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Zhe Feng
,
Adam Varble
,
Joseph Hardin
,
James Marquis
,
Alexis Hunzinger
,
Zhixiao Zhang
, and
Mandana Thieman

Abstract

This study characterizes the wide range of deep convective cloud life cycles and their relationships with ambient environments observed during the Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign near the Sierras de Córdoba (SDC) range in central Argentina. We develop a novel convective cell tracking database for the entire field campaign using C-band polarimetric radar observations. The cell tracking database includes timing, location, area, depth, merge/split information, microphysical properties, collocated satellite-retrieved cloud properties, and sounding-derived environmental conditions. Results show that the SDC exerts a strong control on convection initiation (CI) and growth. CI preferentially occurs east of the SDC ridge during the afternoon, and cells often undergo upscale growth through the evening as they travel eastward toward the plains. Larger and more intense cells tend to occur in more unstable and humid low-level environments, and surface-based cells are stronger than elevated cells. Midtropospheric relative humidity and vertical wind shear also jointly affect the size and depth of the cells. Rapid cell area growth rates exhibit dependence on both large environmental wind shear and low-level moisture. Evolution of convective cell macro- and microphysical properties are strongly influenced by convective available potential energy and low-level humidity, as well as the presence of other cells in their vicinity. This cell tracking database demonstrates a framework that ties measurements from various platforms centering around convective life cycles to facilitate process understanding of factors that control convective evolution.

Significance Statement

The purpose of this study is to develop a framework that ties coordinated radar, satellite, and radiosonde measurements around tracking convective storm life cycles to facilitate process understanding of atmospheric environments that control storm evolution. The processes coupling storm life cycles and local environments remain inadequately understood and are poorly represented in weather and climate models. Our results demonstrate the importance of atmospheric instability, low- and midtropospheric moisture, changes of wind with height, and interactions among nearby storms in affecting the formation and growth of convective storms. The storm database developed in this work enables future studies for comprehensive exploration of processes that lead to improved mechanistic understanding of storm evolution and their representations in models.

Open access
Kristen L. Rasmussen
,
Melissa A. Burt
,
Angela Rowe
,
Rebecca Haacker
,
Deanna Hence
,
Lorena Medina Luna
,
Stephen W. Nesbitt
, and
Julie Maertens

Abstract

This article provides an overview of the Advanced Study Institute: Field Studies of Convection in Argentina (ASI-FSCA) program, a 3-week dynamic and collaborative hands-on experience that allowed 16 highly motivated and diverse graduate students from the United States to participate in the 2018–19 Remote Sensing of Electrification, Lightning, and Mesoscale/Microscale Processes with Adaptive Ground Observations (RELAMPAGO) field campaign. This program is unique as it represents the first effort to integrate an intensive Advanced Study Institute with a field campaign in atmospheric science. ASI-FSCA activities and successful program outcomes for five key elements are described: 1) intensive field research with field campaign instrumentation platforms; 2) recruitment of diverse graduate students who would not otherwise have opportunities to participate in intensive field research; 3) tailored curriculum focused on scientific understanding of cloud and mesoscale processes and professional/academic development topics; 4) outreach to local K–12 schools and the general public; and 5) building a collaborative international research network to promote weather and climate research. These five elements served to increase motivation and improve confidence and self-efficacy of students to participate in scientific research and field work with goals of increasing retention and a sense of belonging in STEM graduate programs and advancing the careers of students from underrepresented groups as evidenced by a formal program evaluation effort. Given the success of the ASI-FSCA program, our team strongly recommends considering this model for expanding the opportunities for a broader and more diverse student community to participate in dynamic and intensive field work in atmospheric science.

Full access
Zhixiao Zhang
,
Adam Varble
,
Zhe Feng
,
Joseph Hardin
, and
Edward Zipser

Abstract

A 6.5-month, convection-permitting simulation is conducted over Argentina covering the Remote Sensing of Electrification, Lightning, And Mesoscale/Microscale Processes with Adaptive Ground Observations and Clouds, Aerosols, and Complex Terrain Interactions (RELAMPAGO-CACTI) field campaign and is compared with observations to evaluate mesoscale convective system (MCS) growth prediction. Observed and simulated MCSs are consistently identified, tracked, and separated into growth, mature, and decay stages using top-of-the-atmosphere infrared brightness temperature and surface rainfall. Simulated MCS number, lifetime, seasonal and diurnal cycles, and various cloud-shield characteristics including growth rate are similar to those observed. However, the simulation produces smaller rainfall areas, greater proportions of heavy rainfall, and faster system propagations. Rainfall area is significantly underestimated for long-lived MCSs but not for shorter-lived MCSs, and rain rates are always overestimated. These differences result from a combination of model and satellite retrieval biases, in which simulated MCS rain rates are shifted from light to heavy, while satellite-retrieved rainfall is too frequent relative to rain gauge estimates. However, the simulation reproduces satellite-retrieved MCS cloud-shield evolution well, supporting its usage to examine environmental controls on MCS growth. MCS initiation locations are associated with removal of convective inhibition more than maximized low-level moisture convergence or instability. Rapid growth is associated with a stronger upper-level jet (ULJ) and a deeper northwestern Argentinean low that causes a stronger northerly low-level jet (LLJ), increasing heat and moisture fluxes, low-level vertical wind shear, baroclinicity, and instability. Sustained growth corresponds to similar LLJ, baroclinicity, and instability conditions but is less sensitive to the ULJ, large-scale vertical motion, or low-level shear. Growth sustenance controls MCS maximum extent more than growth rate.

