Revealing the hidden link of the Walker circulation on heavy rainfall patterns in the Eastern Pacific

Communications Earth & Environment · 2025-02-24

Understanding the relationship between tropical heavy rainfall and large-scale circulation provides valuable insights for improving the climate models. Here we use Gaussian Mixture Model to identify two distinct types of heavy rainfall over the tropical Pacific, “strong deep convection” and “moderately strong deep convection,” using satellite-borne precipitation radar measurements. They differ in two typical climatological deep convection-related rainfall modes between the western and eastern Pacific regions. The occurrence frequency of moderately strong deep convection is significantly different between the western and eastern Pacific, potentially linked to the Walker circulation. The enhanced Walker circulation appears to weaken the local Hadley circulation, thereby reducing strong deep convective activity in the eastern Pacific. This increases moderately heavy rainfall and decreases diabatic heating, which can affect global climate. We propose incorporating the close link between large-scale Walker circulation and mesoscale heavy convective rainfall into the current climate models. Tropical Pacific experiences two types of heavy rainfall including strong deep convection and moderately strong deep convection, which vary by region and are linked to the Walker circulation, according to satellite-borne precipitation radar measurements.

Interactions Between Aerosols, Meteorology, and Early Convective Cloud Lifecycle as Measured During CACTI (Final Technical Report)

2025-08-08

Dependencies of Simulated Convective Cell and System Growth Biases on Atmospheric Instability and Model Resolution

Journal of Geophysical Research Atmospheres · 2024-11-22 · 10 citations

Abstract This study evaluates convective cell properties and their relationships with convective and stratiform rainfall within a season‐long convection‐permitting weather research and forecasting simulation over central Argentina using radar, satellite, and radiosonde measurements from the RELAMPAGO‐CACTI field campaign. The simulation slightly underestimates radar‐estimated rainfall over the ∼3.5‐month evaluation period but underestimates stratiform rainfall by 46% and overestimates convective rainfall by 43%. As convective available potential energy (CAPE) increases, the convective rainfall overestimation decreases, but the stratiform rainfall underestimation increases such that the contribution of convective to total rainfall remains constantly high biased by ∼26%. Overestimated convective rainfall arises from the simulation generating 2.6 times more precipitating convective cells (14,299) than observed by radar (5,662) despite similar observed and simulated cell growth processes, with relatively wide cells contributing mostly to excessive convective rainfall. Relatively shallow cells, typically reaching heights of 4–7 km, contribute most to the cell number bias. This cell number bias increases as CAPE decreases, potentially because cells and their updrafts become narrower and more under‐resolved as CAPE decreases. The gross overproduction of precipitating shallow cells leads to overly efficient precipitation and inadequate detrainment of ice aloft, thereby diminishing the formation of robust stratiform rainfall regions. Decreasing model horizontal grid spacing from 3 to 1 or 0.333 km for low (<300 J kg −1 ) and high CAPE (>1,000 J kg −1 ) cases results in minimal change to cell number, depth, and convective‐to‐stratiform partitioning biases. This suggests that improving prediction of these convective properties depends on factors beyond solely increasing model resolution.

A dataset of tracked mesoscale precipitation systems in the tropics

Geoscience Data Journal · 2024-12-23 · 1 citations

Abstract Mesoscale Convective Systems (MCSs) are often quantified via surface‐based radar network, geostationary satellite, or low earth orbit satellite observations. However, each of these has drawbacks for detecting cloud systems such as a lack of global coverage, a lack of variables to quantify deep convective cloud and precipitation properties, and a lack of continuous observations of individual MCSs, respectively. To generate a dataset of tropical Tracked IMERG Mesoscale Precipitation Systems (TIMPS), we use the Forward in Time tracking algorithm to track precipitation systems in the Integrated Multi‐satellitE Retrievals for the Global Precipitation Mission (IMERG). IMERG is a global gridded precipitation product that incorporates observations from a constellation of satellites with passive microwave sensors and other sources, allowing the TIMPS dataset to have continuous temporal precipitation information for MCSs in a global tropical strip with data every 30 min in time and 0.1° in space. TIMPS are provided in a publicly available data base with a variety of variables including MCS size, motion, and precipitation properties, estimations of MCS life cycle stages, and their proximity to the nearest tropical cyclone. By combining the TIMPS dataset with the University of Washington Convective Features database, we also provide snapshots of information from more spatially detailed space‐borne radar coverage. The TIMPS dataset provides the means for detailed long‐term and large‐scale study of MCSs in all regions of the tropics with applications such as composite studies of MCS life cycles and the evaluation of model performance.

