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Thomas Matejka
and
Diana L. Bartels

Abstract

Eight methods of calculating vertical air velocity in a column are compared. Each method requires some or all of the following data: horizontal divergence, vertical precipitation velocity, hydrometeor terminal fall speed, and vertical air velocity boundary conditions. Some or all of these quantities are commonly deduced or specified by a researcher during the analysis of Doppler radar data. The responses of the methods to different magnitudes and behaviors of errors in the input data are examined with a Monte Carlo method. The experiments are conducted with both random and systematic errors. Two idealized kinds of systematic errors are considered: bias error (a constant error through the column) and trend error (an error of constant magnitude that changes sign at the midpoint of the mass of the column). The performances of the methods are mapped over error space. A researcher, knowing approximately the characteristics of the errors of a particular set of Doppler radar data, can use the results of these experiments to select a method based on how well it performs in the presence of random errors and how well its performance holds up as bias and trend errors increase.

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Leon T. Nguyen
,
John Molinari
, and
Diana Thomas

Abstract

Identifying the center of a tropical cyclone in a high-resolution model simulation has a number of operational and research applications, including constructing a track, calculating azimuthal means and perturbations, and diagnosing vortex tilt. This study evaluated several tropical cyclone center identification methods in a high-resolution Weather Research and Forecasting (WRF) Model simulation of a sheared, intensifying, asymmetric tropical cyclone. The simulated tropical cyclone (TC) contained downshear convective cells and a mesovortex embedded in a broader TC vortex, complicating the identification of the TC vortex center. It is shown that unlike other methods, the pressure centroid method consistently 1) placed the TC center within the region of weak storm-relative wind, 2) produced a smooth track, 3) yielded a vortex tilt that varied smoothly in magnitude and direction, and 4) was insensitive to changes in horizontal grid resolution. Based on these results, the authors recommend using the pressure centroid to define the TC center in high-resolution numerical models.

The pressure centroid was calculated within a circular region representing the size of the TC inner core. To determine this area, the authors propose normalizing by the innermost radius at which the azimuthally averaged storm-relative tangential wind at 2-km height equals 80% of the maximum (R 80) at 2-km height. Although compositing studies have often normalized by the radius of maximum wind (RMW), R 80 proved less sensitive to slight changes in flat tangential wind profiles. This enables R 80 to be used as a normalization technique not only with intense TCs having peaked tangential wind profiles, but also with weaker TCs having flatter tangential wind profiles.

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Thomas M. Hamill
,
Diana R. Stovern
, and
Lesley L. Smith

Abstract

This article describes proposed revised methods for the statistical postprocessing of precipitation amount intended for the NOAA’s National Blend of Models using the Global Ensemble Forecast System version 12 data (GEFSv12). The procedure updates the previously established procedure of quantile mapping, weighting of sorted members, and dressing of the ensemble. The revised method leverages the long reforecast training dataset that has become available to improve quantile mapping of GEFSv12 data by eliminating the use of supplemental locations, that is, training data from other grid points. It establishes improved definitions of cumulative distributions through a spline-fitting approach. It provides updated algorithms for the weighting of sorted members based on closest-member histogram statistics, and it establishes an objective method for the dressing of the quantile-mapped, weighted ensemble. Verification statistics and case studies are provided in the accompanying article (Part II).

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Diana R. Stovern
,
Thomas M. Hamill
, and
Lesley L. Smith

Abstract

This second part of the series presents results from verifying a precipitation forecast calibration method discussed in the first part, based on quantile mapping (QM), weighting of sorted members, and dressing of the ensemble. NOAA’s Global Ensemble Forecast System, version 12 (GEFSv12), reforecasts were used in this study. The method was validated with preoperational GEFSv12 forecasts from December 2017 to November 2019. The method is proposed as an enhancement for GEFSv12 precipitation postprocessing in NOAA’s National Blend of Models. The first part described adaptations to the methodology to leverage the ∼20-yr GEFSv12 reforecast data. As shown here in this part, when compared with probabilistic quantitative precipitation forecasts from the raw ensemble, the adapted method produced downscaled, high-resolution forecasts that were significantly more reliable and skillful than raw ensemble-derived probabilities, especially at shorter lead times (i.e., <5 days) and for forecasts of events from light precipitation to >10 mm (6 h)−1. Cool-season events in the western United States were especially improved when the QM algorithm was applied, providing a statistical downscaling with realistic smaller-scale detail related to terrain features. The method provided less value added for forecasts of longer lead times and for the heaviest precipitation.

