We present our results on the second year of TOTO-Cheyenne (TGFs On Top Of Cheyenne), a continuing collaboration of the US Air Force Academy and the Naval Research Laboratory. The project’s goal is to study the ionizing radiation as lightning strikes near the antenna farm on the top of Cheyenne Mountain, near Colorado Springs CO. Thunderstorms and accompanying lightning produce ionizing radiation on time scales from milliseconds to minutes. This radiation includes terrestrial gamma-ray flashes, hard X-rays from stepped leaders, gamma-ray glows, and thunderstorm ground enhancements. Recent measurements indicate that getting up close and personal with the storms might produce more details about the complex processes inside. The US Rocky Mountains offer the opportunity to do just that by getting closer to the charge layers. This year’s experiment (starting in May 2019 and continuing to October 2019) involved the setup of a high speed camera at the Air Force Academy facing south to watch Cheyenne Mountain plus the reinstallation of a small gamma-ray and X-ray detection system (NaI and plastic scintillators) on the mountain. This year has proven to be a very active storm year. As of 20 July, there were already 25 strikes within 2 km of the detector (compared to 1 strike during the summer 2018).

Assessing the extent and impact of past extreme weather events within cities can help identify vulnerabilities, map potential solutions, and prevent future calamities. Modern urban environments are particularly vulnerable to hydrological extremes due to high population densities, expansive impermeable surfaces, more intense precipitation extremes, and infrastructure designed for a now obsolete climate. Intense rainfall in urban environments can lead to impacts ranging from nuisance flooding to overloading of sewage and drainage systems to neighborhood inundation. In the flood-prone city of Chicago, storm waters are contained in a network of tunnels and reservoirs until treated and released to the waterways. Management decisions for a 600 km^2 metropolitan area are made based on precipitation data collected at just 9 gauge sites. Here, we combine high-resolution radar-derived precipitation data with urban-scale hydrological models to improve our understanding of water flow, advance stormwater management practices, and potentially mitigate flood risks. Proximity of the NEXRAD system to Chicago allows us to improve the spatial resolution of rainfall estimates to 500m, which will be used to produce neighborhood-scale rainfall hindcasts. Different dual-polarimetric radar-rainfall retrieval methods, e.g., rainfall from reflectivity, attenuation, specific differential phase, and differential reflectivity will be examined to determine the most accurate representation of rainfall estimates. This suite of rainfall estimates will be used to derive catchment-level precipitation, and serve as input in a coupled hydrological-hydraulic MetroFlow model. To verify the utility of our radar precipitation data, we examine an April 2013 event that delivered a record-breaking 7 inches of rain in 2 days in some areas. We compare our highly-resolved precipitation-driven hydrological model predictions with those made using the 9 gauge stations. This research is conducted under the premise that hydrological extremes are expected to be exacerbated by climate change. Understanding drivers of urban flooding using high-resolution precipitation data and models can be used to improve resiliency-focused infrastructure design in Chicago neighborhoods.

Soft x-ray and EUV radiation from the Sun is absorbed by and ionizes the atmosphere, creating both the ionosphere and thermosphere. Temporal changes in irradiance energy and spectral distribution can have profound impacts on the ionosphere, impacting technologies such as satellite drag and radio communication. Because of this, it is necessary to estimate and predict changes in Solar EUV spectral irradiance. Ideally, this would be done by direct measurement but the high cost of solar EUV spectrographs makes this prohibitively expensive. Instead, scientists must use data driven models to predict the solar spectrum for a given irradiance measurement. In this study, we further develop the Synthetic Reference Spectral Irradiance Model (SynRef). The SynRef model, which uses broadband EUV irradiance data from the MAVEN EUVM at Mars, was created to mirror the SORCE XPS model which uses data from the TIMED SEE instrument and the SORCE XPS instrument at Earth. Both models superpose theoretical Active Region and Quiet Sun spectra generated by CHIANTI to match daily measured irradiance data, and output a modeled solar EUV spectrum for that day. We use the broadband EUVM measurements to estimate Active Region temperature. This will allow us to select from a library of AR reference spectra with different temperatures. We also investigate how the prevalence of solar minimum coronal holes affects our measurements and how to account for them. We present this updated SynRef model to more accurately characterize the Solar EUV and soft x-ray spectra.

