Advances in the subseasonal prediction of extreme events: relevant case studies across the globe

Extreme weather events have devastating impacts on human health, economic activities, ecosystems, and infrastructure. It is therefore crucial to anticipate extremes and their impacts to allow for preparedness and emergency measures. There is indeed potential for probabilistic subseasonal prediction on time scales of several weeks for many extreme events. Here we provide an overview of subseasonal predictability for case studies of some of the most prominent extreme events across the globe using the ECMWF S2S prediction system: heatwaves, cold spells, heavy precipitation events, and tropical and extratropical cyclones. The considered heatwaves exhibit predictability on time scales of 3–4 weeks, while this time scale is 2–3 weeks for cold spells. Precipitation extremes are the least predictable among the considered case studies. ­Tropical cyclones, on the other hand, can exhibit probabilistic predictability on time scales of up to 3 weeks, which in the presented cases was aided by remote precursors such as the Madden–Julian oscillation. For extratropical cyclones, lead times are found to be shorter. These case studies clearly illustrate the potential for event-dependent advance warnings for a wide range of extreme events. The subseasonal predictability of extreme events demonstrated here allows for an extension of warning horizons, provides advance information to impact modelers, and informs communities and stakeholders affected by the impacts of extreme weather events.Peer Reviewed"Article signat per 40 autors/es: Daniela I. V. Domeisen, Christopher J. White, Hilla Afargan-Gerstman, Ángel G. Muñoz, Matthew A. Janiga, Frédéric Vitart, C. Ole Wulff, Salomé Antoine, Constantin Ardilouze, Lauriane Batté, Hannah C. Bloomfield, David J. Brayshaw, Suzana J. Camargo, Andrew Charlton-Pérez, Dan Collins, Tim Cowan, Maria del Mar Chaves, Laura Ferranti, Rosario Gómez, Paula L. M. González, Carmen González Romero, Johnna M. Infanti, Stelios Karozis, Hera Kim, Erik W. Kolstad, Emerson LaJoie, Llorenç Lledó, Linus Magnusson, Piero Malguzzi, Andrea Manrique-Suñén, Daniele Mastrangelo, Stefano Materia, Hanoi Medina, Lluís Palma, Luis E. Pineda, Athanasios Sfetsos, Seok-Woo Son, Albert Soret, Sarah Strazzo, and Di Tian"Postprint (published version

Interactions between African Easterly Waves and Moist Convection

African easterly waves (AEWs) over tropical Africa and the East Atlantic influence and are themselves influenced by moist convection. Data from the Tropical Rainfall Measuring Mission (TRMM) satellite, reanalyses, and in-situ observations are used to examine both directions of this two-way interaction. This dissertation examines the climatological properties of convection, including their modulation by the diurnal cycle, over tropical Africa and the East Atlantic. Data from the TRMM Precipitation Radar (PR) shows that most of the rainfall which occurs over the Sahel comes from large and intense convective systems. This is due to the presence of high conditional instability and shear in this location. Both reanalysis and TRMM PR data are composited by AEW phase to examine how AEWs modulate the convective environment (lift, moisture, conditional instability, and shear) and how this affects the properties of convection. Over Sahelian West Africa, the highest rain rates are found in the northerly phase of AEWs. Large mesoscale convective systems (MCSs) account for most of the increase in rainfall in this phase of the wave. MCSs found in the northerlies are typically located just to the south of the northern low-level vortex, which is located near the Saharan heat low. This part of the AEW is favorable for convective organization due to the presence of anomalously high conditional instability and shear. Two MCSs developing in association with an intense AEW in 2006 are examined to clarify this relationship. Regional differences in the structure of AEWs between East Africa and the East Atlantic are examined in the context of the climatological zonally varying latent heating. Although AEWs over both regions are on average cold core, much stronger cold cores are observed in AEWs over East Africa. This difference in AEW structure is due to the presence of higher values of low-level latent heating over the East Atlantic, which occurs both climatologically and with the trough of AEWs

MJO Moisture Budget during DYNAMO in a Cloud-Resolving Model

Abstract Contributions by different physical processes and cloud types to the sum of the large-scale vertical moisture advection and apparent moisture sink observed by the DYNAMO field campaign northern sounding array during the passage of a Madden–Julian oscillation (MJO) event are estimated using a cloud-resolving model. The sum of these two moisture budget terms is referred to as the column-confined moisture tendency MC. Assuming diabatic balance, the contribution of different physical processes and cloud types to the large-scale vertical velocity and MC can be estimated using simulated diabatic tendencies and the domain-averaged static stability and vertical moisture gradient. Low-level moistening preceding MJO passage is captured by MC and dominated by the effects of shallow clouds. Because of the large vertical moisture gradient at this level, condensational heating in these clouds generates ascent and vertical moisture advection overwhelming the removal of water vapor by condensation. Shallow convective eddy transport also contributes to low-level moistening during this period. Eddy transport by congestus and deep convective clouds contributes to subsequent mid- and upper-level moistening, respectively, as well as low-level drying. Because the upper-level vertical moisture gradient is small, ice deposition within stratiform clouds has a net drying effect. The weak eddy transport in stratiform clouds is unable to compensate for this drying. Nonprecipitating clouds mainly modulate MC through their effects on radiation. During the enhanced phase, reduced longwave cooling results in less subsidence and drying; the opposite occurs during the suppressed phase. Large-scale horizontal advection, which is not included in MC, is responsible for much of the drying during the dissipating phase

