Clara Orbe

• National Aeronautics and Space Administration

Under climate change driven by increased carbon dioxide (CO2) concentrations, stratospheric ozone will respond to temperature and circulation changes, and lead to chemistry-climate feedback by modulating large-scale atmospheric circulation and Earth's energy budget. However, there is a significant model uncertainty since many processes are involved...

Previous studies found many climate properties such as northern hemisphere (NH) surface temperature and precipitation respond non-monotonically when CO2 is increased from 1× to 8×CO2 relative to pre-industrial levels. Here, we explore the robustness of the non-monotonicity in the NH precipitation response in 11 coupled climate models. Eight models...

Stratosphere-troposphere Processes And their Role in Climate (SPARC) Quasi-Biennial Oscillation initiative (QBOi) project has conducted new experiments to explore the modulation of the QBO by El Niño-Southern Oscillation (ENSO). This paper provides an overview of the experiment design and investigates the modulation of the QBO by ENSO using nine cl...

In the Southern Hemisphere, Earth system models project an intensification of winter storm tracks by the end of the twenty-first century. Previous studies using idealized models showed that storm track intensity saturates with increasing temperatures, suggesting that the intensification of the winter storm tracks might not continue further with inc...

Previous studies found many climate properties such as northern hemisphere (NH) surface temperature and precipitation respond non-monotonically when CO2 is increased from 1x to 8xCO2 relative to pre-industrial levels. Here, we explore the robustness of the non-monotonicity in NH precipitation response in 11 coupled climate models. Eight models show...

Trace gases and aerosols play a crucial role in shaping Arctic climate through their impacts on radiation and chemistry. The concentration of these substances over the Arctic is largely determined by long-range transport originating from midlatitude and tropical source regions. In this study, we explore how atmospheric circulation modulates the int...

Stratospheric ozone, and its response to anthropogenic forcings, provide an important pathway for the coupling between atmospheric composition and climate. In addition to stratospheric ozone’s radiative impacts, recent studies have shown that changes in the ozone layer due to 4xCO 2 have a considerable impact on the Northern Hemisphere (NH) troposp...

Trace gases and aerosols play a crucial role in shaping Arctic climate through their impacts on radiation and chemistry. The concentration of these substances over the Arctic is largely determined by long-range transport originating from midlatitude and tropical source regions. In this study, we explore how atmospheric circulation modulates the int...

Observational studies have shown that the El Niño–Southern Oscillation (ENSO) exerts an influence on the Quasi-Biennial Oscillation (QBO). The downward propagation of the QBO tends to speed up and slow down during El Niño and La Niña, respectively. Recent results from general circulation models have indicated that the ENSO modulation of the QBO req...

Volcanic super-eruptions have been theorized to cause severe global cooling, with the 74 kya Toba eruption purported to have driven humanity to near-extinction. However, this eruption left little physical evidence of its severity and models diverge greatly on the magnitude of post-eruption cooling. A key factor controlling the super-eruption climat...

Apparent hydrological sensitivity (ηa), the change in the global mean precipitation per degree K of global surface warming, is a key aspect of the climate system's response to increasing CO2 forcing. To determine whether ηa depends on the forcing amplitude we analyze idealized experiments over a broad range of abrupt CO2 forcing, from 2× to 8× prei...

Plain Language Summary Observations show a strong link between the stratospheric quasi‐biennial oscillation (QBO)—the alternation of tropical stratospheric zonal winds between easterly and westerly phases—and the Madden‐Julian oscillation (MJO), an eastward propagating phenomenon in the tropical troposphere in which the circulation and convection a...

Effective climate sensitivity (EffCS), commonly estimated from model simulations with abrupt 4×CO2 for 150 years, has been shown to depend on the CO2 forcing level. To understand this dependency systematically, we performed a series of simulations with a range of abrupt CO2 forcing in two climate models. Our results indicate that normalized EffCS v...

Understanding how the transport of gases and aerosols responds to climate change is necessary for policy making and emission controls. There is considerable spread in model projections of tracer transport in climate change simulations, largely because of the substantial uncertainty in projected changes in the large‐scale atmospheric circulation. In...

Climate models project a future weakening of the Atlantic Meridional Overturning Circulation (AMOC), but the impacts of this weakening on climate remain highly uncertain. A key challenge in quantifying the impact of an AMOC decline is in isolating its influence on climate, relative to other changes associated with increased greenhouse gases. Here w...