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Filippo Giorgi
,
Erika Coppola
,
Daniela Jacob
,
Claas Teichmann
,
Sabina Abba Omar
,
Moetasim Ashfaq
,
Nikolina Ban
,
Katharina Bülow
,
Melissa Bukovsky
,
Lars Buntemeyer
,
Tereza Cavazos
,
James Ciarlo`
,
Rosmeri Porfirio da Rocha
,
Sushant Das
,
Fabio di Sante
,
Jason P. Evans
,
Xuejie Gao
,
Graziano Giuliani
,
Russell H. Glazer
,
Peter Hoffmann
,
Eun-Soon Im
,
Gaby Langendijk
,
Ludwig Lierhammer
,
Marta Llopart
,
Sebastial Mueller
,
Rosa Luna-Nino
,
Rita Nogherotto
,
Emanuela Pichelli
,
Francesca Raffaele
,
Michelle Reboita
,
Diana Rechid
,
Armelle Remedio
,
Thomas Remke
,
Windmanagda Sawadogo
,
Kevin Sieck
,
José Abraham Torres-Alavez
, and
Torsten Weber

Abstract

We describe the first effort within the Coordinated Regional Climate Downscaling Experiment–Coordinated Output for Regional Evaluation, or CORDEX-CORE EXP-I. It consists of a set of twenty-first-century projections with two regional climate models (RCMs) downscaling three global climate model (GCM) simulations from the CMIP5 program, for two greenhouse gas concentration pathways (RCP8.5 and RCP2.6), over nine CORDEX domains at ∼25-km grid spacing. Illustrative examples from the initial analysis of this ensemble are presented, covering a wide range of topics, such as added value of RCM nesting, extreme indices, tropical and extratropical storms, monsoons, ENSO, severe storm environments, emergence of change signals, and energy production. They show that the CORDEX-CORE EXP-I ensemble can provide downscaled information of unprecedented comprehensiveness to increase understanding of processes relevant for regional climate change and impacts, and to assess the added value of RCMs. The CORDEX-CORE EXP-I dataset, which will be incrementally augmented with new simulations, is intended to be a public resource available to the scientific and end-user communities for application to process studies, impacts on different socioeconomic sectors, and climate service activities. The future of the CORDEX-CORE initiative is also discussed.

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Jonathan D. Wille
,
Simon P. Alexander
,
Charles Amory
,
Rebecca Baiman
,
Léonard Barthélemy
,
Dana M. Bergstrom
,
Alexis Berne
,
Hanin Binder
,
Juliette Blanchet
,
Deniz Bozkurt
,
Thomas J. Bracegirdle
,
Mathieu Casado
,
Taejin Choi
,
Kyle R. Clem
,
Francis Codron
,
Rajashree Datta
,
Stefano Di Battista
,
Vincent Favier
,
Diana Francis
,
Alexander D. Fraser
,
Elise Fourré
,
René D. Garreaud
,
Christophe Genthon
,
Irina V. Gorodetskaya
,
Sergi González-Herrero
,
Victoria J. Heinrich
,
Guillaume Hubert
,
Hanna Joos
,
Seong-Joong Kim
,
John C. King
,
Christoph Kittel
,
Amaelle Landais
,
Matthew Lazzara
,
Gregory H. Leonard
,
Jan L. Lieser
,
Michelle Maclennan
,
David Mikolajczyk
,
Peter Neff
,
Inès Ollivier
,
Ghislain Picard
,
Benjamin Pohl
,
F. Martin Ralph
,
Penny Rowe
,
Elisabeth Schlosser
,
Christine A. Shields
,
Inga J. Smith
,
Michael Sprenger
,
Luke Trusel
,
Danielle Udy
,
Tessa Vance
,
Étienne Vignon
,
Catherine Walker
,
Nander Wever
, and
Xun Zou

