The AFWA dust emission scheme for the GOCART aerosol model in WRF-Chem v3.8.1

Airborne particles of mineral dust play a key role in Earth’s climate system and affect human activities around the globe. The numerical weather modeling community has undertaken considerable efforts to accurately forecast these dust emissions. Here, for the first time in the literature, we thoroughly describe and document the Air Force Weather Agency (AFWA) dust emission scheme for the Georgia Institute of Technology–Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) aerosol model within the Weather Research and Forecasting model with chemistry (WRF-Chem) and compare it to the other dust emission schemes available in WRF-Chem. The AFWA dust emission scheme addresses some shortcomings experienced by the earlier GOCART-WRF scheme. Improved model physics are designed to better handle emission of fine dust particles by representing saltation bombardment. WRF-Chem model performance with the AFWA scheme is evaluated against observations of dust emission in southwest Asia and compared to emissions predicted by the other schemes built into the WRF-Chem GOCART model. Results highlight the relative strengths of the available schemes, indicate the reasons for disagreement, and demonstrate the need for improved soil source data.

What Sustained Multi-Disciplinary Research Can Achieve: The Space Weather Modeling Framework

MHD-based global space weather models have mostly been developed and maintained at academic institutions. While the ``free spirit'' approach of academia enables the rapid emergence and testing of new ideas and methods, the lack of long-term stability and support makes this arrangement very challenging. This paper describes a successful example of a university-based group, the Center of Space Environment Modeling (CSEM) at the University of Michigan that developed and maintained the Space Weather Modeling Framework (SWMF) and its core element, the BATS-R-US extended MHD code. It took a quarter of a century to develop this capability and reach its present level of maturity that makes it suitable for research use by the space physics community through the Community Coordinated Modeling Center (CCMC) as well as operational use by the NOAA Space Weather Prediction Center (SWPC).

The Space Weather Modeling Framework Goes Open Access

A versatile suite of computational models, already used to forecast magnetic storms and potential power grid and telecommunications disruptions, is preparing to welcome a larger group of users.

Formation and decay of a transpolar arc during a major magnetic storm onset

<p>We examine a transpolar arc that formed at the onset of a geomagnetic storm on 15 May 2005 just prior to the arrival of a magnetic cloud. The theta aurora was recorded over the southern hemisphere by the FUV-WIC camera onboard IMAGE satellite. While in most cases transpolar arcs decay as the IMF turns southward, this arc persisted for almost an hour into the cloud, with peak AL-activity below -1500 nT and Dst at the level of -100 nT.  We use the University of Michigan Space Weather Modeling Framework (SWMF) global geospace simulation to study the magnetotail, inner magnetosphere, and ionospheric conditions during the theta aurora to resolve the origin of the polar cap precipitation. At the time of formation of the theta aurora, the SWMF simulation results indicate a single-cell potential pattern, very low Region 2 currents, and slow inner magnetotail convection. A substorm onset took place as a result of IMF turning, re-creating and enhancing the two-cell convection pattern while the theta aurora persisted. The tail flows were a complex mixture of Earthward flows along the plasma sheet boundary layer and tailward flows at the tail center created by the substorm-associated near-tail reconnection. We analyze the ionospheric mapping of the Earthward flows and the effects of the global current systems on the large-scale auroral precipitation pattern.</p>

The quantification and possible sources of spatially structured and large amplitude geomagnetic depressions during strong geomagnetic storms measured by IMAGE

<p>Geomagnetically Induced Currents (GICs) are a space weather hazard that can negatively impact large ground-based infrastructures such as power lines, pipelines, and railways. They are driven by the dynamic spatiotemporal behaviour of currents flowing in geospace, which drive rapid geomagnetic disturbances on the ground. In some cases, geomagnetic disturbances are highly localised and spatially structured due to the dynamical behaviour of geospace currents and magnetosphere-ionosphere (M-I) coupling dynamics, which are complex and often unclear.</p><p>In this work, we investigate and quantify the spatial structure of large geomagnetic depressions exceeding several hundred nT according to the 10 strongest events measured over Fennoscandia by IMAGE. Using ground magnetometer measurements we connect these spatially structured geomagnetic disturbances to possible M-I coupling processes and identify their likely magnetospheric origin. In addition, the ability for these disturbances to drive large GICs is assessed by calculating their respective geoelectric fields in Sweden using the SMAP ground conductivity model. To compliment the observations, we also utilise high resolution runs (>7 million cells) of the Space Weather Modeling Framework (SWMF) to determine to what extent global MHD models can capture this behaviour.</p>

Explicit IMF By-dependence in geomagnetic activity

<p>The interaction of the solar wind with the Earth’s magnetic field produces geomagnetic activity, which is critically dependent on the orientation of the interplanetary magnetic field (IMF). Most solar wind coupling functions quantify this dependence on the IMF orientation with the so-called IMF clock angle in a way, which is symmetric with respect to the sign of the B<sub>y</sub> component. However, recent studies have shown that IMF B<sub>y</sub> is an additional, independent driver of high-latitude geomagnetic activity, leading to higher (weaker) geomagnetic activity in Northern Hemisphere (NH) winter for B<sub>y</sub> > 0 (B<sub>y</sub> < 0). For NH summer the dependence on the B<sub>y</sub> sign is reversed. We quantify the size of this explicit B<sub>y</sub>-effect with respect to the solar wind coupling function, both for northern and southern high-latitude geomagnetic activity. We show that for a given value of solar wind coupling function, geomagnetic activity is about 40% stronger for B<sub>y</sub> > 0 than for B<sub>y</sub> < 0 in NH winter. We also discuss recent advances in the physical understanding of the B<sub>y</sub>-effect. Our results highlight the importance of the IMF B<sub>y</sub>-component for space weather and must be taken into account in future space weather modeling.</p>

The fate of volcanic ash: premature or delayed sedimentation?

A large amount of volcanic ash produced during explosive volcanic eruptions has been found to sediment as aggregates of various types that typically reduce the associated residence time in the atmosphere (i.e., premature sedimentation). Nonetheless, speculations exist in the literature that aggregation has the potential to also delay particle sedimentation (rafting effect) even though it has been considered unlikely so far. Here, we present the first theoretical description of rafting that demonstrates how delayed sedimentation may not only occur but is probably more common than previously thought. The fate of volcanic ash is here quantified for all kind of observed aggregates. As an application to the case study of the 2010 eruption of Eyjafjallajökull volcano (Iceland), we also show how rafting can theoretically increase the travel distances of particles between 138–710 μm. These findings have fundamental implications for hazard assessment of volcanic ash dispersal as well as for weather modeling.