53 research outputs found
Warm‐air advection, air mass transformation and fog causes rapid ice melt
Direct observations during intense warm-air advection over the East Siberian Sea reveal a period of rapid sea-ice melt. A semi-stationary, high-pressure system north of the Bering Strait forced northward advection of warm, moist air from the continent. Air-mass transfor-mation over melting sea ice formed a strong, surface-based temperature inversion in which dense fog formed. This induced a positive net longwave radiation at the surface, while reduc-ing net solar radiation only marginally; the inversion also resulted in downward turbulent heat flux. The sum of these processes enhanced the surface energy flux by an average of ~15 W m-2 for a week. Satellite images before and after the episode show sea-ice concentrations decreasing from > 90% to ~50% over a large area affected by the air-mass transformation. We argue that this rapid melt was triggered by the increased heat flux from the atmosphere due to the warm-air advection
FLASH Modalities Track (Oral Presentations) OVERVIEW AND CURRENT STATUS OF THE JOINT RESEARCH PROJECT UHDPULSE: “METROLOGY FOR ADVANCED RADIOTHERAPY USING PARTICLE BEAMS WITH ULTRA-HIGH PULSE DOSE RATES”
The climate of a retrograde rotating Earth
To enhance understanding of Earth's climate, numerical experiments are
performed contrasting a retrograde and prograde rotating Earth using the Max
Planck Institute Earth system model. The experiments show that the sense of
rotation has relatively little impact on the globally and zonally averaged
energy budgets but leads to large shifts in continental climates, patterns
of precipitation, and regions of deep water formation.Changes in the zonal asymmetries of the continental climates are expected
given ideas developed more than a hundred years ago. Unexpected was, however,
the switch in the character of the European–African climate with that of the
Americas, with a drying of the former and a greening of the latter. Also
unexpected was a shift in the storm track activity from the oceans to the
land in the Northern Hemisphere. The different patterns of storms and changes
in the direction of the trades influence fresh water transport, which may
underpin the change of the role of the North Atlantic and the Pacific in
terms of deep water formation, overturning and northward oceanic heat
transport. These changes greatly influence northern hemispheric climate and
atmospheric heat transport by eddies in ways that appear energetically
consistent with a southward shift of the zonally and annually averaged
tropical rain bands. Differences between the zonally averaged energy budget
and the rain band shifts leave the door open, however, for an important role
for stationary eddies in determining the position of tropical rains. Changes
in ocean biogeochemistry largely follow shifts in ocean circulation, but the
emergence of a super oxygen minimum zone in the Indian Ocean is not
expected. The upwelling of phosphate-enriched and nitrate-depleted water
provokes a dominance of cyanobacteria over bulk phytoplankton over vast areas – a phenomenon not observed in the prograde model.What would the climate of Earth look like if it would rotate in the reversed
(retrograde) direction? Which of the characteristic climate patterns in the
ocean, atmosphere, or land that are observed in a present-day climate are the
result of the direction of Earth's rotation? Is, for example, the structure
of the oceanic meridional overturning circulation (MOC) a consequence of the
interplay of basin location and rotation direction? In experiments with the
Max Planck Institute Earth system model (MPI-ESM), we investigate the effects
of a retrograde rotation in all aspects of the climate system.The expected consequences of a retrograde rotation are reversals of the zonal
wind and ocean circulation patterns. These changes are associated with major
shifts in the temperature and precipitation patterns. For example, the
temperature gradient between Europe and eastern Siberia is reversed, and the
Sahara greens, while large parts of the Americas become deserts.
Interestingly, the Intertropical Convergence Zone (ITCZ) shifts southward and
the modeled double ITCZ in the Pacific changes to a single ITCZ, a result of
zonal asymmetries in the structure of the tropical circulation.One of the most prominent non-trivial effects of a retrograde rotation is a
collapse of the Atlantic MOC, while a strong overturning cell emerges in the
Pacific. This clearly shows that the position of the MOC is not controlled by
the sizes of the basins or by mountain chains splitting the continents in
unequal runoff basins but by the location of the basins relative to the
dominant wind directions. As a consequence of the changes in the ocean
circulation, a super oxygen minimum zone develops in the Indian Ocean
leading to upwelling of phosphate-enriched and nitrate-depleted water. These
conditions provoke a dominance of cyanobacteria over bulk phytoplankton over
vast areas, a phenomenon not observed in the prograde model.</p
Frequent new particle formation over the high Arctic pack ice by enhanced iodine emissions
In the central Arctic Ocean the formation of clouds and their properties are sensitive to the availability of cloud condensation nuclei (CCN). The vapors responsible for new particle formation (NPF), potentially leading to CCN, have remained unidentified since the first aerosol measurements in 1991. Here, we report that all the observed NPF events from the Arctic Ocean 2018 expedition are driven by iodic acid with little contribution from sulfuric acid. Iodic acid largely explains the growth of ultrafine particles (UFP) in most events. The iodic acid concentration increases significantly from summer towards autumn, possibly linked to the ocean freeze-up and a seasonal rise in ozone. This leads to a one order of magnitude higher UFP concentration in autumn. Measurements of cloud residuals suggest that particles smaller than 30 nm in diameter can activate as CCN. Therefore, iodine NPF has the potential to influence cloud properties over the Arctic Ocean
The PMIP4 Last Glacial Maximum experiments: preliminary results and comparison with the PMIP3 simulations
The Last Glacial Maximum (LGM, ∼ 21 000 years ago) has been a major focus for evaluating how well state-of-the-art climate models simulate climate changes as large as those expected in the future using paleoclimate reconstructions. A new generation of climate models has been used to generate LGM simulations as part of the Paleoclimate Modelling Intercomparison Project (PMIP) contribution to the Coupled Model Intercomparison Project (CMIP). Here, we provide a preliminary analysis and evaluation of the results of these LGM experiments (PMIP4, most of which are PMIP4-CMIP6) and compare them with the previous generation of simulations (PMIP3, most of which are PMIP3-CMIP5). We show that the global averages of the PMIP4 simulations span a larger range in terms of mean annual surface air temperature and mean annual precipitation compared to the PMIP3-CMIP5 simulations, with some PMIP4 simulations reaching a globally colder and drier state. However, the multi-model global cooling average is similar for the PMIP4 and PMIP3 ensembles, while the multi-model PMIP4 mean annual precipitation average is drier than the PMIP3 one. There are important differences in both atmospheric and oceanic circulations between the two sets of experiments, with the northern and southern jet streams being more poleward and the changes in the Atlantic Meridional Overturning Circulation being less pronounced in the PMIP4-CMIP6 simulations than in the PMIP3-CMIP5 simulations. Changes in simulated precipitation patterns are influenced by both temperature and circulation changes. Differences in simulated climate between individual models remain large. Therefore, although there are differences in the average behaviour across the two ensembles, the new simulation results are not fundamentally different from the PMIP3-CMIP5 results. Evaluation of large-scale climate features, such as land–sea contrast and polar amplification, confirms that the models capture these well and within the uncertainty of the paleoclimate reconstructions. Nevertheless, regional climate changes are less well simulated: the models underestimate extratropical cooling, particularly in winter, and precipitation changes. These results point to the utility of using paleoclimate simulations to understand the mechanisms of climate change and evaluate model performance
Methodology for the dissemination of megavoltage photon-beam calibrations from the IAEA Dosimetry Laboratory to SSDLs and end users
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