Large-Scale Atmospheric Drivers of Snowfall on Thwaites Glacier

2020 ◽  
Author(s):  
Michelle Maclennan ◽  
Jan Lenaerts
Keyword(s):  
Temporal Variability ◽  
Large Scale ◽  
Climate Model ◽  
Southern Oscillation ◽  
Regional Climate ◽  
Southern Annular Mode ◽  
Spatial And Temporal Variability ◽  
Atmospheric Conditions ◽  
Amundsen Sea ◽  
Weather Patterns

<p>High snowfall events on Thwaites Glacier are a key influencer of its ice mass change. In this study, we diagnose the mechanisms for orographic precipitation on Thwaites Glacier by analyzing the atmospheric conditions that lead to high snowfall events. A high-resolution regional climate model, RACMO2, is used in conjunction with MERRA-2 and ERA5 reanalysis to map snowfall and associated atmospheric conditions over the Amundsen Sea Embayment. We examine these conditions during high snowfall events over Thwaites Glacier to characterize the drivers of the precipitation and their spatial and temporal variability. Then we examine the seasonal differences in the associated weather patterns and their correlations with El Nino Southern Oscillation and the Southern Annular Mode. Understanding the large-scale atmospheric drivers of snowfall events allows us to recognize how these atmospheric drivers and consequent snowfall climatology will change in the future, which will ultimately improve predictions of accumulation on Thwaites Glacier.</p>

scholarly journals Representation of spatial and temporal variability of daily wind speed and of intense wind events over the Mediterranean Sea using dynamical downscaling: impact of the regional climate model configuration

2011 ◽  
Vol 11 (7) ◽  
pp. 1983-2001 ◽  
Author(s):  
M. Herrmann ◽  
S. Somot ◽  
S. Calmanti ◽  
C. Dubois ◽  
F. Sevault
Keyword(s):  
Wind Speed ◽  
Spatial Variability ◽  
Regional Climate Model ◽  
Mediterranean Sea ◽  
Temporal Variability ◽  
Climate Model ◽  
Dynamical Downscaling ◽  
Regional Climate ◽  
Spatial And Temporal Variability ◽  
Wind Events

Abstract. Atmospheric datasets coming from long term reanalyzes of low spatial resolution are used for different purposes. Wind over the sea is, for example, a major ingredient of oceanic simulations. However, the shortcomings of those datasets prevent them from being used without an adequate corrective preliminary treatment. Using a regional climate model (RCM) to perform a dynamical downscaling of those large scale reanalyzes is one of the methods used in order to produce fields that realistically reproduce atmospheric chronology and where those shortcomings are corrected. Here we assess the influence of the configuration of the RCM used in this framework on the representation of wind speed spatial and temporal variability and intense wind events on a daily timescale. Our RCM is ALADIN-Climate, the reanalysis is ERA-40, and the studied area is the Mediterranean Sea. First, the dynamical downscaling significantly reduces the underestimation of daily wind speed, in average by 9 % over the whole Mediterranean. This underestimation has been corrected both globally and locally, and for the whole wind speed spectrum. The correction is the strongest for periods and regions of strong winds. The representation of spatial variability has also been significantly improved. On the other hand, the temporal correlation between the downscaled field and the observations decreases all the more that one moves eastwards, i.e. further from the atmospheric flux entry. Nonetheless, it remains ~0.7, the downscaled dataset reproduces therefore satisfactorily the real chronology. Second, the influence of the choice of the RCM configuration has an influence one order of magnitude smaller than the improvement induced by the initial downscaling. The use of spectral nudging or of a smaller domain helps to improve the realism of the temporal chronology. Increasing the resolution very locally (both spatially and temporally) improves the representation of spatial variability, in particular in regions strongly influenced by the complex surrounding orography. The impact of the interactive air-sea coupling is negligible for the temporal scales examined here. Using two different forcing datasets induces differences on the downscaled fields that are directly related to the differences between those datasets. Our results also show that improving the physics of our RCM is still necessary to increase the realism of our simulations. Finally, the choice of the optimal configuration depends on the scientific objectives of the study for which those wind datasets are used.

scholarly journals Increased Greenland melt triggered by large-scale, year-round cyclonic moisture intrusions

2019 ◽  
Vol 13 (3) ◽  
pp. 815-825 ◽  
Author(s):  
Marilena Oltmanns ◽  
Fiammetta Straneo ◽  
Marco Tedesco
Keyword(s):  
Mass Loss ◽  
Large Scale ◽  
Climate Model ◽  
Regional Climate ◽  
Mass Gain ◽  
Atmospheric Conditions ◽  
Atmospheric Variability ◽  
Positive Feedbacks ◽  
Run Off ◽  
Precipitation Events

