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Ecosystems Disturbance Recovery: What It Was or What It Could Have Been?

GRL - Fri, 08/30/2024 - 12:23

Abstract

The time it takes for an ecosystem to recover from a disturbance is a key to environmental management. Conventionally, recovery is defined as a return to the pre-disturbance state, assuming ecosystem stationarity. However, this view does not account for the impact of external forces like climate change, imposing non-stationarity and trends. Alternatively, the counterfactual approach views recovery as the state the ecosystem would have achieved if the disturbance had not occurred, accounting for external forces. Here, we present a simple method to estimate the counterfactual recovery time. By implementing our method to the greening of the Arctic region, we showed that counterfactual greening recovery is twice as long as conventional recovery over the region. We argue that the well-documented greening of the region acts as an external force, leading to such a large difference. We advocate for embracing the counterfactual definition of recovery, as it aligns with realistic decision-making processes.

Effects of Eccentricity and Horizontal Electric Field on the Characteristics and Outcomes of Binary Collisions of Water Drops

GRL - Fri, 08/30/2024 - 11:39

Abstract

Effects of eccentricity and horizontal electric field (E H) on the binary-collision outcomes of water drops are examined using numerically calculated collision characteristics from previous studies and results of simulation experiment conducted by the authors. For a fixed collision kinetic energy (CKE), filament breakups can occur at all values of eccentricity but events of coalescence decrease, and that of sheet breakup increase with increasing eccentricity in absence of E H. However, as E H increases to ∼300 kVm−1 it opposes the variability of the coalescence and sheet breakup events with eccentricity. When E H exceeds ∼300 kVm−1 the collision outcomes might be determined only by the CKE and E H. The calculated value of coalescence efficiency and total number of fragments after a binary collision decreases with an increase in E H. It is argued that an electric field can significantly modify drop size distribution in thunderclouds and needs to be considered for development of precipitation.

Stratospheric Chlorine Processing After the Unprecedented Hunga Tonga Eruption

GRL - Fri, 08/30/2024 - 10:39

Abstract

Following the Hunga Tonga–Hunga Ha'apai (HTHH) eruption in January 2022, significant reductions in stratospheric hydrochloric acid (HCl) were observed in the Southern Hemisphere mid-latitudes during the latter half of 2022, suggesting potential chlorine activation. The objective of this study is to comprehensively understand the loss of HCl in the aftermath of HTHH. Satellite measurements and a global chemistry-climate model are employed for the analysis. We find strong agreement of 2022 anomalies between the modeled and the measured data. The observed tracer-tracer relations between nitrous oxide (N2O) and HCl indicate a significant role of chemical processing in the observed HCl reduction, especially during the austral winter of 2022. Further examining the roles of chlorine gas-phase and heterogeneous chemistry, we find that heterogeneous chemistry emerges as the primary driver for the chemical loss of HCl, and the reaction between hypobromous acid (HOBr) and HCl on sulfate aerosols is the dominant loss process.

Shallow Creep on the Laohushan Segment of the Haiyuan Fault, Northeastern Tibetan Plateau, Detected With Dense Near‐Field GPS Measurements

GRL - Fri, 08/30/2024 - 10:05

Abstract

While shallow creep along the Haiyuan fault is a key element in estimating earthquake potential, both the creep rate and spatial distribution inferred from InSAR and repeating earthquakes are still controversial. In this study, we resolve two potentially separated creeping patches along the Laohushan fault (LHSF) based on dense near-field GPS measurements of 39 stations. The largest creeping patch, which extends ∼20 km along-strike and ∼9 km down-dip with a slip rate of 4.2 mm/yr, spatially correlates with seismicity, especially repeating earthquakes. The locked segment is capable of producing an earthquake of Mw 7.3 ± 0.1, with moment rate of (1.08 ± 0.39) × 1017 N⋅m/yr, possibly following the cycle since the 1092 M8 event. The lack of GPS measurements in the near-field makes it unclear whether the 8 km section between these two patches is slowly creeping below detection threshold or has relocked due to change in environmental condition.