Extreme cold events over North America such as the February 2021 cold wave have been suggested to be linked to stratospheric polar vortex stretching. However, it is not resolved how robustly and on which timescales the stratosphere contributes to the surface anomalies. Here we introduce a simple measure of stratospheric wave activity for reanalyses...

Observational studies have shown that the El Niño–Southern Oscillation (ENSO) exerts an influence on the Quasi-Biennial Oscillation (QBO). The downward propagation of the QBO tends to speed up and slow down during El Niño and La Niña, respectively. Recent results from general circulation models have indicated that the ENSO modulation of the QBO req...

A 10-member ensemble simulation with the NASA GISS-E2-1-G climate model shows a clear bifurcation in the Atlantic meridional overturning circulation (AMOC) strength under the SSP2–4.5 extended scenario. At 26°N, the bifurcation leads to 8 strong AMOC and 2 much weaker AMOC states, while at 48°N, it leads to 8 stable AMOC-on and 2 nearly AMOC-off st...

There are a myriad of ways atmospheric circulation responds to increased CO 2 . In the troposphere, the region of the tropical upwelling narrows, the Hadley Cells expand, and the upper level subtropical zonal winds that comprise the subtropical jet strengthen. In the stratosphere, the tropical upwelling narrows and strengthens, enhancing the Brewer...

We examine multiple factors in the representation of satellite‐retrieved atmospheric temperature diagnostics in historical simulations of climate change during the satellite era (specifically 1979–2021) using GISS ModelE contributions to the Coupled Model Intercomparison Project (Phase 6) (CMIP6). The tropospheric and stratospheric trends in these...

This paper presents the response to anthropogenic forcing in the GISS‐E2.1 climate models for the 21st century Shared Socioeconomic Pathways emission scenarios within the Coupled Model Intercomparison Project Phase 6 (CMIP6). The experiments were performed using an updated and improved version of the NASA Goddard Institute for Space Studies (GISS)...

Plain Language Summary Equilibrium climate sensitivity is the global mean warming after doubling CO2 concentrations from those of the year 1850. Since CO2 levels will likely surpass a doubling, it is crucial to know whether the amount of warming per CO2 doubling (which we refer to as the effective climate sensitivity, SG) is constant with each CO2...

We investigate wintertime extreme sea ice loss events on synoptic to subseasonal time scales over the Barents-Kara Sea, where the largest sea ice variability is located. Consistent with previous studies, extreme sea ice loss events are associated with moisture intrusions over the Barents-Kara Sea, which are driven by the large-scale atmospheric cir...

Climate models project an intensification of the wintertime North Atlantic Ocean storm track, over its downstream region, by the end of this century. Previous studies have suggested that ocean–atmosphere coupling plays a key role in this intensification, but the precise role of the different components of the coupling has not been explored and quan...

The impact of volcanic eruptions on surface climate is well‐appreciated, but their in situ impact on the Quasi‐Biennial Oscillation (QBO) has received comparatively little attention. This study examines the QBO responses to Krakatoa and Pinatubo using five configurations of the NASA Goddard Institute for Space Studies Model E2.2 and MERRA‐2 reanaly...

The enhanced warming of the Arctic, relative to other parts of the Earth, a phenomenon known as Arctic amplification, is one of the most striking features of climate change, and has important climatic impacts for the entire Northern Hemisphere. Several mechanisms are believed to be responsible for Arctic amplification; however, a quantitative under...

The mean age since air was last at the Northern Hemisphere (NH) midlatitude surface is a fundamental property of tropospheric transport. Here we approximate the mean age in terms of an “SF6 age” (ΓSF6), derived from surface and aircraft measurements of SF6 that are broader in spatial scope and cover a longer time period (1997–2018) than considered...

This paper describes version 2.0 of the Global Change and Air Pollution (GCAP 2.0) model framework, a one-way offline coupling between version E2.1 of the NASA Goddard Institute for Space Studies (GISS) general circulation model (GCM) and the GEOS-Chem global 3-D chemical-transport model (CTM). Meteorology for driving GEOS-Chem has been archived fr...

The Brewer–Dobson circulation (BDC) is a key feature of the stratosphere that models need to accurately represent in order to simulate surface climate variability and change adequately. For the first time, the Climate Model Intercomparison Project includes in its phase 6 (CMIP6) a set of diagnostics that allow for careful evaluation of the BDC. Her...

