Joel R. Norris

• Ph.D.
• Professor (Full) at University of California, San Diego

We apply the Ralph et al. (2019) scaling method to a reanalysis dataset to examine the climatology and variability of landfalling atmospheric rivers (ARs) along the western North American coastline during 1980–2019. The local perspective ranks AR intensity on a scale from 1 (weak) to 5 (strong) at each grid point along the coastline. The object-bas...

How clouds respond to anthropogenic sulfate aerosols is one of the largest sources of uncertainty in the radiative forcing of climate over the industrial era. This uncertainty limits our ability to predict equilibrium climate sensitivity (ECS)-the equilibrium global warming following a doubling of atmospheric CO2. Here, we use satellite observation...

Shortwave radiative feedbacks from Southern Ocean clouds are a major source of uncertainty in climate projections. Much of this uncertainty arises from changes in cloud scattering properties and lifetimes that are caused by changes in cloud thermodynamic phase. Here we use satellite observations to infer the scattering component of the cloud-phase...

Marine low clouds strongly cool the planet. How this cooling effect will respond to climate change is a leading source of uncertainty in climate sensitivity, the planetary warming resulting from CO2 doubling. Here, we observationally constrain this low cloud feedback at a near-global scale. Satellite observations are used to estimate the sensitivit...

The impact of aerosols produced by biomass burning on the stratocumulus‐to‐cumulus transition (SCT) in the equatorial Atlantic is studied using satellite‐based and reanalysis data for the month of June. The month of June is highlighted because it represents monsoon onset as well as the largest sea surface temperature gradient in the summer, which i...

Combined airborne, shipboard, and satellite measurements provide the first observational assessment of all major terms of the vertically integrated water vapor (IWV) budget for a 150 km × 160 km region within the core of a strong atmospheric river over the northeastern Pacific Ocean centered on 1930 UTC 5 February 2015. Column-integrated moisture f...

We assess evidence relevant to Earth's equilibrium climate sensitivity per doubling of atmospheric CO2, characterized by an effective sensitivity S. This evidence includes feedback process understanding, the historical climate record, and the paleoclimate record. An S value lower than 2 K is difficult to reconcile with any of the three lines of evi...

A variety of satellite and ground-based observations are used to study how diurnal variations of cloud radiative heating affect the life cycle of anvil clouds over the tropical western Pacific Ocean. High clouds thicker than 2 km experience longwave heating at cloud base, longwave cooling at cloud top, and shortwave heating at cloud top. The shortw...

The impact of initial states and meteorological variables on stratocumulus cloud dissipation time over coastal land is investigated using a mixed-layer model. A large set of realistic initial conditions and forcing parameters are derived from radiosonde observations and numerical weather prediction model outputs, including total water mixing ratio...

Understanding how marine low clouds and their radiative effects respond to changing meteorological conditions is crucial to constrain low cloud feedbacks to greenhouse warming and internal climate variability. In this study, we use observations to quantify the low-cloud radiative response to meteorological perturbations over the global oceans to sh...

Despite numerous studies documenting the importance of atmospheric rivers (AR) to the global water cycle and regional precipitation, the evolution of their water vapor fluxes has been difficult to investigate given the challenges of observing and modeling precipitation processes within ARs over the ocean. This study uses satellite-based radar refle...

The pre-cold-frontal low-level jet (LLJ) is an important contributor for water vapor transport within atmospheric rivers, though its dynamics are not completely understood. The present study investigates the LLJ using dropsonde observations from 24 cross-atmospheric river transects taken during the CalWater-2014, 2015 and the AR-Recon 2016, 2018 fi...

This study uses observations and atmospheric reanalysis products in order to understand the impacts of smoke aerosols advected from the Southern Hemisphere on the dynamics of the West African monsoon. Seasonal biomass burning and resulting aerosol emissions have been well documented to affect regional weather patterns, especially low-level convecti...

Analysis of a strong landfalling atmospheric river is presented that compares the evolution of a control simulation with that of an adjoint-derived perturbed simulation using the Coupled Ocean/Atmosphere Mesoscale Prediction System. The initial condition sensitivities are optimized for all state variables to maximize the accumulated precipitation w...

