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Utilizing multistatic specular meteor radar (MSMR) observations, this study delves into global aspects of wind perturbations in the mesosphere and lower thermosphere (MLT) from the unprecedented 2022 eruption of the Hunga Tonga‐Hunga Ha'apai (HTHH) submarine volcano. The combination of MSMR observations from different viewing angles over South America and Europe, and the decomposition of the horizontal wind in components along and transversal to the HTHH eruption's epicenter direction allow an unambiguous detection and identification of MLT perturbations related to the eruption. The performance of this decomposition is evaluated using Whole Atmosphere Community Climate Model with thermosphere/ionosphere extension (WACCM‐X) simulations of the event. The approach shows that indeed the HTHH eruption signals are clearly identified, and other signals can be easily discarded. The winds in this decomposition display dominant Eastward soliton‐like perturbations observed as far as 25,000 km from HTHH, and propagating at 242 m/s. A weaker perturbation observed only over Europe propagates faster (but slower than 300 m/s) in the Westward direction. These results suggest that we might be observing the so‐called Pekeris mode, also consistent with the L1 pseudomode, reproduced by WACCM‐X simulations at MLT altitudes. They also rule out the previous hypothesis connecting the observations in South America to the Tsunami associated with the eruption because these perturbations are observed over Europe as well. Despite the progress, the L0 pseudomode in the MLT reproduced by WACCM‐X remains elusive to observations. Key Points: A decomposition of the horizontal wind in longitudinal and transverse components, allows clear identification of Hunga Tonga‐Hunga Ha'apai eruption signaturesEastward soliton‐like mesosphere and lower thermosphere horizontal wind perturbations are observed propagating at 242 m/s, up to at least 25,500 km from the epicenterWeaker westward propagating perturbations are observed at phase speeds in between the expected L0 and L1 speeds, but up to 17,000 km [ABSTRACT FROM AUTHOR]

Heterogeneous radiative forcing in mid-latitudes, such as that exerted by aerosols, has been found to affect the Arctic climate, though the mechanisms remain debated. In this study, we leverage Deep Learning (DL) techniques to explore the complex response of the Arctic climate system to local radiative forcing over Europe. We conducted sensitivity experiments using the Max Planck Institute Earth System Model (MPI-ESM1.2) coupled with atmosphere-ocean–land surface components. Utilizing a DL-based clustering method, we classify atmospheric circulation patterns in a lower-dimensional space, focusing on Poleward Moist Static Energy Transport (PMSET) as our primary parameter. We developed a novel method to analyze the circulation patterns' contributions to various climatic parameter anomalies. Our findings indicate that the negative forcing over Europe alters existing circulation patterns and their occurrence frequency without introducing new ones. Specifically, we identify changes in a circulation pattern with a high-pressure system over Scandinavia as a key driver for reduced Sea Ice Concentration (SIC) in the Barents-Kara Sea during autumn. This circulation pattern also influences middle atmospheric dynamics, although its contribution is relatively minor compared to other circulation patterns that resemble the phases of the North Atlantic Oscillation (NAO). Our multidimensional approach combines DL algorithms and human expertise to offer a novel analytical tool that could have broader applications in climate science. [ABSTRACT FROM AUTHOR]

To understand the global response of thermospheric‐ionospheric (TI) parameters to variations in solar irradiance measurements from the Global‐Scale Observations of the Limb and Disk (GOLD) ultraviolet imaging spectrograph, solar radio flux F10.7, predictions from the Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) model, and International Global Navigation Satellite System Service total electron content maps (TEC) have been used. Various parameters such as GOLD O/N2, O2, and the nighttime peak electron density (Nmax) have been compared with the CTIPe model simulations. The GOLD observed Nmax shows a number of significant features including a winter anomaly and an equatorial ionization anomaly. The comparison with solar proxies showed that the GOLD QEUV correlates very well with the EUV observations compared to the F10.7 index. The study also examined the relationship between the solar proxies and Nmax on different time scales and found that Nmax responded significantly to QEUV at both medium‐ and long‐term timescales. Furthermore, a low correlation between Nmax in the equatorial region and solar proxies was found. A delayed ionospheric TEC response against solar flux variations within the 27‐day solar rotation was investigated. This ionospheric delay of TEC with respect to solar flux was observed to be less than 1 day, which was reproduced in model simulations. The current study has shown that the GOLD observations can be used to investigate the delayed ionospheric response and to gain a better understanding of the influence of solar activity on the TI system. Key Points: Ionospheric‐thermospheric parameters observed by Global‐Scale Observations of the Limb and Disk (GOLD) ultraviolet imaging spectrograph are compared with Coupled Thermosphere Ionosphere Plasmasphere electrodynamics model simulationsThe delayed ionospheric response against the solar flux is less than 1 day at the time scale of the 27 days solar rotation periodThe integrated 1–45 nm solar energy flux values observed by GOLD correlate well with the F10.7 and EUV [ABSTRACT FROM AUTHOR]

