MJO acts as a tropical heat source to excite Rossby waves that propagate into the mid-latitudes and modulate the mid-latitude circulation and weather. In this talk, using results from idealized model experiments, I will examine how the MJO excited mid-latitude teleconnection may depend on the history of the MJO evolution, as well as how different mid-latitude large-scale background flow may impact the evolution of the MJO mid-latitude teleconnection.
To participate send and email to subseasonal_to_seasonal_prediction_mjo_tel.
After another month of hiatus, we are resuming the monthly series of webinars hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project. Please join us for the October webinar.
Title: Understanding tropical-midlatitude interactions: metrics, dynamical processes, and future change Speaker: Jiabao Wang, School of Marine and Atmospheric Sciences, Stony Brook University
Date: Thursday, October 29, 2020
Time: 1pm EDT | 5pm UTC
Abstract
Tropical convections impact remotely on the midlatitude weather events (e.g., precipitation extremes over California) by forcing changes in circulation patterns. These tropical-midlatitude interactions are particularly important to be accurately simulated and predicted on subseasonal timescales since many management decisions fall within this time range. The Madden-Julian oscillation (MJO) is a unique type of organized tropical convection varying on subseasonal timescales and is recognized as an important source of subseasonal predictability for midlatitude weather phenomena. Better understanding of the MJO-midlatitude interactions is important in improving the simulation, prediction, and the understanding of future changes in MJO associated weather events.
As a joint activity between the WGNE MJO Task Force and WMO S2S teleconnection subproject, we developed a set of standardized diagnostics and metrics to characterize the MJO teleconnections and to understand the associated key dynamical processes (Wang et al. 2020a, b). In this talk, application of these diagnostics to CMIP5 and CMIP6 models will be presented. We will discuss the sensitivity of MJO teleconnections to MJO and basic state representations in models and sources of teleconnection biases. Future changes of MJO teleconnections and the underlying mechanisms will also be discussed.
Wang, J., H. Kim, D. Kim, S. A. Henderson, C. Stan, and E. D. Maloney (2020b): MJO teleconnections over the PNA region in climate models. Part II: Impacts of the MJO and basic state, J. Climate, 33, 5081-5101. doi: 10.1175/JCLI-D-19-0865.1.
Wang, J., H. Kim, D. Kim, S. A. Henderson, C. Stan, and E. D. Maloney (2020a): MJO teleconnections over the PNA region in climate models. Part I: Performance- and process-based skill metrics, J. Climate, 33, 1051-1067. doi: 10.1175/JCLI-D-19-0253.1.
To participate send and email to subseasonal_to_seasonal_prediction_mjo_tel.
We are resuming the monthly series of webinars hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project. Please join us for the January webinar.
Title: Intrinsic Uncertainty in the Euro-Atlantic Response to the MJO heating in boreal winter: Ongoing Results from ECMWF Re-Forecasts Speaker: David Straus, George Mason University
Date: Thursday, January 28, 2021 Time: 10:30am EST | 3:30pm UTC
Abstract While the Euro-Atlantic response to the MJO has been well studied in reanalysis and a hierarchy of models, a factor that is often overlooked is the uncertainty in the response due to the intrinsic variability in the full diabatic heating during even a single phase of the MJO. We examine the heating variability within large (51-member) ensembles of boreal winter reforecasts from the ECMWF model, focusing on forecasts initialized in phases 2 and 3 of the MJO (with heating anomalies located over the Indian Ocean). Results will be shown from new experimental reforecasts in which all the ensemble members utilize identical initial conditions, with the only difference between ensemble members arising from the application of stochastic physics in the target Indian Ocean region. (The stochastic physics is turned off outside the target region.) The resulting uncertainty (ensemble spread) in the Euro-Atlantic response during the first few weeks of the forecasts is also examined, as well as some discussion of ongoing work to link the response uncertainties to those in the heating. The Euro-Atlantic response is seen to be similar to the traditional MJO response early in the forecast (MJO phases 2/3 leading to the NAO+ regime). However, later on in the forecast variability in the heating over the Pacific Ocean may play a role. Further experiments are planned to clarify the roles of ENSO vis-à-vis those of the MJO.
Please join us for the February webinar hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project.
Title: Mapping Large-scale Climate Variability to Hydrological Extremes: An Application of the Linear Inverse Model to Subseasonal Prediction Speaker: Kai-Chih Tseng, GFDL
Date: Thursday, February 25, 2021 Time: 10:30am EST | 3:30pm UTC
Abstract The excitation of the Pacific-North American (PNA) teleconnection pattern by the Madden-Julian Oscillation (MJO) has been considered as one of the most important predictability sources on subseasonal timescales over the extratropical Pacific and North America. However, until recently, the interactions between tropical heating and other extratropical modes and their relationships to subseasonal prediction have received comparatively little attention. In this study, a linear inverse model (LIM) is applied to examine the tropical-extratropical interactions. The LIM provides a means of calculating the response of a dynamical system to a small forcing by constructing a linear operator from the observed covariability statistics of the system. Given the linear assumptions, it is shown that the PNA is one of a few leading modes over the extratropical Pacific that can be strongly driven by tropical convection while other extratropical modes present at most a weak interaction with tropical convection. In the second part of this study, a two-step linear regression is introduced which leverages a LIM and large-scale climate variability to the prediction of hydrological extremes (e.g. atmospheric rivers) on subseasonal timescales. Consistent with the findings of the first part, most of the predictable signals on subseasonal timescales are determined by the dynamics of MJO-PNA teleconnection while other extratropical modes are important only at the shortest forecast leads.
