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Travis Griggs
,
James Flynn
,
Yuxuan Wang
,
Sergio Alvarez
,
Michael Comas
, and
Paul Walter

Abstract

Photochemical modeling outputs showing high ozone concentrations over the Gulf of Mexico and Galveston Bay during ozone episodes in the Houston-Galveston-Brazoria (HGB) region have not been previously verified using in-situ observations. Such data was collected systematically, for the first time, from July-October 2021 from three boats deployed for the Galveston Offshore Ozone Observations (GO3) and Tracking Aerosol Convection Interactions ExpeRiment - Air Quality (TRACER-AQ) field campaigns. A pontoon boat and a commercial vessel operated in Galveston Bay, while another commercial vessel operated in the Gulf of Mexico offshore of Galveston. All three boats had continuously operating sampling systems that included ozone analyzers and weather stations, and the two boats operating in Galveston Bay had a ceilometer. The sampling systems operated autonomously on the two commercial boats as they traveled their daily routes. Thirty-seven ozonesondes were launched over water on forecast high ozone days in Galveston Bay and the Gulf of Mexico. During the campaigns, multiple periods of ozone exceeding 100 ppbv were observed over water in Galveston Bay and the Gulf of Mexico. These events included previously identified conditions for high ozone events in the HGB region, such as the bay/sea breeze recirculation and post-frontal environments, as well as a localized coastal high ozone event after the passing of a tropical system (Hurricane Nicholas) that was not well forecast.

Open access
Chris Vagasky
,
Ronald L. Holle
,
Martin J. Murphy
,
John A. Cramer
,
Ryan K. Said
,
Mitchell Guthrie
, and
Jesse Hietanen

Abstract

The number of cloud-to-ground (CG) flashes over the contiguous U.S. (CONUS) has been estimated to be from as small as 25 million per year to as many as 40 million. In addition, many CG flashes contact the ground in more than one place. To clarify these values, recent data from the National Lightning Detection Network (NLDN) have been examined since the network is performing well enough to make precise updates to the number of CG flashes and their associated ground contact points. The average number of CG flashes is calculated to be about 23.4 million per year over CONUS, and the average number of ground contact points is calculated as 36.8 million per year. Knowledge of these two parameters is critical to lightning protection standards, as well as better understanding of the effects of lightning on forest fire initiation, geophysical interactions, human safety, and applications that benefit from knowing that a single flash may transfer charge to ground in multiple, widely-spaced locations. Sensitivity tests to assess the effects of misclassification of CG and in-cloud (IC) lightning are also made to place bounds on these estimates; and the likely uncertainty is a few percent.

Open access
Fang-Ching Chien
and
Yen-Chao Chiu

Abstract

This paper investigates the impact of the environmental conditions during the first half of the 2020 mei-yu season (Y20) and the southwest vortex (SWV), as well as their interaction, on heavy precipitation in southern Taiwan during late May 2020, based on a quantitative approach through ensemble simulations. The control experiment successfully replicates observed heavy precipitation in southern and central Taiwan and reveals a positive spatial correlation between precipitation occurrence probabilities and mean accumulated precipitation, emphasizing continuous rainfall accumulation over intermittent extreme events. Comparative analyses with sensitivity experiments elucidate that the Y20, featuring an extended western North Pacific subtropical high, intensify pressure gradients and southwesterly flow near Taiwan, favoring precipitation in windward regions but hindering it in the east. The SWV creates a moist and vortical environment near Taiwan, amplifying moisture supply and westerly winds, promoting precipitation in southern Taiwan, and enhancing frontal activity. The interaction between the SWV and the Y20, though limited in its impact on providing favorable wind and moisture conditions for precipitation southwest of Taiwan, significantly contributes to precipitation in southern Taiwan. The reason is that although the SWV primarily enhances moisture and the Y20 predominantly boost southwesterly flow, creating favorable conditions for rainfall, substantial precipitation occurs only when both factors converge in a nonlinear interaction. The interaction increases frontal activity over the Taiwan Strait and influences the movement and strength of the SWV, enhancing southwesterly flow and moisture flux in southwestern Taiwan.

