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Research Interests
I am interested in using a combination of observations, climate model simulations, and model experiments to better understand the processes that form, maintain, and dissipate clouds so that we might better predict how clouds will respond to changes in ambient aerosol concentrations and to global warming. My interests also lie in better understanding what controls precipitation at both the global and local scale. You can find some more details of the different projects below.
Using the ten hundred most common words (reference)
The soft-looking, white things made of water in our sky can help cool the blue and green ball we live on by kicking the sun light back to space. They can also make rain and move water from lower to higher areas in our skies. I study how these soft, white things will respond to world wide warming and to having more tiny bits in the air and check whether a number expression of the world made by computers can show these changes.
Image credits: MODIS
Projects below:
Optical depth feedback
Global water cycle
Precipitation susceptibility
Cold pools
Pocket of Open Cells
Aerosol-cloud interactions in climate models
Image credits: MODIS
Low-cloud optical depth feedback
Low clouds with warming
Models predict brightening
Nay, say satellites*
Satellite analysis
Studies of satellite cloud retrievals from two decades ago showed that optical depths of low-level clouds respond to changes in air temperature at daily to seasonal timescales and that they increase with warming over cold continents. A more recent study by Gordon and Klein (2014) found that in current state-of-the-art climate models, the cloud optical depth response to temperature variations at shorter timescales (daily to seasonal) in the control climate correlate with the low-cloud optical depth response due to CO2-forced warming.
Following on this previous work, our study quantifies the temperature-only mediated response of cloud optical depth by examining the response in AMIP-style simulations where atmosphere-only climate models are constrained by prescribed sea surface temperatures representing the current and warmed climate. As in previous studies, we found that across climate model across climate model, the cloud optical depth responses to temperature at the short timescales (interannual response) correlates with the response from a uniform SST warming of 4K (r < 0.7). However, most models overestimate the increase in optical depth with warming, compared to satellite estimates, and most models also do not capture the increase in optical depth with increased estimated inversion strength.
If we replace the models' optical depth sensitivities with that of the satellites', we find the magnitude of the negative shortwave cloud feedback is reduced by at least 50% in the 40°–70°S latitude band and by at least 65% in the 40°–70°N latitude band.
Terai, C. R., S. A. Klein, and M. D. Zelinka (2016), Constraining the low-cloud optical depth feedback at middle and high latitudes using satellite observations, J. Geophys. Res.
ARM ground-based observation analysis
I worked with Yunyan Zhang and colleagues to examine the ground-based measurements from 3 sites of the ARM (Atmospheric Radiation Measurement) program to test whether there is any evidence in the observations for the various mechanisms that have been proposed in the literature to drive the cloud optical depth feedback.
We find that the optical depth responds to temperature in the same way that previous satellite studies report. Most of the optical depth response can be traced to how the liquid water path responds to temperature. Digging deeper into the data, we also find that at temperatures below freezing, about half of the increase in optical depth with warming can be attributed to an increase in liquid water content that is expected from a shift to a warmer moist adiabat. The other half appears to be related to the phase-shift of the cloud population from more icy clouds to clouds that are composed mainly of liquid drops. At temperatures above freezing, the cloud liquid water path decreases with warming. In these clouds, most of the decrease in cloud water path arises from a weakening of the inversion with warming. The boundary layer also decouples with warming, which appears to be connected to a decrease in cloud water path. The findings from this analysis point to the importance of considering multiple competing mechanisms when trying to determine whether the cloud optical depth will increase or decrease with global-scale warming.
Terai, C. R., Y. Zhang, S. A. Klein, M. D. Zelinka, J. C. Chiu, and Q. Min (2019), Mechanisms Behind the Extratropical Stratiform Low‐Cloud Optical Depth Response to Temperature in ARM Site Observations, JGR-Atmos
*inspired by the twitter feed of Greg Johnson @climate_haiku
Global water cycle diagnosis
Earth's water cycle
Portrayal in lines of code
How well do we do?
This research started off as a study examining the water cycle in the Department of Energy's Accelerated Climate Modeling for Energy climate model. The study evaluated how well an early version (v0.3) of the climate model is able to represent various aspects of the global water cycle and how those simulations change when the horizontal resolution of the model is increased from 1 to 0.25 degree resolution. Although both resolutions exhibit longstanding biases, such as a global-mean precipitation rate that is too high and a precipitation distribution that is too frequent and too light, increasing the resolution does lead to improvements, such as better representing the frequency of heavy precipitation rates and the fraction of total precipitation that falls over land.
Another aspect of the study examines the effect of horizontal resolution on the general features of the global water cycle. Although the differences are not striking, there are increases in the intensity of the most intense precipitation events and a remarkable shift of precipitation from that created by the convection scheme to that created by the large-scale scheme.
In the paper, we provide an analysis framework to separate the effect of environmental features, such as column integrated humidity (precipitable water) and large-scale circulation (omega500), and the effect of model physics on the precipitation partitioning. The framework shows that the decrease in the convective precipitation with increasing resolution is mainly explained by a shift of the column relative humidity to lower values. On the other hand, the increase in the large-scale precipitation is due to an increase in the precipitation rate for given precipitable water and omega500, which is surprising because previous studies have attributed the increase in large-scale precipitation to better being able to resolve strong updrafts in the high-resolution model.
Terai, C. R., P. M. Caldwell, S. A. Klein, Q. Tang, and M. L. Branstetter (2017), The Atmospheric Hydrologic Cycle in the ACME v0.3 Model, Clim. Dyn.
Precipitation susceptibility
Tiny particles
Can more of them suppress rain?
Yes! But by how much?