Please join us for the April webinar hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project.
Title: Tropical origins of Weeks 2-4 forecasts errors during Northern Hemisphere cool season Speaker: Juliana Dias, NOAA, Physical Sciences Laboratory
Date: Thursday, April 29, 2021 Time: 10:30am EST | 2:30pm UTC
Abstract A set of 30-day reforecast experiments is used to quantify the remote impacts of tropical forecast errors on the National Centers for Environmental Prediction (NCEP) global forecast system (GFS). The approach is to nudge the model towards reanalyses in the tropics and then measure the change in skill at higher latitudes as a function of lead time. In agreement with previous analogous studies, results show that midlatitude GFS predictions tend to be improved in association with reducing tropical forecast errors during weeks 2-4, particularly over the North Pacific and western North America, where gains in subseasonal precipitation anomaly pattern correlations are substantial. It is also found that tropical nudging is more effective at improving NH subseasonal predictions in cases where skill is relatively low in the control reforecast, whereas it tends to improve less cases that are already relatively skillful. A time dependent analysis suggests a roughly one week lag between a decrease in tropical errors and an increase in NH predictive skill. The presentation will also include a combined tropical nudging and conditional skill analysis indicating that improved Madden Julian Oscillation (MJO) predictions throughout its lifecycle in the GFS could improve weeks 3-4 NH precipitation predictions.
Please join us for the May webinar hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project.
Title: The importance of a stratospheric route for MJO teleconnections to the Euro-Atlantic sector Speaker: Chaim Garfinkel, Hebrew University
Date: Thursday, May 27, 2021 Time: 1:30pm EST | 5:30pm UTC
Abstract The effect of the Madden‐Julian Oscillation (MJO) on the Northern Hemisphere wintertime stratospheric polar vortex and major, mid‐winter stratospheric sudden warmings (SSWs) is evaluated using a meteorological reanalysis dataset. The MJO influences the region in the tropospheric North Pacific sector that is most strongly associated with a SSW. Consistent with this, SSWs in the reanalysis record have tended to follow certain MJO phases. SSW events are more predictable if they are preceded by an MJO event. The magnitude of the influence of the MJO on the vortex is comparable to that associated with the Quasi‐Biennial Oscillation and El Niño. The MJO could be used to improve intra‐seasonal projections of the Northern Hemisphere high latitude circulation, and in particular of the tropospheric Northern Annular Mode and North Atlantic Oscillation, at lags exceeding one month. The ability of operational subseasonal forecasting models archiving their data as part of the S2S project to capture this is assessed, and most models are found to underestimate the magnitude of the observed effect.
If you would like to attend the webinar, please email to cstan AT gmu DOT edu
Please join us for the June webinar hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project.
Title: On the relationship between intraseasonal and interannual teleconnections from Indo-Pacific heating Speaker: Franco Molteni, ECMWF
Date: Thursday, June 24, 2021 Time: 10:30am EST | 2:30pm UTC
Abstract Many studies on the extratropical teleconnections of the Madden-Julian Oscillation (MJO) in boreal-winter have associated an increased frequency of positive North Atlantic Oscillation (NAO) anomalies with the occurrence of MJO phase-3 10 to 15 days earlier, when increased convection is located in the eastern Indian Ocean. Connections between the NAO and the MJO phase-2 (when increased convection is located further west) appear to be weaker in intra-seasonal diagnostics. On the other hand, on the interannual time scale, teleconnections computed from 2-month or 3-month means indicate a stronger connection of positive NAO with convection in the western-to-central part of the tropical Indian Ocean.
This discrepancy between results on the two time-scales are due, to a large extent, to the impact of ENSO on the inter-annual component of Indian Ocean circulation and heating anomalies. This implies that the way in which the seasonal-to-interannual signal is (or is not) filtered out may significantly affect the estimation of intra-seasonal teleconnections. Since the impact of ENSO on both Indian Ocean convection and the NAO varies between early and late winter, results are also dependent on the specific period of the year considered.
In this talk, diabatic heating computed from ERA-5 data (specifically, as a residual between total and adiabatic temperature tendencies) in a 36-year period, and 200-hPa geopotential height from the same re-analysis, are used to investigate the relationship between inter-annual and intra-seasonal teleconnections of MJO-like heating anomalies over the Indian Ocean and the Maritime Continents. Results show that the interannual signal dominates the NAO teleconnection from the Indian Ocean in early winter (Nov.-Dec.); in this period the interannual teleconnections from the western and eastern part of the ocean are anti-correlated over the North Atlantic, and differ significantly from the intra-seasonal signals. Later in the winter (Jan.-Feb.), intraseasonal variability explains a larger fraction of the large-scale diabatic heating variance, and intra-seasonal teleconnections are more similar to those computed without any scale separation.
