Papers by Sheng-hung Wang
Data from: Flexible flight response to challenging wind conditions in a commuting Antarctic seabird: do you catch the drift?
Flight is intrinsically an energetically costly way of moving and birds have developed morphologi... more Flight is intrinsically an energetically costly way of moving and birds have developed morphological, physiological and behavioural adaptations to minimize these costs. Central-place foraging seabirds commute regularly between nesting and foraging areas, providing us with opportunities to investigate their behavioural response to environmental conditions that may affect flight, such as wind. Here we tested hypotheses on how wind conditions influence flight behaviour in situations devoid of the confounding effect that, for instance, active foraging behaviour can have on movement patterns. We studied the Antarctic petrel, Thalassoica antarctica, a seabird breeding far inland in Antarctica and commuting through vast ice-covered areas characterized by steady and strong winds as well as a strict absence of foraging opportunities. We combined the three-dimensional location data from 79 GPS tracks with atmospheric wind data over three consecutive breeding seasons (2011-2013) in order to as...
Large-scale moisture flux analysis for the United States
PhDT, 2004
The seasonal and annual United States moisture budget (precipitation minus evaporation, P-E) is c... more The seasonal and annual United States moisture budget (precipitation minus evaporation, P-E) is calculated using monthly NCEP/NCAR reanalysis data. Statistical methodologies, primarily Rotated Principal Component Analysis (RPCA), are used to evaluate the variability in the moisture budget. RPCA was performed on monthly moisture budget data and each pattern identifies an individual region of the data domain exhibiting unique variability characteristics. Time series of the RPC patterns are correlated and compared to station precipitation records, and composites of atmospheric circulation fields are obtained during sets of years when extreme values of RPC scores occur. RPCA was performed on the annual mean values of total P-E in to examine the inter-annual and inter-decadal variability of the moisture budget changes. The seasonal RPCA analyses of P-E fields revealed patterns with similar characteristics. For example, the first principal component was centered over the continental interior, indicating high seasonal P-E variation in that area, while subsequent patterns are located near coastal areas including the Gulf of Mexico. The RPC scores were correlated to atmospheric and oceanic teleconnection indices and the links between the teleconnections and the P-E patterns were further evaluated. In winter, for example, the Pacific/North American teleconnection is best linked to continental interior moisture flux. The study indicates the possibility of detecting Great Plains low-level jet events in the NCEP/NCAR reanalysis by using spatial patterns of wind speed, locations of vertical maximum winds and the nocturnal characteristics of the low-level wind maximum. RPCA was performed on the monthly April-May-June P-E data in order to evaluate the low-level jet's role in U.S. moisture flux. One RPC pattern in particular seems associated with low-level jet events in the central United States, having an association to drought and flood events in the Midwest and central United States.
Arctic System Reanalysis Interim (ASR-interim) output - A 30 km resolution dataset
Impact of downward longwave radiative deficits on Antarctic sea-ice extent predictability during the sea ice growth period
Environmental Research Letters, Jul 18, 2022
Forecasting Antarctic atmospheric, oceanic, and sea ice conditions on subseasonal to seasonal sca... more Forecasting Antarctic atmospheric, oceanic, and sea ice conditions on subseasonal to seasonal scales remains a major challenge. During both the freezing and melting seasons current operational ensemble forecasting systems show a systematic overestimation of the Antarctic sea-ice edge location. The skill of sea ice cover prediction is closely related to the accuracy of cloud representation in models, as the two are strongly coupled by cloud radiative forcing. In particular, surface downward longwave radiation (DLW) deficits appear to be a common shortcoming in atmospheric models over the Southern Ocean. For example, a recent comparison of ECMWF reanalysis 5th generation (ERA5) global reanalysis with the observations from McMurdo Station revealed a year-round deficit in DLW of approximately 50 Wm−2 in marine air masses due to model shortages in supercooled cloud liquid water. A comparison with the surface DLW radiation observations from the Ocean Observatories Initiative mooring in the South Pacific at 54.08° S, 89.67° W, for the time period January 2016–November 2018, confirms approximately 20 Wm−2 deficit in DLW in ERA5 well north of the sea-ice edge. Using a regional ocean model, we show that when DLW is artificially increased by 50 Wm−2 in the simulation driven by ERA5 atmospheric forcing, the predicted sea ice growth agrees much better with the observations. A wide variety of sensitivity tests show that the anomalously large, predicted sea-ice extent is not due to limitations in the ocean model and that by implication the cause resides with the atmospheric forcing.