Full access
James N. Marquis
,
Adam C. Varble
,
Paul Robinson
,
T. Connor Nelson
, and
Katja Friedrich

Abstract

Data from scanning radars, radiosondes, and vertical profilers deployed during three field campaigns are analyzed to study interactions between cloud-scale updrafts associated with initiating deep moist convection and the surrounding environment. Three cases are analyzed in which the radar networks permitted dual-Doppler wind retrievals in clear air preceding and during the onset of surface precipitation. These observations capture the evolution of (i) the mesoscale and boundary layer flow, and (ii) low-level updrafts associated with deep moist convection initiation (CI) events yielding sustained or short-lived precipitating storms. The elimination of convective inhibition did not distinguish between sustained and unsustained CI events, though the vertical distribution of convective available potential energy may have played a role. The clearest signal differentiating the initiation of sustained versus unsustained precipitating deep convection was the depth of the low-level horizontal wind convergence associated with the mesoscale flow feature triggering CI, a sharp surface wind shift boundary, or orographic upslope flow. The depth of the boundary layer relative to the height of the LFC failed to be a consistent indicator of CI potential. Widths of the earliest detectable low-level updrafts associated with sustained precipitating deep convection were ~3–5 km, larger than updrafts associated with surrounding boundary layer turbulence (~1–3 km wide). It is hypothesized that updrafts of this larger size are important for initiating cells to survive the destructive effects of buoyancy dilution via entrainment.

Open access
Stephen W. Nesbitt
,
Paola V. Salio
,
Eldo Ávila
,
Phillip Bitzer
,
Lawrence Carey
,
V. Chandrasekar
,
Wiebke Deierling
,
Francina Dominguez
,
Maria Eugenia Dillon
,
C. Marcelo Garcia
,
David Gochis
,
Steven Goodman
,
Deanna A. Hence
,
Karen A. Kosiba
,
Matthew R. Kumjian
,
Timothy Lang
,
Lorena Medina Luna
,
James Marquis
,
Robert Marshall
,
Lynn A. McMurdie
,
Ernani de Lima Nascimento
,
Kristen L. Rasmussen
,
Rita Roberts
,
Angela K. Rowe
,
Juan José Ruiz
,
Eliah F.M.T. São Sabbas
,
A. Celeste Saulo
,
Russ S. Schumacher
,
Yanina Garcia Skabar
,
Luiz Augusto Toledo Machado
,
Robert J. Trapp
,
Adam C. Varble
,
James Wilson
,
Joshua Wurman
,
Edward J. Zipser
,
Ivan Arias
,
Hernán Bechis
, and
Maxwell A. Grover

Abstract

This article provides an overview of the experimental design, execution, education and public outreach, data collection, and initial scientific results from the Remote Sensing of Electrification, Lightning, and Mesoscale/Microscale Processes with Adaptive Ground Observations (RELAMPAGO) field campaign. RELAMPAGO was a major field campaign conducted in the Córdoba and Mendoza provinces in Argentina and western Rio Grande do Sul State in Brazil in 2018–19 that involved more than 200 scientists and students from the United States, Argentina, and Brazil. This campaign was motivated by the physical processes and societal impacts of deep convection that frequently initiates in this region, often along the complex terrain of the Sierras de Córdoba and Andes, and often grows rapidly upscale into dangerous storms that impact society. Observed storms during the experiment produced copious hail, intense flash flooding, extreme lightning flash rates, and other unusual lightning phenomena, but few tornadoes. The five distinct scientific foci of RELAMPAGO—convection initiation, severe weather, upscale growth, hydrometeorology, and lightning and electrification—are described, as are the deployment strategies to observe physical processes relevant to these foci. The campaign’s international cooperation, forecasting efforts, and mission planning strategies enabled a successful data collection effort. In addition, the legacy of RELAMPAGO in South America, including extensive multinational education, public outreach, and social media data gathering associated with the campaign, is summarized.

