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Alan Robock
,
Konstantin Ya Vinnikov
,
C. Adam Schlosser
,
Nina A. Speranskaya
, and
Yongkang Xue

Abstract

Soil moisture observations in sites with natural vegetation were made for several decades in the former Soviet Union at hundreds of stations. In this paper, the authors use data from six of these stations from different climatic regimes, along with ancillary meteorological and actinometric data, to demonstrate a method to validate soil moisture simulations with biosphere and bucket models. Some early and current general circulation models (GCMS) use bucket models for soil hydrology calculations. More recently, the Simple Biosphere Model (SiB) was developed to incorporate the effects of vegetation on fluxes of moisture, momentum, and energy at the earth's surface into soil hydrology models. Until now, the bucket and SiB have been verified by comparison with actual soil moisture data only on a limited basis. In this study, a Simplified SiB (SSIB) soil hydrology model and a 15-cm bucket model are forced by observed meteorological and actinometric data every 3 h for 6-yr simulations at the six stations. The model calculations of soil moisture are compared to observations of soil moisture, literally “ground truth,” snow cover, surface albedo, and net radiation” and with each other.

For three of the stations, the SSIB and 15-cm bucket models produce good simulations of seasonal cycles and interannual variations of soil moisture. For the other three stations, there are large errors in the simulations by both models. Inconsistencies in specification of field capacity may be partly responsible. There is no evidence that the SSiB simulations are superior in simulating soil moisture variations. In fact, the models are quite similar since SSiB implicitly has a bucket embedded in it. One of the main differences between the models is in the treatment of runoff due to melting snow in the spring-SSiB incorrectly puts all the snowmelt into runoff. While producing similar soil moisture simulations, the models produce very different surface latent and sensible beat fluxes, which would have large effects on GCM simulations.

Full access
Xiang Gao
,
C. Adam Schlosser
,
Paul A. O’Gorman
,
Erwan Monier
, and
Dara Entekhabi

Abstract

Precipitation-gauge observations and atmospheric reanalysis are combined to develop an analogue method for detecting heavy precipitation events based on prevailing large-scale atmospheric conditions. Combinations of atmospheric variables for circulation (geopotential height and wind vector) and moisture (surface specific humidity, column and up to 500-hPa precipitable water) are examined to construct analogue schemes for the winter [December–February (DJF)] of the “Pacific Coast California” (PCCA) region and the summer [June–August (JJA)] of the Midwestern United States (MWST). The detection diagnostics of analogue schemes are calibrated with 1979–2005 and validated with 2006–14 NASA Modern-Era Retrospective Analysis for Research and Applications (MERRA). All analogue schemes are found to significantly improve upon MERRA precipitation in characterizing the occurrence and interannual variations of observed heavy precipitation events in the MWST. When evaluated with the late twentieth-century climate model simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5), all analogue schemes produce model medians of heavy precipitation frequency that are more consistent with observations and have smaller intermodel discrepancies than model-based precipitation. Under the representative concentration pathways (RCP) 4.5 and 8.5 scenarios, the CMIP5-based analogue schemes produce trends in heavy precipitation occurrence through the twenty-first century that are consistent with model-based precipitation, but with smaller intermodel disparity. The median trends in heavy precipitation frequency are positive for DJF over PCCA but are slightly negative for JJA over MWST. Overall, the analyses highlight the potential of the analogue as a powerful diagnostic tool for model deficiencies and its complementarity to an evaluation of heavy precipitation frequency based on model precipitation alone.

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A. P. Sokolov
,
P. H. Stone
,
C. E. Forest
,
R. Prinn
,
M. C. Sarofim
,
M. Webster
,
S. Paltsev
,
C. A. Schlosser
,
D. Kicklighter
,
S. Dutkiewicz
,
J. Reilly
,
C. Wang
,
B. Felzer
,
J. M. Melillo
, and
H. D. Jacoby
Full access
A. P. Sokolov
,
P. H. Stone
,
C. E. Forest
,
R. Prinn
,
M. C. Sarofim
,
M. Webster
,
S. Paltsev
,
C. A. Schlosser
,
D. Kicklighter
,
S. Dutkiewicz
,
J. Reilly
,
C. Wang
,
B. Felzer
,
J. M. Melillo
, and
H. D. Jacoby