Global radiative‐convective equilibrium simulations are used to investigate the hypothesis that mutual interactions among cloud albedo, sea surface temperature gradients, and atmospheric circulation constrain the net cloud radiative effect (CRE) to be similar in convective and nonconvective regions over the tropical warm pools. We perform an experi...

A research vessel sailing across a warm eddy in the Kuroshio Extension on 13 April 2016 captured an abrupt development of stratocumulus under synoptic high pressure. Shipboard observations and results from regional atmospheric model simulations indicate that increased surface heat flux over the ocean eddy lowered surface pressure and thereby accele...

Understanding the drivers of surface melting in West Antarctica is crucial for understanding future ice loss and global sea level rise. This study identifies atmospheric drivers of surface melt on West Antarctic ice shelves and ice sheet margins and relationships with tropical Pacific and high-latitude climate forcing using multi-decadal reanalysis...

This study examines changes in Earth’s energy budget during and after the global warming “pause” (or “hiatus”) using observations from the Clouds and the Earth’s Radiant Energy System. We find a marked 0.83 ± 0.41 Wm−2 reduction in global mean reflected shortwave (SW) top-of-atmosphere (TOA) flux during the three years following the hiatus that res...

The response to warming of tropical low-level clouds including both marine stratocumulus and trade cumulus is a major source of uncertainty in projections of future climate. Climate model simulations of the response vary widely, reflecting the difficulty the models have in simulating these clouds. These inadequacies have led to alternative approach...

Clouds play a major role in the climate system, but large uncertainties remain about their decadal variations. Here we report a widespread decrease in cloud cover since the 1970 s over the Mediterranean region, in particular during the 1970 s–1980 s, especially in the central and eastern areas and during springtime. Confidence in these findings is...

Using data from the International Satellite Cloud Climatology Project (ISCCP), we examine how near-global (60°N–60°S) high cloud fraction varies over time in the past three decades. Our focus is on identifying dominant modes of variability and associated spatial patterns, and how they are related to sea surface temperature. By performing the princi...

The response to warming of tropical low-level clouds including both marine stratocumulus and trade cumulus is a major source of uncertainty in projections of future climate. Climate model simulations of the response vary widely, reflecting the difficulty the models have in simulating these clouds. These inadequacies have led to alternative approach...

Clouds substantially affect Earth's energy budget by reflecting solar radiation back to space and by restricting emission of thermal radiation to space. They are perhaps the largest uncertainty in our understanding of climate change, owing to disagreement among climate models and observational datasets over what cloud changes have occurred during r...

Clouds are an important regulator of climate due to their connection to the water balance of the atmosphere and their interaction with solar and infrared radiation. In this study, monthly total cloud cover (TCC) records from different sources have been inter-compared on annual and seasonal basis for the Mediterranean region and the period 1984–2005...

The breakup of stratocumulus clouds over coastal land areas is studied using a combination of large-eddy simulations (LESs) and mixed-layer models (MLMs) with a focus on mechanisms regulating the timing of the breakup. In contrast with stratocumulus over ocean, strong sensible heat flux over land prevents the cloud layer from decoupling during day....

The Atlantic Multidecadal Oscillation (AMO) is characterized by a horseshoe pattern of sea surface temperature (SST) anomalies and has a wide range of climatic impacts. While the tropical arm of AMO is responsible for many of these impacts, it is either too weak or completely absent in many climate model simulations. Here we show, using both observ...

Large uncertainty remains on how subtropical clouds will respond to anthropogenic climate change and therefore whether they will act as a positive feedback that amplifies global warming or negative feedback that dampens global warming by altering Earth's energy budget. Here, we reduce this uncertainty using an observationally constrained formulatio...

The summertime California Current System (CCS) is characterized by energetic mesoscale eddies, whose sea surface temperature (SST) and surface current can significantly modify the wind stress and Ekman pumping. Relative importance of the eddy-wind interactions via SST and surface current in the CCS is examined using a high-resolution (7 km) regiona...

