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We plot the surface temperatures at LVi and LVa for three temperature minimums including the extreme cold event of 14 July 2018. Keywords: climate; extreme; meteorology; temperature; weather EN climate extreme meteorology temperature weather 120 123 4 05/16/23 20230401 NES 230401 Introduction The McMurdo Dry Valleys in East Antarctica represents the largest ice-free area on the continent. It is notable that LVi and VV stations show very similar temperature trends in 2018, providing more confidence in the LVi numbers. Results During a long calm period on 14 July 2018 at 01h00 local time (13 July at 12h00 GMT), the LVi 3 m temperature sensor measured a record low temperature for the entire McMurdo Dry Valley meteorological dataset of -69.1°C (Fig. [Extracted from the article]

The Polar Weather Research and Forecasting Model (Polar WRF), a polar-optimized version of the WRF Model, is developed and made available to the community by Ohio State University's Polar Meteorology Group (PMG) as a code supplement to the WRF release from the National Center for Atmospheric Research (NCAR). While annual NCAR official releases contain polar modifications, the PMG provides very recent updates to users. PMG supplement versions up to WRF version 3.4 include modified Noah land surface model sea ice representation, allowing the specification of variable sea ice thickness and snow depth over sea ice rather than the default 3-m thickness and 0.05-m snow depth. Starting with WRF V3.5, these options are implemented by NCAR into the standard WRF release. Gridded distributions of Arctic ice thickness and snow depth over sea ice have recently become available. Their impacts are tested with PMG's WRF V3.5-based Polar WRF in two case studies. First, 20-km-resolution model results for January 1998 are compared with observations during the Surface Heat Budget of the Arctic Ocean project. Polar WRF using analyzed thickness and snow depth fields appears to simulate January 1998 slightly better than WRF without polar settings selected. Sensitivity tests show that the simulated impacts of realistic variability in sea ice thickness and snow depth on near-surface temperature is several degrees. The 40-km resolution simulations of a second case study covering Europe and the Arctic Ocean demonstrate remote impacts of Arctic sea ice thickness on midlatitude synoptic meteorology that develop within 2 weeks during a winter 2012 blocking event. [ABSTRACT FROM AUTHOR]

Many aspects of reanalysis data are of high quality over regions with sufficiently dense data, but the accuracy is uncertain over areas with sparse observations. NCEP–NCAR reanalysis (NNR) and ECMWF 15/40-Yr Re-Analysis (ERA-15 and ERA-40) variables are compared to two independent rawinsonde datasets from the periphery of the Arctic Ocean during the late 1980s and early 1990s: the Coordinated Eastern Arctic Research Experiment (CEAREX) and the Lead Experiment (LeadEx). The study is prompted by J. A. Francis who found that the NNR and ERA-15 upper-level winds are very different from those observed during these two field experiments. All three reanalyses display large biases in comparisons of the wind components and wind speeds with CEAREX observations, particularly above the 500-hPa level, but exhibit smaller discrepancies with respect to the LeadEx data, generally consistent with the previous findings of J. A. Francis. However, all three reanalyses well capture the wind variability during both experiment periods. For the geopotential height, temperature, and moisture fields, the reanalyses demonstrate close agreement with the CEAREX rawinsonde observations. From comparisons with surrounding fixed rawinsonde stations and examination of the average vertical wind speed shear, it is concluded that the CEAREX upper-level wind speeds (especially above the 500-hPa level) are erroneous and average about half of the actual values. Thus, this evaluation suggests that the three reanalyses perform reliably for tropospheric-state variables from the edge of the Arctic Ocean during the modern satellite era. [ABSTRACT FROM AUTHOR]

Regional climate simulations are conducted using the Polar fifth-generation Pennsylvania State University (PSU)–NCAR Mesoscale Model (MM5) with a 60-km horizontal resolution domain over North America to explore the summer climate of the Last Glacial Maximum (LGM: 21 000 calendar years ago), when much of the continent was covered by the Laurentide Ice Sheet (LIS). Output from a tailored NCAR Community Climate Model version 3 (CCM3) simulation of the LGM climate is used to provide the initial and lateral boundary conditions for Polar MM5. LGM boundary conditions include continental ice sheets, appropriate orbital forcing, reduced CO2 concentration, paleovegetation, modified sea surface temperatures, and lowered sea level. The simulated LGM summer climate is characterized by a pronounced low-level thermal gradient along the southern margin of the LIS resulting from the juxtaposition of the cold ice sheet and adjacent warm ice-free land surface. This sharp thermal gradient anchors the midtropospheric jet stream and facilitates the development of synoptic cyclones that track over the ice sheet, some of which produce copious liquid precipitation along and south of the LIS terminus. Precipitation on the southern margin is orographically enhanced as moist southerly low-level flow (resembling a contemporary Great Plains low-level jet configuration) in advance of the cyclone is drawn up the ice sheet slope. Composites of wet and dry periods on the LIS southern margin illustrate two distinctly different atmospheric flow regimes. Given the episodic nature of the summer rain events, it may be possible to reconcile the model depiction of wet conditions on the LIS southern margin during the LGM summer with the widely accepted interpretation of aridity across the Great Plains based on geological proxy evidence. [ABSTRACT FROM AUTHOR]

