Antarctic Peninsula warming and precipitation phase transition during atmospheric river events

<p><span lang="en-US">Polar amplification has been pronounced in the Arctic with near-surface air temperatures increasing at more than twice the global warming rate d</span>uring the last several decades<span lang="en-US">. At the same time, over Antarctica temperature trends have exhibited a large regional variability. In particular, the </span>Antarctic Peninsula (AP) <span lang="en-US">stands out as having a </span>warming<span lang="en-US"> rate much higher than</span> the rest of the Antarctic ice sheet and other land areas in the Southern Hemisphere (SH)<span lang="en-US">.</span> <span lang="en-US">F</span>uture projections indicate that <span lang="en-US">warming and ice loss will intensify in both polar regions with important impacts</span> globally. In addition to the warming amplification, there has been also an enhancement of the polar water cycle with increase<span lang="en-US">s</span> <span lang="en-US">in </span>poleward moisture transport and precipitation in both polar regions. An important process linking warming and precipitation enhancement is a shift towards more frequent rainfall compared to snowfall<span lang="en-US">. F</span>uture projections show that the rain fraction will significantly increase in coastal Antarctica, especially in the AP. Atmospheric rivers (ARs), long corridors of intense moisture transport from subtropical and mid-latitude regions poleward, are known for <span lang="en-US">their </span>prominent role in <span lang="en-US">both </span>heat and moisture transport with impacts ranging from intense precipitation to temperature records and major melt events in Antarctica.<span lang="en-US"> Limited observations have hampered process understanding and correct representation of these extreme events in models.</span> <span lang="en-US">This presentation will give an overview of the </span>enhanced observations targeting ARs in the A<span lang="en-US">P</span> (<span lang="en-US">including </span>surface meteorology, radiosonde, cloud and precipitation remote sensing, <span lang="en-US">and </span>radiative fluxes) as part of the <span lang="en-US">Year of Polar Prediction (</span>YOPP<span lang="en-US">)</span>-SH international collaborative effort<span lang="en-US">. </span>In-depth analysis of transport of heat and moisture, <span lang="en-US">atmospheric vertical structure, </span>cloud properties<span lang="en-US"> and precipitation phase transition from snowfall to rainfall </span>during selected <span lang="en-US">AR </span>case<span lang="en-US">s</span> will be<span lang="en-US"> presented and compared with ERA5 reanalysis and high-resolution Polar-WRF model simulations</span>.<span lang="en-US"> We will highlight three different local regimes around the AP: large-scale precipitation over the Southern Ocean north of the AP, orographic enhancement of precipitation in the western AP and the role of foehn, cloud/precipitation clearing and temperature increase in the northeastern AP. </span></p>

Aging precipitation behavior of σ phase in 22Cr15Ni3.5Cu austenitic stainless steel

σ phase is one of the main precipitates affecting the toughness of austenitic stainless steel, V-notch impact test, SEM, EDS and TEM analysis were conducted on the newly developed 22Cr15Ni3.5Cu stainless steel after 650°C aging. Precipitation mechanism of σ phase and its effect on the toughness of the material were analyzed. The test results show that toughness of the material decreases to 25.6J after 300h aging, σ phase started to precipitate along the grain boundary after 500h aging, and in the crystal after 1000h aging. The precipitation spacing is about 100 nm, forming a gradually increasing size from crystal to grain boundary. As the precipitation time 500h of σ phase was later than the critical aging time of ductile brittle transition, it can be inferred from the test result that σ phase is not the main precipitation phase affecting the toughness of 22Cr15Ni3.5Cu.