The importance of low-level cloud feedbacks to climate sensitivity motivates an investigation of how low-level cloud amount and related meteorological conditions have changed in recent decades in subtropical stratocumulus regions. Using satellite cloud datasets corrected for inhomogeneities, it is found that during 1984-2009 low-level cloud amount...

One the main limitations when studying clouds and their associated radiative effects is related to the difficulties in obtaining temporal homogeneous observations of clouds. In this study, total cloud cover trends from surface observations over land (EECRA) for the Mediterranean area since 1971 have been examined. Then, the observed changes have be...

Climate models' simulation of clouds over the eastern subtropical oceans contributes to large uncertainties in projected cloud feedback to global warming. Here, interannual relationships of cloud radiative effect and cloud fraction to meteorological variables are examined in observations and in models participating in phases 3 and 5 of the Coupled...

Adetailed derivation of stratocumulus cloud thickness and liquid water path tendencies as a function of the well-mixed boundary layer mass, heat, and moisture budget equations is presented. The derivation corrects an error in the cloud thickness tendency equation derived by R. Wood to make it consistent with the liquid water path tendency equation...

The International Satellite Cloud Climatology Project (ISCCP) dataset and the Pathfinder Atmospheres-Extended (PATMOS-x) dataset are two commonly used multidecadal satellite cloud records. Because they are constructed from weather satellite measurements lacking long-term stability, ISCCP and PATMOS-x suffer from artifacts that inhibit their use for...

The main limitation when studying changes in cloud forcing and their associated radiative fluxes effects is related to the difficulties in obtaining long-term and homogeneous observations of clouds. In this study, total cloud cover trends provided by different global databases have been compared among them for the Mediterranean region, and for the...

Recent estimates indicate that the Antarctic sea ice cover is expanding at a statistically significant rate with a magnitude one-third as large as the rapid rate of sea ice retreat in the Arctic. However, during the mid-2000s, with several fewer years in the observational record, the trend in Antarctic sea ice extent was reported to be considerably...

A sharp sea surface temperature front develops between the warm water of the Gulf Stream and cold continental shelf water in boreal winter. This front has a substantial impact on the marine boundary layer. The present study analyzes and synthesizes satellite observations and reanalysis data to examine how the sea surface temperature front influence...

The evidence of climate change from observations of the atmosphere and surface has grown significantly during recent years. At the same time new improved ways of characterizing and quantifying uncertainty have highlighted the challenges that remain for developing long-term global and regional climate quality data records. Currently, the obser¬vatio...

The tropical belt has widened by several degrees latitude since 1979, as evidenced by shifts in atmospheric circulation and climate zones1–5. Global climate models also simulate tropical belt widening, but less so than observed6,7. Reasons for this discrepancy and the mechanisms driving the expansion are uncertain. Here we analyse multidecadal vari...

Constraining intermodel spread in cloud feedback with observations is problematic because available cloud datasets are affected by spurious behavior in long-term variability. This problem is addressed by examining cloud amount in three independent ship-based [Extended Edited Cloud Reports Archive (EECRA)] and satellite-based [International Satellit...

Recent estimates indicate that the Antarctic sea ice cover is expanding at a statistically significant rate with a magnitude one third as large as the rapid rate of sea ice retreat in the Arctic. However, during the mid-2000s, with several fewer years in the observational record, the trend in Antarctic sea ice extent was reported to be considerably...

Conventional wisdom suggests that subsidence favors the presence of marine stratus and stratocumulus because regions of enhanced boundary layer cloudiness are observed to climatologically co-occur with regions of enhanced subsidence. Here it is argued that the climatological positive correlation between subsidence and cloudiness is not the result o...

1] Observations from the Global Energy Balance Archive indicate regional decreases in all sky surface solar radiation from 1950s to 1980s, followed by an increase during the 1990s. These periods are popularly called dimming and brightening, respectively. Removal of the radiative effects of cloud cover variability from all sky surface solar radiatio...

Measurements by the Multiangle Imaging SpectroRadiometer (MISR) instrument exhibit a decreasing trend in global mean effective cloud top height (2000-2011). Here we show that this trend is likely related to an artifact in the data present during the early years of the MISR mission that caused a systematic reduction in the number of retrievals of cl...