The responses of tropical anvil cloud and low-level cloud to a warming climate are among the largest sources of uncertainty in our estimates of climate sensitivity. However, most research on cloud feedbacks relies on either global climate models with parameterized convection, which do not explicitly represent small-scale convective processes, or small-domain models, which cannot directly simulate large-scale circulations. We investigate how self-aggregation, the spontaneous clumping of convection in idealized numerical models, depends on cloud-radiative interactions with different cloud types, sea surface temperatures (SSTs), and stages of aggregation in simulations that form part of RCEMIP (the Radiative-Convective Equilibrium Model Intercomparison Project). Analysis shows that the presence of anvil cloud, which tends to enhance aggregation when collocated with anomalously moist environments, is reduced in nearly all models when SSTs are increased, leading to a corresponding reduction in the aggregating influence of cloud-longwave interactions. We also find that cloud-longwave radiation interactions are stronger in the majority of General Circulation Models (GCMs), typically resulting in faster aggregation compared to Cloud-system Resolving Models (CRMs). GCMs that have stronger cloud-longwave interactions tend to aggregate faster, whereas the influence of circulations is the main factor affecting the aggregation rate in CRMs.

Using the horizontal neutral wind observations from the MIGHTI instrument onboard NASA’s ICON (Ionospheric Connection Explorer) spacecraft with continuous coverage, we determine the climatology of the mean zonal and meridional winds and the associated mean circulation at low- to middle latitudes (10S-45N) for Northern Hemisphere solstice conditions between 90 km and 200 km altitudes, specifically on 20 June 2020 solstice as well as for a one-month period from 8 June-7 July 2020. The data are averaged within appropriate altitude, longitude, latitude, solar zenith angle, and local time bins to produce mean wind distributions. The geographical distributions and local time variations of the mean horizontal circulation are evaluated. The instantaneous horizontal winds exhibit a significant degree of spatiotemporal variability often exceeding ~150 m/s. The daily averaged zonal mean winds demonstrate day-to-day variability. Eastward zonal winds and northward (winter-to-summer) meridional winds are prevalent in the lower thermosphere, which provides indirect observational evidence of the eastward momentum deposition by small-scale gravity waves. The mean neutral winds and circulation exhibit smaller scale structures in the lower thermosphere (90-120 km), while they are more homogeneous in the upper thermosphere, indicating the increasingly dissipative nature of the thermosphere. The mean wind and circulation patterns inferred from ICON/MIGHTI measurements can be used to constrain and validate general circulation models, as well as input for numerical wave models.

More and more optical records have exhibited that multiple upward leaders (MULs) occur frequently on a structure in the flash attachment process. An interesting issue is why a structure can continue to launch upward leader (UL) after the first one appears. This phenomenon is analyzed in the present paper. Considering the influence of the leader behaviors on the ambient electric field, an improved 3-D fine-resolution lightning attachment model with MULs is established to simulate cloud-to-ground flash events with diverse leader spatial morphologies. The simulation results show that MULs may initiate almost simultaneously or with an obvious delay and the variation range of UL length is large. From this, the flash events of lightning terminating on a structure are divided into four scenarios and each scenario is analyzed. It can be found that the spatial location of downward leader, the length and propagation direction of the first UL and the time interval from the inception of the first UL to final jump significantly affect the electric fields at top corners of structure and further affect the inception of the second UL. Based on qualitative analysis, four factors are proposed to explain why the above four scenarios happen.

Observations by the Emirates eXploration Imager (EXI) on-board the Emirates Mars Mission are used to characterize the diurnal, seasonal, and spatial behavior of Aphelion Cloud Belt during Mars Year 36 L$_S$$\sim$30$^\circ$-190$^\circ$. Building from previously work with the Mars Color Imager (MARCI) onboard the Mars Reconnaissance Orbiter, we retrieve water ice extinction optical depth ($\tau_{ice}$) with an uncertainty $\pm$0.022 (excluding particle size effects). We connect EXI and MARCI using radiance and $\tau_{ice}$. Zonal and meridional diurnal trends are analyzed over 6h-18h Local True Solar Time. The retrievals show large morning-evening asymmetries about a minimum near 12h. The latitudinal distributions in early morning are extensive and particularly striking near mid-summer. Comparisons to the Mars Planetary Climate Model show reasonable agreement with the basic diurnal behavior, but noticeable departures include too much water ice in early morning, the general latitudinal extent, and behavior smaller scales like the volcanoes and other topographically distinct features.