Abstract

Between 15 and 19 March 2022, East Antarctica experienced an exceptional heat wave with widespread 30°–40°C temperature anomalies across the ice sheet. This record-shattering event saw numerous monthly temperature records being broken including a new all-time temperature record of −9.4°C on 18 March at Concordia Station despite March typically being a transition month to the Antarctic coreless winter. The driver for these temperature extremes was an intense atmospheric river advecting subtropical/midlatitude heat and moisture deep into the Antarctic interior. The scope of the temperature records spurred a large, diverse collaborative effort to study the heat wave’s meteorological drivers, impacts, and historical climate context. Here we focus on describing those temperature records along with the intricate meteorological drivers that led to the most intense atmospheric river observed over East Antarctica. These efforts describe the Rossby wave activity forced from intense tropical convection over the Indian Ocean. This led to an atmospheric river and warm conveyor belt intensification near the coastline, which reinforced atmospheric blocking deep into East Antarctica. The resulting moisture flux and upper-level warm-air advection eroded the typical surface temperature inversions over the ice sheet. At the peak of the heat wave, an area of 3.3 million km2 in East Antarctica exceeded previous March monthly temperature records. Despite a temperature anomaly return time of about 100 years, a closer recurrence of such an event is possible under future climate projections. In Part II we describe the various impacts this extreme event had on the East Antarctic cryosphere.

Significance Statement

In March 2022, a heat wave and atmospheric river caused some of the highest temperature anomalies ever observed globally and captured the attention of the Antarctic science community. Using our diverse collective expertise, we explored the causes of the event and have placed it within a historical climate context. One key takeaway is that Antarctic climate extremes are highly sensitive to perturbations in the midlatitudes and subtropics. This heat wave redefined our expectations of the Antarctic climate. Despite the rare chance of occurrence based on past climate, a future temperature extreme event of similar magnitude is possible, especially given anthropogenic climate change.

Open access
Jonathan D. Wille
,
Simon P. Alexander
,
Charles Amory
,
Rebecca Baiman
,
Léonard Barthélemy
,
Dana M. Bergstrom
,
Alexis Berne
,
Hanin Binder
,
Juliette Blanchet
,
Deniz Bozkurt
,
Thomas J. Bracegirdle
,
Mathieu Casado
,
Taejin Choi
,
Kyle R. Clem
,
Francis Codron
,
Rajashree Datta
,
Stefano Di Battista
,
Vincent Favier
,
Diana Francis
,
Alexander D. Fraser
,
Elise Fourré
,
René D. Garreaud
,
Christophe Genthon
,
Irina V. Gorodetskaya
,
Sergi González-Herrero
,
Victoria J. Heinrich
,
Guillaume Hubert
,
Hanna Joos
,
Seong-Joong Kim
,
John C. King
,
Christoph Kittel
,
Amaelle Landais
,
Matthew Lazzara
,
Gregory H. Leonard
,
Jan L. Lieser
,
Michelle Maclennan
,
David Mikolajczyk
,
Peter Neff
,
Inès Ollivier
,
Ghislain Picard
,
Benjamin Pohl
,
F. Martin Ralph
,
Penny Rowe
,
Elisabeth Schlosser
,
Christine A. Shields
,
Inga J. Smith
,
Michael Sprenger
,
Luke Trusel
,
Danielle Udy
,
Tessa Vance
,
Étienne Vignon
,
Catherine Walker
,
Nander Wever
, and
Xun Zou

Abstract

Between 15 and 19 March 2022, East Antarctica experienced an exceptional heat wave with widespread 30°–40°C temperature anomalies across the ice sheet. In Part I, we assessed the meteorological drivers that generated an intense atmospheric river (AR) that caused these record-shattering temperature anomalies. Here, we continue our large collaborative study by analyzing the widespread and diverse impacts driven by the AR landfall. These impacts included widespread rain and surface melt that was recorded along coastal areas, but this was outweighed by widespread high snowfall accumulations resulting in a largely positive surface mass balance contribution to the East Antarctic region. An analysis of the surface energy budget indicated that widespread downward longwave radiation anomalies caused by large cloud-liquid water contents along with some scattered solar radiation produced intense surface warming. Isotope measurements of the moisture were highly elevated, likely imprinting a strong signal for past climate reconstructions. The AR event attenuated cosmic ray measurements at Concordia, something previously never observed. Last, an extratropical cyclone west of the AR landfall likely triggered the final collapse of the critically unstable Conger Ice Shelf while further reducing an already record low sea ice extent.