This manuscript describes version 2.0 of the Global Change and Air Pollution (GCAP 2.0) model framework, a one-way offline coupling between version E2.1 of the NASA Goddard Institute for Space Studies (GISS) general circulation model (GCM) and the GEOS-Chem global 3-D chemical-transport model (CTM). Meteorology for driving GEOS-Chem has been archiv...

The Brewer-Dobson circulation (BDC) is a key feature of the stratosphere that models need to accurately represent in order to improve the representation of surface climate variability. For the first time, the Climate Model Intercomparison Project includes in its phase 6 (CMIP6) a set of diagnostics that allow for careful evaluation of the BDC. Here...

We explore the climate system response to abrupt CO2 forcing, spanning the range 1× to 8×CO2, with two state-of-the-art coupled atmosphere-ocean-sea-ice-land models: the NASA Goddard Institute for Space Studies Model E2.1-G (GISS-E2.1-G) and the Community Earth System Model (CESM-LE). We find that the effective climate sensitivity is a non-monotoni...

Long‐term projections of the Quasi‐Biennial Oscillation (QBO) remain uncertain. Using the high‐top “Middle Atmosphere” (MA) version of the NASA Goddard Institute for Space Studies (GISS) ModelE (E2.2‐AP), we show that increased CO2 reduces the QBO period and weakens its amplitude, consistent with results from recent multimodel studies. The amplitud...

Observational studies show a strong connection between the intraseasonal Madden-Julian oscillation (MJO) and the stratospheric quasi-biennial oscillation (QBO): the boreal winter MJO is stronger, more predictable, and has different teleconnections when the QBO in the lower stratosphere is easterly versus westerly. Despite the strength of the observ...

Trace gases and aerosols play an important role in Arctic chemistry and climate. As most Arctic tracers and aerosols are transported from midlatitude source regions, long‐range transport into the Arctic is one of the key factors to understand the current and future states of Arctic climate. While previous studies have investigated the airmass fract...

Simulations of the CMIP6 historical period 1850–2014, characterized by the emergence of anthropogenic climate drivers like greenhouse gases, are presented for different configurations of the NASA Goddard Institute for Space Studies (GISS) Earth System ModelE2.1. The GISS-E2.1 ensembles are more sensitive to greenhouse gas forcing than their CMIP5 p...

Here we examine the large‐scale transport characteristics of the new “Middle Atmosphere” NASA Goddard Institute for Space Studies (GISS) climate model (E2.2). First, we evaluate the stratospheric transport circulation in historical atmosphere‐only simulations integrated with interactive trace gas and aerosol chemistry. Compared to lower vertical re...

Plain Language Summary Long‐range transport plays a crucial role in determining the distribution of pollutants in the Arctic, as many pollutants have their sources in northern middle latitudes. Recent studies show large differences in transport into the Arctic among models, and it has been suggested that this is related to differences in the northe...

This paper describes the GISS-E2.1 contribution to the Coupled Model Intercomparison Project, Phase 6 (CMIP6). This model version differs from the predecessor model (GISS-E2) chiefly due to parameterization improvements to the atmospheric and ocean model components, while keeping atmospheric resolution the same. Model skill when compared to modern...

We compare the performance of several modes of variability across six US climate modeling groups, with a focus on identifying robust improvements in recent models (including those participating in the Coupled Model Intercomparison Project (CMIP) Phase 6) compared to previous versions. In particular, we examine the representation of the Madden-Julia...

One of the key questions in the air quality and climate sciences is how tropospheric ozone concentrations will change in the future. This will depend on two factors: changes in stratosphere-to-troposphere transport (STT) and changes in tropospheric chemistry. Here we aim to identify robust changes in STT using simulations from the Chemistry Climate...

We introduce a new climate model (GISS E2.2) that has been specially optimized for the middle atmosphere and whose output is being contributed to the CMIP6 archive. The top of the model is at a geopotential altitude of 89 km, and parameterizations of moist convection and various forms of gravity wave drag based on tropospheric processes are chosen...

Previous studies have robustly identified a decrease since 1998 in lower stratospheric (LS) ozone in the Northern Hemisphere (NH). While this ozone decrease is qualitatively explained as resulting from changes in the large‐scale circulation, there is not yet a quantitative mechanistic explanation of these changes. Here, we explore the drivers of re...