Themospheric conditions during a minor geomagnetic event of 3 and 4 February 2022 has been investigated using disk temperature (T$_{disk}$) observations from Global-scale Observations of the Limb and Disk (GOLD) mission and model simulations. GOLD observed that the T$_{disk}$ increases by more than 60 K during the storm event when compared with pre-storm quiet days. A comparison of the T$_{disk}$ with effective temperatures (i.e., a weighted average based on airglow emission layer) from Mass Spectrometer Incoherent Scatter radar version 2 (MSIS2) and Multiscale Atmosphere-Geospace Environment (MAGE) models shows that MAGE outperforms MSIS2 during this particular event. MAGE underestimates the T$_{eff}$ by about 2\%, whereas MSIS2 underestimates it by 7\%. As temperature enhancements lead to an expansion of the thermosphere and resulting density changes, the value of the temperature enhancement observed by GOLD can be utilized to find a GOLD equivalent MSIS2 (GOLD-MSIS) simulation $\textendash$ from a set of MSIS2 runs obtained by varying geomagnetic ap index values. From the MSIS2 runs we find that an ap value of 116 nT produces a T$_{eff}$ perturbation that matches with the GOLD T$_{disk}$ enhancement. Note that during this storm the highest value of the 3 hr cadence ap was 56 nT. From the MSIS-GOLD run we found that the thermospheric density enhancement varies with altitude from 15\% (at 150 km) to 80\% (at 500 km). Independent simulations from the MAGE model also show a comparable enhancement in neutral density. These results suggest that even a modest storm could impact the thermospheric densities significantly.

A key component of data assimilation methods is the specification of univariate spatial correlations, which appear in the background-error covariance. For realistic problems in meteorology and oceanography, correlation length scales are nonstationary (variable in space) and anisotropic (variable in each direction). Variational approaches typically use an operator to enforce correlation length scales, and thus the operator must be designed to capture desired levels of nonstationarity and anisotropy. For systems with complex boundaries, such as the ocean, it is natural to use a filtering approach based on the application of an elliptic, Laplacian-like operator. Here we show how an elliptic operator can be formulated to capture a general Matérn-type correlation structure. We show how nonstationarity and anisotropy can be encoded into the operator via a simple change of variables based on user-defined normalization length scales. The change of variables defines a mapping between the computational domain and a space where the analytical Matérn correlation function applies. In addition to the mapping, two other hyperparameters separately control the correlation length scale (i.e. range) and shape. As a practical use-case, we apply the operator to a global ocean model. We show that when the normalizing length scales correspond to the local grid scale, the range parameter has an intuitive interpretation as the number of neighboring grid cells at which correlation drops to 0.14. Finally, the correlation model is shown to be computationally efficient in two regards. First, the necessary linear solve can be performed with a high tolerance (∼10^{-3}) while still achieving the correct statistics, requiring few iterations to converge. Secondly, the operator’s exponent, which controls the correlation shape, is linearly related to the diagonal elements of its matrix representation. As a result, using an exponent greater than one can improve convergence properties. Thus, the framework provides flexibility in controlling correlation shape.