Restricted access
Yoshiro Yamada
,
Subrena Harris
,
Michael Hayes
,
Rob Simpson
,
Werenfrid Wimmer
,
Raymond Holmes
,
Tim Nightingale
,
Arrow Lee
,
Nis Jepsen
,
Nicole Morgan
,
Frank-M. Göttsche
,
Raquel Niclòs
,
Martín Perelló
,
Craig Donlon
, and
Nigel Fox

Abstract

An international comparison of field deployed radiometers for sea surface skin temperature (SSTskin) retrieval was conducted in June 2022. The campaign comprised a laboratory and a field comparison. In the laboratory part the radiometers were compared against reference standard blackbodies, while the same was done with the blackbodies used for the calibration of the radiometers against a transfer standard radiometer. Reference values were provided by the National Physical Laboratory (NPL), traceable to the primary standard on the International Temperature Scale of 1990. This was followed by the field comparison at a seaside pier on the south coast of England, where the radiometers were compared against each other while viewing the closely adjacent surface of the sea. This paper reports the results of the laboratory comparison of radiometers and blackbodies.

For the blackbody comparison, the brightness temperature of the blackbody reported by the participants agreed with the reference value measured by the NPL transfer standard radiometer within the uncertainties for all temperatures and for all blackbodies. For the radiometer comparison, the temperature range of most interest from the SSTskin retrieval point of view is 10 °C to 30 °C, and in this temperature range, and up to the maximum comparison temperature of 50 °C, all participants’ reported results were in agreement with the reference. On the other hand, below 0 °C the reported values showed divergence from the reference and the differences exceeded the uncertainties. The divergence shows there is room for improvement in uncertainty estimation at lower temperatures, although it will have limited implication in the SSTskin retrieval.

Restricted access
Yoshiro Yamada
,
Subrena Harris
,
Werenfrid Wimmer
,
Raymond Holmes
,
Tim Nightingale
,
Arrow Lee
,
Nis Jepsen
,
Nicole Morgan
,
Frank-M. Göttsche
,
Raquel Niclòs
,
Martín Perelló
,
Vicente Garcia-Santos
,
Craig Donlon
, and
Nigel Fox

Abstract

An international comparison of field-deployed radiometers for sea surface skin temperature (SSTskin) retrieval was conducted during two weeks in June 2022. The comparison comprised a laboratory comparison and a field comparison. The field comparison of the radiometers took place on the second week at a seaside pier on the south coast of England. Six thermal infrared radiometers were compared against each other while continuously viewing the closely adjacent surface of the sea from the end of the pier. This paper reports the results of this field comparison.

All participants’ radiometers agreed with the reference value, evaluated as the simple mean of the participant reported values, within the claimed uncertainties. The SSTskin variation during the five-day period was within 3 °C around 18.3 °C, which is two times larger in range than in the previous comparison in 2016, while the mean of the difference from the reference value over the period evaluated for each participant, was found to be within 0.07 °C, which is a two-times improvement on the previous results.

During the comparison an insignificant but noticeable abrupt shift in measured value occurred in one of the radiometers, which could not have been detected without comparison with other instruments. This demonstrated the effectiveness of having long term stable internal reference sources in the instrument, a feature this particular radiometer did not have.

The combined results from the laboratory comparison and the field comparison contribute to improve confidence in the retrieved SSTskin.

Restricted access
Xinru Liu
,
Hang Jie
,
Yulin Zou
,
Shengjun Liu
,
Yamin Hu
,
Shuyi Liu
,
Dangfu Yang
,
Liang Zhao
, and
Jian He

Abstract

According to HadGEM3 (CMIP6) models, anthropogenic forcing reduced the probability of 2022-like June mean precipitation by about 32% (15%) and increased 5-day rainfall extreme probability by about 1.8 (1.3) times.

Open access
Bosi Sheng
,
Buwen Dong
,
Haolin Wang
,
Mingming Zhang
,
Shuheng Lin
,
Peng Si
,
Fraser C. Lott
, and
Qingxiang Li

Abstract

Precipitation in southern China during April–June 2022 was the highest since 1961. Anthropogenic forcing has reduced the probability of 2022-like Rx30day precipitation by about 45% based on CMIP6 simulations.