Finally, results from a set of sub-seasonal ensembles run with the ECMWF coupled model, and initialized on 1 Nov. 1981 to 2016, will be compared with ERA-5 results for the Nov.-Dec. period. Confirming earlier findings on ECMWF sub-seasonal forecasts, a good agreement is found on the patterns of tropical heating variability, but the amplitude of their extratropical teleconnections is significantly under-estimated.
If you would like to attend the webinar, please email to cstan AT gmu DOT edu
Please join us for the July webinar hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project.
Title: Linear inverse modeling: A framework for subseasonal forecasting and the diagnosis of physical sources of forecast skill Speaker: John Albers, NOAA PSL/CIRES/University of Colorado Boulder
Date: Thursday, July 29, 2021 Time: 10:30am EST | 2:30pm UTC
Abstract We introduce the linear inverse model (LIM) framework and discuss its application as a subseasonal forecast model, a free-running climate model, and as a tool to isolate physical sources of subseasonal forecast skill. A LIM is an observationally based, statistical-dynamical model that approximates the chaotic evolution of a ‘coarse-grained’ climate anomaly as the sum of slowly evolving, predictable linear dynamics and rapidly evolving, unpredictable white noise. Here we construct a LIM that models the coupled dynamics of tropical heating, tropical sea-surface temperatures, extratropical tropospheric and stratospheric dynamical variability, and 2m temperature. Using this LIM, we examine the predictability and sources of forecast skill of the North Atlantic Oscillation (NAO) and the record breaking February 2021 North American cold air outbreak (CAO). First, we demonstrate that the LIM can be used to decompose the dynamics that drive NAO variability and predictability. A LIM-based dynamical (‘nonnormal’) filter identifies those dynamical modes that, despite capturing only a fraction of overall NAO variability, are largely responsible for extended-range NAO skill. Predictable NAO events stem from the linear superposition of these modes, which represent joint tropical sea-surface temperature-lower stratosphere variability plus a single mode capturing downward propagation from the upper stratosphere. The joint tropical-stratosphere modes are associated with non-canonical ENSO teleconnections that extend upwards into the lower stratosphere, while the downward propagating mode captures stratospheric NAM anomalies that are commonly associated with sudden stratospheric warmings. The predictable LIM subspace identifies high skill NAO forecasts, both for the LIM and for the state-of-the-art European Centre for Medium-Range Weather Forecasts Integrated Forecast System (IFS), for the 1997-2016 period. For the 2021 CAO, the LIM had high confidence in a cold surge at least 4 weeks in advance of the event onset, which was contrary to the dynamical forecast model guidance. When the LIM’s nonnormal filter is applied to the CAO, it is shown that the cold surge was due primarily to (predictable) SST-stratosphere based teleconnections and (unpredictable) internal variability, with small cold anomaly contributions from the MJO and the early January sudden stratospheric warming.
If you would like to attend the webinar, please email to cstan AT gmu DOT edu
Please join us for the August webinar hosted by the WWRP/WCRP/S2S/MJO and Teleconnections sub-project.
Title: Predictability of Sahelian heatwaves and importance of tropical modes of variability Speaker: Guigma Kiswendsida, Red Cross Red Crescent Climate Center
Date: Thursday, August 26, 2021 Time: 1:00pm EDT | 5:00pm UTC
Abstract Heatwaves are a growing threat to human health worldwide, but remain poorly documented over Africa. This study addresses the predictability of Sahelian heatwaves during the February-March and April to June seasons as well as their large-scale drivers, with a focus on the role of the Madden-Julian Oscillation (MJO), the equatorial Rossby (ER) and Kelvin (EK) waves. The ECMWF ENS extendedrange forecasting system (ENS-ext), with a forecast horizon of 46 days, is used for the prediction skill assessment, the ERA5 reanalysis being the main reference dataset. Heatwaves are defined as spells of three or more consecutive days, where a given thermal index exceeds both the 75th percentile of its total distribution and the 90th percentile of its calendar day distribution. Tropical modes are obtained through a wavenumber-frequency decomposition of OLR anomalies.
The results show that ENS-ext is able to predict heatwaves with relatively good skill out to two to three weeks ahead. The highest forecast scores are obtained for daytime heatwaves and for the shortest leadtimes. With increasing lead-times, heatwaves become more predictable at nighttime than at daytime. Likewise, the prediction skill is initially higher during the February-March season for the shortest leadtimes, whereas for week 2 of the forecast and beyond, the April to June season heatwaves have a better predictability.
Tropical modes significantly affect the occurrence of heatwaves in the Sahel. Depending on their convective phase, they can either increase or decrease their probability. The MJO has the greatest effect, closely followed by the ER wave whereas the EK wave is less important to heatwave occurrence.
The observed relationship between heatwave occurrence and tropical mode activity is relatively well simulated by ENS-ext. The heatwave prediction skill is also found to be higher when the MJO and the ER wave are predicted to be active than when they are predicted to be inactive. Whilst this gain in prediction skill is limited to the first week of forecast for the ER wave, it extends out to the third week for the MJO.
Therefore, improving the representation of tropical modes in models will positively impact heatwave prediction at the subseasonal scale in the Sahel, and gain more time and precision for anticipatory actions.
If you would like to attend the webinar, please email to cstan AT gmu DOT edu
Please join us for the September webinar hosted by the WWRP/WCRP/S2S/MJO and Teleconnections sub-project.