Major surface melting over the Ross Ice Shelf part <scp>II</scp> : Surface energy balance
Quarterly Journal of the Royal Meteorological Society, Jun 7, 2021
The West Antarctic climate is under the combined impact of synoptic and regional drivers. Regiona... more The West Antarctic climate is under the combined impact of synoptic and regional drivers. Regional factors have contributed to more frequent surface melting with a similar pattern recently, which accelerates ice loss and favors global sea‐level rise. Part I of this research identified and quantified the two leading drivers of Ross Ice Shelf (RIS) melting, viz. foehn effect and direct marine air advection, based on Polar WRF (PWRF) simulations. In this article (Part II), the impact of clouds and the pattern of surface energy balance (SEB) during melting are analyzed, as well as the relationship among these three factors. In general, net shortwave radiation dominates the surface melting with a daily mean value above 100 W·m−2. Foehn clearance and decreasing surface albedo respectively increase the downward shortwave radiation and increase the absorbed shortwave radiation, significantly contributing to surface melting in areas such as western Marie Byrd Land. Also, extensive downward longwave radiation caused by low‐level liquid cloud favors the melting expansion over the middle and coastal RIS. With significant moisture transport occurring over more than 40% of the time during the melting period, the impact from net radiation can be amplified. Moreover, frequent foehn cases can enhance the turbulent mixing on the leeside. With a Froude number (Fr) around 1 or slightly larger, fast downdrafts or reversed wind flows can let the warm foehn air penetrate down to the surface with up to 20 W·m−2 in sensible heat flux transfer to the ground. However, when the Froude number is close to infinity with breaking waves on the leeside, the contribution of turbulence to the surface warming is reduced. With better understanding of the regional factors for the surface melting, prediction of the future stability of West Antarctic ice shelves can be improved.
Geophysical Research Letters, 2004
Studies such as those by and suggest that the northeastern Atlantic Arctic warmed in the early 19... more Studies such as those by and suggest that the northeastern Atlantic Arctic warmed in the early 1990s and that regional sea level pressure (SLP) variations and the NAO may be responsible. Sea surface temperature changes in Fram Strait and the Barents Sea depend, respectively, on SLP variations over the Barents Sea and Norwegian Sea. Since winter 1972, SLP over the Barents and Norwegian Seas has been unusually low during NAO+ winters. Little pressure field change occurred during NAO-winters or around the Denmark Strait, the normal location of the Icelandic Low. Simultaneously, the NAO+ mode became highly persistent on a month-to-month basis throughout the NAO+ winters and ultimately throughout all seasons during a multiyear episode in which the Arctic reached peak warming. A similar NAO+ persistence episode is shown to have occurred from 1920-1925, during another notable Arctic warming event.
Influence of local scale and oceanic teleconnections on regional fire danger and wildfire trends
Science of The Total Environment, Jul 1, 2023
Journal of Applied Meteorology and Climatology, Nov 1, 2016
Flight operations in Antarctica rely on accurate weather forecasts aided by the numerical predict... more Flight operations in Antarctica rely on accurate weather forecasts aided by the numerical predictions primarily produced by the Antarctic Mesoscale Prediction System (AMPS) that employs the polar version of the Weather Research and Forecasting (Polar WRF) Model. To improve the performance of the model's Mellor-Yamada-Janjic ´(MYJ) planetary boundary layer (PBL) scheme, this study examines 1.5 yr of meteorological data provided by the 30-m Alexander Tall Tower! (ATT) automatic weather station on the western Ross Ice Shelf from March 2011 to July 2012. Processed ATT observations at 10-min intervals from the multiple observational levels are compared with the 5-km-resolution AMPS forecasts run daily at 0000 and 1200 UTC. The ATT comparison shows that AMPS has fundamental issues with moisture and handling stability as a function of wind speed. AMPS has a 10-percentage-point (i.e., RH unit) relative humidity dry bias year-round that is highest when katabatic winds from the Byrd and Mulock Glaciers exceed 15 m s 21 . This is likely due to nonlocal effects such as errors in the moisture content of the katabatic flow and AMPS not parameterizing the sublimation from blowing snow. AMPS consistently overestimates the wind speed at the ATT by 1-2 m s 21 , in agreement with previous studies that attribute the high wind speed bias to the MYJ scheme. This leads to reduced stability in the simulated PBL, thus affecting the model's ability to properly simulate the transfer of heat and momentum throughout the PBL.