This paper highlights how the emerging record of satellite observations from the Earth Observation System (EOS) and A-Train constellation are advancing our ability to more completely document and understand the underlying processes associated with variations in the Earth’s top-of-atmosphere (TOA) radiation budget. Large-scale TOA radiation changes...

Several recent studies have shown the width of the tropical belt has increased over the last several decades. The mechanisms driving tropical expansion are not well known and the recent expansion is underpredicted by state-of-the art GCMs. We use the CAM3 GCM to investigate how tropical width responds to idealized atmospheric heat sources, focusing...

Observational analyses have shown the width of the tropical belt increasing in recent decades as the world has warmed. This expansion is important because it is associated with shifts in large-scale atmospheric circulation and major climate zones. Although recent studies have attributed tropical expansion in the Southern Hemisphere to ozone depleti...

Large and persistent decks of marine stratocumulus clouds (MSC) exist under large-scale free-tropospheric subsidence over the eastern subtropical oceans. Over seasonal and inter-annual timescales, MSC fraction is positively correlated to pressure vertical velocity, such that enhanced subsidence tends to occur when MSC fraction is large. We hypothes...

One robust projection of global climate models is that the height of high-level cloud tops will increase with CO2 warming due to fixed anvil temperature in the tropics and rising tropopause height in the extratropics. A rise in cloud top height will generally lead to less LW cloud top emission relative to surface emission and thus act as a positive...

Several recent studies have shown the width of the tropical belt has increased over the last several decades. The mechanisms driving tropical expansion are not well known and the recent expansion is underpredicted by state-of-the art GCMs. We use the CAM3 GCM to investigate how tropical width responds to idealized atmospheric heat sources, focusing...

Recent research indicates that the width of the Tropics has expanded during the past several decades. One likely consequence of this expansion is the poleward retreat of optically thick clouds associated with the extratropical storm tracks. A shift of these strongly reflective clouds to higher latitudes would cause more solar radiation to be absorb...

Clouds play an important role in the climate system by reducing the amount of shortwave radiation reaching the surface and the amount of longwave radiation escaping to space. Accurate simulation of clouds in computer models remains elusive, however, pointing to a lack of understanding of the connection between large-scale dynamics and cloud propert...

Après avoir brièvement rappelé les propriétés des nuages et leurs effets sur le bilan radiatif de la Terre, cet article aborde la question de leurs évolutions au cours de ces dernières décennies. Il fait un tour d'horizon des difficultés rencontrées dans l'observation, qu'elle soit terrestre ou par satellite. Pour les études de climat global, la pr...

This study presents findings from the application of a new Lagrangian method used to evaluate the meteorological sensitivities of subtropical clouds in the northeast Atlantic. Parcel back trajectories are used to account for the influence of previous meteorological conditions on cloud properties, whereas forward trajectories highlight the continued...

Previous research indicates that clear-sky downward solar radiation measured at the surface over China significantly decreased by about -8.6 W m-2 per decade during 1961-1989 and insignificantly increased during 1990-1999. Furthermore, solar radiation over Japan remained relatively constant during 1971-1989 and significantly increased by +5.3 W m-2...

Aerosol indirect effects are some of the largest uncertainties of anthropogenic climate change. To estimate the first aerosol indirect radiative effect (or cloud albedo effect), we analyzed global solar irradiance measurements under completely overcast skies during the recent period of aerosol optical depth decline in Europe. Although measurements...

Clouds play an important role in the climate system by reducing the amount of shortwave radiation reaching the surface and the amount of longwave radiation escaping to space. Although dependent on type and location, clouds produce more cooling than warming in the global average. Accurate simulation of clouds in computer models remains elusive, howe...

Clouds have a large impact on Earth's radiation budget by reflecting incoming solar radiation and trapping longwave radiation emitted from the surface. The present balance could change as the atmosphere warms from increasing anthropogenic greenhouse gases, thus altering the net radiation flux and mitigating or exacerbating the initial temperature i...

Shallow subsidence and nighttime radiation inversions are a common feature throughout California, present more than 65 percent of winter days and nearly 100 percent of summer days. Our study, aimed at determining whether global changes may affect these shallow inversions, concentrated on California's South Coast and San Joaquin air basins where str...