Title: Systematic Decomposition, Dynamics and Secular Changes of the Madden-Julian Oscillation Speaker: Christian Franzke, Pusan National University, Busan, South Korea
Date: Thursday, September 30, 2021 Time: 6:00pm EDT | 10:00pm UTC
Abstract The Madden–Julian Oscillation (MJO) is the dominant form of intra-seasonal variability in the Tropics and has pronounced impacts on surface weather and extremes extending to the extra-tropics. The MJO is a complex convectively coupled phenomenon, which is still poorly represented in the current generation of climate models, and our understanding of its essential dynamics and its influence on the midlatitude circulation is still incomplete. Here, we use a normal-mode decomposition method to decompose the MJO systematically into Kelvin, inertio-gravity (IG), and Rossby-wave components to provide a climatology of the eight MJO phases for the Kelvin, IG, and Rossby-wave components. In my presentation, I will discuss the relative contributions of these modes to the MJO, the extra-tropical response to the MJO and the secular change of the MJO over the last 2 decades and its connection to Western Pacific SST.
Meeting Recording: Topic: S2S/MJO and Teleconnections Monthly Webinar Date: Sep 30, 2021 05:42 PM Eastern Time (US and Canada)
test comment from A Robertson
The MJO-Teleconnection sub-project is launching a webinar series once a month on the last Thursday of the month.
Dear Colleagues,
Please join us for the first webinar of the monthly series of webinars hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project.
Date: Thursday, April 30, 2020, 10:30 am | (UTC-04:00) Eastern Time (US & Canada) | 1 hr
Title: On the Subseasonal-to-seasonal Variability of Extra-tropics
Speaker: Cristiana Stan, George Mason University, USA
Abstract
Recent advancements in understanding the subseasonal-to-seasonal (S2S) variability outside of the tropics will be discussed. I will introduce the multi-channel singular spectral analysis (MSSA) method used to isolate the S2S variability in the extra-tropics, present the oscillatory modes dominating the extra-tropics on these time scales and their relationship with tropical and stratospheric variability, and discuss the implications of midlatitude oscillatory modes for the predictability at Week 3&4.
The S2S variability of the extra-tropics is dominated by three propagating oscillations with broad-band spectra centered at 120, 45, and 28 days are found. The first oscillatory mode is referred to as the midlatitude seasonal oscillation (MLSO), and the other two are referred to as midlatitude intraseasonal oscillation 1 and 2 (MLISO 1 and MLISO2). When combined, the oscillations explain up to 30% of the natural variability of the extra-tropics on the intra-seasonal to seasonal time scales. These oscillations share some features with the circumglobal wave guide and in some phases of their lifecycles they project onto the canonical teleconnection patterns.
MLSO and MLISO-1 are related to the intraseasonal convective activity of the tropics and MLISO-1 shows some connection with the stratospheric variability associated with QBO.
When used as predictors in a simple linear regression model with 2-meter temperature as predictand, the mid-latitude oscillations extend the potential predictability of dependent variable to about 20 days.
To participate send and email to subseasonal_to_seasonal_prediction_mjo_tel
Webinar Recording:
https://gmu.webex.com/recordingservice/sites/gmu/recording/playback/85d85c8913a6409caaabfc51ee7cd84e
Dear Colleagues,
Please join us for the May Webinar of the monthly series of webinars hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project.
Date: Thursday, May 28, 2020, 10:30am | (UTC-04:00) Eastern Time (US & Canada) | 1hr
Title: Non-normal optimal growth of the Pacific-North American pattern
Speaker: Stephanie Henderson, University of Wisconsin-Madison, USA
Abstract
The Pacific-North American (PNA) pattern has been previously linked to tropical variability including the Madden-Julian Oscillation (MJO) and the El Niño-Southern Oscillation (ENSO), as well as internal extratropical variability. However, many questions remain regarding how these various relationships act, both together and individually, to yield observed PNA variability. The role of tropical heating and the extratropical circulation on PNA pattern growth is examined using linear inverse modeling (LIM). Optimal PNA growth is found to occur via the non-normal interference between the modes strongly coupled to sea surface temperatures (SST), including ENSO, and the modes internal to the atmosphere, such as the MJO. PNA growth beyond this interference is also examined through the development of an “internal atmospheric” LIM that excludes the modes strongly coupled to SST, such as ENSO, while retaining MJO variability. Optimal PNA growth in the internal atmospheric LIM is driven by MJO Indian Ocean heating with suppressed heating over the tropical western Pacific, and a retrograding northeast Pacific streamfunction anomaly. The separate contributions of tropical heating and the extratropical circulation on PNA growth are also investigated.
Importantly, the non-normal PNA growth highlights the difficulty in partitioning PNA variance into contributions from different phenomena and should be considered in attribution studies.
To participate send and email to subseasonal_to_seasonal_prediction_mjo_tel
Webinar Recording:
https://gmu.webex.com/recordingservice/sites/gmu/recording/playback/df07e2c1ced24c69933be4edcb8bd4aa
Dear Colleagues,
Please join us for the June webinar of the monthly series of webinars hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project.
Title: MJO Teleconnections to the Euro-Atlantic sector
Speaker: Robert Lee, National Centre for Atmospheric Science and Department of Meteorology, University of Reading, UK
Abstract
The teleconnection from the Madden-Julian Oscillation (MJO) provides a source of subseasonal variability and predictability to the North Atlantic-European (NAE) region.