Abstract

The Massachusetts Institute of Technology (MIT) Integrated Global System Model is used to make probabilistic projections of climate change from 1861 to 2100. Since the model’s first projections were published in 2003, substantial improvements have been made to the model, and improved estimates of the probability distributions of uncertain input parameters have become available. The new projections are considerably warmer than the 2003 projections; for example, the median surface warming in 2091–2100 is 5.1°C compared to 2.4°C in the earlier study. Many changes contribute to the stronger warming; among the more important ones are taking into account the cooling in the second half of the twentieth century due to volcanic eruptions for input parameter estimation and a more sophisticated method for projecting gross domestic product (GDP) growth, which eliminated many low-emission scenarios.

However, if recently published data, suggesting stronger twentieth-century ocean warming, are used to determine the input climate parameters, the median projected warming at the end of the twenty-first century is only 4.1°C. Nevertheless, all ensembles of the simulations discussed here produce a much smaller probability of warming less than 2.4°C than implied by the lower bound of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) projected likely range for the A1FI scenario, which has forcing very similar to the median projection in this study. The probability distribution for the surface warming produced by this analysis is more symmetric than the distribution assumed by the IPCC because of a different feedback between the climate and the carbon cycle, resulting from the inclusion in this model of the carbon–nitrogen interaction in the terrestrial ecosystem.

Full access
M. Rodell
,
H. K. Beaudoing
,
T. S. L’Ecuyer
,
W. S. Olson
,
J. S. Famiglietti
,
P. R. Houser
,
R. Adler
,
M. G. Bosilovich
,
C. A. Clayson
,
D. Chambers
,
E. Clark
,
E. J. Fetzer
,
X. Gao
,
G. Gu
,
K. Hilburn
,
G. J. Huffman
,
D. P. Lettenmaier
,
W. T. Liu
,
F. R. Robertson
,
C. A. Schlosser
,
J. Sheffield
, and
E. F. Wood

Abstract

This study quantifies mean annual and monthly fluxes of Earth’s water cycle over continents and ocean basins during the first decade of the millennium. To the extent possible, the flux estimates are based on satellite measurements first and data-integrating models second. A careful accounting of uncertainty in the estimates is included. It is applied within a routine that enforces multiple water and energy budget constraints simultaneously in a variational framework in order to produce objectively determined optimized flux estimates. In the majority of cases, the observed annual surface and atmospheric water budgets over the continents and oceans close with much less than 10% residual. Observed residuals and optimized uncertainty estimates are considerably larger for monthly surface and atmospheric water budget closure, often nearing or exceeding 20% in North America, Eurasia, Australia and neighboring islands, and the Arctic and South Atlantic Oceans. The residuals in South America and Africa tend to be smaller, possibly because cold land processes are negligible. Fluxes were poorly observed over the Arctic Ocean, certain seas, Antarctica, and the Australasian and Indonesian islands, leading to reliance on atmospheric analysis estimates. Many of the satellite systems that contributed data have been or will soon be lost or replaced. Models that integrate ground-based and remote observations will be critical for ameliorating gaps and discontinuities in the data records caused by these transitions. Continued development of such models is essential for maximizing the value of the observations. Next-generation observing systems are the best hope for significantly improving global water budget accounting.

Full access
Tristan S. L’Ecuyer
,
H. K. Beaudoing
,
M. Rodell
,
W. Olson
,
B. Lin
,
S. Kato
,
C. A. Clayson
,
E. Wood
,
J. Sheffield
,
R. Adler
,
G. Huffman
,
M. Bosilovich
,
G. Gu
,
F. Robertson
,
P. R. Houser
,
D. Chambers
,
J. S. Famiglietti
,
E. Fetzer
,
W. T. Liu
,
X. Gao
,
C. A. Schlosser
,
E. Clark
,
D. P. Lettenmaier
, and
K. Hilburn