To evaluate and improve the treatment of clouds and radiation by the climate models of the National Center for Atmospheric Research (NCAR), simulations by the NCAR Community Climate Model version 3 (CCM3), as well as the recently released Community Atmosphere Model version 2 (CAM2), are examined. The Rasch and Kristjánsson prognostic cloud condensate scheme, which is now the standard scheme for CAM2, is included in a version of CCM3 and evaluated. Furthermore, the Rapid Radiative Transfer Model (RRTM), which alleviates the deficit in downward clear-sky longwave radiation, is also included in a version of CCM3. The new radiation scheme in CAM2 also alleviates the clear-sky longwave bias, although RRTM is not included. The impact of the changes is especially large over the interior of Antarctica. The changes induced by the introduction of the prognostic cloud scheme are found to have a much larger impact on the CCM3 simulations than do those from the introduction of RRTM. The introduction of the prognostic cloud scheme increases cloud emissivity in the upper troposphere, reduces cloud emissivity in the lower troposphere, and results in a better vertical distribution of cloud radiative properties over interior Antarctica. The climate simulations have a very large cold bias in the stratosphere, especially during summer. There are significant deficiencies in the simulation of Antarctic cloud radiative effects. The optical thickness of Antarctic clouds appears to be excessive. This contributes to a warm bias in surface temperature during winter and a deficit in downward shortwave radiation during summer. Some biases for Antarctica are larger for CCM3 with the prognostic cloud condensate scheme than with the standard diagnostic clouds. When the mixing ratio threshold for autoconversion from suspended ice cloud to falling precipitation is reduced toward a more realistic value, the Antarctic clouds are thinned and some of the biases are reduced. To improve the surface energy balance, not only must the radiative effects of clouds be improved, it is also necessary to improve the representation of sensible heat flux. Insufficient vertical resolution of the frequently very shallow, very stable surface boundary layer apparently contributes to an excessive heat flux from the atmosphere to the surface during winter. The representations of Antarctic clouds and radiation by the new NCAR CAM2 are not clearly improved compared to those of the earlier CCM3. For example, the surface albedo over Antarctica is descreased in CAM2 and Community Climate System Model version 2 (CCSM2) simulations in comparison to CCM3 simulations, contributing to a summer warm bias in tropospheric temperature for the former. [ABSTRACT FROM AUTHOR]

The impacts of the El Niño–Southern Oscillation (ENSO) on the Antarctic region are of special importance in evaluating the variability and change of the climate system in high southern latitudes. In this study, the ENSO signal in modeled precipitation over West Antarctica since 1979 is evaluated using forecast precipitation from several meteorological analyses and reanalyses. Additionally, a dynamical retrieval method (DRM) for precipitation is applied. Over the last two decades, the Southern Oscillation index (SOI) has an overall anticorrelation with precipitation over the West Antarctic sector bounded by 75°–90°S, 120°W–180° while it is positively correlated with precipitation over the South Atlantic sector bounded by 65°–75°S, 30°–60°W. Decadal variations are found as the relationship between the SOI and West Antarctic precipitation is stronger in the 1990s than that in the 1980s. The polar front jet stream, West Antarctic precipitation, and the SOI show a well-ordered correspondence during the 1990s as the jet zonal speed is negatively correlated to the SOI and positively correlated to West Antarctic precipitation. These relationships are weaker during the 1980s, consistent with the change in sign of the correlation between the SOI and West Antarctic precipitation. The decadal variations are apparently related to changes in the quasi-stationary eddies that determine the local onshore and offshore flow over West Antarctica. [ABSTRACT FROM AUTHOR]

Analyses and medium-range numerical weather forecasts produced by the National Centers for Environmental Prediction are evaluated poleward of 50°S during the July 1994 special observing period of the Antarctic First Regional Observing Study of the Troposphere project. Over the Antarctic plateau, the poor representation of the continent's terrain creates ambiguity in assessing the quality of surface variables. An examination of the vertical temperature profile, however, finds the near-surface temperature inversion strength to be substantially smaller than the observed climatology at the zero forecast hour. This arises from surface temperatures that are warmer than expected. Significant adjustment occurs in a variety of fields over the first few days of the medium-range forecast, which likely results from the initial hour's suspect temperature profile. A spatially oscillating series of forecast anomalies in the zonally averaged temperature cross section stretches to middle latitudes by day 3. Near-surface and upper-troposphere values are found actually to improve at the South Pole with forecast time, although some fields continue to adjust through day 7. Although the examination presented here does not give a complete diagnosis, differences between observations and analyses suggest deficiencies with the model initial fields have a major role in producing the substantial model drift found. Atmospheric moisture over the continental interior does not change significantly with forecast hour, although the distinct contrast between nearshore and interior conditions lessens with forecast time. A spurious high-latitude wave pattern is found for a variety of variables. The pattern of this distortion remains constant with forecast hour. Over the ocean, large forecast pressure and height differences with analyses are associated with blocking conditions. However, it is unclear whether this results from deficiencies in the forecast model or the meager observational... [ABSTRACT FROM AUTHOR]

Editorial. Introduces a series of articles concerning weather forecasting, compiled as of December 1, 1999. Antarctic First Regional Observing Study of the Troposphere research projects; Circulation of high-latitude areas of Southern Hemisphere; Development of automatic depression tracking method; Depression activity in the Antarctic interior.