Significance Statement

Using our diverse collective expertise, we explored the impacts from the March 2022 heat wave and atmospheric river across East Antarctica. One key takeaway is that the Antarctic cryosphere is highly sensitive to meteorological extremes originating from the midlatitudes and subtropics. Despite the large positive temperature anomalies driven from strong downward longwave radiation, this event led to huge amounts of snowfall across the Antarctic interior desert. The isotopes in this snow of warm airmass origin will likely be detectable in future ice cores and potentially distort past climate reconstructions. Even measurements of space activity were affected. Also, the swells generated from this storm helped to trigger the final collapse of an already critically unstable Conger Ice Shelf while further degrading sea ice coverage.

Open access
Christiane Voigt
,
Ulrich Schumann
,
Andreas Minikin
,
Ahmed Abdelmonem
,
Armin Afchine
,
Stephan Borrmann
,
Maxi Boettcher
,
Bernhard Buchholz
,
Luca Bugliaro
,
Anja Costa
,
Joachim Curtius
,
Maximilian Dollner
,
Andreas Dörnbrack
,
Volker Dreiling
,
Volker Ebert
,
Andre Ehrlich
,
Andreas Fix
,
Linda Forster
,
Fabian Frank
,
Daniel Fütterer
,
Andreas Giez
,
Kaspar Graf
,
Jens-Uwe Grooß
,
Silke Groß
,
Katharina Heimerl
,
Bernd Heinold
,
Tilman Hüneke
,
Emma Järvinen
,
Tina Jurkat
,
Stefan Kaufmann
,
Mareike Kenntner
,
Marcus Klingebiel
,
Thomas Klimach
,
Rebecca Kohl
,
Martina Krämer
,
Trismono Candra Krisna
,
Anna Luebke
,
Bernhard Mayer
,
Stephan Mertes
,
Sergej Molleker
,
Andreas Petzold
,
Klaus Pfeilsticker
,
Max Port
,
Markus Rapp
,
Philipp Reutter
,
Christian Rolf
,
Diana Rose
,
Daniel Sauer
,
Andreas Schäfler
,
Romy Schlage
,
Martin Schnaiter
,
Johannes Schneider
,
Nicole Spelten
,
Peter Spichtinger
,
Paul Stock
,
Adrian Walser
,
Ralf Weigel
,
Bernadett Weinzierl
,
Manfred Wendisch
,
Frank Werner
,
Heini Wernli
,
Martin Wirth
,
Andreas Zahn
,
Helmut Ziereis
, and
Martin Zöger

Abstract

The Midlatitude Cirrus experiment (ML-CIRRUS) deployed the High Altitude and Long Range Research Aircraft (HALO) to obtain new insights into nucleation, life cycle, and climate impact of natural cirrus and aircraft-induced contrail cirrus. Direct observations of cirrus properties and their variability are still incomplete, currently limiting our understanding of the clouds’ impact on climate. Also, dynamical effects on clouds and feedbacks are not adequately represented in today’s weather prediction models.

Here, we present the rationale, objectives, and selected scientific highlights of ML-CIRRUS using the G-550 aircraft of the German atmospheric science community. The first combined in situ–remote sensing cloud mission with HALO united state-of-the-art cloud probes, a lidar and novel ice residual, aerosol, trace gas, and radiation instrumentation. The aircraft observations were accompanied by remote sensing from satellite and ground and by numerical simulations.

In spring 2014, HALO performed 16 flights above Europe with a focus on anthropogenic contrail cirrus and midlatitude cirrus induced by frontal systems including warm conveyor belts and other dynamical regimes (jet streams, mountain waves, and convection). Highlights from ML-CIRRUS include 1) new observations of microphysical and radiative cirrus properties and their variability in meteorological regimes typical for midlatitudes, 2) insights into occurrence of in situ–formed and lifted liquid-origin cirrus, 3) validation of cloud forecasts and satellite products, 4) assessment of contrail predictability, and 5) direct observations of contrail cirrus and their distinction from natural cirrus. Hence, ML-CIRRUS provides a comprehensive dataset on cirrus in the densely populated European midlatitudes with the scope to enhance our understanding of cirrus clouds and their role for climate and weather.