Aerosol radiative forcings are key uncertainties in climate change. IPCC-AR4 20th century simulations, for example, largely fail to reproduce the recent observed trends in surface solar irradiance, even when radiative effects of cloud cover variations are removed. Incorrect aerosol histories are the most likely cause for the disagreement between mo...

Positve Feedback The uncertain effect of feedback between climate and clouds is one of the largest obstacles to producing more confident projections of global climate. Clement et al. (p. 460 ) examined how clouds, sea surface temperature, and large-scale atmospheric circulation vary in the Northeast Pacific region. Change in cloud coverage was the...

1] This study examines multidecadal changes in surface downward shortwave (SW) radiation flux, total cloud cover, SW cloud effect, and related parameters over China and Japan during 1960–2004 using monthly gridded data from the Global Energy Balance Archive, synoptic cloud reports, and the International Satellite Cloud Climatology Project. We use t...

1] A multidecadal decrease in downward surface solar radiation (solar ''dimming'') followed by a multidecadal increase in surface radiation (solar ''brightening'') have been reported over Europe. The trends mainly occur under cloud-free skies, and they are primarily caused by the direct aerosol radiative effect. The present study compares observed...

This chapter investigates variations in cloudiness and changes in the Earth’s radiation budget (ERB), including their connection with other parameters of the climate system. Anthropogenic aerosol emissions cause a perturbation to the physical and radiative properties of clouds. The chapter examines the radiative impacts of anthropogenic aerosol emi...

Experts consider the many roles that clouds play in the the changing climate—one of the least understood and most puzzling aspects of atmospheric science. More than half the globe is covered by visible clouds. Clouds control major parts of the Earth's energy balance, influencing both incoming shortwave solar radiation and outgoing longwave thermal...

Experts consider the many roles that clouds play in the the changing climate—one of the least understood and most puzzling aspects of atmospheric science. More than half the globe is covered by visible clouds. Clouds control major parts of the Earth's energy balance, influencing both incoming shortwave solar radiation and outgoing longwave thermal...

This chapter examines aerosol–cloud relationships, focusing on the temporal and spatial variability of clouds and aerosols. It first describes the strategies for separating aerosol and meteorological effects on clouds. The chapter then assesses the potential large-scale aerosol impacts on cloud albedo, cloud amount, and precipitation by looking at...

A multidecadal decrease in downward surface solar radiation (solar dimming) followed by a multidecadal increase in surface radiation (solar brightening) have been reported over Europe. Aerosol emissions and aerosol optical depth measurements show concurrent trends of opposite sign. Because solar irradiance trends mainly occur under cloud-free skies...

Feedbacks involving low clouds are one of the primary causes of the large range of future warming projected by climate models under increasing greenhouse gases. It has been difficult to narrow this range because the true sensitivity of these clouds to long-term changes in climate is not known. Here, we address this issue by examining decadal timesc...

Numerous studies highlight boundary-layer cloud parameterizations as the chief source of uncertainty in climate projections (IPCC 2007, ch.10). Cloud parameterizations are typically assessed through comparison of monthly mean climatologies. The present study provides a complement to this approach by instead focusing on synoptic-scale sensitivities....

Observations indicate that the amount of solar radiation reaching the surface of the Earth has varied significantly over decadal timescales during the past half century. A workshop of the Israel Science Foundation evaluated the observational evidence for global dimming and brightening (GDB), its possible causes, and its implications for the Earths...

Abstract Available from http://www.agu.org

The representation of clouds in simulations of future climate is the largest source in uncertainty in predicting the surface temperature response to a doubling of atmospheric carbon dioxide. Since climate models do not consistently represent the sign and magnitude of cloud feedbacks on the climate system, we instead estimate these quantities from o...

This study uses MODIS cloud-top temperature, MISR stereoscopic cloud-top height, (AMSR-E) sea surface temperature, and AIRS tropospheric temperature to estimate the jump in temperature at the marine boundary layer-free troposphere interface as well as the magnitude of decoupling between the cloud layer and subcloud layer in marine stratocumulus reg...