Abstract

New objectively balanced observation-based reconstructions of global and continental energy budgets and their seasonal variability are presented that span the golden decade of Earth-observing satellites at the start of the twenty-first century. In the absence of balance constraints, various combinations of modern flux datasets reveal that current estimates of net radiation into Earth’s surface exceed corresponding turbulent heat fluxes by 13–24 W m−2. The largest imbalances occur over oceanic regions where the component algorithms operate independent of closure constraints. Recent uncertainty assessments suggest that these imbalances fall within anticipated error bounds for each dataset, but the systematic nature of required adjustments across different regions confirm the existence of biases in the component fluxes. To reintroduce energy and water cycle closure information lost in the development of independent flux datasets, a variational method is introduced that explicitly accounts for the relative accuracies in all component fluxes. Applying the technique to a 10-yr record of satellite observations yields new energy budget estimates that simultaneously satisfy all energy and water cycle balance constraints. Globally, 180 W m−2 of atmospheric longwave cooling is balanced by 74 W m−2 of shortwave absorption and 106 W m−2 of latent and sensible heat release. At the surface, 106 W m−2 of downwelling radiation is balanced by turbulent heat transfer to within a residual heat flux into the oceans of 0.45 W m−2, consistent with recent observations of changes in ocean heat content. Annual mean energy budgets and their seasonal cycles for each of seven continents and nine ocean basins are also presented.

Full access
T. H. Chen
,
A. Henderson-Sellers
,
P. C. D. Milly
,
A. J. Pitman
,
A. C. M. Beljaars
,
J. Polcher
,
F. Abramopoulos
,
A. Boone
,
S. Chang
,
F. Chen
,
Y. Dai
,
C. E. Desborough
,
R. E. Dickinson
,
L. Dümenil
,
M. Ek
,
J. R. Garratt
,
N. Gedney
,
Y. M. Gusev
,
J. Kim
,
R. Koster
,
E. A. Kowalczyk
,
K. Laval
,
J. Lean
,
D. Lettenmaier
,
X. Liang
,
J.-F. Mahfouf
,
H.-T. Mengelkamp
,
K. Mitchell
,
O. N. Nasonova
,
J. Noilhan
,
A. Robock
,
C. Rosenzweig
,
J. Schaake
,
C. A. Schlosser
,
J.-P. Schulz
,
Y. Shao
,
A. B. Shmakin
,
D. L. Verseghy
,
P. Wetzel
,
E. F. Wood
,
Y. Xue
,
Z.-L. Yang
, and
Q. Zeng

Abstract

In the Project for Intercomparison of Land-Surface Parameterization Schemes phase 2a experiment, meteorological data for the year 1987 from Cabauw, the Netherlands, were used as inputs to 23 land-surface flux schemes designed for use in climate and weather models. Schemes were evaluated by comparing their outputs with long-term measurements of surface sensible heat fluxes into the atmosphere and the ground, and of upward longwave radiation and total net radiative fluxes, and also comparing them with latent heat fluxes derived from a surface energy balance. Tuning of schemes by use of the observed flux data was not permitted. On an annual basis, the predicted surface radiative temperature exhibits a range of 2 K across schemes, consistent with the range of about 10 W m−2 in predicted surface net radiation. Most modeled values of monthly net radiation differ from the observations by less than the estimated maximum monthly observational error (±10 W m−2). However, modeled radiative surface temperature appears to have a systematic positive bias in most schemes; this might be explained by an error in assumed emissivity and by models’ neglect of canopy thermal heterogeneity. Annual means of sensible and latent heat fluxes, into which net radiation is partitioned, have ranges across schemes of30 W m−2 and 25 W m−2, respectively. Annual totals of evapotranspiration and runoff, into which the precipitation is partitioned, both have ranges of 315 mm. These ranges in annual heat and water fluxes were approximately halved upon exclusion of the three schemes that have no stomatal resistance under non-water-stressed conditions. Many schemes tend to underestimate latent heat flux and overestimate sensible heat flux in summer, with a reverse tendency in winter. For six schemes, root-mean-square deviations of predictions from monthly observations are less than the estimated upper bounds on observation errors (5 W m−2 for sensible heat flux and 10 W m−2 for latent heat flux). Actual runoff at the site is believed to be dominated by vertical drainage to groundwater, but several schemes produced significant amounts of runoff as overland flow or interflow. There is a range across schemes of 184 mm (40% of total pore volume) in the simulated annual mean root-zone soil moisture. Unfortunately, no measurements of soil moisture were available for model evaluation. A theoretical analysis suggested that differences in boundary conditions used in various schemes are not sufficient to explain the large variance in soil moisture. However, many of the extreme values of soil moisture could be explained in terms of the particulars of experimental setup or excessive evapotranspiration.