Energy Efficiency of Historic Meetinghouse on Pleasant Street

With increasing fuel prices, energy consumption is a huge factor in the cost of heating a house. The goal of the project "Energy efficiency of Worcester Friends Meetinghouse" was to reduce overall energy consumption of the entire building. The main focus of research included the heating system, thermostat, windows, and insulation. Another focus was to identify how the residents interacted with the building in regards to energy usage. Afterwards recommendations were made that can be implemented both in this building and others like it in order to improve energy efficiency

Efficient Pulse Width Modulation LED Headlight Driver

LED headlights can provide better luminescence and less power consumption when compared to traditional halogen headlights. The adoption of LEDs in automobiles has been slow as the technology is more expensive than halogen bulbs, more complex to integrate, and younger. As such, an efficient, simplistic, and easy to use illumination driver was developed to spur on the widespread adoption of LED use in automobile lighting. The circuit developed is capable of providing the necessary illumination for a fraction of the energy input required by traditional lighting

Evolution of precipitation structure during the November dynamo MJO event: Cloud-resolving model intercomparison and cross validation using radar observations

Evolution of precipitation structures are simulated and compared with radar observations for the November Madden-Julian Oscillation (MJO) event during the DYNAmics of the MJO (DYNAMO) field campaign. Three ground-based, ship-borne, and spaceborne precipitation radars and three cloud-resolving models (CRMs) driven by observed large-scale forcing are used to study precipitation structures at different locations over the central equatorial Indian Ocean. Convective strength is represented by 0-dBZ echo-top heights, and convective organization by contiguous 17-dBZ areas. The multi-radar and multi-model framework allows for more stringent model validations. The emphasis is on testing models' ability to simulate subtle differences observed at different radar sites when the MJO event passed through. The results show that CRMs forced by site-specific large-scale forcing can reproduce not only common features in cloud populations but also subtle variations observed by different radars. The comparisons also revealed common deficiencies in CRM simulations where they underestimate radar echo-top heights for the strongest convection within large, organized precipitation features. Cross validations with multiple radars and models also enable quantitative comparisons in CRM sensitivity studies using different large-scale forcing, microphysical schemes and parameters, resolutions, and domain sizes. In terms of radar echo-top height temporal variations, many model sensitivity tests have better correlations than radar/model comparisons, indicating robustness in model performance on this aspect. It is further shown that well-validated model simulations could be used to constrain uncertainties in observed echo-top heights when the low-resolution surveillance scanning strategy is used.This study is mainly funded by grant DE-SC0008568 of the U.S. Department of Energy, Regional and Global Climate Modeling Program and Atmospheric System Research Program. X. Li would like to acknowledge additional funding from NASA grant NNX13AQ29G. S. Wang acknowledges support from National Science Foundation under grants AGS-1062206, AGS-1305788, and AGS-1543932. W.-K. Tao is also supported by the NASA Precipitation Measurement Mission (PMM) and NASA Modeling Analysis and Prediction (MAP) program. Both S-PolKa and C-band radar data are archived at DOE ASR's data site https://asr.science.energy.gov/data. TRMM PR data can be obtained through NASA website https://pmm.nasa.gov/data-access/downloads/trmm. The model simulations are archived on DOE server http://portal.nersc.gov/project/cpmmjo and NASA's mesoscale model webserver https://cloud.gsfc.nasa.gov. The RMM index is from www.bom.gov/au/climate/mjo/. Shaocheng Xie and Yunyan Zhang from Lawrence Livermore National Laboratory and Paul Ciesielski from Colorado State University provided large-scale forcing data and many insights in the interpretations. We would also like to thank Samson Hagos at PNNL for his help in archiving data. Zhe Feng at PNNL and Courtney Shumacher at Texas A&M provided valuable suggestion on using surface-based radar data. Acknowledgment is also made to the NASA Center for Climate Simulation, NASA Advance Supercomputing Division, and NASA Precipitation Processing System, for resources used in this research. PMEL contribution 4684 (C. Z.)