Weakening of La Niña Impact on Negative Indian Ocean Dipole Under Global Warming

GRL - Fri, 08/30/2024 - 10:05

Abstract

As global warming intensifies, the coupling relationship between negative Indian Ocean Dipole (nIOD) and La Niña has substantially changed. However, the characteristics and mechanisms of these changes are not yet fully understood. Here, we find that the impact of La Niña on nIOD has considerably weakened since 1999, with the frequency of nIOD occurrences during La Niña years plummeting to a mere one-third of the pre-1999 levels. This is primarily attributed to the early onset of Indian summer monsoon and the decrease in La Niña intensity, while the effect of variations in Bjerknes feedback is relatively minor. Model simulations suggest that the influence of La Niña on nIOD will continue to weaken under future global warming through similar mechanisms as in the observations, increasing the complexity of air-sea coupling in the Indian Ocean.

TIMED Doppler Interferometer Measurements of Neutral Winds at the Mesosphere and Lower Thermosphere and Comparison to Meteor Radar Winds

Последние статьи в Annales Geophysicae - Fri, 08/30/2024 - 10:00

TIMED Doppler Interferometer Measurements of Neutral Winds at the Mesosphere and Lower Thermosphere and Comparison to Meteor Radar Winds
Arthur Gauthier, Claudia Borries, Alexander Kozlovsky, Diego Janches, Peter Brown, Denis Vida, Christoph Jacobi, Damian Murphy, Masaki Tsutsumi, Njål Gulbrandsen, Satonori Nozawa, Mark Lester, Johan Kero, Nicholas Mitchell, Tracy Moffat-Griffin, and Gunter Stober
Ann. Geophys. Discuss., https//doi.org/10.5194/angeo-2024-13,2024
Preprint under review for ANGEO (discussion: open, 0 comments)
This study focuses on the TIMED Doppler Interferometer (TIDI)-Meteor Radar(MR) comparison of zonal and meridional winds and their dependence on local time and latitude. The correlation calculation between TIDI winds measurements and MR winds shows good agreement. A TIDI-MR seasonal comparison and the altitude-latitude dependence for winds is performed. TIDI reproduce the mean circulation well when compared with the MRs and might be useful as a lower boundary for general circulation models.

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Continent‐Side Uplifted Mantle and Geological Imprints Along a Paleo Rift in the Western East Sea (Sea of Japan)

JGR–Solid Earth - Fri, 08/30/2024 - 07:45

Abstract

We investigate the continent-size lithospheric structures of paleo rift around the central Korean Peninsula using ambient noise tomography and earthquake-based Eikonal tomography based on dense seismic networks. We determine Rayleigh-wave group velocities at periods of 1–15 s from ambient noise tomography and Rayleigh-wave phase velocities at periods of 20–80 s from earthquake-based Eikonal tomography. We determine a 3-D shear-wave velocity model in the lithosphere from the Rayleigh wave velocities. The model exhibits high lateral variations ranging from ∼ ${\sim} $‒9% to ∼ ${\sim} $8%, depending on depth. The shear-wave velocities at shallow depths (≤ ${\le} $2 km) are relatively high in mountain regions and low in coastal and basin regions. Strong velocity contrasts are observed around major earthquake hypocenters at depths of 3–20 km, which may be due to the presence of seismogenic faults. Shear-wave velocities at depths of ∼ ${\sim} $30–40 km are high along the east coast, suggesting uplifted mantle that is responsible for the opening of the East Sea (Sea of Japan). High velocity structures beneath Moho around the coast may suggest solidified underplated magma caused by the paleo rifting. The root of coast-parallel high-mountain range (Taebaek Mountain Range) is bounded by the uplifted mantle, presenting mountain range development in rift flank along paleo-rift axis. Low shear-wave velocities along the coast at depths ≥60 ${\ge} 60$ km may imply elevated temperature beneath the solidified underplated magma. The continent-side paleo rift affects the geological, thermal, and seismological properties around the continental margin at present.