Continuous wind measurements using partial-reflection radars and specular meteor radars have been carried out for nearly 2 decades (2004–2022) at middle and high latitudes over Germany (∼ 54 ∘ N) and northern Norway (∼ 69 ∘ N), respectively. They provide crucial data for understanding the long-term behavior of winds in the mesosphere and lower thermosphere. Our investigation focuses on the summer season, characterized by the low energy contribution from tides and relatively stable stratospheric conditions. This work presents the long-term behavior, variability, and trends of the maximum velocity of the summer eastward, westward, and southward winds. In addition, the geomagnetic influence on the summer zonal and meridional wind is explored at middle and high latitudes. The results show a mesospheric westward summer maximum located around 75 km with velocities of 35–54 m s -1 , while the lower-thermospheric eastward wind maximum is observed at ∼ 97 km with wind speeds of 25–40 m s -1. A weaker southward wind peak is found around 86 km, ranging from 9 to 16 m s -1. The findings indicate significant trends at middle latitudes in the westward summer maxima with increasing winds over the past decades, while the southward winds show a decreasing trend. On the other hand, only the eastward wind in July has a decreasing trend at high latitudes. Evidence of oscillations around 2–3, 4, and 6 years modulate the maximum velocity of the summer winds. In particular, a periodicity between 10.2 and 11.3 years found in the westward component is more significant at middle latitudes than at high latitudes, possibly due to solar radiation. Furthermore, stronger geomagnetic activity at high latitudes causes an increase in eastward wind velocity, whereas the opposite effect is observed in zonal jets at middle latitudes. The meridional component appears to be disturbed during high geomagnetic activity, with a notable decrease in the northward wind strength below approximately 80 km at both latitudes. [ABSTRACT FROM AUTHOR]

The Hunga Tonga-Hunga Ha'apai volcano erupted on 15th January 2022, launching Lamb waves and gravity waves into the atmosphere. In this study, we present results using 13 globally distributed meteor radars and identify the volcanic-caused gravity waves in the mesospheric/lower thermospheric winds. Leveraging the High-Altitude Mechanistic General Circulation Model (HIAMCM), we compare the global propagation of these gravity waves. We observed an eastward propagating gravity wave packet with an observed phase speed of 240 ± 5 5.7 m/s and a westward propagating gravity wave with an observed phase speed of 166.5 ± 6.4 m/s. We identified these waves in the HIAMCM and obtained very good agreement of the observed phase speeds of 239.5 ± 4.3 m/s and 162.2 ± 6.1 m/s for the eastward and the westward waves, respectively. Considering that HIAMCM perturbations in the mesosphere/lower thermosphere were the result of the secondary waves generated by the dissipation of the primary gravity waves from the volcanic eruption affirms the importance of higher-order wave generation. Furthermore, based on meteor radar observations of the gravity wave propagation around the globe, we estimate the eruption time to be within 6 minutes of the nominal value of 15th January 2022 04:15 UTC and localized the volcanic eruption to be within 78 km relative to the World Geodetic System 84 coordinates of the volcano confirming our estimates to be realistic. [ABSTRACT FROM AUTHOR]

The stratospheric polar vortex (SPV) is a phenomenon comprising strong westerly winds during winter in both hemispheres. Especially in the Northern Hemisphere (NH) the SPV is highly variable and is frequently disrupted by sudden stratospheric warmings (SSWs). SPV dynamics are relevant because of both ozone chemistry and its impact on tropospheric dynamics. In this study, we evaluate the capability of climate models to simulate the NH SPV by comparing large ensembles of historical simulations to the ERA5 reanalysis data. For this, we analyze geometric-based diagnostics at 3 pressure levels that describe SPV morphology. Moreover, we assess the ability of the models to simulate SSWs subdivided into SPV split and displacement events. A rank histogram analysis reveals that no model exactly reproduces ERA5 in all diagnostics at all levels. Concerning SPV aspect ratio and centroid latitude, most models are biased to some extent, but the strongest deviations can be found for the kurtosis. Some models underestimate the variability of the SPV area. Assessing the reliability of the ensembles in distinguishing SPV displacement and split events, we find large differences between the model ensembles. In general, SPV displacements are represented better than splits in the simulation ensembles, and high-top models and models with finer vertical resolution perform better. A good performance in representing the geometric-based diagnostics in rank histograms is found to be not necessarily connected to a good performance in simulating displacements and splits. Understanding the biases and improving the representation of SPV dynamics in climate model simulations can help to improve credibility of climate projections, in particular with focus on polar stratospheric dynamics and ozone. [ABSTRACT FROM AUTHOR]