The El Niño-Southern Oscillation (ENSO) modulates the seasonal mean state, through which the MJO and its teleconnection pattern propagates; however, its impact on this teleconnection to the NAE region has not been investigated. In this webinar I will present evidence of a robust dependence of the teleconnections from the MJO to NAE weather regimes on the phase of ENSO. I will demonstrate that the MJO to NAO+ regime tropospheric teleconnection is strongly enhanced during El Niño years, via enhanced Rossby wave activity, and inactive during La Niña. Conversely the MJO to NAO− regime stratospheric teleconnection is enhanced during La Niña years, and inactive during El Niño. This dependence on the background state has strong implications for subseasonal predictability, including interannual variations in subseasonal predictive skill.
I will go on to show statistical analysis of the MJO-NAE teleconnections using a larger set of 29 patterns, known as the Grosswetterlagen (GWL), to represent the European weather. Since the GWL patterns are smaller in spatial scale, they capture more synoptic detail. These findings demonstrate how the MJO can modify the preferred evolution of the NAE atmospheric flow.
To participate send and email to subseasonal_to_seasonal_prediction_mjo_tel.
Webinar recording:
https://gmu.webex.com/recordingservice/sites/gmu/recording/playback/eb77f773e6584d8cbe93ecafd4f742bf
Why does MJO follow almost exactly the SOI time series ?
https://imagizer.imageshack.com/img921/7305/bXNFwm.png
Dear Colleagues,
After a month of hiatus, we are resuming the monthly series of webinars hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project. Please join us for the August webinar.
Title: Impact of MJO propagation and background flow variability on the evolution of the MJO mid-latitude teleconnection
Speaker: Prof. Edmund Chang, School of Marine and Atmospheric Sciences, Stony Brook University
Date: Thursday, August 27, 2020
Time: 1pm EDT | 5pm UTC
Abstract
The MJO acts as a tropical heat source to excite Rossby waves that propagate into the mid-latitudes and modulate the mid-latitude circulation and weather. In this talk, using results from idealized model experiments, I will examine how the MJO excited mid-latitude teleconnection may depend on the history of the MJO evolution, as well as how different mid-latitude large-scale background flow may impact the evolution of the MJO mid-latitude teleconnection.
To participate send and email to subseasonal_to_seasonal_prediction_mjo_tel.
Webinar recording:
https://gmu.webex.com/recordingservice/sites/gmu/recording/playback/569c57769c04466eba33d1d2abf83643
Dear Colleagues,
After another month of hiatus, we are resuming the monthly series of webinars hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project. Please join us for the October webinar.
Title: Understanding tropical-midlatitude interactions: metrics, dynamical processes, and future change
Speaker: Jiabao Wang, School of Marine and Atmospheric Sciences, Stony Brook University
Date: Thursday, October 29, 2020
Time: 1pm EDT | 5pm UTC
Abstract
Tropical convections impact remotely on the midlatitude weather events (e.g., precipitation extremes over California) by forcing changes in circulation patterns. These tropical-midlatitude interactions are particularly important to be accurately simulated and predicted on subseasonal timescales since many management decisions fall within this time range. The Madden-Julian oscillation (MJO) is a unique type of organized tropical convection varying on subseasonal timescales and is recognized as an important source of subseasonal predictability for midlatitude weather phenomena. Better understanding of the MJO-midlatitude interactions is important in improving the simulation, prediction, and the understanding of future changes in MJO associated weather events.
As a joint activity between the WGNE MJO Task Force and WMO S2S teleconnection subproject, we developed a set of standardized diagnostics and metrics to characterize the MJO teleconnections and to understand the associated key dynamical processes (Wang et al. 2020a, b). In this talk, application of these diagnostics to CMIP5 and CMIP6 models will be presented. We will discuss the sensitivity of MJO teleconnections to MJO and basic state representations in models and sources of teleconnection biases. Future changes of MJO teleconnections and the underlying mechanisms will also be discussed.
Wang, J., H. Kim, D. Kim, S. A. Henderson, C. Stan, and E. D. Maloney (2020b): MJO teleconnections over the PNA region in climate models. Part II: Impacts of the MJO and basic state, J. Climate, 33, 5081-5101. doi: 10.1175/JCLI-D-19-0865.1.
Wang, J., H. Kim, D. Kim, S. A. Henderson, C. Stan, and E. D. Maloney (2020a): MJO teleconnections over the PNA region in climate models. Part I: Performance- and process-based skill metrics, J. Climate, 33, 1051-1067. doi: 10.1175/JCLI-D-19-0253.1.
To participate send and email to subseasonal_to_seasonal_prediction_mjo_tel.
Webinar recording:
S2S MJO-Teleconnections Webinar-20201029 1703-1
https://gmu.webex.com/recordingservice/sites/gmu/recording/playback/4011e1ce5a8b49149c295c2382f2159f
Dear Colleagues,
We are resuming the monthly series of webinars hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project. Please join us for the January webinar.