Abstract. Surface melting is a major driver of Greenland's mass loss. Yet, the mechanisms that trigger melt are still insufficiently understood because seasonally based studies blend processes initiating melt with positive feedbacks. Here, we focus on the triggers of melt by examining the synoptic atmospheric conditions associated with 313 rapid melt increases, detected in a satellite-derived melt extent product, equally distributed throughout the year over the period 1979–2012. By combining reanalysis and weather station data, we show that melt is initiated by a cyclone-driven, southerly flow of warm, moist air, which gives rise to large-scale precipitation. A decomposition of the synoptic atmospheric variability over Greenland suggests that the identified, melt-triggering weather pattern accounts for ∼40 % of the net precipitation, but increases in the frequency, duration and areal extent of the initiated melting have shifted the line between mass gain and mass loss as more melt and rainwater run off or accumulate in the snowpack. Using a regional climate model, we estimate that the initiated melting more than doubled over the investigated period, amounting to ∼28 % of the overall surface melt and revealing that, despite the involved mass gain, year-round precipitation events are participating in the ice sheet's decline.

scholarly journals New Perspectives on Frontal Variability in the Southern Ocean

2017 ◽  
Vol 47 (5) ◽  
pp. 1151-1168 ◽  
Author(s):  
Christopher C. Chapman
Keyword(s):  
Southern Ocean ◽  
Temporal Variability ◽  
Detection Method ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Spatial And Temporal Variability ◽  
Dynamic Topography ◽  
Tracer Transport ◽  
Time Period ◽  
Frontal Structure

AbstractThe frontal structure of the Southern Ocean is investigated using the Wavelet/Higher Order Statistics Enhancement (WHOSE) frontal detection method, introduced in Chapman’s work. This methodology is applied to 21 yr of daily gridded absolute dynamic topography (ADT) data to obtain daily maps of the locations of the fronts. By forming frontal occurrence frequency maps and then approximating these occurrence maps by a superposition of simple functions, the time-mean locations of the fronts, as well as a measure of their capacity to meander, are obtained and related to the frontal locations found by previous studies. The spatial and temporal variability of the frontal structure is then considered. The number of fronts is found to be highly variable throughout the Southern Ocean, increasing (splitting) downstream of large bathymetric features and decreasing (merging) in regions where the fronts are tightly controlled by the underlying topography. These splitting/merging events are related to changes in the underlying frontal structure whereby regions of high frontal occurrence cross or spread over streamfunction contours. In contrast to the number of fronts, frontal meandering remains relatively constant throughout the Southern Ocean. Little to no migration of the fronts over the 1993–2014 time period is found, and there is only weak sensitivity of frontal positions to atmospheric forcing related to the southern annular mode or the El Niño–Southern Oscillation. Finally, the implications of these results for the study of cross-stream tracer transport are discussed.

scholarly journals Synoptic Weather Types for the Ross Sea Region, Antarctica

2013 ◽  
Vol 26 (2) ◽  
pp. 636-649 ◽  
Author(s):  
Lana Cohen ◽  
Sam Dean ◽  
James Renwick
Keyword(s):  
Large Scale ◽  
Ross Sea ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Amundsen Sea ◽  
Transport Pathways ◽  
Local Climate ◽  
Synoptic Classification ◽  
Synoptic Conditions ◽  
Precipitation And Temperature

Abstract Synoptic classifications over the Southern Ocean in the Ross Sea region of Antarctica (50°S–Antarctic coast, 150°E–90°W) have been derived from NCEP reanalysis data (1979–2011), producing a set of six synoptic types for the region. These types describe realistic synoptic conditions for the region and represent the moisture-bearing low pressure systems that circulate around Antarctica. The types are described as follows: low Bellingshausen/Amundsen (L-BA), low (L), zonal (Z), low Ross (L-R), ridge (R), and low Amundsen (L-A). Seasonal frequencies of the synoptic types reflect the seasonal zonal shift of the Amundsen Sea low (ASL) and also correlate well with the Southern Oscillation index (SOI) and the southern annular mode (SAM). Variability in the occurrences of the synoptic types L-R and L-BA indicate a shifting of the position of the ASL farther east (west) toward (away from) the Antarctic Peninsula during La Niña (El Niño) and positive (negative) SAM conditions. A joint linear regression of the SOI and SAM indices show the strongest correlations with the types L-BA and L-R in the spring and quantifies the joint forcing effect of these climate cycles on synoptic variability in the region. As a demonstration of how synoptic classification provides links between large-scale atmospheric circulation and local climate parameters, the synoptic types are related to precipitation and temperature at Roosevelt Island, an ice core site on the Ross Ice Shelf (80°S, 160°W). The synoptic types provide quantification of distinct precipitation and temperature regimes at this site, which allows for more fundamental understanding of the precipitation source regions and transport pathways that drive the variability in snow and ice proxies.

scholarly journals Increased Greenland melt triggered by large-scale, year-round precipitation events

2018 ◽  
Author(s):  
Marilena Oltmanns ◽  
Fiammetta Straneo ◽  
Marco Tedesco
Keyword(s):  
Mass Loss ◽  
Large Scale ◽  
Climate Model ◽  
Regional Climate ◽  
Mass Gain ◽  
Atmospheric Conditions ◽  
Atmospheric Variability ◽  
Positive Feedbacks ◽  
Run Off ◽  
Precipitation Events