An evaluation of the ERA-Interim global reanalysis at high latitudes
Arctic System Reanalysis (ASR) Project
The Arctic System Reanalysis (ASR) is produced using a high-resolution version of the Polar Weath... more The Arctic System Reanalysis (ASR) is produced using a high-resolution version of the Polar Weather Forecast Model (PWRF) and High Resolution Land Data Assimilation (HRLDAS) systems that have been optimized for the Arctic. The final version of 30 km horizontal resolution data set which spans 2000-2012 is released in September 2014 and available on line through the NCAR's RDA. The interim version, released in May 2012, is also available for a limited period of time.\n\nThe final version has 29 pressure levels, 27 surface and 10 upper air analysis variables, 74 surface and 16 upper air forecast variables, and 3 soil variables. Both the u- and v- winds relative to grid and relative to earth are present in the final version. The wind speed is also added.\n\nNOTE: This dataset has been superseded by the Arctic System Reanalysis version 2, which is available in RDA dataset ds631.1 [https://rda.ucar.edu/datasets/ds631.1/]. Users are advised to access this newer dataset version.
Quaternary International, Sep 1, 2002
The 50+ years National Centers for Environmental Prediction-National Center for Atmospheric Resea... more The 50+ years National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis data set is used to locate distinct atmospheric circulation patterns favoring glacial initiation over northeastern North America (50-801N, 60-901W). These patterns yield abundant winter snowfall and anomalously cool summer temperatures. We assume that atmosphere/ ocean boundary conditions during the last interglacial and today are similar. Atmospheric circulation patterns inferred from composite mean sea level pressure (MSLP) anomaly fields for the extreme cold summers and wet winters are consistent with the respective composite summer 2-m temperature and winter precipitation anomaly patterns. Summer 2-m temperatures (winter precipitation rate) are strongly (weakly) correlated with North Atlantic sea surface temperatures (SST). Extreme season MSLP anomalies and associated wind stress may augment the SST anomalies via Ekman transport. The contemporary climate record over the study region shows substantial interannual variability, consistent with the lack of glaciation. The extreme cold summer/wet winter criteria for glaciation occur in the contemporary record, but are rare. Mass balance calculations using NNR demonstrate that a perennial snowfield is possible in the study region, but glacial onset requires a change in the frequency distribution of climatic events to yield a sustained (decadal) period of cold summers that preserve the winter accumulation.
Addendum: Impact of downward longwave radiative deficits on Antarctic sea-ice extent predictability during the sea ice growth period (2022 Environ. Res. Lett. 17 084008)
Environmental Research Letters, Jan 20, 2023
Quarterly Journal of the Royal Meteorological Society, 2019
The Ross Ice Shelf (RIS) buttresses ice streams from the Antarctic continent and restrains the gr... more The Ross Ice Shelf (RIS) buttresses ice streams from the Antarctic continent and restrains the grounded ice sheet from flowing into the ocean, which is important for the stability of the ice sheet. In recent decades, West Antarctic ice shelves, including the RIS, have experienced more frequent surface melting during summer. We investigated the role of warm, descending föhn winds in a major melt event that occurred on the RIS in January 2016. Only a few summer melt events of this magnitude have been observed since 1979. Backward trajectories from the area of earliest melting were constructed using the Antarctic Mesoscale Prediction System to investigate the dominant mechanisms at the beginning of the melt event, mainly from 10 to 13 January. Analysis was conducted over two distinct areas. The föhn effect contributed around 2-4 • C to the surface temperature increase over the coastal mountains of Marie Byrd Land and around 1 • C over the much lower Edward VII Peninsula. Most of the föhn warming was caused by isentropic drawdown of air aloft. On 10 January, the second-most important contributor for both mountain ranges was the thermodynamic mechanism. On 11 January, the second-most important mechanism was the sensible and radiative heat flux. This study contributes to a better understanding of surface melt events over the RIS and benefits research associated with the stability of West Antarctic ice shelves.
Journal of Climate, Sep 1, 2007
A 124 summer record of total surface energy content consisting of time series of surface equivale... more A 124 summer record of total surface energy content consisting of time series of surface equivalent temperature (T E ) and its components T (mean air temperature) and Lq/c p (moist enthalpy, denoted Lq) is developed, quality controlled, and analyzed for Columbus, Ohio, where long records of monthly dewpoint temperature are available. The analysis shows that the highest T E occurs during the summer of 1995 when both T and Lq were very high, associated with a severe midwestern heat wave. That year contrasts with the hot summers of 1930-36, when Lq and T E had relatively low or negative anomalies (low humidity) compared to those of T. Following the 1930-36 summers, T and Lq departures are much more typically the same sign in individual summers, and the two parameters develop a statistically significant high positive correlation into the twenty-first century. Mean T and Lq departures from the long-term normal have opposite signs, however, when summers are stratified either by seasonal total rainfall amounts or by the Palmer drought severity soil moisture index. Normalized trends of T, Lq, and T E are downward from 1940 to 1964 with those of T E exceeding T. Since 1965, however, significant positive T trends slightly exceed T E in magnitude and those of dewpoint temperature and Lq are comparatively lower. A highly significant upward trend in minimum temperatures especially dominates the T variability, creating a significant downward trend in the temperature range that dominates recent summer climate variability more than moisture trends. Regional moisture flux variations are largest away from Columbus, over the upper Midwest and western Atlantic Ocean, during its seasonal extremes in total surface energy.