Several recent studies have reported a substantial correlation between satellite retrievals of aerosol optical depth (AOD) and cloud fraction, which is ascribed to an aerosol microphysical mechanism. Another possible explanation, however, is that the history of meteorological forcing controls both AOD and cloud fraction. The present study examines...

We examine multidecadal changes in surface downward shortwave (SW) radiation flux, total cloud cover, SW cloud effect, and related parameters over Europe during 1965-2004 using monthly gridded data from the Global Energy Balance Archive (GEBA), synoptic cloud reports, and the International Satellite Cloud Climatology Project (ISCCP). One key issue...

An examination of interannual low-level cloud variability within and on the northern edge of the South American stratocumulus deck indicates atmospheric advection over varying SST has a prominent role on the southern edge of the equatorial cold tongue. Analysis of International Satellite Cloud Climatology Project (ISCCP) and NCEP reanalysis data sh...

This study documents multidecadal variations in low-level, upper-level, and total cloud cover over land and ocean independently obtained from surface synoptic observations and from satellite data produced by the International Satellite Cloud Climatology Project. Substantial agreement exists between global mean time series of surface- and satellite-...

Global changes in cloud properties have the potential to significantly impact the Earth's energy balance. Due to the strong cooling effect of stratocumulus clouds, it is of particular importance to quantify their sensitivities to changing aerosol and dynamical forcings. Prior observational studies have shown instantaneous correlations between aeros...

A new technique is presented for quantifying the impacts of aerosols on clouds while controlling for variations in meteorology. Few observational studies have quantified aerosol-cloud impacts at regional or larger scales. The recent work of Kaufman et al (PNAS, 2005) has shown observational evidence for large aerosol effects on clouds. We present w...

Analysis of surface and satellite measurements of clouds and downward solar radiation at the surface shows a decreasing trend in surface solar flux until the mid 1980s followed by an increasing trend thereafter. The occurrence of "solar dimming" followed by "solar brightening" is especially obvious after the radiative effects of interannual cloud c...

Extratropical atmosphere–ocean variability over the Northern Hemisphere of the Community Climate System Model version 3 (CCSM3) is examined and compared to observations. Results are presented for an extended control integration with a horizontal resolution of T85 (1.4°) for the atmosphere and land and 1° for the ocean and sea ice. Several atmosphe...

Contrasts in high-elevation surface and free-tropospheric temperatures between 1971 and 1996 are examined by comparing surface temperatures from a subset of 72 stations in the GHCN (Global Historical Climate Network) and CRU (Climatic Research Unit) homogeneity adjusted surface data sets with free-air temperatures interpolated to the same locations...

Previous studies indicate that substantial changes in solar radiation measured at the surface have occurred over the past several decades in many regions of the world, but it has been difficult to validate these results with independent data since many of the trends happened before the satellite record began. Synoptic cloud reports provide an alter...

1] This study investigates the spatial pattern of linear trends in surface-observed upper-level (combined midlevel and high-level) cloud cover, precipitation, and surface divergence over the tropical Indo-Pacific Ocean during 1952–1997. Cloud values were obtained from the Extended Edited Cloud Report Archive (EECRA), precipitation values were obtai...

ABSTRACT Daily satellite cloud observations,and reanalysis dynamical,parameters,are analyzed,to determine,how midtropospheric,vertical velocity and advection,over the sea surface temperature gradient control midlati- tude North Pacific cloud properties. Optically thick clouds with high tops are generated by synoptic ascent, but two different cloud...

1] Global climate models typically do not correctly simulate cloudiness associated with midlatitude synoptic systems because coarse grid spacing prevents them from resolving dynamics occurring at smaller scales and there exist no adequate parameterizations for the effects of these subgrid-scale dynamics. Comparison of modeled and observed cloud pro...

1] Global climate models (GCMs) produce large errors in cloudiness and cloud radiative forcing when simulating midlatitude, synoptic-scale cloud systems. This is because they do not represent the subgrid-scale processes in these systems that create subgrid variability in cloud optical thickness and cloud top pressure. Improving GCM performance will...