Abstract. Surface melting is a major driver of Greenland's mass loss. Yet, the mechanisms that trigger melt are still insufficiently understood because seasonally-based studies blend processes initiating melt with positive feedbacks. Here, we focus on the triggers of melt by examining the synoptic atmospheric conditions associated with 313 rapid melt increases, detected in a satellite-derived melt extent product, equally distributed throughout the year over the period 1979–2012. By combining reanalysis and weather station data, we show that melt is initiated by a cyclone-driven, southerly flow of warm, moist air, which gives rise to large-scale precipitation. A decomposition of the synoptic atmospheric variability over Greenland suggests that the identified, melt-triggering weather pattern accounts for ~ 40 % of the net precipitation but increases in the frequency, duration and areal extent of the initiated melting have shifted the line between mass gain and mass loss as more melt and rainwater run off or accumulate in the snowpack. Using a regional climate model, we estimate that the initiated melting more than doubled over the investigated period, amounting to ~ 28 % of the overall surface melt and revealing that, despite the involved mass gain, year-round precipitation events are participating in the ice sheet's decline.

scholarly journals The Influence of the Amundsen–Bellingshausen Seas Low on the Climate of West Antarctica and Its Representation in Coupled Climate Model Simulations

2013 ◽  
Vol 26 (17) ◽  
pp. 6633-6648 ◽  
Author(s):  
J. Scott Hosking ◽  
Andrew Orr ◽  
Gareth J. Marshall ◽  
John Turner ◽  
Tony Phillips
Keyword(s):  
Annual Cycle ◽  
Large Scale ◽  
Climate Models ◽  
Climate Model ◽  
Regional Climate ◽  
Southern Annular Mode ◽  
Central Pressure ◽  
West Antarctica ◽  
Pressure System ◽  
Longitudinal Position

Abstract In contrast to earlier studies, the authors describe the climatological deep low pressure system that exists over the South Pacific sector of the Southern Ocean, referred to as the Amundsen–Bellingshausen Seas low (ABSL), in terms of its relative (rather than actual) central pressure by removing the background area-averaged mean sea level pressure (MSLP). Doing so removes much of the influence of large-scale variability across the ABSL sector region (e.g., due to the southern annular mode), allowing a clearer understanding of ABSL variability and its effect on the regional climate of West Antarctica. Using ECMWF Interim Re-Analysis (ERA-Interim) fields, the annual cycle of the relative central pressure of the ABSL for the period from 1979 to 2011 shows a minimum (maximum) during winter (summer), differing considerably from the earlier studies based on actual central pressure, which suggests a semiannual oscillation. The annual cycle of the longitudinal position of the ABSL is insensitive to the background pressure, and shows it shifting westward from ∼250° to ∼220°E between summer and winter, in agreement with earlier studies. The authors demonstrate that ABSL variability, and in particular its longitudinal position, play an important role in controlling the surface climate of West Antarctica and the surrounding ocean by quantifying its influence on key meteorological parameters. Examination of the ABSL annual cycle in 17 CMIP5 climate models run with historical forcing shows that the majority of them have definite biases, especially in terms of longitudinal position, and a correspondingly poor representation of West Antarctic climate.

Hydrological evaluation of high-resolution precipitation estimates from the WRF model in the Third Pole river basins

2021 ◽  
Author(s):  
He Sun ◽  
Fengge Su ◽  
Zhihua He ◽  
Tinghai Ou ◽  
Deliang Chen ◽  
...  
Keyword(s):  
Land Surface ◽  
Large Scale ◽  
Hydrological Modeling ◽  
Climate Model ◽  
Regional Climate ◽  
Wrf Model ◽  
Infiltration Capacity ◽  
Flood Prediction ◽  
Daily Streamflow ◽  
Precipitation Estimates

AbstractIn this study, two sets of precipitation estimates based on the regional Weather Research and Forecasting model (WRF) –the high Asia refined analysis (HAR) and outputs with a 9 km resolution from WRF (WRF-9km) are evaluated at both basin and point scales, and their potential hydrological utilities are investigated by driving the Variable Infiltration Capacity (VIC) large-scale land surface hydrological model in seven Third Pole (TP) basins. The regional climate model (RCM) tends to overestimate the gauge-based estimates by 20–95% in annual means among the selected basins. Relative to the gauge observations, the RCM precipitation estimates can accurately detect daily precipitation events of varying intensities (with absolute bias < 3 mm). The WRF-9km exhibits a high potential for hydrological application in the monsoon-dominated basins in the southeastern TP (with NSE of 0.7–0.9 and bias of -11% to 3%), while the HAR performs well in the upper Indus (UI) and upper Brahmaputra (UB) basins (with NSE of 0.6 and bias of -15% to -9%). Both the RCM precipitation estimates can accurately capture the magnitudes of low and moderate daily streamflow, but show limited capabilities in flood prediction in most of the TP basins. This study provides a comprehensive evaluation of the strength and limitation of RCMs precipitation in hydrological modeling in the TP with complex terrains and sparse gauge observations.

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