Title: Intrinsic Uncertainty in the Euro-Atlantic Response to the MJO heating in boreal winter: Ongoing Results from ECMWF Re-Forecasts
Speaker: David Straus, George Mason University
Date: Thursday, January 28, 2021
Time: 10:30am EST | 3:30pm UTC
Abstract
While the Euro-Atlantic response to the MJO has been well studied in reanalysis and a hierarchy of models, a factor that is often overlooked is the uncertainty in the response due to the intrinsic variability in the full diabatic heating during even a single phase of the MJO.
We examine the heating variability within large (51-member) ensembles of boreal winter reforecasts from the ECMWF model, focusing on forecasts initialized in phases 2 and 3 of the MJO (with heating anomalies located over the Indian Ocean). Results will be shown from new experimental reforecasts in which all the ensemble members utilize identical initial conditions, with the only difference between ensemble members arising from the application of stochastic physics in the target Indian Ocean region. (The stochastic physics is turned off outside the target region.)
The resulting uncertainty (ensemble spread) in the Euro-Atlantic response during the first few weeks of the forecasts is also examined, as well as some discussion of ongoing work to link the response uncertainties to those in the heating. The Euro-Atlantic response is seen to be similar to the traditional MJO response early in the forecast (MJO phases 2/3 leading to the NAO+ regime). However, later on in the forecast variability in the heating over the Pacific Ocean may play a role. Further experiments are planned to clarify the roles of ENSO vis-à-vis those of the MJO.
Webinar recording:
https://gmu.webex.com/gmu/ldr.php?RCID=2aa2cd26f8ab42b18eef886e5ce34cd8
Dear Colleagues,
Please join us for the February webinar hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project.
Title: Mapping Large-scale Climate Variability to Hydrological Extremes: An Application of the Linear Inverse Model to Subseasonal Prediction
Speaker: Kai-Chih Tseng, GFDL
Date: Thursday, February 25, 2021
Time: 10:30am EST | 3:30pm UTC
Abstract
The excitation of the Pacific-North American (PNA) teleconnection pattern by the Madden-Julian Oscillation (MJO) has been considered as one of the most important predictability sources on subseasonal timescales over the extratropical Pacific and North America. However, until recently, the interactions between tropical heating and other extratropical modes and their relationships to subseasonal prediction have received comparatively little attention. In this study, a linear inverse model (LIM) is applied to examine the tropical-extratropical interactions. The LIM provides a means of calculating the response of a dynamical system to a small forcing by constructing a linear operator from the observed covariability statistics of the system. Given the linear assumptions, it is shown that the PNA is one of a few leading modes over the extratropical Pacific that can be strongly driven by tropical convection while other extratropical modes present at most a weak interaction with tropical convection. In the second part of this study, a two-step linear regression is introduced which leverages a LIM and large-scale climate variability to the prediction of hydrological extremes (e.g. atmospheric rivers) on subseasonal timescales. Consistent with the findings of the first part, most of the predictable signals on subseasonal timescales are determined by the dynamics of MJO-PNA teleconnection while other extratropical modes are important only at the shortest forecast leads.
Webinar recording:
https://gmu.webex.com/gmu/ldr.php?RCID=48afbbc7b5324ac9b40ebfc1c8a3523c
Dear Colleagues,
Please join us for the April webinar hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project.
Title: Tropical origins of Weeks 2-4 forecasts errors during Northern Hemisphere cool season
Speaker: Juliana Dias, NOAA, Physical Sciences Laboratory
Date: Thursday, April 29, 2021
Time: 10:30am EST | 2:30pm UTC
Abstract
A set of 30-day reforecast experiments is used to quantify the remote impacts of tropical forecast errors on the National Centers for Environmental Prediction (NCEP) global forecast system (GFS). The approach is to nudge the model towards reanalyses in the tropics and then measure the change in skill at higher latitudes as a function of lead time. In agreement with previous analogous studies, results show that midlatitude GFS predictions tend to be improved in association with reducing tropical forecast errors during weeks 2-4, particularly over the North Pacific and western North America, where gains in subseasonal precipitation anomaly pattern correlations are substantial. It is also found that tropical nudging is more effective at improving NH subseasonal predictions in cases where skill is relatively low in the control reforecast, whereas it tends to improve less cases that are already relatively skillful. A time dependent analysis suggests a roughly one week lag between a decrease in tropical errors and an increase in NH predictive skill. The presentation will also include a combined tropical nudging and conditional skill analysis indicating that improved Madden Julian Oscillation (MJO) predictions throughout its lifecycle in the GFS could improve weeks 3-4 NH precipitation predictions.
Webinar recording:
https://gmu.webex.com/gmu/ldr.php?RCID=0c6dcf8cc65849698f9dcffdd80df75b
Dear Colleagues,
Please join us for the May webinar hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project.
Title: The importance of a stratospheric route for MJO teleconnections to the Euro-Atlantic sector
Speaker: Chaim Garfinkel, Hebrew University
Date: Thursday, May 27, 2021
Time: 1:30pm EST | 5:30pm UTC
Abstract
The effect of the Madden‐Julian Oscillation (MJO) on the Northern Hemisphere wintertime stratospheric polar vortex and major, mid‐winter stratospheric sudden warmings (SSWs) is evaluated using a meteorological reanalysis dataset. The MJO influences the region in the tropospheric North Pacific sector that is most strongly associated with a SSW. Consistent with this, SSWs in the reanalysis record have tended to follow certain MJO phases. SSW events are more predictable if they are preceded by an MJO event. The magnitude of the influence of the MJO on the vortex is comparable to that associated with the Quasi‐Biennial Oscillation and El Niño. The MJO could be used to improve intra‐seasonal projections of the Northern Hemisphere high latitude circulation, and in particular of the tropospheric Northern Annular Mode and North Atlantic Oscillation, at lags exceeding one month. The ability of operational subseasonal forecasting models archiving their data as part of the S2S project to capture this is assessed, and most models are found to underestimate the magnitude of the observed effect.
