Northwest Research Associates

Abstract A demonstrated failure mode for operational solar flare forecasting is the inability to forecast flares that occur near, or just beyond, the solar limb. To address this shortcoming, we develop a “” full‐heliosphere event forecasting framework and evaluate its statistical classification ability against this specific challenge. A magnetic surface flux transport model is used to generate full‐sun maps of the photospheric radial magnetic field from which active regions (ARs) are identified and tracked using a new labeling scheme that is observer‐location agnostic and allows for post‐facto modifications. Flare‐relevant magnetic parameters couple to a “visibility” index that specifies AR location relative to the visible solar limb and expected flare detection. Flare labels are assigned according to peak Soft X‐ray flux, and a statistical classification is performed using nonparametric discriminant analysis. A version where new or emerging ARs on the far (“invisible”) side of the Sun are incorporated into the model by way of far‐side helioseismology, is also tested. We evaluate the new framework by its performance specifically including the limb areas using Brier Skill Score and ROC Skill Score, finding improvement at the level or less. However, we do find that the number of False Negatives, or “missed” forecasts decreases, and find strong evidence that the additional information provided by the far‐side helioseismology can help predict near‐ and just‐beyond‐limb flares, particularly for East‐limb events. While individual components of this framework could be improved, we demonstrate that a known failure mode for solar flare forecasting can be mitigated with available resources.

Analysis of nonlinear plasma waves, formulated and applied for ionospheric HF heating experiments, indicates that Langmuir/upper hybrid waves excited by parametric instabilities can evolve into traveling solitary waves accompanied by self-induced cavitons. To explore these cavitons, a digisonde operating in fast mode was utilized. Significant results were observed in ionograms recorded two minutes after the activation of the O-mode heater. These ionograms displayed two distinct bumps in the virtual height spread, located slightly below both the HF reflection height and the upper hybrid resonance height. It is notable that these heights are also slightly below the excitation regions where Langmuir/upper hybrid Parametric Decay Instabilities (PDIs) are typically generated by an O-mode HF heater. These observations correlate with the theory and provide valuable insights into the dynamics of nonlinear plasma waves and their interaction with the ionosphere during HF heating experiments.

Abstract The tropical tropopause layer (TTL) is studied during 2015/16 and 2019/20 quasi‐biennial oscillation (QBO) disruption events using GNSS‐RO and SWOOSH satellite observations and the ERA5 reanalysis. By compositing temperature, water vapor, and tropical upwelling during different phases of QBO and QBO disruptions (XQBO), we show that XQBO events lead to cold anomalies (relative to WQBO winters) of as much as −4.6 K during April 2016 at 60 hPa and −3.9 K during December 2019 at 50 hPa. These cold anomalies initiate around 50 hPa and propagate downward, cooling the cold point tropopause (CPT). We investigate regional CPT temperature anomalies in relation to different modes of natural variability such as the QBO, the El Niño‐Southern Oscillation (ENSO), and the Indian Ocean Dipole (IOD) using multiple linear regression. The warm‐then‐cold evolution of the CPT during November 2015–October 2016 and November 2019–October 2020 can be explained in part by the modulation of convection and Walker circulation by ENSO and the IOD and by the impact of QBO on the stratospheric upwelling as all play major roles in regulating regional CPT. CPT temperatures during the boreal summer following the two disruptions are both colder than almost all summers following WQBO winters; CPT temperatures during summer 2016 are the coldest since 1979, suggesting that any increased frequency of QBO disruptions is likely to impact atmospheric stability near the tropopause.

Abstract This paper is a collaborative effort that originated at the International Space Science Institute Workshop on “Physical links between Weather and Climate in Space and the Lower Atmosphere” held 22–26 January 2024. Many scientists attended that workshop and contributed their expertise related to polar vortex impacts on upper atmosphere variability. This paper summarizes well-known and newly reported signatures of polar vortex weakening on mesosphere–lower-thermosphere (MLT) temperature, winds, composition, planetary waves, gravity waves, tides, and ionospheric foF2. A variety of observational and modeling results are shown and are consistent with previously published variations in the dynamical and chemical state of the MLT and ionosphere during weak vortex events. We present Superposed Epoch Analysis (SEA) of upper atmosphere diagnostics and phenomena where day 0 is the onset of major SSWs. We also present SEAs where day 0 is the onset of stratopause warmings followed by elevated stratopause events. Our goal in performing two SEAs is to test the sensitivity of 10 hPa versus 1 hPa winds to predict upper atmosphere variability. Results suggest that zonal winds and the semidiurnal migrating solar tide (SW2) in the MLT are more sensitive to zonal wind reversals at 1 hPa rather than 10 hPa. Alternatively, the non-migrating DW2 tide in the equatorial upper mesosphere is best predicted by planetary wave-1 amplitudes in the winter high-latitude upper stratosphere rather than zonal wind reversals. A notable aspect of both SEAs is extremely large event-to-event variability in all diagnostics. Thus, conclusions drawn based on any one event are less robust than those based on many events.

