Atmospheric and Environmental Research

The GECCO3 synthesis is used to infer a dynamically consistent decomposition of sea level changes (variability and trends) on interannual to decadal periods.Over most parts of the global ocean equatorward of 60 latitude, sea level variability and trends can be explained almost completely by the upper ocean steric component alone.We find a strong but negative relation between the deep steric component and the manometric changes on decadal and longer time scales.Such a relation, albeit weaker, can also be identified on annual to decadal timescales in CMIP6 MPI-ESM climate model results.Sea level variability over all shallow regions and some fraction of the Southern Ocean appears to be dominated by the manometric component.Enhanced but short spatial scale manometric contributions exist also in boundary current regions, such as the North Atlantic or the Antarctic Circumpolar Current region.Our findings suggest that without a full depth steric sea level information available, observed sea level change on decadal and longer time scales might best be explained by just using the steric estimate available from the top 2000m depth as provided by Argo.Adding additionally information from the GRACE bottom pressure fields will likely degrade the decomposition of sea level in many regions of the world ocean.Implications of our findings for estimating ocean heat content changes from altimetry remain to be explored.We encountered large differences between the GECCO3 manometric component and what the GRACE project provides, suggesting remaining uncertainties to exist in the GRACE ocean products and/or GECCO3 fields.

Abstract. Atmospheric ammonia (NH3), primarily emitted from agriculture, poses significant threats to ecosystems, climate, and human health through nitrogen deposition and secondary aerosol formation. NH3 flux estimates remain highly uncertain due to limited direct observations and complex emission–deposition processes. Here, we estimated NH3 fluxes over the contiguous United States using satellite observations from the Infrared Atmospheric Sounding Interferometer (IASI, 2008–2022) and Cross-track Infrared Sounder (CrIS, 2012–2022) by applying a directional derivative approach. Our results highlight major agricultural emission hotspots, including the San Joaquin Valley in California, the Snake River Valley in Idaho, the Texas panhandle, the Great Plains, Southeastern Pennsylvania, and Eastern North Carolina. NH3 removal is predominantly driven by deposition near source areas rather than chemical transformation, with strong sinks in vegetation-dense regions such as forests, grasslands, shrublands, and wetlands. Seasonal flux variations show peaks in warm months and lower values in winter, driven by temperature-dependent volatilization from livestock production and fertilizer application. Compared with bottom-up inventory, satellite-based estimates capture general spatial and seasonal patterns, while also revealing additional insights into key flux hotspots and peak periods. CrIS consistently reports higher fluxes than IASI, especially in spring, reflecting differences in their overpass times. Combining IASI (morning overpass) and CrIS (midday overpass) observations enables a better understanding of diurnal NH3 flux dynamics. These findings provide critical insights into NH3 spatiotemporal variabilities, complementing inventory-based approaches and informing nitrogen management and environmental policy, particularly in regions with limited ground-based monitoring.

The surface energy budget of the Arctic Ocean governs sea ice growth and melt. Correctly representing it in models is a prerequisite for understanding and projecting Arctic climate change. Direct observations of surface fluxes are scarce, and reanalys

Abstract The processes that dictate hail melt and hail terminal velocity are complex, poorly understood, and important to the characteristics of the hail that ultimately reaches the ground. Multiple parameterizations describing hail melt and terminal velocity have been developed since the 1960s. However, there has never been a systematic comparison of these parameterizations and how they respond to different environments. The current study combines unique in-cloud hail size distribution data with a melt-only, one-dimensional version of the HAILCAST hail trajectory model, termed HAILMELT, to explore how different hail melt (HMP) and terminal velocity (TVP) parameterizations simulate falling hail in the midlatitudes and tropics. We also explore how sensitive the falling hail is to temperature, moisture, and in-cloud vertical velocity changes. For hail smaller than 40 mm, simulations are frequently at least as sensitive, and often more sensitive, to which parameterization is used than to changes in the environmental conditions. In tropical oceanic environments, results suggest that hail initially smaller than 10 mm requires unrealistically cool or dry conditions to reach the surface. However, initially larger hailstones in tropical environments are shown to be capable of reaching the surface. These results indicate that there are likely larger uncertainties than previously understood in our hail simulations of the current and future climate. Additionally, they suggest all the hail identified by satellite-based hail climatologies in the tropics entirely melts before reaching the surface in some cases. Significance Statement This study is the first systematic comparison of different hail melt and hail fall speed relationships in the midlatitudes and tropics. It explores the environmental sensitivity of these relationships for hail smaller than 40 mm. The amount that hailstones melt is often more sensitive to which relationship is being used than to changes in environmental conditions. This sensitivity likely adds additional uncertainty to simulations that predict the size of hail. We also show that the initial in-cloud hailstone sizes have a larger impact on determining if hail will reach the surface in the tropics than the environmental conditions.

