ALBERT

Description: Free traveling Rossby wave normal modes (RNMs) are often investigated through large‐scale space‐time spectral analyses, which therefore is subject to observational availability, especially in the mesosphere. Ground‐based mesospheric observations were broadly used to identify RNMs mostly according to the periods of RNMs without resolving their horizontal scales. The current study diagnoses zonal wave numbers of RNM‐like oscillations occurring in mesospheric winds observed by two meteor radars at about 79°N. We explore four winters comprising the major stratospheric sudden warming events (SSWs) 2009, 2010, and 2013. Diagnosed are predominant oscillations at the periods of 10 and 16 days lasting mostly for three to five whole cycles. All dominant oscillations are associated with westward zonal wave number m =1, excepting one 16‐day oscillation associated with m =2. We discuss the m =1 oscillations as transient RNMs and the m =2 oscillation as a secondary wave of nonlinear interaction between an RNM and a stationary Rossby wave. All the oscillations occur around onsets of the three SSWs, suggesting associations between RNMs and SSWs. For comparison, we also explore the wind collected by a similar network at 54°N during 2012–2016. Explored is a manifestation of 5‐day wave, namely, an oscillation at 5–7 days with m =1), around the onset of SSW 2013, supporting the associations between RNMs and SSWs.

Description: Mesospheric winds from three longitudinal sectors at 65°N and 54°N latitude are combined to diagnose the zonal wave numbers (m) of spectral wave signatures during the Southern Hemisphere sudden stratospheric warming (SSW) 2019. Diagnosed are quasi‐10‐ and 6‐day planetary waves (Q10DW and Q6DW, m = 1), solar semidiurnal tides with m = 1, 2, 3 (SW1, SW2, and SW3), lunar semidiurnal tide, and the upper and lower sidebands (USB and LSB, m = 1 and 3) of Q10DW‐SW2 nonlinear interactions. We further present 7‐year composite analyses to distinguish SSW effects from climatological features. Before (after) the SSW onset, LSB (USB) enhances, accompanied by the enhancing (fading) Q10DW, and a weakening of climatological SW2 maximum. These behaviors are explained in terms of Manley‐Rowe relation, that is, the energy goes first from SW2 to Q10DW and LSB, and then from SW2 and Q10DW to USB. Our results illustrate that the interactions can explain most wind variabilities associated with the SSW.

Description: For GEOMAR’s time-domain CSEM data excited with two perpendicular horizontal dipole polarizations (Figure 1, Hölz et al., 2015), the use of rotational invariants is advantageous because it can provide representations of measured horizontal field components which are independent of the orientations of both the transmitters (TXs) and receivers (RXs, Figure 2). The use of rotational invariants was successfully applied for the 1D interpretation of timedomain CSEM data in Hölz et al. (2015) and Swidinsky et al. (2015). For performing 2D CSEM inversion in frequency domain, the GEOMAR’s time-domain data is first transformed into frequency-domain. It is worth mentioning that the acquired data were first processed to yield transient E fields for each RX-TX pair. The CSEM data selected in a varying frequency range can be used for interpretation, which includes both the low and high frequency data. In this study, we have developed a frequency-domain 2D inversion code using rotational invariants, which could be used for inverting the GEOMAR‘s CSEM data. The forward solver for 2D inversion is based on a staggered finite-difference code for simulating frequencydomain CSEM responses using the total field approach (Li et al., 2017). The singular source point is distributed by a pseudo delta function for numerical accuracy. The rotational invariants will also be computed in the frequency domain. For inversion, the Gauss-Newton (GN) optimization is used for fast convergence and accutate resistivity image reconstruction. Synthetic tests indicate its validity. Future work will focus on the interpretation of CSEM data collected in the Black Sea area for gas hydrate exploration.

Description: Benefiting from the special design of BeiDou Navigation Satellite System (BDS) constellation, its Geostationary Earth Orbit (GEO) satellites observations can provide favorable conditions to investigate the ionospheric plasma bubble at low latitudes. This study proposes using BDS GEO Rate of Total Electron Content Index observations to analyze the equatorial plasma bubble characteristics. We use GEO satellites instead of ground-based GNSS stations as a reference and compare the onset time of plasma bubbles observed by different GEO satellites, i.e., the reference GEO, the west and east GEO satellites, during geomagnetically quiet days, and determine plasma bubbles that are generated locally or drifted from elsewhere. According to this strategy, it is found that there is a significant difference in the occurrence rates of plasma bubbles generated locally over two closely located stations, i.e., LALX (18.19 °N, 104.98 °E; geomagnetic latitude: 11.31 °N) and YONG (16.83 °N, 112.34 °E; geomagnetic latitude: 9.96 °N) during the whole year of 2014. Statistical results indicate that during March and September equinoxes, the occurrence rates of plasma bubbles generated locally at the eastern station YONG are 52% and 34%, while at the western station LALX, they are only 34% and 25%. Further analysis reveals a close relationship between the higher bubble generation rates and the active atmospheric inter-tropical convergence zone.

Description: Snow cornices are common snow patterns in mountain ridge, which have potential to trigger snow avalanches. In this work, we present a series of wind tunnel experiments in a cold laboratory to simulate the formation processes of snow cornices. We quantitatively investigated the growth rates of snow cornice in length and in thickness, as well as the airborne particle concentration by using a COMOS camera. From a micro view, we also observed the snow particle trajectory that can stick on the edge and form the cornice through high-speed camera. Based on the experimental results, we explained the mechanism of the formation and development of snow cornices, and the effects of the environmental factors on the cornice growth such as air temperature, wind speed. A conceptual model that can predict the horizontal growth rate of snow cornice in field is established. Our predicted results are in good agreement with the field observation data from Gruvefjellet, Svalbard. Based on the physics of drifting snow, our results provide a new insight into snow cornice formation and improve the understanding of cornice processes that can influence avalanche activities. The experimental results and the conceptual model can be useful in future snow cornice simulation and prediction work for cornice-induced avalanches.