<strong class="journal-contentHeaderColor">Abstract.</strong> The European Space Agency's Aeolus satellite, equipped with the Atmospheric LAser Doppler INstrument (ALADIN), provides global provides near-global wind profiles from the surface to about 30 km altitude. These wind measurements enable the investigation of atmospheric dynamics, including gravity waves (GWs) in the upper troposphere and lower stratosphere (UTLS). This study analyzes ALADIN wind observations and ERA5 reanalysis, by deriving GWs kinetic energy (Ek) distributions, examining their temporal and spatial variability throughout the tropical UTLS. A prominent hotspot of enhanced GW activity is identified by Aeolus, migrating from the Indian Ocean in Boreal Summer to the Maritime Continent in Boreal Winter, closely matching outgoing longwave radiation minima and thus highlighting convective origins. Results show that ERA5 consistently underestimates Ek in convective regions, especially over the Indian Ocean, where conventional wind measurements are sparse. Additional comparisons with Global Navigation Satellite System Radio Occultation (GNSS-RO) measurements of GW potential energy (Ep) corroborate these findings and suggest significant underrepresentation of convection-driven wave activity in reanalyses. A multi-instrumental exploratory analysis also allows to verify the empirical grounding of the established Ek to Ep ratio, as well as the wavelength of the waves retrieved by Aeolus. By filling critical wind data gaps, Aeolus emerges as a key tool for improving the representation of GWs, particularly in remote tropical regions. When combined with GNSS-RO measurements, Aeolus data provides new insights into how convective processes drive GW generation, revealing opportunities to refine reanalysis products and model parameterizations, as well as improving the energy ratio.

Climate models struggle to accurately represent polar regions, particularly during polar night, when cloud cover is especially prevalent. The uncertainty budget is dominated by cloud and cloud-aerosol interactions, but the difficulty in maintaining robust field observations means a lack of long-term validation datasets for key cloud parameters. Long-term measurements of the downwelling thermal infrared (400 - 3000 cm-1) have been recorded since 2008 with an Atmosphere Emitted Radiance Interferometer (AERI) at the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka, Nunavut, Canada (80&amp;#176;N, 86&amp;#176;W) and operated by the Canadian Network for the Detection of Atmospheric Change (CANDAC), while a similar instrument was deployed at McMurdo Station for 2016 as part of the ARM [Atmosphere Radiation Measurement] West Antarctic Radiation Experiment (AWARE) program. We analyse the downwelling infrared emission of the polar atmosphere recorded by these AERI instruments, with supplementary data from observations and models, to derive a climatology of microphysical and optical properties of clouds at Eureka (since 2008) and McMurdo (2016), including optical depth, thermodynamic phase, and liquid droplet and ice crystal effective scattering radii. A comparison of these Arctic and Antarctic cloud properties reveals an abundance of cloud morphological states at these two polar locations. This presentation will also describe the temperature dependence of cloud microphysics, seasonality in the timeseries, and the effect of inversions on cloud boundaries, as well as challenges in performing these retrievals.