Dynamics of Atmospheres and Oceans, Mar 1, 2008
A survey of the spatial and temporal behavior of the atmospheric general circulation as it relate... more A survey of the spatial and temporal behavior of the atmospheric general circulation as it relates to both polar regions is presented. The review is based on the European Centre for Medium-Range Weather Forecasts (ECMWF) 40-year reanalysis (ERA-40), updated using ECMWF operational analyses. The analysis spans 1960-2005 in the Northern Hemisphere, but is restricted to 1979-2005 in the Southern Hemisphere because of difficulties experienced by ERA-40 prior to the modern satellite era. The seasonal cycle of atmospheric circulation is illustrated by focusing on winter and summer. The huge circulation contrasts between the land-dominated Northern Hemisphere and the ocean-dominated Southern Hemisphere stand out. The intensification of the North Atlantic Oscillation/Northern Annular Mode and the Southern Annular Mode in DJF is highlighted and likely due to warming of the tropical Indian Ocean. The Arctic frontal zone during northern summer and the semi-annual oscillation throughout the year in the Southern Hemisphere are prominent features of the high latitude circulation in the respective hemispheres. Rotated principal component analysis (RPCA) is used to describe the primary modes of temporal variability affecting both polar regions, especially the links with the tropical forcing. The North Atlantic Oscillation is a key modulator of the atmospheric circulation in the North Atlantic sector, especially in winter, and is the dominant control on the moisture transport into the Arctic Basin. The Pacific-South American teleconnection patterns are primary factors in the high southern latitude circulation variability throughout the year, especially in the Pacific sector of Antarctica where the majority of moisture transport into the continent occurs.
Monthly Weather Review, Dec 1, 2005
Many aspects of reanalysis data are of high quality over regions with sufficiently dense data, bu... more 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.
Influence of Local Scale and Oceanic Teleconnections on Regional Fire Danger and Wildfire Trends
SSRN Electronic Journal
Arctic System Reanalysis Interim (ASR-interim) output - A 30 km resolution dataset
Arctic System Reanalysis (ASR) Project
The Arctic System Reanalysis (ASR) is produced using a high-resolution version of the Polar Weath... more The Arctic System Reanalysis (ASR) is produced using a high-resolution version of the Polar Weather Forecast Model (PWRF) and High Resolution Land Data Assimilation (HRLDAS) systems that have been optimized for the Arctic. The final version of 30 km horizontal resolution data set which spans 2000-2012 is released in September 2014 and available on line through the NCAR's RDA. The interim version, released in May 2012, is also available for a limited period of time.\n\nThe final version has 29 pressure levels, 27 surface and 10 upper air analysis variables, 74 surface and 16 upper air forecast variables, and 3 soil variables. Both the u- and v- winds relative to grid and relative to earth are present in the final version. The wind speed is also added.\n\nNOTE: This dataset has been superseded by the Arctic System Reanalysis version 2, which is available in RDA dataset ds631.1 [https://rda.ucar.edu/datasets/ds631.1/]. Users are advised to access this newer dataset version.
Major surface melting over the Ross Ice Shelf part I: Foehn effect
Quarterly Journal of the Royal Meteorological Society, 2021
West Antarctica (WA), especially the Ross Ice Shelf (RIS), has experienced more frequent surface ... more West Antarctica (WA), especially the Ross Ice Shelf (RIS), has experienced more frequent surface melting during the austral summer recently. The future is likely to see enhanced surface melting that will jeopardize the stability of ice shelves and cause ice loss. We investigate four major melt cases over the RIS via Polar Weather Research and Forecasting (WRF) simulations (4 km resolution) driven by European Centre for Medium‐Range Weather Forecasts (ECMWF) Reanalysis 5th Generation (ERA5) reanalysis data and Moderate Resolution Imaging Spectroradiometer (MODIS) observed albedo. Direct warm air advection, recurring foehn effect, and cloud/upper warm air introduced radiative warming are the three major regional causes of surface melting over WA. In this paper, Part I, the first two factors are identified and quantified. The second paper, Part II, discusses the impact of clouds and summarizes all three factors from a surface energy balance perspective. With a high‐pressure ridge locat...
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Papers by Sheng-hung Wang