Description: The 660-km discontinuity (660) plays an important role in deep slab dynamics and mantle convection. Increasing numbers of seismic observations suggest controversial morphologies of the Pacific slab beneath the Kuril-Kamchatka located in the northwest rim of the Pacific Ocean, highlighting the poorly understood interaction of the slab and mantle discontinuities. Here we collect near-source SdP converted waves from a large dataset with several dense seismic networks and systematically image the new 660 topographic map around the Pacific slab beneath the Kuril-Kamchatka. We conduct detailed comparisons of the 660 depths and seismicity along some vertical cross sections. In comparison with the discontinuity depth in the IASP91 model, the 660 exhibits broad depressions up to 32–63 km with apparent downward deflections beneath the Kamchatka Peninsula and northern Kuril (region I), supporting slab penetration into the lower mantle; in contrast, the 660 depressions beneath southern Kuril (region II) are less than 21–28 km with a relatively flat configuration, implying a stagnating slab with possible hot entrained mantle materials and/or partial melts below it. We interpret these regional variations in the 660 topography as reflecting local low-temperature anomalies due to different slab morphologies associated with contrasting subduction modes. We suggest compound effects of pressure-driven mantle flow and trench retreat for inducing the inferred subduction mode change of the Pacific slab from region I to region II. Our results can provide direct seismic evidence for the 660 with slab-induced depressions and shed new light on the morphology and subduction dynamics of the northwestern Pacific slab.

Description: The isotopic and hydrochemical signatures measured from various waters in a catchment have been widely used to separate flow components, identify recharge sources, and integrate such tracers into hydrological models to help model evaluation. However, the reliability of using auxiliary data for strengthening hydrological functioning heavily depends on if the sampling is representative of hydro-chemical dynamic behaviors in a catchment. Herein, we illustrate the necessary sampling resolution or frequency to facilitate our understanding and illustrating the complex hydrological functioning in two catchments respectively characterizing the high aquifer heterogeneity in karst landform and the multi-recharge sources in the cryosphere environment. Our comprehensive analysis and modeling show that the sampling intervals of stable isotope should be shorter than hours for aiding hydrological models in capturing the sharp rise and decline of hydrograph in the cockpit karst catchment of southwest China. The daily sampling of stable isotope and chemistry can identify turning points of dominant recharge sources (rainwater, melt water from glacier and snowpack, and shallow and deep groundwater) and their contributions to streamflow in the glacierized catchment of the Tibet Plateau in China.

Description: Wind-blowing snow reshapes the snow patterns in high mountain areas and results in a significant impact on local energy balance and hydrological processes. High Mountain Asia, with the most abundant snow budget outside of polar regions, contributes a huge uncertainty to the estimation of terrestrial snow mass balance due to the interactions of blowing snow processes and complex terrain. In this work, we present a framework combining field observations, remote sensing, and high-resolution modeling to predict the snow cover evolution in the typical basins of High Mountain Asia. A mobile 3-D comprehensive observation system including radar systems, automatic weather station, and snow particle counters, was built to characterize the characteristics of wind – temperature – humidity – blowing snow flux profiles, as well as the resulting snow distribution patterns. Snow redistribution, blowing snow sublimation, snow cornice formation, and snow avalanche are processes considered in the framework. The field observations were compared to both remote sensing data and high-resolution modeling with CRYOWRF, a new modeling framework for atmospheric flow simulations for Cryospheric-regions, which couples the state-of-the-art and widely used atmospheric model WRF with the detailed snow cover model SNOWPACK. Our work has the potential to contribute to precise estimates of snow distribution in mountains.

Description: Carbonaceous aerosols (CAs) scatter and absorb incident solar radiation in the atmosphere, thereby influencing the regional climate and hydrological cycle, particularly in the Third Pole (TP). Here, we present the characteristics of CAs at 19 observation stations from the Atmospheric Pollution and Cryospheric Change network to obtain a deep understanding of pollutant status in the TP. The organic carbon (OC) and elemental carbon (EC) concentrations decreased noticeably inwards from outside to inland of the TP, consistent with their emission load and also affected by transport process and meteorological condition. Urban areas, such as Kathmandu, Karachi, and Mardan, exhibited extremely high OC and EC concentrations, with low and high values occurring in the monsoon and non-monsoon seasons, respectively. However, remote regions inland the TP (e.g., Nam Co and Ngari) demonstrated much lower OC and EC concentrations. Different seasonal variations were observed between the southern and northern parts of the TP, suggesting differences in the patterns of pollutant sources and in distance from the sources between the two regions. In addition to the influence of long-range transported pollutants from the Indo-Gangetic Plain (IGP), the TP was affected by local emissions (e.g., biomass burning). The OC/EC ratio also suggested that biomass burning was prevalent in the center TP, whereas the marginal sites (e.g., Jomsom, Dhunche, and Laohugou) were affected by fossil fuel combustion from the up-wind regions. The mass absorption cross-section of EC (MACEC) at 632 nm ranged from 6.56 to 14.7 m2 g−1, with an increasing trend from outside to inland of the TP. Urban areas had low MACEC values because such regions were mainly affected by local fresh emissions. In addition, large amount of brown carbon can decrease the MACEC values in cities of South Asia. Remote sites had high MACEC values because of the coating enhancement of aerosols. Influenced by emission, transport process, and weather condition, the CA concentrations and MACEC presented decreasing and increasing trends, respectively, from outside to inland of the TP.