The thermal and chemical structure of the middle atmosphere is determined by molecules of air absorbing high-energy, solar, ultraviolet radiation. The dominant photochemical reaction for forming the stratosphere is dissociation of a molecule of oxygen into two atoms of oxygen. When a molecule is dissociated, the two pieces fly apart at high velocity. Temperature of air is directly proportional to the average velocity of all its molecules and atoms squared. Thus, photochemical dissociation converts bond energy efficiently and completely into air temperature. A molecule of oxygen is dissociated by absorbing ultraviolet-C radiation with frequencies around 1237 terahertz, energies around 5.1 electronvolts. Since oxygen makes up 20.95% of Earth’s atmosphere, there is ample oxygen to absorb all solar ultraviolet-C of appropriate frequencies that reaches the stratosphere, keeping the stratopause 30 to 40 oC warmer than the tropopause. Thus, the stratosphere forms an “electric” blanket warming Earth—electric in the sense that the thermal energy comes from a distant source, Sun, not from the body under the blanket, Earth. The second most important photochemical reaction in the stratosphere is dissociation of ozone by ultraviolet-B radiation with frequencies around 967 terahertz, energies around 4.0 electronvolts. While ozone concentrations, even in the ozone layer, are less than 10 parts per million, ozone is continually being formed and dissociated in the endless ozone-oxygen cycle, absorbing most solar ultraviolet-B radiation. When atoms of chlorine reach the lower stratosphere especially in winter, ozone concentrations that normally increase in winter can be depleted. One atom of chlorine, under the right conditions, can destroy 100,000 molecules of ozone. Depletion of the ozone layer allows more ultraviolet-B radiation than normal to reach Earth. Ultraviolet-B radiation is observed to cause sunburn, cataracts, skin cancer and mutations. It also dissociates ground-level ozone pollution, warming air in populated regions and penetrates oceans more than one hundred meters, very efficiently increasing ocean heat content as observed. Because of the ozone-oxygen cycle, where there are increased concentrations of ozone in the atmosphere, there is increased temperature. Sudden stratospheric warmings of 30-40 oC within days are typically associated with high concentrations of ozone and occur most frequently at altitudes of 30-50 km where dissociation of oxygen and ozone are most efficient. In 1798, Sir Benjamin Thompson proposed the mechanical theory of heat generated by friction when boring canon. This mechanical theory evolved into two fundamental assumptions: 1) heat is a flux of thermal energy measured in watts per square meter and 2) the greater the amount of flux absorbed, the hotter the body will become. Note that this approach never addresses the issue of what heat or thermal energy are, physically. (Complete abstract in poster file.)

Using reanalysis data, observations, and seasonal forecasts, the March Arctic ozone hole events in 1997, 2011, and 2020 and their predictability are compared. All of the three ozone hole events were accompanied by an extremely strong and cold polar vortex. The shape and centroid of the ozone holes are mainly controlled by the simultaneous polar vortex. The March 2020 ozone hole was displaced towards Canada and Greenland, the March 2011 ozone low was evenly distributed over the North Pole, while the 1997 ozone hole was displaceds toward Arctic Russia. The predictability of the 2011 ozone hole event is longer (1–2 months) than the other two (~1 month) possibly due to La Niña and Quasi-Biennial westerly winds, favorable for formation of a strong polar vortex. Surprisingly, an empirical model using a substitute index to forecast the Arctic ozone might be as skillful as the general circulation model with a chemistry module.

The Quasi-Biennial Oscillation (QBO) is a major mode of climate variability with periodically descending westerly and easterly winds in the tropical stratosphere, modulating transport and distributions of key greenhouse gases such as water vapor and ozone. In 2016 and 2020, anomalous QBO easterlies disrupted the QBO’s 28–month period previously observed. Here, we quantify the impact of these QBO disruptions on lower stratospheric circulation, and water vapour and ozone using reanalyses and satellite observations, respectively. Both constituents decrease globally from early spring to late autumn during 2016, while they only weakly decrease during 2020. These dissimilarities result from differences in upwelling and cold-point tropopause temperatures caused by anomalous planetary and gravity wave forcing. Our results highlight the need for a better understanding of the causes of QBO disruptions, their interplay with other modes of climate variability, and their impacts on water vapor and ozone in the face of a changing climate.

The investigation of atmospheric tsunamigenic acoustic and gravity wave (TAGW) dynamics, from the ocean surface to the thermosphere, is performed through the numerical computations of the 3D compressible nonlinear Navier-Stokes equations. Tsunami propagation is first simulated using a nonlinear shallow water model, which incorporates instantaneous or temporal evolutions of initial tsunami distributions (ITD). Surface dynamics are then imposed as a boundary condition to excite TAGWs into the atmosphere from the ground level. We perform a case study of a large tsunami associated with the 2011 M9.1 Tohuku-Oki earthquake, and parametric studies with simplified and demonstrative bathymetry and ITD. Our results demonstrate that TAGW propagation, controlled by the atmospheric state, can evolve nonlinearly and lead to wave self-acceleration effects and instabilities, followed by the excitation of secondary acoustic-gravity waves (SAGWs), spanning a broad frequency range. The variations of the ocean depth result in a change of tsunami characteristics and subsequent tilt of the TAGW packet, as the wave’s intrinsic frequency spectrum is varied. In addition, focusing of tsunamis and their interactions with seamounts and islands may result in localized enhancements of TAGWs, which further indicates the crucial role of bathymetry variations. Along with SAGWs, leading long-period phases of the TAGW packet propagate ahead of the tsunami wavefront and thus can be observed prior to the tsunami arrival. Our modeling results suggest that TAGWs from large tsunamis can drive detectable and quantifiable perturbations in the upper atmosphere under a wide range of scenarios, and uncover new challenges and opportunities for their observations.