If you would like to attend the webinar, please email to cstan AT gmu DOT edu
Dear Colleagues,
Please join us for the June webinar hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project.
Title: On the relationship between intraseasonal and interannual teleconnections from Indo-Pacific heating
Speaker: Franco Molteni, ECMWF
Date: Thursday, June 24, 2021
Time: 10:30am EST | 2:30pm UTC
Abstract
Many studies on the extratropical teleconnections of the Madden-Julian Oscillation (MJO) in boreal-winter have associated an increased frequency of positive North Atlantic Oscillation (NAO) anomalies with the occurrence of MJO phase-3 10 to 15 days earlier, when increased convection is located in the eastern Indian Ocean. Connections between the NAO and the MJO phase-2 (when increased convection is located further west) appear to be weaker in intra-seasonal diagnostics.
On the other hand, on the interannual time scale, teleconnections computed from 2-month or 3-month means indicate a stronger connection of positive NAO with convection in the western-to-central part of the tropical Indian Ocean.
This discrepancy between results on the two time-scales are due, to a large extent, to the impact of ENSO on the inter-annual component of Indian Ocean circulation and heating anomalies. This implies that the way in which the seasonal-to-interannual signal is (or is not) filtered out may significantly affect the estimation of intra-seasonal teleconnections. Since the impact of ENSO on both Indian Ocean convection and the NAO varies between early and late winter, results are also dependent on the specific period of the year considered.
In this talk, diabatic heating computed from ERA-5 data (specifically, as a residual between total and adiabatic temperature tendencies) in a 36-year period, and 200-hPa geopotential height from the same re-analysis, are used to investigate the relationship between inter-annual and intra-seasonal teleconnections of MJO-like heating anomalies over the Indian Ocean and the Maritime Continents. Results show that the interannual signal dominates the NAO teleconnection from the Indian Ocean in early winter (Nov.-Dec.); in this period the interannual teleconnections from the western and eastern part of the ocean are anti-correlated over the North Atlantic, and differ significantly from the intra-seasonal signals. Later in the winter (Jan.-Feb.), intraseasonal variability explains a larger fraction of the large-scale diabatic heating variance, and intra-seasonal teleconnections are more similar to those computed without any scale separation.
Finally, results from a set of sub-seasonal ensembles run with the ECMWF coupled model, and initialized on 1 Nov. 1981 to 2016, will be compared with ERA-5 results for the Nov.-Dec. period. Confirming earlier findings on ECMWF sub-seasonal forecasts, a good agreement is found on the patterns of tropical heating variability, but the amplitude of their extratropical teleconnections is significantly under-estimated.
If you would like to attend the webinar, please email to cstan AT gmu DOT edu
Meeting Recording:
https://gmu.zoom.us/rec/share/FGzhe-QBQDfHQcR_PRABSEPpLY8kiDSqk7ANn7Kfh7Rs3Y6aliLkYVcQqEuPrCaD.4zpTyrTkNIQqOM10
Dear Colleagues,
Please join us for the July webinar hosted by the WWRP/WCRP/S2S/MJO-Teleconnections sub-project.
Title: Linear inverse modeling: A framework for subseasonal forecasting and the diagnosis of physical sources of forecast skill
Speaker: John Albers, NOAA PSL/CIRES/University of Colorado Boulder
Date: Thursday, July 29, 2021
Time: 10:30am EST | 2:30pm UTC
Abstract
We introduce the linear inverse model (LIM) framework and discuss its application as a subseasonal forecast model, a free-running climate model, and as a tool to isolate physical sources of subseasonal forecast skill. A LIM is an observationally based, statistical-dynamical model that approximates the chaotic evolution of a ‘coarse-grained’ climate anomaly as the sum of slowly evolving, predictable linear dynamics and rapidly evolving, unpredictable white noise. Here we construct a LIM that models the coupled dynamics of tropical heating, tropical sea-surface temperatures, extratropical tropospheric and stratospheric dynamical variability, and 2m temperature. Using this LIM, we examine the predictability and sources of forecast skill of the North Atlantic Oscillation (NAO) and the record breaking February 2021 North American cold air outbreak (CAO). First, we demonstrate that the LIM can be used to decompose the dynamics that drive NAO variability and predictability. A LIM-based dynamical (‘nonnormal’) filter identifies those dynamical modes that, despite capturing only a fraction of overall NAO variability, are largely responsible for extended-range NAO skill. Predictable NAO events stem from the linear superposition of these modes, which represent joint tropical sea-surface temperature-lower stratosphere variability plus a single mode capturing downward propagation from the upper stratosphere. The joint tropical-stratosphere modes are associated with non-canonical ENSO teleconnections that extend upwards into the lower stratosphere, while the downward propagating mode captures stratospheric NAM anomalies that are commonly associated with sudden stratospheric warmings. The predictable LIM subspace identifies high skill NAO forecasts, both for the LIM and for the state-of-the-art European Centre for Medium-Range Weather Forecasts Integrated Forecast System (IFS), for the 1997-2016 period. For the 2021 CAO, the LIM had high confidence in a cold surge at least 4 weeks in advance of the event onset, which was contrary to the dynamical forecast model guidance. When the LIM’s nonnormal filter is applied to the CAO, it is shown that the cold surge was due primarily to (predictable) SST-stratosphere based teleconnections and (unpredictable) internal variability, with small cold anomaly contributions from the MJO and the early January sudden stratospheric warming.
