During austral summer (DJF) 2017/18, the New Zealand region experienced an unprecedented coupled ocean-atmosphere heatwave, covering an area of 4 million km2. Regional average air temperature ...anomalies over land were +2.2 °C, and sea surface temperature anomalies reached +3.7 °C in the eastern Tasman Sea. This paper discusses the event, including atmospheric and oceanic drivers, the role of anthropogenic warming, and terrestrial and marine impacts. The heatwave was associated with very low wind speeds, reducing upper ocean mixing and allowing heat fluxes from the atmosphere to the ocean to cause substantial warming of the stratified surface layers of the Tasman Sea. The event persisted for the entire austral summer resulting in a 3.8 0.6 km3 loss of glacier ice in the Southern Alps (the largest annual loss in records back to 1962), very early Sauvignon Blanc wine-grape maturation in Marlborough, and major species disruption in marine ecosystems. The dominant driver was positive Southern Annular Mode (SAM) conditions, with a smaller contribution from La Niña. The long-term trend towards positive SAM conditions, a result of stratospheric ozone depletion and greenhouse gas increase, is thought to have contributed through association with more frequent anticyclonic 'blocking' conditions in the New Zealand region and a more poleward average latitude for the Southern Ocean storm track. The unprecedented heatwave provides a good analogue for possible mean conditions in the late 21st century. The best match suggests this extreme summer may be typical of average New Zealand summer climate for 2081-2100, under the RCP4.5 or RCP6.0 scenario.
ABSTRACT
Saturn's F ring is a unique narrow ring that lies (radially) close to the tidally disruptive Roche limit of water ice for Saturn. Significant work has been done that shows it to be one of ...the most dynamic places in the Solar system. Aggregates that are fortunate enough to form constantly battle against the strong tidal forces of Saturn and the nearby moons Prometheus and Pandora, which act to gravitationally stir up ring material. Planetary rings are also known to radially spread. Therefore, as the F ring lies at the edge of the main rings, we investigate the effect of an outwardly migrated F ring and its interaction with Prometheus. An increase in the maximum number density of particles at the channel edges is observed with decreasing local tidal environment. Radial velocity dispersions are also observed to fall below the typical escape velocity of a $150\,{\rm m}$ icy moonlet (${\lt}10\ {\rm cm}\ {\rm s^{ - 1}}$) where density is enhanced, and are gravitationally unstable with Toomre parameters $Q \lt 2$. Additionally, in locations of the ring where $Q \lt 2$ is observed, more particles are seen to fall below or close to the critical Toomre parameter as the radial location of the ring increases.
Evidence from physical and geochemical tracers measured during the World Ocean Circulation Experiment (WOCE) shows that there are four sub-types of Antarctic Intermediate Water (AAIW) in the South ...Pacific. The main formation region of AAIW is the southeast Pacific, where fresh, cold, high oxygen, low nutrient, intermediate waters are created. This AAIW is transported north and mixes with Equatorial Pacific Intermediate Waters (EqPIW), themselves a combination of AAIW and nutrient rich, old North Pacific deep waters. ‘Tasman’ AAIW found in the Coral and Tasman Seas is more saline and warmer than the main subtropical gyre, and appears to have formed from mixing of AAIW with thermocline waters in the Tasman Gyre. Tasman AAIW leaks out of the Tasman basin to the north of New Zealand and along Chatham Rise, and also in the South Tasman Sea via the Tasman Leakage. Another source of relatively fresh, high oxygen, low nutrient, young AAIW comes directly from the Southern Ocean, flowing into the southwest and central South Pacific Basin, west of the East Pacific Rise. This ‘Southern Ocean’ (SO) AAIW is most likely a mixture of AAIW formed locally at the Subantarctic Front (SAF), and AAIW formed along the SAF in the southeast Pacific or Indian oceans and transported by the Antarctic Circumpolar Current (ACC). Interpreting physical and geochemical tracers, combined with velocity estimates from Argo floats, and previous research, has allowed us to refine the detailed circulation pattern of AAIW in the South Pacific, especially in the topographically complex southwest Pacific.
► 4 types of AAIW are identified in the South Pacific from their geochemical characteristics. ► AAIW circulation in the South Pacific is revised from the geochemistry, Argo trajectories and previous studies. ► Improved understanding of the mixing and circulation of AAIW in the topographically complex SW Pacific.
During austral summers (DJF) 1934/35, 2017/18 and 2018/19, the New Zealand (NZ) region (approximately 4 million km
2
) experienced the most intense coupled ocean-atmosphere heatwaves on record. ...Average air temperature anomalies over land were + 1.7 to 2.1 °C while sea surface temperatures (SST) were 1.2 to 1.9 °C above average. All three heatwaves exhibited maximum SST anomalies west of the South Island of NZ. Atmospheric circulation anomalies showed a pattern of blocking centred over the Tasman Sea extending south-east of NZ, accompanied by strongly positive Southern Annular Mode conditions, and reduced trough activity over NZ. Rapid melt of seasonal snow occurred in all three cases. For the two most recent events, combined ice loss in the Southern Alps was estimated at 8.9 km
3
(22% of the 2017 volume). Sauvignon blanc and Pinot noir wine grapes had above average berry number and bunch mass in 2018 but were below average in 2019. Summerfruit harvest (cherries and apricots) was 14 and 2 days ahead of normal in 2017/18 and 2018/19 respectively. Spring wheat simulations suggested earlier flowering and lower grain yields compared to average, and below-average yield and tuber quality in potatoes crops occurred. Major species disruption occurred in marine ecosystems. Hindcasts indicate that the heatwaves were either atmospherically driven or arose from combinations of atmospheric surface warming and oceanic heat advection.