Open access
Fan Mei
,
Hailong Wang
,
Zihua Zhu
,
Damao Zhang
,
Qi Zhang
,
Jerome D. Fast
,
William I. Gustafson Jr.
,
Xiangyu Li
,
Beat Schmid
,
Christopher Niedek
,
Jason Tomlinson
, and
Connor Flynn

Abstract

The spatial distribution of ambient aerosol particles significantly impacts aerosol- radiation-cloud interactions, which contribute to the largest uncertainty in global anthropogenic radiative forcing estimations. However, the atmospheric boundary layer and lower free troposphere have not been adequately sampled in terms of spatiotemporal resolution, hindering a comprehensive characterization of various atmospheric processes and impeding our understanding of the Earth system. To address this research data gap, we have leveraged the development of uncrewed aerial systems (UAS) and advanced measurement techniques to obtain mesoscale spatial data on aerosol microphysical and optical properties around the U.S. Southern Great Plains (SGP) atmospheric observatory. Our study also benefits from state-of-the-art laboratory facilities that include 3-dimensional molecular imaging techniques enabled by secondary ion mass spectrometry and nanogram-level chemical composition analysis via micronebulization aerosol mass spectrometry.

Through our study, we have developed a framework for observation-modeling integration, enabling an examination of how various assumptions about the organic-inorganic components mixing state, inferred from chemical analysis, affect clouds and radiation in observation-constrained model simulations. By integrating observational constraints (derived from offline chemical analysis of the aerosol surface using collected samples) with in-situ UAS observations, we have identified a prominent role of organic-enriched nanometer layers located at the surface of aerosol particles in determining profiles of aerosol optical and hygroscopic properties over the SGP observatory. Furthermore, we have improved the agreement between predicted clouds and ground-based cloud lidar measurements. This UAS-model-laboratory integration exemplifies how these new advanced capabilities can significantly enhance our understanding of aerosol-radiation-cloud interactions.

Open access
Luigi Cavaleri
,
Sabique Langodan
,
Paolo Pezzutto
, and
Alvise Benetazzo

Abstract

We have explored the earliest stages of wind wave generation in the open sea, from the first initial wavelets appearing on an otherwise flat surface or low, smooth undulations until the practically fully developed conditions for the very low range of wind speeds we have considered. We suggest the minimal wind speed for the appearance of the first wavelets to be close to 1.8 m s−1. The peculiar conditions associated with the development of coastal sea breezes allow us to consider the local waves as generated under time-limited conditions. The 2D spectra measured during these very early stages provide the first evidence of an active Phillips process generation in the field. After appearing in these very early stages, wavelets quickly disappear as soon as the developing wind waves take a leading role. We suggest that this process is due to the strong spatial gradients in the surface orbital velocity, which impedes the instability mechanism at the base of their formation, while at a later stage of development, these gradients decrease and wavelets reappear. On a decadal perspective, the progressive decrease of the intensity of the sea breezes in the northern Adriatic Sea, where we have carried out our measurements, is associated with the steadily milder winters, and therefore not sufficiently cold local sea temperatures in early summer.

Significance Statement

We have explored for the first time the earliest stages of wind wave generation (millimeter scale) in the open sea. This was possible with the combination of the daily sea breeze development and the availability of an oceanographic tower 15 km offshore. The minimum wind speed for wave generation was 1.8 m s−1, lower than previously assumed. The data provide strong indications on the different stages of the generation process, offering measured and visual evidence, under these very light wind conditions, of the Phillips one. The presence of wind-related ripples, essential for remote sensing measurements, turns out to be dependent on the stage of generation.

Open access
Audrey Delpech
,
Roy Barkan
,
Kaushik Srinivasan
,
James C. McWilliams
,
Brian K. Arbic
,
Oladeji Q. Siyanbola
, and
Maarten C. Buijsman

Abstract

Oceanic mixing, mostly driven by the breaking of internal waves at small scales in the ocean interior, is of major importance for ocean circulation and the ocean response to future climate scenarios. Understanding how internal waves transfer their energy to smaller scales from their generation to their dissipation is therefore an important step for improving the representation of ocean mixing in climate models. In this study, the processes leading to cross-scale energy fluxes in the internal wave field are quantified using an original decomposition approach in a realistic numerical simulation of the California Current. We quantify the relative contribution of eddy–internal wave interactions and wave–wave interactions to these fluxes and show that eddy–internal wave interactions are more efficient than wave–wave interactions in the formation of the internal wave continuum spectrum. Carrying out twin numerical simulations, where we successively activate or deactivate one of the main internal wave forcing, we also show that eddy–near-inertial internal wave interactions are more efficient in the cross-scale energy transfer than eddy–tidal internal wave interactions. This results in the dissipation being dominated by the near-inertial internal waves over tidal internal waves. A companion study focuses on the role of stimulated cascade on the energy and enstrophy fluxes.

Open access