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Manfred Wendisch
,
Ulrich Pöschl
,
Meinrat O. Andreae
,
Luiz A. T. Machado
,
Rachel Albrecht
,
Hans Schlager
,
Daniel Rosenfeld
,
Scot T. Martin
,
Ahmed Abdelmonem
,
Armin Afchine
,
Alessandro C. Araùjo
,
Paulo Artaxo
,
Heinfried Aufmhoff
,
Henrique M. J. Barbosa
,
Stephan Borrmann
,
Ramon Braga
,
Bernhard Buchholz
,
Micael Amore Cecchini
,
Anja Costa
,
Joachim Curtius
,
Maximilian Dollner
,
Marcel Dorf
,
Volker Dreiling
,
Volker Ebert
,
André Ehrlich
,
Florian Ewald
,
Gilberto Fisch
,
Andreas Fix
,
Fabian Frank
,
Daniel Fütterer
,
Christopher Heckl
,
Fabian Heidelberg
,
Tilman Hüneke
,
Evelyn Jäkel
,
Emma Järvinen
,
Tina Jurkat
,
Sandra Kanter
,
Udo Kästner
,
Mareike Kenntner
,
Jürgen Kesselmeier
,
Thomas Klimach
,
Matthias Knecht
,
Rebecca Kohl
,
Tobias Kölling
,
Martina Krämer
,
Mira Krüger
,
Trismono Candra Krisna
,
Jost V. Lavric
,
Karla Longo
,
Christoph Mahnke
,
Antonio O. Manzi
,
Bernhard Mayer
,
Stephan Mertes
,
Andreas Minikin
,
Sergej Molleker
,
Steffen Münch
,
Björn Nillius
,
Klaus Pfeilsticker
,
Christopher Pöhlker
,
Anke Roiger
,
Diana Rose
,
Dagmar Rosenow
,
Daniel Sauer
,
Martin Schnaiter
,
Johannes Schneider
,
Christiane Schulz
,
Rodrigo A. F. de Souza
,
Antonio Spanu
,
Paul Stock
,
Daniel Vila
,
Christiane Voigt
,
Adrian Walser
,
David Walter
,
Ralf Weigel
,
Bernadett Weinzierl
,
Frank Werner
,
Marcia A. Yamasoe
,
Helmut Ziereis
,
Tobias Zinner
, and
Martin Zöger

Abstract

Between 1 September and 4 October 2014, a combined airborne and ground-based measurement campaign was conducted to study tropical deep convective clouds over the Brazilian Amazon rain forest. The new German research aircraft, High Altitude and Long Range Research Aircraft (HALO), a modified Gulfstream G550, and extensive ground-based instrumentation were deployed in and near Manaus (State of Amazonas). The campaign was part of the German–Brazilian Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems–Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (Global Precipitation Measurement) (ACRIDICON– CHUVA) venture to quantify aerosol–cloud–precipitation interactions and their thermodynamic, dynamic, and radiative effects by in situ and remote sensing measurements over Amazonia. The ACRIDICON–CHUVA field observations were carried out in cooperation with the second intensive operating period of Green Ocean Amazon 2014/15 (GoAmazon2014/5). In this paper we focus on the airborne data measured on HALO, which was equipped with about 30 in situ and remote sensing instruments for meteorological, trace gas, aerosol, cloud, precipitation, and spectral solar radiation measurements. Fourteen research flights with a total duration of 96 flight hours were performed. Five scientific topics were pursued: 1) cloud vertical evolution and life cycle (cloud profiling), 2) cloud processing of aerosol particles and trace gases (inflow and outflow), 3) satellite and radar validation (cloud products), 4) vertical transport and mixing (tracer experiment), and 5) cloud formation over forested/deforested areas. Data were collected in near-pristine atmospheric conditions and in environments polluted by biomass burning and urban emissions. The paper presents a general introduction of the ACRIDICON– CHUVA campaign (motivation and addressed research topics) and of HALO with its extensive instrument package, as well as a presentation of a few selected measurement results acquired during the flights for some selected scientific topics.

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