We provide an overview of the REF-C1SD specified-dynamics experiment that was conducted as part of phase 1 of the Chemistry-Climate Model Initiative (CCMI). The REF-C1SD experiment, which consisted of mainly nudged general circulation models (GCMs) constrained with (re)analysis fields, was designed to examine the influence of the large-scale circul...

Major sudden stratospheric warmings (SSWs), vortex formation, and final breakdown dates are key highlight points of the stratospheric polar vortex. These phenomena are relevant for stratosphere‐troposphere coupling, which explains the interest in understanding their future changes. However, up to now, there is not a clear consensus on which project...

This study identifies the fast (i.e., ∼ days–weeks) transport pathways that connect the Northern Hemisphere surface to the upper troposphere and lower stratosphere (UTLS) during northern summer by integrating a large (90 member) ensemble of Boundary Impulse Response tracers in the Whole Atmosphere Community Climate Model version 5. We show that the...

Major sudden stratospheric warmings (SSWs), vortex formation and final breakdown dates are key highlight points of the stratospheric polar vortex. These phenomena are relevant for stratosphere-troposphere coupling, which explains the interest in understanding their future changes. However, up to now, there is not a clear consensus on which projecte...

Here we provide an overview of the REF-C1SD Specified-Dynamics experiment that was conducted as part of Phase 1 of the Chemistry-Climate Model Initiative (CCMI). The REF-C1SD experiment, which consisted of mainly online general circulation models (GCMs) constrained with (re)analysis fields, was designed to examine the influence of the large-scale c...

One of the key questions in the air quality and climate sciences is how will tropospheric ozone concentrations change in the future. This will depend on two factors: changes in stratosphere-to-troposphere transport (STT) and changes in tropospheric chemistry. Here we aim to identify robust changes in STT using simulations from the Chemistry Climate...

Transport from the Northern Hemisphere (NH) midlatitudes to the Arctic plays a crucial role in determining the abundance of trace gases and aerosols that are important to Arctic climate via impacts on radiation and chemistry. Here we examine this transport using an idealized tracer with a fixed lifetime and predominantly midlatitude land-based sour...

Plain Language Summary Transport of air between hemispheres is important as most air pollutants are emitted predominantly in northern midlatitudes, and the rate of this interhemispheric transport influences the global distribution of these gases. Two recent studies analyzed simulations from two different model intercomparison projects and reached d...

Previous observational studies have found a persistent maximum in stratospheric water vapor (SWV) in the upper troposphere lower stratosphere (UTLS) confined by the upper-level anticyclone over the Asian summer monsoon region. This study investigates the simulation of SWV in the Community Earth System Model, version 1 with the Whole Atmosphere Comm...

Transport from the Northern Hemisphere (NH) midlatitudes to the Arctic plays a crucial role in determining the abundance of trace gases and aerosols that are important to Arctic climate via impacts on radiation and chemistry. Here we examine this transport using an idealized tracer with fixed lifetime and predominantly midlatitude land-based source...

The seasonal and interannual variability of transport times from the northern midlatitude surface into the Southern Hemisphere is examined using simulations of three idealized “age” tracers: an ideal age tracer that yields the mean transit time from northern midlatitudes and two tracers with uniform 50- and 5-day decay. For all tracers the largest...

Understanding and modeling the large-scale transport of trace gases and aerosols is important for interpreting past (and projecting future) changes in atmospheric composition. Here we show that there are large differences in the global-scale atmospheric transport properties among the models participating in the IGAC SPARC Chemistry–Climate Model In...

1998‐2016 ozone trends in the lower stratosphere (LS) are examined using the Modern‐Era Retrospective Analysis for Research and Applications Version 2 (MERRA‐2) and related NASA products. After removing biases resulting from step‐changes in the MERRA‐2 ozone observations, a discernible negative trend of ‐1.67±0.54 Dobson units per decade (DU/decade...

The seasonal and interannual variability of transport times from the northern mid-latitude surface into the southern hemisphere is examined using simulations of three idealized age tracers: A ideal age tracer that yields the mean transit time from northern mid-latitudes and two tracers with uniform 50-day and 5-day decay. For all tracers the larges...

Understanding and modeling the large-scale transport of trace gases and aerosols is important for interpreting past (and projecting future) changes in atmospheric composition. Here we show that there are large differences in the global-scale atmospheric transport properties among models participating in the IGAC SPARC Chemistry-Climate Model Initia...