Full access
V. Masson-Delmotte
,
S. Hou
,
A. Ekaykin
,
J. Jouzel
,
A. Aristarain
,
R. T. Bernardo
,
D. Bromwich
,
O. Cattani
,
M. Delmotte
,
S. Falourd
,
M. Frezzotti
,
H. Gallée
,
L. Genoni
,
E. Isaksson
,
A. Landais
,
M. M. Helsen
,
G. Hoffmann
,
J. Lopez
,
V. Morgan
,
H. Motoyama
,
D. Noone
,
H. Oerter
,
J. R. Petit
,
A. Royer
,
R. Uemura
,
G. A. Schmidt
,
E. Schlosser
,
J. C. Simões
,
E. J. Steig
,
B. Stenni
,
M. Stievenard
,
M. R. van den Broeke
,
R. S. W. van de Wal
,
W. J. van de Berg
,
F. Vimeux
, and
J. W. C. White

Abstract

A database of surface Antarctic snow isotopic composition is constructed using available measurements, with an estimate of data quality and local variability. Although more than 1000 locations are documented, the spatial coverage remains uneven with a majority of sites located in specific areas of East Antarctica. The database is used to analyze the spatial variations in snow isotopic composition with respect to geographical characteristics (elevation, distance to the coast) and climatic features (temperature, accumulation) and with a focus on deuterium excess. The capacity of theoretical isotopic, regional, and general circulation atmospheric models (including “isotopic” models) to reproduce the observed features and assess the role of moisture advection in spatial deuterium excess fluctuations is analyzed.

Full access
Jonathan D. Wille
,
Simon P. Alexander
,
Charles Amory
,
Rebecca Baiman
,
Léonard Barthélemy
,
Dana M. Bergstrom
,
Alexis Berne
,
Hanin Binder
,
Juliette Blanchet
,
Deniz Bozkurt
,
Thomas J. Bracegirdle
,
Mathieu Casado
,
Taejin Choi
,
Kyle R. Clem
,
Francis Codron
,
Rajashree Datta
,
Stefano Di Battista
,
Vincent Favier
,
Diana Francis
,
Alexander D. Fraser
,
Elise Fourré
,
René D. Garreaud
,
Christophe Genthon
,
Irina V. Gorodetskaya
,
Sergi González-Herrero
,
Victoria J. Heinrich
,
Guillaume Hubert
,
Hanna Joos
,
Seong-Joong Kim
,
John C. King
,
Christoph Kittel
,
Amaelle Landais
,
Matthew Lazzara
,
Gregory H. Leonard
,
Jan L. Lieser
,
Michelle Maclennan
,
David Mikolajczyk
,
Peter Neff
,
Inès Ollivier
,
Ghislain Picard
,
Benjamin Pohl
,
F. Martin Ralph
,
Penny Rowe
,
Elisabeth Schlosser
,
Christine A. Shields
,
Inga J. Smith
,
Michael Sprenger
,
Luke Trusel
,
Danielle Udy
,
Tessa Vance
,
Étienne Vignon
,
Catherine Walker
,
Nander Wever
, and
Xun Zou

Abstract

Between 15 and 19 March 2022, East Antarctica experienced an exceptional heat wave with widespread 30°–40°C temperature anomalies across the ice sheet. This record-shattering event saw numerous monthly temperature records being broken including a new all-time temperature record of −9.4°C on 18 March at Concordia Station despite March typically being a transition month to the Antarctic coreless winter. The driver for these temperature extremes was an intense atmospheric river advecting subtropical/midlatitude heat and moisture deep into the Antarctic interior. The scope of the temperature records spurred a large, diverse collaborative effort to study the heat wave’s meteorological drivers, impacts, and historical climate context. Here we focus on describing those temperature records along with the intricate meteorological drivers that led to the most intense atmospheric river observed over East Antarctica. These efforts describe the Rossby wave activity forced from intense tropical convection over the Indian Ocean. This led to an atmospheric river and warm conveyor belt intensification near the coastline, which reinforced atmospheric blocking deep into East Antarctica. The resulting moisture flux and upper-level warm-air advection eroded the typical surface temperature inversions over the ice sheet. At the peak of the heat wave, an area of 3.3 million km2 in East Antarctica exceeded previous March monthly temperature records. Despite a temperature anomaly return time of about 100 years, a closer recurrence of such an event is possible under future climate projections. In Part II we describe the various impacts this extreme event had on the East Antarctic cryosphere.