Full access
Adam C. Varble
,
Stephen W. Nesbitt
,
Paola Salio
,
Joseph C. Hardin
,
Nitin Bharadwaj
,
Paloma Borque
,
Paul J. DeMott
,
Zhe Feng
,
Thomas C. J. Hill
,
James N. Marquis
,
Alyssa Matthews
,
Fan Mei
,
Rusen Öktem
,
Vagner Castro
,
Lexie Goldberger
,
Alexis Hunzinger
,
Kevin R. Barry
,
Sonia M. Kreidenweis
,
Greg M. McFarquhar
,
Lynn A. McMurdie
,
Mikhail Pekour
,
Heath Powers
,
David M. Romps
,
Celeste Saulo
,
Beat Schmid
,
Jason M. Tomlinson
,
Susan C. van den Heever
,
Alla Zelenyuk
,
Zhixiao Zhang
, and
Edward J. Zipser

Abstract

The Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign was designed to improve understanding of orographic cloud life cycles in relation to surrounding atmospheric thermodynamic, flow, and aerosol conditions. The deployment to the Sierras de Córdoba range in north-central Argentina was chosen because of very frequent cumulus congestus, deep convection initiation, and mesoscale convective organization uniquely observable from a fixed site. The C-band Scanning Atmospheric Radiation Measurement (ARM) Precipitation Radar was deployed for the first time with over 50 ARM Mobile Facility atmospheric state, surface, aerosol, radiation, cloud, and precipitation instruments between October 2018 and April 2019. An intensive observing period (IOP) coincident with the RELAMPAGO field campaign was held between 1 November and 15 December during which 22 flights were performed by the ARM Gulfstream-1 aircraft. A multitude of atmospheric processes and cloud conditions were observed over the 7-month campaign, including numerous orographic cumulus and stratocumulus events; new particle formation and growth producing high aerosol concentrations; drizzle formation in fog and shallow liquid clouds; very low aerosol conditions following wet deposition in heavy rainfall; initiation of ice in congestus clouds across a range of temperatures; extreme deep convection reaching 21-km altitudes; and organization of intense, hail-containing supercells and mesoscale convective systems. These comprehensive datasets include many of the first ever collected in this region and provide new opportunities to study orographic cloud evolution and interactions with meteorological conditions, aerosols, surface conditions, and radiation in mountainous terrain.

Full access
Jeremiah O. Piersante
,
Russ. S. Schumacher
, and
Kristen L. Rasmussen

Abstract

Ensemble forecasts using the WRF Model at 20-km grid spacing with varying parameterizations are used to investigate and compare precipitation and atmospheric profile forecast biases in North and South America. By verifying a 19-member ensemble against NCEP Stage-IV precipitation analyses, it is shown that the cumulus parameterization (CP), in addition to precipitation amount and season, had the largest influence on precipitation forecast skill in North America during 2016–17. Verification of an ensemble subset against operational radiosondes in North and South America finds that forecasts in both continents feature a substantial midlevel dry bias, particularly at 700 hPa, during the warm season. Case-by-case analysis suggests that large midlevel error is associated with mesoscale convective systems (MCSs) east of the high terrain and westerly subsident flow from the Rocky and Andes Mountains in North and South America. However, error in South America is consistently greater than North America. This is likely attributed to the complex terrain and higher average altitude of the Andes relative to the Rockies, which allow for a deeper low-level jet and long-lasting MCSs, both of which 20-km simulations struggle to resolve. In the wake of data availability from the RELAMPAGO field campaign, the authors hope that this work motivates further comparison of large precipitating systems in North and South America, given their high impact in both continents.

Full access
Jeremiah O. Piersante
,
Kristen L. Rasmussen
,
Russ S. Schumacher
,
Angela K. Rowe
, and
Lynn A. McMurdie

Abstract

Subtropical South America (SSA) east of the Andes Mountains is a global hotspot for mesoscale convective systems (MCSs). Wide convective cores (WCCs) are typically embedded within mature MCSs, contribute over 40% of SSA’s warm-season rainfall, and are often associated with severe weather. Prior analysis of Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) data identified WCCs in SSA and associated synoptic conditions during austral summer. As WCCs also occur during the austral spring, this study uses the 16-yr TRMM PR and ERA5 datasets to compare anomalies in environmental conditions between austral spring (SON) and summer (DJF) for the largest and smallest WCCs in SSA. During both seasons, large WCCs are associated with an anomalous midlevel trough that slowly crosses the Andes Mountains and a northerly South American low-level jet (SALLJ) over SSA, though the SON trough and SALLJ anomalies are stronger and located farther northeastward than in DJF. A synoptic pattern evolution resembling large WCC environments is illustrated through a multiday case during the RELAMPAGO field campaign (10–13 November 2018). Unique high-temporal-resolution soundings showed strong midlevel vertical wind shear associated with this event, induced by the juxtaposition of the northerly SALLJ and southerly near-surface flow. It is hypothesized that the Andes help create a quasi-stationary trough–ridge pattern such that favorable synoptic conditions for deep convection persist for multiple days. For the smallest WCCs, anomalously weaker synoptic-scale forcing was present compared to the largest events, especially for DJF, pointing to future work exploring MCS formation under weaker synoptic conditions.