Evaporation is the phenomenon by which a substance is converted from its liquid into its vapor phase, independently of where it lies in nature. However, language is alive, and just like regular speech, scientific terminology changes. Frequently those changes are grounded on a solid rationale; but sometimes these semantic transitions have a fragile foundation. That is the case with ‘evapotranspiration’. A growing generation of scientists have been educated on using this terminology, and are unaware of the historical controversy and physical inconsistency that surrounds it. Here, we present what may appear to some as an esoteric linguistic discussion, yet it is triggered by the increasing time some of us have devoted to justifying our word choice to reviewers, editors and peers. By clarifying our arguments for using the term ‘evaporation’, we seek to prevent having to revive this discussion every time a new article is submitted, so that we can move directly on to more scientifically relevant matters.

A mountain wave with a significant brightness temperature amplitude and ~500 km horizontal wavelength was observedover the Southern Andes on 24–25 July 2017 in AIRS/Aqua satellite data. In the MERRA-2 reanalysis data, a mesoscale vortex-like pattern appeared to the west of the Andes at 2 km, and the wind flowed over the Andes. VIIRS/Suomi-NPP did not detect the mountain waves; however, it observed concentric ring-like waves in the nightglow emissions at ~87 km with ~100 km wavelengths on the same night over and leeward of the Southern Andes. A ray tracing analysis showed that the mountain waves propagated to the east of the Andes, where concentric ring-like waves appeared while mountain waves broke. Therefore, the concentric ring-like waves were likely secondary gravity waves generated by momentum deposition that accompanied mountain wave breaking. These results provide the first direct evidence for secondary gravity waves generated by momentum deposition.

This work mainly concerns low-frequency variations of Atmospheric Angular Momentum (AAM), emphasizing the role of the equatorial region and its relationships with the length of day LOD, whose observed time series indicate an accelerating Earth’s rotation over the last several decades. We applied bivariate and trivariate Empirical Mode Decomposition methods to extract coherent nonstationary signals from the monthly time series of $LOD$ and the two components of AAM, i.e., the mass term MΩ and the motion term Mr. It is found that, over the global domain, a decreasing trend of LOD during the last five decades correlates with an increasing trend in MΩ, whereas the trend in Mr is negligible. However, there is a significantly positive trend in Mr of the equatorial lower troposphere (1000 to 700 hPa), which can be associated with a larger transfer of eastward momentum due to the accelerating Earth. Further analyses of spatio-temporal distribution of Mr anomalies suggest that, at multidecadal time scales, residual changes in the motion term of AAM across the globe tend to be in balance. The long-term positive trend in MΩ, which is dominant over the equatorial latitude belt, is most likely attributed to prolonged effects of the global increase in surface pressure from the mid-1970s until the 1990s. Low-frequency variations of LOD are also found to have a high correlation with the Atlantic Meridional Oscillation index. Our results suggest that long-term changes in the Earth’s rotation rate are partially attributable to the atmospheric and oceanic variability of comparable time scales.

The US National Center for Atmospheric Research (NCAR) has published several large datasets in the Amazon Web Services (AWS) cloud, thanks to support from the NCAR “Science at Scale” project, the AWS Open Data Sponsorship program, and the Amazon Sustainability Data Initiative. In each case we selected a subset comprising the most useful variables from the original data, and converted that subset from NetCDF to Zarr before publication. The Zarr format supports the same data model as netCDF and is well suited to object storage and distributed computing in the cloud using the Pangeo libraries in Python. Each dataset has an accompanying Intake-ESM catalog to facilitate data discovery and reading via Xarray, and each also has a sample Jupyter Notebook to illustrate how to access and analyze the data. Egress for these data are free, but users are encouraged to bring their compute to the data. The datasets currently published are: Community Earth System Model Large Ensemble (CESM LENS): https://doi.org/10.26024/wt24-5j82 North American Coordinated Regional Downscaling Experiment (NA-CORDEX): https://doi.org/10.26024/9xkm-fp8 CESM version 2 Large Ensemble (CESM2-LE): https://doi.org/10.26024/y48t-q717 Data Assimilation Research Testbed (DART) Reanalysis: https://doi.org/10.26024/sprq-2d04 This paper will provide information about the datasets and summarize lessons learned from the data conversion and publication.