The impacts of climate change on tropospheric transport, diagnosed from a carbon monoxide (CO)-like tracer species emitted from global CO sources, are evaluated from an ensemble of four chemistry–climate models (CCMs) contributing to the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP). Model time-slice simulations for prese...

Offline chemical transport models (CTMs) have traditionally been used to perform studies of atmospheric chemistry in a fixed dynamical environment. An alternative to using CTMs is to constrain the flow in a general circulation model using winds from meteorological analyses. The Goddard Earth Observing System (GEOS) "replay" approach involves readin...

The impacts of climate change on tropospheric transport, diagnosed from a carbon monoxide (CO)-like tracer species emitted from global CO sources, are evaluated from an ensemble of four chemistry-climate model (CCMs) contributing to the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP). Model time-slice simulations for presen...

While the importance of the seasonal migration of the zonally averaged Hadley circulation on interhemispheric transport of trace gases has been recognized, few studies have examined the role of the zonally asymmetric monsoonal circulation. This study investigates the role of monsoon-like zonally asymmetric heating on interhemispheric transport usin...

The transport of chemicals is a major uncertainty in the modeling of tropospheric composition. A common approach is to transport gases using the winds from meteorological analyses, either using them directly in a chemical transport model or by constraining the flow in a general circulation model. Here we compare the transport of idealized tracers i...

Carbon-concentration feedbacks and carbon-climate feedbacks constitute one of the largest sources of uncertainty in future climate. Since the beginning of the modern atmospheric CO2 record, seasonal variations in CO2 have been recognized as a signal of the metabolism of land ecosystems, and quantitative attribution of changes in the seasonal cycle...

The distribution of transit times from the Northern Hemisphere (NH) midlatitude surface is a fundamental property of tropospheric transport. Here, the authors present an analysis of the transit-time distribution (TTD) since air last contacted the NH midlatitude surface, as simulated by the NASA Global Modeling Initiative Chemistry Transport Model....

Future changes in transport from Northern Hemisphere (NH) midlatitudes into the Arctic are examined using rigorously defined air-mass fractions that partition air in the Arctic according to where it last had contact with the planetary boundary layer (PBL). Boreal winter (December-February) and summer (June-August) air-mass fraction climatologies ar...

A climatology of air-mass origin in the tropical lower stratosphere is presented for the Goddard Earth Observing System Chemistry Climate Model. During late boreal summer and fall, air-mass fractions reveal that as much as 20% of the air in the tropical lower stratosphere last contacted the planetary boundary layer (PBL) over Asia; by comparison, t...

The first climatology of airmass origin in the Arctic is presented in terms of rigorously defined airmass fractions that partition air according to where it last contacted the planetary boundary layer (PBL). Results from a present-day climate integration of the Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM) reveal that the majorit...

We present an analysis of the seasonally varying ventilation of the stratosphere using one-way flux distributions. Robust transport diagnostics are computed using GEOSCCM subject to fixed present-day climate forcings. From the one-way flux, we determine the mass of the stratosphere that is in transit since entry through the tropical tropopause to i...

[1] We introduce rigorously defined air masses as a diagnostic of tropospheric transport. The fractional contribution from each air mass partitions air at any given point according to either where it was last in the planetary boundary layer or where it was last in contact with the stratosphere. The utility of these air-mass fractions is demonstrate...

Stratospheric mean residence time τ¯ and mean age on the tropopause ΓΩ are shown to measure physically distinct aspects of stratospheric transport. Both ΓΩ and τ¯ are mean transit times through the stratosphere of air that enters through tropopause region Ωi and exits through region Ωf, but they represent averages over different populations of flui...

We perform the first analysis of stratosphere-troposphere exchange in terms of distributions that partition the one-way flux across the thermal tropopause according to stratospheric residence time τ and the regions where air enters and exits the stratosphere. These distributions robustly quantify one-way flux without being rendered ill defined by t...

1] The coupling between the stratosphere and troposphere following Stratospheric Sudden Warming (SSW) events is investigated in an idealized atmospheric General Circulation Model, with focus on the influence of stratospheric memory on the troposphere. Ensemble forecasts are performed to confirm the role of the stratosphere in the observed equatorwa...

Third political parties are influential in shaping American politics. In this work we study the spread of a third party ideology in a voting population where we assume that party members/activists are more influential in recruiting new third party voters than non-member third party voters. The study uses an epidemiological metaphor to develop a the...