Dependencies of Simulated Convective Cell and System Growth Biases on Atmospheric Instability and Model Resolution

2024-03-13 · 2 citations

This study evaluates convective cell properties and their relationships with convective and stratiform rainfall within a season-long convection-permitting simulation over central Argentina using measurements from the RELAMPAGO-CACTI field campaign. While the simulation reproduces the total observed rainfall, it underestimates stratiform rainfall by 46% and overestimates convective rainfall by 43%. As Convective Available Potential Energy (CAPE) increases, the overestimation of convective rainfall decreases, but the underestimation of stratiform rainfall increases such that the high bias in the contribution of convective rainfall to total rainfall remains approximately constant at 26% across all CAPE conditions. Overestimated convective rainfall arises from the simulation generating 2.6 times more convective cells than observed despite similar observed and simulated cell growth processes, with relatively wide cells contributing most to excessive convective rainfall. Relatively shallow cells, typically reaching heights of 4–7 km, contribute most to the cell number bias. This bias increases as CAPE decreases, potentially because cells and their updrafts become narrower and more under-resolved as CAPE decreases. The gross overproduction of shallow cells leads to overly efficient precipitation and inadequate detrainment of ice aloft, thereby diminishing the formation of robust stratiform rainfall regions. Decreasing the model’s horizontal grid spacing from 3 to 1 or 0.333 km for representative low and high CAPE cases results in minimal change to the cell number and depth biases, while the stratiform and convective rainfall biases also fail to improve. This suggests that improving prediction of deep convective system growth depends on factors beyond solely increasing model resolution.

Tracking Mesoscale Convective Systems in IMERG and Regional Variability of Their Properties in the Tropics

Journal of Geophysical Research Atmospheres · 2023-12-15 · 21 citations

Abstract Mesoscale convective systems (MCSs) constitute only a fraction of convective systems in the tropics but significantly impact tropical weather and global climate. Early studies used satellite infrared (IR) data to track MCSs and study their properties but only for a short period due to computing limitations. Though valuable, the IR brightness temperature (Tb)‐derived precipitation properties have biases. The recent availability of Integrated Multi‐satEllite Retrieval for Global (IMERG) precipitation mission rainfall data of lesser bias than IR Tb‐based rainfall and access to high‐performance computers motivated us to track MCSs over global tropics for 10 years, using the Forward in Time (FiT) algorithm. Though IMERG is advantageous, it poses challenges to tracking MCSs due to convective systems connected by light rain areas and resolution differences between contributing passive microwave sensors. The precipitation field is smoothed and normalized to overcome these problems; then, the FiT algorithm identifies MCSs and tracks them. Our results show that MCSs contribute ∼70% of annual precipitation, though they are only ∼7% of all tracked systems. MCSs occur more often over the Amazon basin and Maritime Continent than in central Africa, known for high thunderstorm frequency, highlighting the contrasting convective regimes. The large, long‐lived, and intensely precipitating MCSs occur more often over the ocean than land, except for the Amazon basin. Fast‐moving MCSs often occur over West Africa, the Amazon basin, and the western Pacific, whereas slow‐moving MCSs are common over Colombia and the Maritime Continent.

Investigating the evolution of a tropical wave observed during JATAC/CPEX-CV using the campaign data portal