Significance Statement

In March 2022, a heat wave and atmospheric river caused some of the highest temperature anomalies ever observed globally and captured the attention of the Antarctic science community. Using our diverse collective expertise, we explored the causes of the event and have placed it within a historical climate context. One key takeaway is that Antarctic climate extremes are highly sensitive to perturbations in the midlatitudes and subtropics. This heat wave redefined our expectations of the Antarctic climate. Despite the rare chance of occurrence based on past climate, a future temperature extreme event of similar magnitude is possible, especially given anthropogenic climate change.

Open access
Jonathan D. Wille
,
Simon P. Alexander
,
Charles Amory
,
Rebecca Baiman
,
Léonard Barthélemy
,
Dana M. Bergstrom
,
Alexis Berne
,
Hanin Binder
,
Juliette Blanchet
,
Deniz Bozkurt
,
Thomas J. Bracegirdle
,
Mathieu Casado
,
Taejin Choi
,
Kyle R. Clem
,
Francis Codron
,
Rajashree Datta
,
Stefano Di Battista
,
Vincent Favier
,
Diana Francis
,
Alexander D. Fraser
,
Elise Fourré
,
René D. Garreaud
,
Christophe Genthon
,
Irina V. Gorodetskaya
,
Sergi González-Herrero
,
Victoria J. Heinrich
,
Guillaume Hubert
,
Hanna Joos
,
Seong-Joong Kim
,
John C. King
,
Christoph Kittel
,
Amaelle Landais
,
Matthew Lazzara
,
Gregory H. Leonard
,
Jan L. Lieser
,
Michelle Maclennan
,
David Mikolajczyk
,
Peter Neff
,
Inès Ollivier
,
Ghislain Picard
,
Benjamin Pohl
,
F. Martin Ralph
,
Penny Rowe
,
Elisabeth Schlosser
,
Christine A. Shields
,
Inga J. Smith
,
Michael Sprenger
,
Luke Trusel
,
Danielle Udy
,
Tessa Vance
,
Étienne Vignon
,
Catherine Walker
,
Nander Wever
, and
Xun Zou

Abstract

Between 15 and 19 March 2022, East Antarctica experienced an exceptional heat wave with widespread 30°–40°C temperature anomalies across the ice sheet. In Part I, we assessed the meteorological drivers that generated an intense atmospheric river (AR) that caused these record-shattering temperature anomalies. Here, we continue our large collaborative study by analyzing the widespread and diverse impacts driven by the AR landfall. These impacts included widespread rain and surface melt that was recorded along coastal areas, but this was outweighed by widespread high snowfall accumulations resulting in a largely positive surface mass balance contribution to the East Antarctic region. An analysis of the surface energy budget indicated that widespread downward longwave radiation anomalies caused by large cloud-liquid water contents along with some scattered solar radiation produced intense surface warming. Isotope measurements of the moisture were highly elevated, likely imprinting a strong signal for past climate reconstructions. The AR event attenuated cosmic ray measurements at Concordia, something previously never observed. Last, an extratropical cyclone west of the AR landfall likely triggered the final collapse of the critically unstable Conger Ice Shelf while further reducing an already record low sea ice extent.

Significance Statement

Using our diverse collective expertise, we explored the impacts from the March 2022 heat wave and atmospheric river across East Antarctica. One key takeaway is that the Antarctic cryosphere is highly sensitive to meteorological extremes originating from the midlatitudes and subtropics. Despite the large positive temperature anomalies driven from strong downward longwave radiation, this event led to huge amounts of snowfall across the Antarctic interior desert. The isotopes in this snow of warm airmass origin will likely be detectable in future ice cores and potentially distort past climate reconstructions. Even measurements of space activity were affected. Also, the swells generated from this storm helped to trigger the final collapse of an already critically unstable Conger Ice Shelf while further degrading sea ice coverage.

Open access