Projecting the impacts of end of century climate extremes on the hydrology in California

In California, it is essential to understand the evolution of water resources in response to a changing climate to sustain its economy and agriculture and build resilient communities. Although extreme conditions have characterized the historical hydroclimate of California, climate change will likely intensify hydroclimatic extremes by the End of Century (EoC). However, few studies have investigated the impacts of EoC extremes on watershed hydrology. We use cutting-edge global climate and integrated hydrologic models to simulate EoC extremes and their effects on the water-energy balance. We assess the impacts of projected driest, median, and wettest water years under a Representative Concentration Pathway (RCP) 8.5 on the hydrodynamics of the Cosumnes river basin. High temperatures (> 2.5 °C) and precipitation (> 38 %) will characterize the EoC extreme water years compared to their historical counterparts. Also, precipitation, mostly in the form of rain, is projected to fall earlier. This change reduces snowpack by more than 90 %, increases peak surface water and groundwater storages up to 75 % and 23 %, respectively, and makes these peak storages occur earlier in the year. Because EoC temperatures and soil moisture are high, both potential and actual evapotranspiration (ET) increase. The latter, along with the lack of snowmelt in the warm EoC, cause surface water and groundwater storages to significantly decrease in summer, with groundwater showing the highest rates of decrease. Besides, the changes in the precipitation phase lead the lower-order streams to dry out in EoC summer whereas the mainstream experiences an increase in storage.

The latitudinal dependence in the trend of snow event to precipitation event ratio

Precipitation phase is expected to shift from solid to liquid with temperature rising, which would in turn bring challenges to regional water resource management. Although in recent decades, consistent decreasing trends in the ratio of snowfall to precipitation rate in a warming climate have been found across multiple regions, a global view of the trends in the precipitation partitioning has not been established. In this study, we investigated the global trends of annual rain and snow frequency of occurrences and the ratio of number of snow events to number of precipitation events (SE/PE ratio) using land station and shipboard synoptic present weather reports from 1978 to 2019. Results show that when averaged over all qualified land stations and over the shipboard reports, both the annual rain frequency and snow frequency decrease over the 42 years. Over both land and ocean, the averaged SE/PE ratio has a significant decreasing trend. Moreover, the trend of SE/PE ratio shows a strong latitudinal dependence. At the mid- and low latitudes in the Northern Hemisphere, the SE/PE ratio has a decreasing trend. In contrast, at high latitudes, the SE/PE ratio has an increasing trend.

On the Global Contrasting Temperature-Precipitation Phase Mechanisms in the Last Century

Global precipitation patterns have changed compared to the before 1960 (pre-industrial period). By now the temperature has risen by approximately 1°C. The atmospheric heat-retaining constituents have been raised by human-induced activities. It is influencing the composition of the atmospheric gases and water vapour leading to tropospheric energy budget imbalance affecting atmospheric pressure systems. Increased atmospheric warming leads water holding capacity to rise. Such changes insinuated contrasting phases: decreased (increased) temperature- increased (decreased) precipitation in the last century. Mechanisms of these in- and out- phases are investigated. In the total four (two colder-wet and two warmer-dry) global conditions are observed. These time slices indicate a gradual increase in global temperature and a decrease in precipitation. Clausius-Clapeyron relation suggests abrupt warming and increased water vapour pressure in recent decades. In addition, the global climate system is shifting towards abnormal warm-wet or warm-dry conditions. Further, contrasting changes in global precipitation have been seen, in particular after 1960 (post-industrial period). It is significantly noted that there has been a global contrasting temperature-precipitation phase mechanism in the last century.

Occurrence, Variability and Trends in Snowfall and Rainfall under the background of air temperature and Atmospheric Circulation in Poland

