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M. Sand
,
T. Iversen
,
P. Bohlinger
,
A. Kirkevåg
,
I. Seierstad
,
Ø. Seland
, and
A. Sorteberg

Abstract

The climate response to an abrupt increase of black carbon (BC) aerosols is compared to the standard CMIP5 experiment of quadrupling CO2 concentrations in air. The global climate model NorESM with interactive aerosols is used. One experiment employs prescribed BC emissions with calculated concentrations coupled to atmospheric processes (emission-driven) while a second prescribes BC concentrations in air (concentration-driven) from a precalculation with the same model and emissions, but where the calculated BC does not force the climate dynamics. The difference quantifies effects of feedbacks between airborne BC and other climate processes. BC emissions are multiplied with 25, yielding an instantaneous top-of-atmosphere (TOA) radiative forcing (RF) comparable to the quadrupling of atmospheric CO2. A radiative kernel method is applied to estimate the different feedbacks.

In both BC runs, BC leads to a much smaller surface warming than CO2. Rapid atmospheric feedbacks reduce the BC-induced TOA forcing by approximately 75% over the first year (10% for CO2). For BC, equilibrium is quickly re-established, whereas for CO2 equilibration requires a much longer time than 150 years. Emission-driven BC responses in the atmosphere are much larger than the concentration-driven. The northward displacement of the intertropical convergence zone (ITCZ) in the BC emission-driven experiment enhances both the vertical transport and deposition of BC from Southeast Asia. The study shows that prescribing BC concentrations may lead to seriously inaccurate conclusions, but other models with less efficient transport may produce results with smaller differences.

Full access
J. E. Kristjánsson
,
I. Barstad
,
T. Aspelien
,
I. Føre
,
Ø. Godøy
,
Ø. Hov
,
E. Irvine
,
T. Iversen
,
E. Kolstad
,
T. E. Nordeng
,
H. McInnes
,
R. Randriamampianina
,
J. Reuder
,
Ø. Saetra
,
M. Shapiro
,
T. Spengler
, and
H. Ólafsson

From a weather forecasting perspective, the Arctic poses particular challenges for mainly two reasons: 1) The observational data are sparse and 2) the weather phenomena responsible for severe weather, such as polar lows, Arctic fronts, and orographic influences on airflow, are poorly resolved and described by the operational numerical weather prediction (NWP) models. The Norwegian International Polar Year (IPY)– The Observing System Research and Predictability Experiment (THORPEX) project (2007–10) sought to significantly improve weather forecasts of these phenomena through a combined modeling and observational effort. The crux of the observational effort was a 3-week international field campaign out of northern Norway in early 2008, combining airborne and surface-based observations. The main platform of the field campaign was the Deutsches Zentrum für Luft- und Raumfahrt (DLR) research aircraft Falcon, equipped with lidar systems for profiling of aerosols, humidity, and wind, in addition to in situ measurements and dropsondes. A total of 12 missions were flown, yielding detailed observations of polar lows, Arctic fronts, and orographic low-level jets near Spitsbergen, the coast of northern Norway, and the east coast of Greenland. The lidar systems enabled exceptionally detailed measurements of orographic jets caused by the orography of Spitsbergen. Two major polar low developments over the Norwegian Sea were captured during the campaign. In the first polar low case, three f lights were carried out, providing a first-ever probing of the full life cycle of a polar low. Targeting observations by the aircraft in sensitive areas led to improvements in predicted track and intensity of the polar low. Here highlights from the field campaign, as well as from ongoing follow-up investigations, are presented. Highlights from the development of a new limitedarea model ensemble prediction system for the Arctic, as well as an exploitation of new satellite data [Infrared Atmospheric Sounding Interferometer (IASI) data], are also included.

