ALBERT

Description: Despite considerable community effort, there is no general set of equations to model long‐term landscape evolution. In order to determine a suitable set of landscape evolution process laws for a site where postglacial erosion has incised valleys up to 50~m deep, we generate a set of alternative models and perform a multi‐model analysis. The most basic model we consider includes stream‐power channel incision, uniform lithology, hillslope transport by linear diffusion, and surface‐water discharge proportional to drainage area. We systematically add one, two, or three elements of complexity to this model from one of four categories: hillslope processes, channel processes, surface hydrology, and representation of geologic materials. We apply methods of formal model analysis to the 37 alternative models. The global Method of Morris sensitivity analysis method is used to identify model input parameters that most and least strongly influence model outputs. Only a few parameters are identified as “important” and this finding is consistent across two alternative model outputs: one based on a collection of topographic metrics, and one that uses an objective function based on a topographic difference. Parameters that control channel erosion are consistently important, while hillslope diffusivity is important for only select model outputs. Uncertainty in initial and boundary conditions is associated with low sensitivity. Sensitivity analysis provides insight to model dynamics and is a critical step in using model analysis for mechanistic hypothesis testing in landscape evolution theory.

Description: Observations of changes in the geomagnetic field provide unique information about pro-cesses in the outer core where the field is generated. Recent geomagnetic field reconstructionsbased on palaeomagnetic data show persistent westward drift at high northern latitudes at thecore–mantle boundary (CMB) over the past 4000 yr, as well as intermittent occurrence ofhigh-latitude weak or reverse flux patches. To further investigate these features, we analysedtime-longitude plots of a processed version of the geomagnetic field model pfm9k.1a, filteredto remove quasi-stationary features of the field. Our results suggest that westward drift at bothhigh northern and southern latitudes of the CMB have been a persistent feature of the field overthe past 9000 yr. In the Northern Hemisphere we detect two distinct signals with drift rates of0.09◦and 0.25◦yr−1and dominant zonal wavenumbers ofm=2 and 1, respectively. Com-parisons with other geomagnetic field models support these observations but also highlightthe importance of sedimentary data that provide crucial information on high-latitude geomag-netic field variations. The two distinct drift signals detected in the Northern Hemisphere canlargely be decomposed into two westward propagating waveforms. We show that constructiveinterference between these two waveforms accurately predicts both the location and timing ofpreviously observed high-latitude weak/reverse flux patches over the past 3–4 millennia. Inaddition, we also show that the 1125-yr periodicity signal inferred from the waveform inter-ference correlates positively with variations in the dipole tilt over the same time period. Thetwo identified drift signals may partially be explained by the westward motion of high-latitudeconvection rolls. However, the dispersion relation might also imply that part of the drift signalcould be caused by magnetic Rossby waves riding on the mean background flow.

Description: The path-breaking observations of the two Voyager spacecraft (V1 & V2) crossing both the termination shock and the heliopause (HP), have revolutionized our understanding of the heliosphere’s interaction with the Very Local Interstellar Medium (VLISM). Despite some similarities between the two HP crossings, some puzzling differences were also identified. For example, the V1 crossing of the HP was associated with the discovery of a flow stagnation region, possibly due to flux tube interchange instability. Further, V1 showed the existence of a radial inflow of ~40-139 keV ions within the HS for ~9 AU before the HP, and a radial outflow over a spatial scale of at least 28 AU past the HP, that corresponds to an ion population leaking from the HS into interstellar (IS) space. The Voyager in-situ measurements were complemented by remote images of ~5.2-55 keV ENAs from Cassini/INCA, showing that the heliosphere forms a roughly symmetric time-dependent obstacle to the inward interstellar flow, following the outward propagating changes of the solar wind pressure through the solar cycle. Since the Voyagers became interstellar (IS) missions, it was identified that the primary driver of the interaction of the heliosphere with the VLISM is the pressure of the IS magnetic field. The solar wind plasma is confined between the TS and the HP globally, forming a heliosheath that exhibits diamagnetic behavior and interacts directly with the strong interstellar magnetic field. The use of these observations drive the requirements for the particle and fields measurements from the future Interstellar Probe mission.

Description: The 2022 revision of Aotearoa New Zealand National Seismic Hazard Model (NZ NSHM2022) has involved significant revision of all datasets and model components. In this article, we present a subset of many results from the model as well as an overview of the governance, scientific, and review processes followed by the NZ NSHM team. The calculated hazard from the NZ NSHM 2022 has increased for most of New Zealand when compared with the previous models. The NZ NSHM 2022 models and results are available online.