We perform simulations of the
M
⊕
self-gravitating exoring thought to orbit the large exoplanet J1407b. We use a mass of
M
J
1407
b
=
20
M
J
(which is close to the revised upper limit) and a ...semi-major axis of
a
=
5
A
U
, equating to an orbital period of
∼
11
y
r
s
about the primary. As J1407b is expected to have a high eccentricity, we test eight different models: where e = 0.2, 0.4, 0.6 and 0.8 in both the prograde and retrograde configurations. All prograde models show a strongly perturbed ring within the first orbit. As expected, the retrograde rings demonstrate a higher degree of stability, with the lower eccentricity models (e = 0.2 and 0.4) able to survive multiple orbits. However, even the higher eccentricity (e = 0.6 and 0.8) retrograde models quickly result in the loss of the ring after 200 years. Excitation of eccentricities in all retrograde rings are stable to gravitational collapse. When assuming the most recent mass estimate of
M
J
1407
b
=
20
M
J
the ring is unfavourable to the accretion of moons when J1407b is on an elliptical orbit. An interesting consequence of the strong perturbation for one model (retrograde and e = 0.6) during the first close passage is a transient gap located at 0.4AU. This is the same location as the inferred gap from the single transit in 2007 and does not require a nearby exomoon.
Saturn's rings, reminiscent of an early Solar system present a unique opportunity to investigate experimentally some mechanisms thought to be responsible for planet and planetesimal formation in ...protoplanetary discs. Here, we extended the comparison of our numerical models of Prometheus encountering the F ring employing non-interacting and interacting particles. Higher resolution analysis revealed that the density increases known to exist at channel edges is more complex and localized than previously thought. Asymmetry between density increases on channel edges revealed that the channel edge facing way from Prometheus to be the most stable but with lowest maximum increases. However, on the channel edge facing Prometheus the interacting model showed large chaotic fluctuations in the maximum density of some clumps, much larger than those of the other channel. The likely cause of this asymmetry is a variance in localized turbulence introduced into the F ring by Prometheus. High-resolution velocity dispersion maps showed that there was a spatial link between the highest densities and the highest velocity dispersions in the interacting model. Thus, suggesting that the high velocity dispersion we see is the reason for the observed inhomogeneous distribution of fans (evidence of embedded moonlets) on some of the channel edges facing Prometheus.
During austral warm seasons (November - March, NDJFM) of 1934/35, 2017/18, 2018/19 and 2021/22 the New Zealand (NZ) region experienced the most intense coupled ocean/atmosphere (MHW/AHW) heatwaves on ...record. Average temperature anomalies over land and sea were +1.2 to 1.4°C above average. Common to all four events were maximum sea surface temperature (SST) anomalies to the west of the South Island of NZ. Atmospheric circulation anomalies showed a pattern of blocking high pressure over the Tasman Sea and Pacific Ocean to the south, and southeast of NZ, and reduced trough activity over and to the east of NZ, accompanied by strongly positive Southern Annular Mode conditions.
Hindcasts for 2017/18, 2018/19 and 2021/22 NDJFM indicate that positive temperature anomalies around 1°C occurred in the Tasman Sea, and near 1.5°C for the Chatham Rise. The temperature anomalies in the upper 50m of the ocean are consistent with the 500hPa atmospheric height anomalies. The temperature anomalies in the upper 50m of the ocean are consistent with the 500hPa atmospheric height anomalies and associated winds. The eastern Tasman Sea during August 2021 to July 2022 experienced the highest annual number of MHW days during the satellite-era (1981-present) from OISSTv2.1 data. Under 1.5°C of global warming the four events would have ERIs of 2-3 years, and with 2°C of warming all would be considered cool years relative to the +2°C climate. For the 1957-2022 period, the two most intense heatwaves have ERIs of between 30 to 150 years.
Major loss of glacial ice occurred from Southern Alps glaciers with rapid melt of seasonal snow in all cases. Slow advances in grape phenology since 1948 may be associated with increases in temperature over the same period. Cherries and apricot harvest dates advanced by one to two weeks. Marine impacts may be linked to starvation of kororā/Little Penguin (Eudyptula minor) chicks in the Bay of Plenty. Chicks weighed less and had a lower body condition score in 2020 and 2021 compared to 2019 and rescue calls in 2021 reached the highest volumes since 2015. The first record of warm-water prey species in the diet of yellow-eyed penguins at Moeraki occurred, as well as widespread sea-sponge bleaching around northern and southern NZ.
Saturn’s rings are known to show remarkable real time variability in their structure. Many of which can be associated to interactions with nearby moons and moonlets. Possibly the most interesting and ...dynamic place in the rings, probably in the whole Solar System, is the F ring. A highly disrupted ring with large asymmetries both radially and azimuthally. Numerically non-zero components to the curl of the velocity vector field (vorticity) in the perturbed area of the F ring post encounter are witnessed, significantly above the background vorticity. Within the perturbed area rich distributions of local rotations is seen located in and around the channel edges. The gravitational scattering of ring particles during the encounter causes a significant elevated curl of the vector field above the background F ring vorticity for the first 1–3 orbital periods post encounter. After 3 orbital periods vorticity reverts quite quickly to near background levels. This new found dynamical vortex life of the ring will be of great interest to planet and planetesimals in proto-planetary disks where vortices and turbulence are suspected of having a significant role in their formation and migrations. Additionally, it is found that the immediate channel edges created by the close passage of Prometheus actually show high radial dispersions in the order ~20–50 cm/s, up to a maximum of 1 m/s. This is much greater than the value required by Toomre for a disk to be unstable to the growth of axisymmetric oscillations. However, an area a few hundred km away from the edge shows a more promising location for the growth of coherent objects.
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