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L. Liu
,
D. Shawki
,
A. Voulgarakis
,
M. Kasoar
,
B. H. Samset
,
G. Myhre
,
P. M. Forster
,
Ø. Hodnebrog
,
J. Sillmann
,
S. G. Aalbergsjø
,
O. Boucher
,
G. Faluvegi
,
T. Iversen
,
A. Kirkevåg
,
J.-F. Lamarque
,
D. Olivié
,
T. Richardson
,
D. Shindell
, and
T. Takemura

Abstract

Atmospheric aerosols such as sulfate and black carbon (BC) generate inhomogeneous radiative forcing and can affect precipitation in distinct ways compared to greenhouse gases (GHGs). Their regional effects on the atmospheric energy budget and circulation can be important for understanding and predicting global and regional precipitation changes, which act on top of the background GHG-induced hydrological changes. Under the framework of the Precipitation Driver Response Model Intercomparison Project (PDRMIP), multiple models were used for the first time to simulate the influence of regional (Asian and European) sulfate and BC forcing on global and regional precipitation. The results show that, as in the case of global aerosol forcing, the global fast precipitation response to regional aerosol forcing scales with global atmospheric absorption, and the slow precipitation response scales with global surface temperature response. Asian sulfate aerosols appear to be a stronger driver of global temperature and precipitation change compared to European aerosols, but when the responses are normalized by unit radiative forcing or by aerosol burden change, the picture reverses, with European aerosols being more efficient in driving global change. The global apparent hydrological sensitivities of these regional forcing experiments are again consistent with those for corresponding global aerosol forcings found in the literature. However, the regional responses and regional apparent hydrological sensitivities do not align with the corresponding global values. Through a holistic approach involving analysis of the energy budget combined with exploring changes in atmospheric dynamics, we provide a framework for explaining the global and regional precipitation responses to regional aerosol forcing.

Open access
C. Holstein-Rathlou
,
J. Merrison
,
J. J. Iversen
,
A. B. Jakobsen
,
R. Nicolajsen
,
P. Nørnberg
,
K. Rasmussen
,
A. Merlone
,
G. Lopardo
,
T. Hudson
,
D. Banfield
, and
G. Portyankina

Abstract

Reliable and accurate environmental sensing is a cornerstone of modern meteorology. This paper presents a laboratory environmental simulator capable of reproducing extreme environments and performing tests and calibrations of meteorological sensor systems under controlled conditions. This facility is available to the research community as well as industry and is intended to encourage advancement in the field of sensor metrology applied to meteorology and climatology. Discussion will be made of the temperature, pressure, humidity and wind flow control, and sensing systems with reference to specific sensor test programs and future research activities.

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G. Myhre
,
P. M. Forster
,
B. H. Samset
,
Ø. Hodnebrog
,
J. Sillmann
,
S. G. Aalbergsjø
,
T. Andrews
,
O. Boucher
,
G. Faluvegi
,
D. Fläschner
,
T. Iversen
,
M. Kasoar
,
V. Kharin
,
A. Kirkevåg
,
J.-F. Lamarque
,
D. Olivié
,
T. B. Richardson
,
D. Shindell
,
K. P. Shine
,
C. W. Stjern
,
T. Takemura
,
A. Voulgarakis
, and
F. Zwiers

Abstract

As the global temperature increases with changing climate, precipitation rates and patterns are affected through a wide range of physical mechanisms. The globally averaged intensity of extreme precipitation also changes more rapidly than the globally averaged precipitation rate. While some aspects of the regional variation in precipitation predicted by climate models appear robust, there is still a large degree of intermodel differences unaccounted for. Individual drivers of climate change initially alter the energy budget of the atmosphere, leading to distinct rapid adjustments involving changes in precipitation. Differences in how these rapid adjustment processes manifest themselves within models are likely to explain a large fraction of the present model spread and better quantifications are needed to improve precipitation predictions. Here, the authors introduce the Precipitation Driver and Response Model Intercomparison Project (PDRMIP), where a set of idealized experiments designed to understand the role of different climate forcing mechanisms were performed by a large set of climate models. PDRMIP focuses on understanding how precipitation changes relating to rapid adjustments and slower responses to climate forcings are represented across models. Initial results show that rapid adjustments account for large regional differences in hydrological sensitivity across multiple drivers. The PDRMIP results are expected to dramatically improve understanding of the causes of the present diversity in future climate projections.

Full access