Previous studies indicate that climate models misrepresent southeast United States coastal sea level variability but do not propose a definitive mechanistic explanation. Here, by isolating a mode of variability responsible for the majority of observed

Hail is the leading driver of severe convective storm losses in the United States and globally, with early estimates though June in 2025 approaching 20 billion dollars insured loss in the U.S. alone. Despite this impact, many questions remain unanswered within hail science, ranging from hailstone properties to swath properties, to environmental drivers and storm kinematic and microphysical structures and how these can be remotely sensed. To address this gap the In Situ Collaborative Experiment for the Collection of Hail in the Plains (ICECHIP) campaign was conducted between May 15 and June 28th of 2025. Active periods of convection persisted throughout the campaign yielding over 20 intensive observation periods.ICECHIP field assets included over 100 ground deployable instruments, multiple atmospheric profiling systems, mobile doppler radars with a team of 15 institutions and 6 countries. Numerous cases ranging from accumulating small to storms with hail in excess of 75mm were sampled, with the largest hailstone observed >140mm and weighing 462 grams. ICECHIP addressed observations necessary for 5 major research themes: 1) embryo development and hailstone growth and fall behavior; 2) in-storm hail trajectory and convective updraft relationships; 3) environmental impacts on hail processes and predictability; 4) surface properties of hailstones and associated impacts; and 5) relationship of hailstone physical properties and growth processes to radar observations.This presentation will focus on an overview of major project cases and preliminary significant findings. Examples of the data collected include ground observed arrays at horizontal resolutions of a few hundred meters across hailswaths, updraft measurements of both supercell and non-supercellular hail producing storms, dual-doppler and high-resolution radar coverage overlapping detailed ground mapping, and numerous examples of near storm environmental profiles.

<strong class="journal-contentHeaderColor">Abstract.</strong> GNSS radio occultation (GNSS RO) performance in the planetary boundary layer is strongly dependent on retrieval algorithms. In this work, we explore how differences in retrieval methodology across three major processing centers of GNSS RO data &mdash; NASA JPL, ROM SAF, and UCAR &mdash; impact refractivity retrievals in the planetary boundary layer. Using a shared base of occultations from the FORMOSAT-3/COSMIC-1 GNSS RO mission, we identify key differences between the three processing centers that are especially strong in the regions of frequent super-refraction. We find that the minimum penetration height allowed by each processing center is correlated with the amount of super-refraction, resulting in poorer penetration and higher refractivity biases in the Tropics. We found JPL to have the most conservative minimum height in this region at 1 km, followed by ROM SAF (640 m), and UCAR (420 km). We identify two key geopotential heights &mdash; 0.8 km and 2.6 km &mdash; to sample the global distribution of inter-center refractivity bias, finding differences of 0.3&ndash;0.5 % in the Tropics. We also find negative refractivity biases of up to -4 % relative to ERA5 reanalysis in regions of persistent high stratocumulus coverage, and areas along the descending branch of the Hadley circulation, with negligible bias along the intertropical convergence zone. A comparison to ERA5 also reveals areas of weak (0.2&ndash;0.5 %) positive refractivity biases in polar regions. We hypothesize potential causes for these biases based on truncation schemes, radio-holographic filtering choices, and quality control, and identify findings deserving of further investigation.

In the past, measures of the “Earth-likeness” of exoplanets have been qualitative, considering an abiotic Earth, or requiring discretionary choices of what parameters make a planet Earth-like. With the advent of high-resolution exoplanet spectroscopy, there is a growing need for a method of quantifying the Earth-likeness of a planet that addresses these issues while making use of the data available from modern telescope missions. In this work, we introduce an informational–entropic metric that makes use of the spectrum of an exoplanet to directly quantify how Earth-like the planet is. To illustrate our method, we generate simulated transmission spectra of a series of Earth-like and super-Earth exoplanets, as well as an exoJupiter and several gas giant exoplanets. As a proof of concept, we demonstrate the ability of the information metric to evaluate how similar a planet is to Earth, making it a powerful tool in the search for a candidate Earth 2.0.

Credible projections of Arctic warming and wetting (AWW) are essential for informed decision-making in a changing climate. However, current AWW projections from state-of-the-art climate models carry uncertainties. Using observational datasets and CMIP6 model simulations, we demonstrate that the observed historical global warming trend and the climatological mean pattern of Arctic sea ice can serve as effective constraints on AWW projections. Under SSP2-4.5, the constrained warming by the end of the century is reduced from 5.5° to 4.6°C. Similarly, the projected wetting decreases from 6.8to 5.7millimeter per month. The inter-model spread in warming and wetting is reduced by 25 and 15%, respectively. The reduction is the largest in the Barents-Kara seas, reducing warming by 1.2°C, lessening wetting by 1.7millimeter per month, and decreasing the inter-model spread by one-third. Our findings suggest that unconstrained CMIP6 projections overestimate future AWW, particularly in the Barents-Kara seas, due to an overestimation of historical global warming and excessive sea ice in the models.