2023-02-26

The Joint Aeolus Tropical Atlantic Campaigns (JATAC) 2021 and 2022 deployed on the US Virgin Islands and Cabo Verde, respectively, with science objectives related to the life cycle of convective systems, the long-range transport of dust and its impact on air quality, and the satellite calibration/validation of current and the preparation of future ESA and NASA missions (Aeolus, EarthCARE, AOS, WIVERN). The NASA components of JATAC, Convective Processes Experiment-Aerosols and Winds (CPEX-AW) and CPEX–Cabo Verde (CPEX-CV), included a focus on the complex multi-scale processes and interactions that lead to convective development and its upscale growth: Understanding the environmental conditions supporting the development of tropical cyclones (TCs) remains a research and operational challenge, owing in part to limited observations of the lifecycle of convective activity that eventually become TCs. In the Atlantic basin, early stages of TC development favor the region off the west coast of Africa as African Easterly Waves move offshore and provide, at times, favorable conditions for TC development. CPEX-CV provided airborne measurements in this region, with a total of 13 research flights throughout September 2022. The payload included a triple-frequency precipitation radar, Doppler wind lidar, and dropsondes, among other remote sensing and in situ instrumentation, offering a rare 4-D look at tropical oceanic convective systems and their environment. To support the campaign goals, we developed the JPL CPEX-AW/CV portal (https://cpex-aw.jpl.nasa.gov), which integrates model forecasts with multi-parameter satellite and airborne observations from a variety of instruments. The portal provides an interactive system for multi-scale visualization and on-line analysis, allowing for the interrogation of a large number of variables for flight planning and execution and for post-campaign analysis, including the large-scale context of the detailed airborne observations. In this presentation, the portal will be used to provide an initial investigation into the evolution of a tropical wave observed during CPEX-CV. The 16 September 2022 flight targeted a growing convective system associated with a broad circulation, the wave structure itself, an Aeolus validation underflight, and dust over Mindelo in coordination with other JATAC measurements. While the wave was not forecasted to immediately develop into a TC downstream, the convection sampled on the western edge of the wave was intense with lightning, although did not grow upscale into a large organized mesoscale convective system during or immediately after the flight. A focus of this initial portal-based analysis is on gradients in environmental moisture, evolution of environmental wind shear in the vicinity of the precipitation, and the presence (or absence) of large-scale convergence as we suspect some combination of these factors limited the initial development of this convective system into a tropical cyclone. Potential later large-scale ties to the development of Hurricane Ian in the Caribbean will also be explored with the portal as it provided a useful tool for this purpose.

Relocation of GATE from the Pacific to the Atlantic

Bulletin of the American Meteorological Society · 2022-08-01 · 3 citations

Abstract This article documents historically the planning of the Global Atmospheric Research Program’s (GARP) Atlantic Tropical Experiment (GATE), the largest atmospheric field program of all time. In its earliest planning, GATE was called the Tropical Meteorological Experiment (TROMEX) and was designed to be in the tropical western Pacific. For reasons including concerns of the U.S. Department of Defense, the international project was relocated to the tropical Atlantic and renamed GATE.

A Storm Safari in Subtropical South America: Proyecto RELAMPAGO

Bulletin of the American Meteorological Society · 2021 · 116 citations

• Political Science
• Meteorology
• Geography

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.

Comparisons of IMERG Version 06 Precipitation At and Between Passive Microwave Overpasses in the Tropics

Journal of Hydrometeorology · 2021-07-08 · 29 citations

Abstract The Integrated Multi-Satellite Retrievals for Global Precipitation Measurement Mission (IMERG) is a global precipitation product that uses precipitation retrievals from the virtual constellation of satellites with passive microwave (PMW) sensors, as available. In the absence of PMW observations, IMERG uses a Kalman filter scheme to morph precipitation from one PMW observation to the next. In this study, an analysis of convective systems observed during the Convective Process Experiment (CPEX) suggests that IMERG precipitation depends more strongly on the availability of PMW observations than previously suspected. Following this evidence, we explore systematic biases in IMERG through bulk statistics. In two CPEX case studies, cloud photographs, pilot’s radar, and infrared imagery suggest that IMERG represents the spatial extent of precipitation relatively well when there is a PMW observation but sometimes produces spurious precipitation areas in the absence of PMW observations. Also, considering an observed convective system as a precipitation object in IMERG, the maximum rain rate peaked during PMW overpasses, with lower values between them. Bulk statistics reveal that these biases occur throughout IMERG Version 06. We find that locations and times without PMW observations have a higher frequency of light precipitation rates and a lower frequency of heavy precipitation rates due to retrieval artifacts. These results reveal deficiencies in the IMERG Kalman Filter scheme, which have led to the development of the Scheme for Histogram Adjustment with Ranked Precipitation Estimates in the Neighborhood (SHARPEN; described in a companion paper) that will be applied in the next version of IMERG.