Testing Vertical Wind Shear and Nonlinear MJO-ENSO Interactions as Predictors for Subseasonal Atlantic Tropical Cyclone Forecasts

Hansen et al. found patterns of vertical wind shear, relative humidity (RH), and nonlinear interactions between the Madden-Julian oscillation and El Nino-Southern Oscillation that impact subseasonal Atlantic TC activity. We test whether these patterns can be used to improve subseasonal predictions. To do this we build a statistical-dynamical hybrid model using Navy-ESPC reforecasts as a part of the SUBX project. By adding and removing Navy-ESPC reforecasted values of predictors from a logistic regression model, we assess the contribution of skill from each predictor. We find that Atlantic SSTs and the MJO are the most important factors governing subseasonal Atlantic TC activity. RH contributes little to subseasonal TC predictions; however, shear predictors improve forecast skill at 5-10-day lead times, before forecast shear errors become too large. Nonlinear MJO-ENSO interactions did not improve skill compared to separate linear considerations of these factors but did improve the reliability of predictions for high-probability active TC periods. Both nonlinear MJO-ENSO interactions and the subseasonal shear signal appear linked to PV streamer activity. This study suggests that correcting model shear biases and improving representation of Rossby wave breaking is the most efficient way to improve subseasonal Atlantic TC forecasts

Impact of MJO Propagation Speed on Active Atlantic Tropical Cyclone Activity Periods

The Madden‐Julian Oscillation (MJO) is often used for subseasonal forecasting of tropical cyclone (TC) activity. However, TC activity still has considerable variability even given the state of the MJO. This study evaluates the connection between MJO propagation speed with Atlantic TC activity and possible physical mechanisms guiding this relation. We find the Atlantic sees the highest accumulated cyclone energy (ACE) during MJO phase 2. However, the odds of above average ACE in the Atlantic is greatest during slow MJO propagation. We find that slow propagation of the MJO results in lower vertical wind shear anomalies over the Caribbean and main development region compared with typical MJO propagation. Typical MJO propagation produces an amplified height pattern and lower height anomalies along the region of the tropical upper tropospheric trough which is known to impede Atlantic TC activity. Slow MJO propagation sees weaker height anomalies over the Atlantic. Plain Language Summary The Madden‐Julian Oscillation (MJO) is a large region of storminess and winds that moves slowly eastward from the Indian ocean eastward into the Pacific over the course of 40–90 days. When the MJO is over the Indian Ocean it produces more hurricanes in the Atlantic because it reduces wind shear which is the difference in winds at different heights of the atmosphere. When the MJO moves slowly or is nearly stationary over the Indian Ocean there is even more hurricane activity in the Atlantic. When the MJO moves at a normal pace, it influences the jet stream which can then dip into the Atlantic creating high wind shear. When the MJO moves slowly there is less shear over the Atlantic. Key Points The Atlantic basin sees the most subseasonal tropical cyclone activity when the Madden‐Julian Oscillation (MJO) is moving slowly prior to entering phase 2 Under normal MJO propagation higher shear occurs in the main development region than during slow propagating MJOs Under slow propagating MJO regimes the 500 mb geopotential height pattern has smaller wavelengths and weaker anomalies over the Atlanti

A dusty gust front of synoptic scale initiated and maintained by moist convection over the Sahara desert

International audienceIn this study we document the evolution, the synoptic trigger and the characteristics of an intense dust event which occurred over the Sahara desert on August 3-5, 2006. The motivation for this study is to highlight the large scale dust production over the Sahara associated with gust fronts of squall lines. The dust emission during this event was initiated by a large-scale cold pool emanated from a squall line that developed over Niger and Mali on August 3. We examine the development of this squall line and its subsequent dust lifting using high temporal resolution false color dust product images from the Meteosat Second Generation Spinning Enhanced Visible and Infrared Imager (MSG-SEVIRI). Observations from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) are used to characterize the vertical structure of the dust plume as it spreads over the Sahara and near the Atlantic coast line. The European Centre for Medium-Range Weather Forecasting African Monsoon Multidisciplinary Analysis (ECMWF-AMMA) special reanalysis was used to provide the synoptic-scale conditions that favored the occurrence of this event. Particular attention was paid to the intrusion of a mid-level extratropical streamer of potential vorticity that interacts with an African Easterly Wave (AEW) and favored the growth of a low-level cyclonic circulation along the intertropical discontinuity zone over the course of the event. The subsequent coupling of the ITD low-level circulation to an AEW aided both on the formation of the squall line and on the pronounced northward transport of the uplifted dust over the Sahara. The dusty cold pool extended over 2-3 km in altitude and exhibited an aerosol optical depth on the order of 1.5 and a dust load of about 1 Tg on average. Large amount of the dust produced during this event was subject to westward transport over the Atlantic Ocean after being mixed up by the diurnal heating over the Sahara to altitudes as high as 5 km. The pump of moisture by the cold pool into the dry desert favored the development of new convection over the Sahara which resulted on weak precipitation of about 3 mm per hour