Global-scale changes in water vapor and responses to surface temperature variability since 1979 are evaluated across a range of satellite and ground-based observations, a reanalysis (ERA5) and coupled and atmosphere-only CMIP6 climate model simulations. Global-mean column integrated water vapor increased by 1\%/decade during 1988-2014 in observations and atmosphere-only simulations but coupled simulations overestimate trends because internal climate variability suppressed observed warming in this period. Decreases in low-altitude tropical water vapor in ERA5 and ground-based observations before around 1993 are inconsistent with simulations and increased column integrated water vapor in a satellite dataset since 1987. AIRS satellite data does not capture the increased tropospheric water vapor since 2002 in other satellite, reanalysis and model products. However, global water vapor responses to interannual temperature variability is consistent across datasets with increases of $\sim$4-5\% per K near the surface and 10-15\%/K at 300 hPa. Global water vapor responses are explained by thermodynamic amplification of upper tropospheric temperature changes and the Clausius Clapeyron temperature dependence of saturation vapor pressure that are dominated by the tropical ocean responses. Upper tropospheric moistening is larger in climate model simulations with greater upper tropospheric warming.

Electric field measurements are necessary to understand thunderstorm evolution and lightning initiation. However, most existing measurements are made with single instruments carried by weather balloons. It is difficult to interpret such data since a change in observed electric field could be due either to motion of the instrument or charging/discharging currents. In order to decouple these behaviors, it is necessary to make simultaneous measurements at multiple locations. To avoid the complexity of multiple balloon launches, we describe a single balloon instrument with multiple, independent dropsondes to be released at desired time intervals. The dropsondes are designed to rotate and be self stabilizing, enabling them to measure electric fields as they fall. The dropsondes are lightweight, robust, and low-cost, and include a preamplifier, GPS receiver, search coil and accelerometer for orientation sensing, microcontroller, and a telemetry system to transmit data to a ground station. Prototype instruments have been drop-tested to demonstrate aerodynamic stability and rotation and have been calibrated for electric field measurement. A balloon payload set to release a set of such dropsondes via hot-wire release mechanisms can thus accomplish the goal of multi-point measurements of thunderstorm electrical structures.

The unusually cold springtime Arctic stratospheres of 2011, 2016 and 2020 generated substantial Polar Stratospheric Clouds (PSCs) activity and a significant ozone hole. These events were accompanied by an unusual presence of precipitating liquid clouds in the high Arctic. Satellite lidar measurements helped to identify a possible mechanistic link between tropospheric cloud formation and the PSCs. The synoptic meteorological context provided by the ERA 5 reanalysis was instrumental in the identification of potential liquid-precipitation formation scenarios related to atmospheric rivers.

The widespread presence of meteoric smoke particles (MSPs) within a distinct class of stratospheric aerosol particles has become clear from in-situ measurements in the Arctic, Antarctic and at mid-latitudes. We apply an adapted version of the interactive stratosphere aerosol configuration of the composition-climate model UM-UKCA, to predict the global distribution of meteoric-sulphuric particles nucleated heterogeneously on MSP cores. We compare the UM-UKCA results to new MSP-sulphuric simulations with the European stratosphere-troposphere chemistry-aerosol modelling system IFS-CB05-BASCOE-GLOMAP. The simulations show a strong seasonal cycle in meteoric-sulphuric particle abundance results from the winter-time source of MSPs transported down into the stratosphere in the polar vortex. Coagulation during downward transport sees high latitude MSP concentrations reduce from ~500 per cm3 at 40km to ~20 per cm3 at 25km, the uppermost extent of the stratospheric aerosol particle layer (the Junge layer). Once within the Junge layer’s supersaturated environment, meteoric-sulphuric particles form readily on the MSP cores, growing to 50-70nm dry-diameter (Dp) at 20-25km. Further inter-particle coagulation between these non-volatile particles reduces their number to 1-5 per cc at 15-20km, particle sizes there larger, at Dp ~100nm. The model predicts meteoric-sulphurics in high-latitude winter comprise >90% of Dp > 10nm particles above 25km, reducing to ~40% at 20km, and ~10% at 15km. These non-volatile particle fractions are slightly less than measured from high-altitude aircraft in the lowermost Arctic stratosphere (Curtius et al., 2005; Weigel et al., 2014), and consistent with mid-latitude aircraft measurements of lower stratospheric aerosol composition (Murphy et al., 1998), total particle concentrations also matching in-situ balloon measurements from Wyoming (Campbell and Deshler, 2014). The MSP-sulphuric interactions also improve agreement with SAGE-II observed stratospheric aerosol extinction in the quiescent 1998-2002 period. Simulations with a factor-8-elevated MSP input form more Dp>10nm meteoric-sulphurics, but the increased number sees fewer growing to Dp ~100nm, the increased MSPs reducing the stratospheric aerosol layer’s light extinction.