Sea breezes are mesoscale phenomena formed in coastal regions when winds at the synoptic scale are weak. During the daytime, their general (and well-known) picture includes sea-to-land winds at the surface and land-to-sea ones at a certain height, closing the breeze circulation. However, this canonical picture is rarely observed from observations due to the interactions of the sea breezes with other flows, such as those related to the background (weak to moderate) synoptic conditions, the development of other local flows and/or the interactions with other processes within the atmospheric boundary layer, among others. This study shows an in-depth analysis of these interactions based on data gathered from surface stations and radiosoundings launched during different sea-breeze events detected in the northern zone of the Gulf of C&amp;#225;diz (SW Spain). These winds have important impacts in this area during summer, especially due to their capacity to refresh warm temperatures and transport humidity.This study has been developed within the LATMOS-i1, WINDABL2, and WIND4US3 projects, all of which include, among their objectives, the study of the interaction between coastal breezes and upper winds through different observational and modelling strategies. In this work, we present part of the observational strategy developed at the Gulf of C&amp;#225;diz, which consisted of 1) the installation of meteorological and atmospheric turbulence stations at strategic locations for the long-term monitoring of breezes, as well as; 2) the launching of atmospheric radiosoundings during intensive observation periods characterised by sea-breeze conditions. We also present some results from the analysis of events with different characteristics, allowing us to highlight how they differ during contrasting background winds and under conditions with different thermodynamic vertical structures of the atmospheric boundary layer.1 The LATMOS-i project (PID2020-115321RB-I00) (Land-ATMOSphere interactions in a changing environment: How do they impact on atmospheric-boundary-layer processes at the meso, sub-meso and local scales in mountainous and coastal areas?), funded by MCIN/AEI/ 10.13039/501100011033.2 The WINDABL project (PR2022-055) (How are the Surface Thermally Driven Winds influenced by the vertical structure and horizontal inhomogeneities of the Atmospheric Boundary Layer?), funded by Plan Propio de la Universidad de C&amp;#225;diz, Convocatoria 2022 de Proyectos para investigadores n&amp;#243;veles.3The WIND4US project (CNS2023-144885) (Disentangling the complexity of the WIND systems in coastal areas FOR a better Understanding of their impacts on Society), funded by Convocatoria 2023 de Proyectos de Consolidaci&amp;#243;n Investigadora.

Solar energetic events are caused by the release of magnetic energy accumulated in the solar atmosphere. To understand their initiating physical mechanisms, the dynamics of the coronal magnetic fields must be studied. Unfortunately, the dominant mechanisms are still unclear due to a lack of direct measurements. Numerical simulations based on magnetohydrodynamics (MHD) can reproduce the dynamical evolution of solar coronal magnetic field, providing a useful tool to explore flare initiation. Data-driven MHD simulations, in which the time-series observational data of the photospheric magnetic field is used as the simulation boundary condition, can explore different mechanisms. To investigate the accumulation of free magnetic energy through a solar eruption, we simulated the first of several large flares in NOAA active region 11283. We used a data-driven model that was governed by zero-beta MHD, focusing on the free magnetic energy accumulation prior to the M5.3 flare (2011 September 6 at 01:59 UT). We reproduced the flare-associated eruption following the formation of twisted magnetic fields, or a magnetic flux rope (MFR), formed by photospheric motions at its footpoints. We found that the eruption was first triggered by the growth of the torus instability. The erupting MFR caused magnetic reconnections with neighboring magnetic field lines located along the direction of the eruption. Using the simulation results and an axial-radial decay index centered on the MFR, we find a natural explanation for the inclination of the eruption and a possible approach to predict the direction of solar eruptive events.

The familiar divergence and Kelvin–Stokes theorem are generalized by a tensor-valued identity that relates the volume integral of the gradient of a vector field to the integral over the bounding surface of the tensor product of the vector field with the exterior normal. The importance of this long-established yet relatively little-known result is discussed. In flat two-dimensional space, it reduces to a relationship between an integral over an area and that over its bounding curve, combining the two-dimensional divergence and Kelvin–Stokes theorems together with two related theorems involving the strain, as is shown through a decomposition using a suitable tensor basis. A fluid dynamical application to oceanic observations along the trajectory of a moving platform is given. The potential extension of the generalized two-dimensional identity to curved surfaces is considered and is shown not to hold. Finally, the paper includes a substantial background section on tensor analysis, and presents results in both symbolic notation and index notation in order to emphasize the correspondence between these two notational systems.

Automatic Modulation Recognition (AMR) is an important part of spectrum management. Existing work and datasets focus on variety in the modulations transmitted and only apply rudimentary channel effects. We propose a new dataset which supports AMR tasks which focuses on only a few common modulations but introduces a large variation to the propagation channel. Simple scenarios with rural and urban areas are randomly generated using Simplex noise and a receiver/transmitter pair is placed in the scenario. The 3GPP model is combined with the propagation vector from the scenario generator to simulate a signal propagating across the generated terrain. This dataset brings more realism to the AMR task and will allow machine learning models to adapt to changing environments.