The research on precipitation susceptibility attempts to get at the question: Can the concentration of aerosol particles in the air affect precipitation rates in marine stratocumulus? And by how much? Because precipitation is one of the processes by which clouds disperse, this is a relevant quantity to estimate in observations and then to compare in models if we are interested in knowing the extent to which anthropogenic aerosol emissions affect cloud properties, and hence the amount of sunlight that gets absorbed at the surface.
Many previous observational studies have found that if you increase the concentration of aerosol particles, the rain rate in warm clouds (liquid) decreases. An increase in aerosol concentration leads to more numerous and smaller cloud droplets (assuming the same amount of cloud water). This slows down the rate at which cloud droplets collide with each other to form drizzle drops. And in short, for two clouds with the same liquid water we get less rain if we have higher concentrations of aerosol particles.
Evidence supporting this hypothesis, which pertains mainly to clouds with liquid water droplets, is found in observations from past field experiments, but quantifying the sole effect of aerosol particles has always been difficult. Changes in aerosol concentrations coexist with changes in meteorology, such as changes in the thickness of clouds.
Our study accounts for the meteorology by grouping the clouds by their thickness and then examining the relationship between aerosol concentrations and rain rate in each group. When we group the clouds by their thickness, we find that the effect of aerosols on the precipitation varies with the thickness of the cloud. If we use a metric that quantifies the fractional decrease in precipitation due to the fractional increase in aerosol concentration (precipitation susceptibility), we find that the precipitation susceptibility decreases with increasing cloud thickness. We argue that most of the variation exists because in thinner clouds, aerosol concentrations can determine whether it drizzles or not, while in thicker clouds there is so much cloud water that it drizzles regardless of the aerosol concentration.
More details can be found in our paper below and related papers.
Terai, C. R., R. Wood, D. C. Leon, and P. Zuidema (2012), Does precipitation susceptibility vary with increasing cloud thickness in marine stratocumulus?, Atmos. Chem. Phys.
Gettelman, A., H. Morrison, C. R. Terai, and R. Wood (2013), Microphysical Process Rates and Global Aerosol-Cloud Interactions, Atmos. Chem. Phys.
Terai, C. R., R. Wood, and T. L. Kubar (2015), Satellite estimates of precipitation susceptibility in low-level marine stratiform clouds, J. Geophys. Res. Atmos.
Cold pools under stratocumulus
Drizzle falls from clouds
Cooling and stratifying
Plane captures their traits
In this study, we characterized the cold pools that were observed by the C-130 aircraft over the southeast Pacific Ocean. Cold pools form from the cooling induced by the evaporation of drizzle under precipitating clouds. Usually, previous studies have mainly examined cold pools that form under deep cumulonimbus and their effects on the storm. Although their exact effect on stratocumulus cloud fields is still being examined, cold pools have been found under stratocumulus cloud decks that transition from stratiform to cumulus-like clouds due to heavy drizzle (POCs) and model simulations also suggest that cold pools help speed up this transition.
Using data from the research flights of the NSF/NCAR C-130 flown during VOCALS, we documented the environment and conditions in which we observed the cold pools. We also looked at the thermodynamic, dynamic, and chemical characteristics associated with the cold pool air mass.
More details can be found in our paper below.
Terai, C. R. and R. Wood (2013), Aircraft observations of cold pools under marine stratocumulus, Atmos. Chem. Phys.
Pocket of open cells (POCs)
Break in the cloud sheet
Pocket in the white blanket
Cleanest place on Earth?
Pockets of open cells, or POCs, are regions of organized cumulus clouds (open-cell convection) that form largely embedded within a larger overcast deck of stratocumulus clouds (closed-cell convection - see satellite image on the right). One of the main objectives of the VOCALS field program was to make measurements within POCs to determine the shared properties among different POCs and those properties that vary from POC to POC.
Aircraft measurements from five different POC cases were used to quantify the cloud, boundary layer, and aerosol properties that differentiate the POC from the surrounding overcast clouds. At the same time, we asked whether the POCs formed under special circumstances, compared to the typical conditions found over the southeast Pacific.
As found by previous studies reporting measurements made within POCs, we found that all POCs shared the characteristic of having higher frequencies of intense precipitation, a more decoupled boundary layer, and very low accumulation-mode aerosol concentrations (24 to 40 cm-3). However, the surface and free-tropospheric conditions under which these POCs were observed show no remarkable difference from the observed conditions during the whole two months of the field campaign. Our paper with the findings can be found in the link below.
Terai, C. R., C. S. Bretherton, R. Wood, and G. Painter (2014), Aircraft observations of aerosol, cloud, precipitation, and boundary layer properties in pockets of open cells over the southeast Pacific, Atmos. Chem. Phys.
Related work on POCs has involved examining and quantifying the collision-coalescence rates in POC clouds. These process rates help us understand the rates at which precipitation is formed in clouds and the rate at which aerosols are cleaned out from the collision of cloud and drizzle drops.
Aerosol-cloud interactions in climate models
My most recently completed project has involved studying aerosol-cloud interactions in the climate modeling framework. We investigated the impact of semi-resolving the largest of boundary layer eddies on the strength of ACI and the processes underlying any differences in a global model. We found that in the UPCAM model (with more resolved boundary-layer eddies), the liquid water path does not increase as much in response to increased aerosol concentrations because there are fewer raining clouds and there are decreases in the liquid water path with increased aerosols in non-raining clouds in UPCAM .
Skim (or read) our publication for more details: C. R. Terai, M. S. Pritchard, P. Blossey, and C. S. Bretherton (2020), The impact of resolving sub-kilometer processes on aerosol-cloud interactions in global model simulations, JAMES
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