If you would like to attend the webinar, please email to cstan AT gmu DOT edu
Meeting Recording:
https://gmu.zoom.us/rec/share/MSf8LdLWs0wyFsVMUaB3G5dDwSPXazmho2BUNWDyT71N9o789eV1fY3R3CWsE1sh.S0G8eS1PlxxRFFRT
Dear Colleagues,
Please join us for the August webinar hosted by the WWRP/WCRP/S2S/MJO and Teleconnections sub-project.
Title: Predictability of Sahelian heatwaves and importance of tropical modes of variability
Speaker: Guigma Kiswendsida, Red Cross Red Crescent Climate Center
Date: Thursday, August 26, 2021
Time: 1:00pm EDT | 5:00pm UTC
Abstract
Heatwaves are a growing threat to human health worldwide, but remain poorly documented over Africa. This study addresses the predictability of Sahelian heatwaves during the February-March and April to June seasons as well as their large-scale drivers, with a focus on the role of the Madden-Julian Oscillation (MJO), the equatorial Rossby (ER) and Kelvin (EK) waves. The ECMWF ENS extendedrange forecasting system (ENS-ext), with a forecast horizon of 46 days, is used for the prediction skill assessment, the ERA5 reanalysis being the main reference dataset. Heatwaves are defined as spells of three or more consecutive days, where a given thermal index exceeds both the 75th percentile of its total distribution and the 90th percentile of its calendar day distribution. Tropical modes are obtained through a wavenumber-frequency decomposition of OLR anomalies.
The results show that ENS-ext is able to predict heatwaves with relatively good skill out to two to three weeks ahead. The highest forecast scores are obtained for daytime heatwaves and for the shortest leadtimes. With increasing lead-times, heatwaves become more predictable at nighttime than at daytime. Likewise, the prediction skill is initially higher during the February-March season for the shortest leadtimes, whereas for week 2 of the forecast and beyond, the April to June season heatwaves have a better predictability.
Tropical modes significantly affect the occurrence of heatwaves in the Sahel. Depending on their convective phase, they can either increase or decrease their probability. The MJO has the greatest effect, closely followed by the ER wave whereas the EK wave is less important to heatwave occurrence.
The observed relationship between heatwave occurrence and tropical mode activity is relatively well simulated by ENS-ext. The heatwave prediction skill is also found to be higher when the MJO and the ER wave are predicted to be active than when they are predicted to be inactive. Whilst this gain in prediction skill is limited to the first week of forecast for the ER wave, it extends out to the third week for the MJO.
Therefore, improving the representation of tropical modes in models will positively impact heatwave prediction at the subseasonal scale in the Sahel, and gain more time and precision for anticipatory actions.
If you would like to attend the webinar, please email to cstan AT gmu DOT edu
Recording of presentation:
https://docs.google.com/presentation/d/1ABqtjVGczf_oXxc8BlGsYh6kppjrQF06/edit?usp=sharing&ouid=101993203456660376262&rtpof=true&sd=true
Dear Colleagues,
Please join us for the September webinar hosted by the WWRP/WCRP/S2S/MJO and Teleconnections sub-project.
Title: Systematic Decomposition, Dynamics and Secular Changes of the Madden-Julian Oscillation
Speaker: Christian Franzke, Pusan National University, Busan, South Korea
Date: Thursday, September 30, 2021
Time: 6:00pm EDT | 10:00pm UTC
Abstract
The Madden–Julian Oscillation (MJO) is the dominant form of intra-seasonal variability in the Tropics and has pronounced impacts on surface weather and extremes extending to the extra-tropics. The MJO is a complex convectively coupled phenomenon, which is still poorly represented in the current generation of climate models, and our understanding of its essential dynamics and its influence on the midlatitude circulation is still incomplete. Here, we use a normal-mode decomposition method to decompose the MJO systematically into Kelvin, inertio-gravity (IG), and Rossby-wave components to provide a climatology of the eight MJO phases for the Kelvin, IG, and Rossby-wave components. In my presentation, I will discuss the relative contributions of these modes to the MJO, the extra-tropical response to the MJO and the secular change of the MJO over the last 2 decades and its connection to Western Pacific SST.
Meeting Recording:
Topic: S2S/MJO and Teleconnections Monthly Webinar
Date: Sep 30, 2021 05:42 PM Eastern Time (US and Canada)
Meeting Recording:
https://gmu.zoom.us/rec/share/6XJSw0D2T3j2cx-J4qPf4sydkRTGhi5WP6z0qOMnu2bDtn09RMI5kosy5UHRITQq.pt01-_UvgW1JtMRG