Full access
Russ S. Schumacher
,
Deanna A. Hence
,
Stephen W. Nesbitt
,
Robert J. Trapp
,
Karen A. Kosiba
,
Joshua Wurman
,
Paola Salio
,
Martin Rugna
,
Adam C. Varble
, and
Nathan R. Kelly

Abstract

During the Remote Sensing of Electrification, Lightning, and Mesoscale/Microscale Processes with Adaptive Ground Observations-Cloud, Aerosol, and Complex Terrain Interactions (RELAMPAGO-CACTI) field experiments in 2018–19, an unprecedented number of balloon-borne soundings were collected in Argentina. Radiosondes were launched from both fixed and mobile platforms, yielding 2712 soundings during the period 15 October 2018–30 April 2019. Approximately 20% of these soundings were collected by highly mobile platforms, strategically positioned for each intensive observing period, and launching approximately once per hour. The combination of fixed and mobile soundings capture both the overall conditions characterizing the RELAMPAGO-CACTI campaign, as well as the detailed evolution of environments supporting the initiation and upscale growth of deep convective storms, including some that produced hazardous hail and heavy rainfall. Episodes of frequent convection were characterized by sufficient quantities of moisture and instability for deep convection, along with deep-layer vertical wind shear supportive of organized or rotating storms. A total of 11 soundings showed most unstable convective available potential energy (MUCAPE) exceeding 6000 J kg−1, comparable to the extreme instability observed in other parts of the world with intense deep convection. Parameters used to diagnose severe-storm potential showed that conditions were often favorable for supercells and severe hail, but not for tornadoes, primarily because of insufficient low-level wind shear. High-frequency soundings also revealed the structure and evolution of the boundary layer leading up to convection initiation, convectively generated cold pools, the South American low-level jet (SALLJ), and elevated nocturnal convection. This sounding dataset will enable improved understanding and prediction of convective storms and their surroundings in subtropical South America, as well as comparisons with other heavily studied regions such as the central United States that have not previously been possible.

Full access
Stephen W. Nesbitt
,
Paola V. Salio
,
Eldo Ávila
,
Phillip Bitzer
,
Lawrence Carey
,
V. Chandrasekar
,
Wiebke Deierling
,
Francina Dominguez
,
Maria Eugenia Dillon
,
C. Marcelo Garcia
,
David Gochis
,
Steven Goodman
,
Deanna A. Hence
,
Karen A. Kosiba
,
Matthew R. Kumjian
,
Timothy Lang
,
Lorena Medina Luna
,
James Marquis
,
Robert Marshall
,
Lynn A. McMurdie
,
Ernani Lima Nascimento
,
Kristen L. Rasmussen
,
Rita Roberts
,
Angela K. Rowe
,
Juan José Ruiz
,
Eliah F.M.T. São Sabbas
,
A. Celeste Saulo
,
Russ S. Schumacher
,
Yanina Garcia Skabar
,
Luiz Augusto Toledo Machado
,
Robert J. Trapp
,
Adam Varble
,
James Wilson
,
Joshua Wurman
,
Edward J. Zipser
,
Ivan Arias
,
Hernán Bechis
, and
Maxwell A. Grover

Abstract

This article provides an overview of the experimental design, execution, education and public outreach, data collection, and initial scientific results from the Remote sensing of Electrification, Lightning, And Mesoscale/microscale Processes with Adaptive Ground Observations (RELAMPAGO) field campaign. RELAMPAGO was a major field campaign conducted in Córdoba and Mendoza provinces in Argentina, and western Rio Grande do Sul State in Brazil in 2018-2019 that involved more than 200 scientists and students from the US, Argentina, and Brazil. This campaign was motivated by the physical processes and societal impacts of deep convection that frequently initiates in this region, often along the complex terrain of the Sierras de Córdoba and Andes, and often grows rapidly upscale into dangerous storms that impact society. Observed storms during the experiment produced copious hail, intense flash flooding, extreme lightning flash rates and other unusual lightning phenomena, but few tornadoes. The 5 distinct scientific foci of RELAMPAGO: convection initiation, severe weather, upscale growth, hydrometeorology, and lightning and electrification are described, as are the deployment strategies to observe physical processes relevant to these foci. The campaign’s international cooperation, forecasting efforts, and mission planning strategies enabled a successful data collection effort. In addition, the legacy of RELAMPAGO in South America, including extensive multi-national education, public outreach, and social media data-gathering associated with the campaign, is summarized.

Full access