Equatorial noise is an electromagnetic emission with line spectral structure, predominantly located in the vicinity of the geomagnetic equatorial plane at radial distances ranging from 2 to 8 Earth’s radii. Here we focus on the rare events of equatorial noise occurring at ionospheric altitudes during periods of strongly increased geomagnetic activity. We use multicomponent electromagnetic measurements from the entire 2004–2010 DEMETER spacecraft mission and present a statistical analysis of wave propagation properties. We show that, close to the Earth, these emissions experience a larger spread in latitudes than they would at large radial distances and that their wave normals can significantly deviate from the direction perpendicular to local magnetic field lines. These results are compared to ray tracing simulations, in which whistler mode rays with initially nearly perpendicular wave vectors propagate down to the low altitudes with wave properties corresponding to the observations. We perform nonlinear fitting of the simulated latitudinal distribution of incident rays to the observed occurrence and estimate the distribution of wave normal angles in the source. The assumed Gaussian distribution provides the best fit with a standard deviation of $2^{\circ}$ from the perpendicular direction. Ray tracing analysis further shows that small initial deviations from the meridional plane can rapidly increase during the propagation and result in deflection of the emissions before they can reach the altitudes of DEMETER.

We have developed a new experimental system to study the pyrolysis of the refractory organic constituents in cosmic dust. Pyrolysis is observed by mass spectrometric detection of CO2 and SO2, and starts from around 850 K. The time-resolved kinetic behaviour is consistent with two organic components – one significantly more refractory than the other, which probably correspond to the insoluble and soluble organic fractions, respectively. The laboratory results are then incorporated into the Leeds Chemical Ablation Model (CABMOD), which is used to predict the conditions under which organic pyrolysis should be detectable using a high performance/large aperture radar. It has been proposed that loss of the organics leads to fragmentation of cometary dust particles into micron-sized fragments. If fragmentation of dust particles from Jupiter Family and Halley Type Comets does occur to a significant extent, there are several important implications: 1) slow-moving particles, particularly from Jupiter Family Comets, will be undetectable by radar, so that the total dust input to the atmosphere may be considerably larger than current estimates of 20 – 50 tonnes per day; 2) experiments at Leeds show that meteoritic fragments are excellent ice nuclei for freezing stratospheric droplets in the polar lower stratosphere, producing polar stratospheric clouds which activate chlorine and cause ozone depletion; and 3) the measured accumulation rates of meteoric smoke particles, micrometeorites and cosmic spherules in the polar regions can now be explained self-consistently.

In a recent study by Shekhar et. al. 2021, a moderate geomagnetic storm (sym-H$\sim$-100 nT) during 28th-29th June 2013 was studied using CIMI (Comprehensive Inner Magnetosphere-Ionosphere) simulations and results were compared with TWINS (Two wide-angle Imaging Neutral-atom Spectrometers) observations. The CIMI simulations did not include ion injections. As a result, TWINS and CIMI results were found to disagree on the number and locations of ion pressure peaks and ion drift patterns. In this study, CIMI simulations were performed with the inclusion of ion injections using the geosynchronous particle flux data from 6 LANL satellites as boundary conditions. Comparisons of the spatial and temporal evolution of ring current (RC) ions including ion pressure, anisotropy, intensity and median energy, the ion spectrum at the ion pressure peak locations show improved agreements with TWINS observations, specifically in the recovery phase post 06 UT on 29th June, when rapid AE index fluctuations were observed.