<p>The reaction of precipitation on current warming is ambiguous and differs depending on the region. Particular precipitation phases were found to respond more significantly to recent climate change in many areas located in North America, Asia, Europe and mountains. Since precipitation is an important factor in many environmental processes, trends in its occurrence and totals may trigger various changes in the Earth system and affect life.</p><p>This study aims to recognize the influence of air temperature and atmospheric circulation on the occurrence, variability and trends in precipitation phase indices. We used sub-daily data (every 3h) on air temperature, precipitation totals, notation of weather phenomena in the form of a current (ww) and past weather (W1W2) and cloud types from 38 synoptic stations located in Poland. Moreover, we used various teleconnection patterns to describe macroscale circulation and circulation types to describe regional circulation. Unlike in most studies, precipitation phase was identified based on notation of weather phenomena. Such an approach allowed us to assess a real range of surface air temperature (2m above ground) where snowfall and rainfall occur. Both frequency, totals and quotient of particular precipitation phases were analysed over the period of 1966-2020.  </p><p>Our preliminary results showed that each precipitation phase occurred over a wide range of temperatures; however, most snowfall registered during air temperatures far above freezing point (even 6°C) fell during the existence of cumulonimbus, which indicates strong convection. The highest probability of solid precipitation was linked to air advection from the north-eastern sector under the influence of cyclone (ca.15-20%). Mixed precipitation could be most expected during days with a cyclone centre located over Poland (ca. 20%). The highest probability of liquid precipitation (ca. 70%) was most characteristic of the west and north-west advection under the influence of cyclone and during the cyclone centre or trough over Poland.  </p><p>High year-to-year variability in the indices of precipitation phases impacted their trends. However, liquid precipitation tended to increase in winter over most of the stations. Mixed precipitation exhibited various trend directions depending on the region in winter and decreasing spring and autumn trends. In transitional seasons, a significant decrease was also found in solid precipitation. Most of these changes were significantly related to changes in air temperature except for solid precipitation in winter. Variability in precipitation phases was also correlated with teleconnection patterns, including NAO (negative correlation with solid precipitation in spring and autumn and liquid precipitation in summer, positive correlation with mixed pre in winter), EA (negative correlation with mixed precipitation in autumn) and SCAND (negative correlation with mixed precipitation in winter).</p><p> </p><p>The research performed within the project No. 2017/27/B/ST10/00923, financed by National Science Centre,</p>

The Precipitation Imaging Package: Phase Partitioning Capabilities

Surface precipitation phase is a fundamental meteorological property with immense importance. Accurate classification of phase from satellite remotely sensed observations is difficult. This study demonstrates the ability of the Precipitation Imaging Package (PIP), a ground-based, in situ precipitation imager, to distinguish precipitation phase. The PIP precipitation phase identification capabilities are compared to observer records from the National Weather Service (NWS) office in Marquette, Michigan, as well as co-located observations from profiling and scanning radars, disdrometer data, and surface meteorological measurements. Examined are 13 events with at least one precipitation phase transition. The PIP-determined onsets and endings of the respective precipitation phase periods agree to within 15 min of NWS observer records for the vast majority of the events. Additionally, the PIP and NWS liquid water equivalent accumulations for 12 of the 13 events were within 10%. Co-located observations from scanning and profiling radars, as well as reanalysis-derived synoptic and thermodynamic conditions, support the accuracy of the precipitation phases identified by the PIP. PIP observations for the phase transition events are compared to output from a parameterization based on wet bulb and near-surface lapse rates to produce a probability of solid precipitation. The PIP phase identification and the parameterization output are consistent. This work highlights the ability of the PIP to properly characterize hydrometeor phase and provide dependable precipitation accumulations under complicated mixed-phase and rain and snow (or vice versa) transition events.

Reducing misclassified precipitation phase in conceptual models using cloud base heights and relative humidity to adjust air temperature thresholds

In cold region, conceptual models assigned precipitation phase, liquid (rain) or solid (snow), cause vastly different atmospheric, hydrological, and ecological responses, along with significant differences in evaporation, runoff, and infiltration fates for measured precipitation mass. A set air temperature threshold (ATT) applied to the over 30% annual precipitation events occurring with surface air temperatures between −3 and 5 °C resulted in 11.0 and 9.8% misclassified precipitation in Norway and Sweden, respectively. Surface air temperatures do not account for atmospheric properties causing precipitation phase changes as snow falls toward the ground. However, cloud base height and relative humidity (RH) measured from the surface can adjust ATT for expected hydrometeor-atmosphere interactions. Applying calibrated cloud base height ATTs or a linear RH function for Norway (Sweden) reduced to 4.3% (2.8%) and 14.6% (8.9%) misclassified precipitation, respectively. Cloud base height ATTs had lower miss-rates with low cloud bases, 100 m in Norway and 300 m in Sweden. Combining the RH method with cloud base ATT in low cloud conditions resulted in 16.1 and 10.8% reduction in misclassified precipitation in Norway and Sweden, respectively. Therefore, the conceptual model output should improve through the addition of available surface data without coupling to an atmospheric model.