Warm rain processes over tropical oceans and climate implications

Lau, K.-M.; Wu, Hong

doi:10.1029/2003gl018567

Cited by 197 publications

(187 citation statements)

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“…Based on a comparison of observations between monthly OLR from National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer, and daily brightness temperature from Tropical Rainfall Measuring Mission (Fig. S2), and findings from previous studies (27)(28)(29), we identify a high monthly OLR (>270 W·m −2 ) with low clouds; a moderate OLR (270-220 W·m −2 ) with middle clouds, and a low OLR (<220 W·m −2 ) with high clouds associated with deep convection. We have computed the MMM climatological probability distribution functions (pdf) of OLR and their changes due to global warming.…”

Section: Tropical Convectionmentioning

confidence: 99%

Robust Hadley Circulation changes and increasing global dryness due to CO ₂ warming from CMIP5 model projections

Lau

Kim

2015

Proc. Natl. Acad. Sci. U.S.A.

206

195

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In this paper, we investigate changes in the Hadley Circulation (HC) and their connections to increased global dryness (suppressed rainfall and reduced tropospheric relative humidity) under CO 2 warming from Coupled Model Intercomparison Project Phase 5 (CMIP5) model projections. We find a strengthening of the HC manifested in a "deep-tropics squeeze" (DTS), i.e., a deepening and narrowing of the convective zone, enhanced ascent, increased high clouds, suppressed low clouds, and a rise of the level of maximum meridional mass outflow in the upper troposphere (200−100 hPa) of the deep tropics. The DTS induces atmospheric moisture divergence and reduces tropospheric relative humidity in the tropics and subtropics, in conjunction with a widening of the subsiding branches of the HC, resulting in increased frequency of dry events in preferred geographic locations worldwide. Among various water-cycle parameters examined, global dryness is found to have the highest signal-to-noise ratio. Our results provide a physical basis for inferring that greenhouse warming is likely to contribute to the observed prolonged droughts worldwide in recent decades.Hadley Circulation | global dryness | global warming | drought T he Hadley Circulation (HC), the zonally averaged meridional overturning motion connecting the tropics and midlatitude, is a key component of the global atmospheric general circulation. How the HC has been or will be changed as a result of global warming has tremendous societal implications on changes in weather and climate patterns, especially the occurrences of severe floods and droughts around the world (1, 2). Recent studies have suggested that the global balance requirement for water vapor and precipitation weakens the tropical circulation in a warmer climate (3, 4). So far, the most robust signal of weakening of tropical circulation from models appears to come from the Walker circulation but not from the HC, possibly because of the large internal variability in the latter (5, 6). Observations based on reanalysis data have shown weak signals of increasing, decreasing, or no change in HC strength in recent decades, with large uncertainties depending on the data source and the period of analyses (7-10). Meanwhile, studies have also shown that even though water vapor is increased almost everywhere as global temperature rises, increased dryness (lack of rainfall and reduced surface relative humidity) is found in observations and in model projections, especially in many land regions around the world (11-13). Reduction in midtropospheric relative humidity and clouds in the subtropics and midlatitude under global warming have also been noted in models and observations, suggesting the importance of cloud feedback and circulation changes (14-16). Even though robust global warming signals have been found in changing rainfall characteristics (2,17,18), in the widening of the subtropics, and in the relative contributions of circulation and surface warming to tropical rainfall from climate model projections and observation...

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Section: Tropical Convectionmentioning

confidence: 99%

Robust Hadley Circulation changes and increasing global dryness due to CO ₂ warming from CMIP5 model projections

Lau

Kim

2015

Proc. Natl. Acad. Sci. U.S.A.

206

195

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“…Rainfall from 'warm clouds' (with cloud top below the freezing level) accounts for approximately 30% of the total rainfall on the planet and approximately 70% of all rainfall in the Tropics (Lau and Wu, 2003). The interaction of cloud and raindrops with radiation plays a significant role in driving the atmospheric circulation, and hence the correct representation of cloud microphysics in general circulation models for numerical weather and climate prediction is of obvious importance.…”

Section: Introductionmentioning

confidence: 99%

Droplet growth in warm turbulent clouds

Devenish

Bartello

Brenguier

et al. 2012

Quart J Royal Meteoro Soc

243

281

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In this survey we consider the impact of turbulence on cloud formation from the cloud scale to the droplet scale. We assess progress in understanding the effect of turbulence on the condensational and collisional growth of droplets and the effect of entrainment and mixing on the droplet spectrum. The increasing power of computers and better experimental and observational techniques allow for a much more detailed study of these processes than was hitherto possible. However, much of the research necessarily remains idealized and we argue that it is those studies which include such fundamental characteristics of clouds as droplet sedimentation and latent heating that are most relevant to clouds. Nevertheless, the large body of research over the last decade is beginning to allow tentative conclusions to be made. For example, it is unlikely that small-scale turbulent eddies (i.e. not the energy-containing eddies) alone are responsible for broadening the droplet size spectrum during the initial stage of droplet growth due to condensation. It is likely, though, that small-scale turbulence plays a significant role in the growth of droplets through collisions and coalescence. Moreover, it has been possible through detailed numerical simulations to assess the relative importance of different processes to the turbulent collision kernel and how this varies in the parameter space that is important to clouds. The focus of research on the role of turbulence in condensational and collisional growth has tended to ignore the effect of entrainment and mixing and it is arguable that they play at least as important a role in the evolution of the droplet spectrum. We consider the role of turbulence in the mixing of dry and cloudy air, methods of quantifying this mixing and the effect that it has on the droplet spectrum. Copyright

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“…On one hand aerosols have the ability to scatter and/or absorb the incoming solar and terrestrial radiation (aerosol direct effect), e.g Haywood and Boucher (2000). On the other hand, aerosols play a major role in the formation of clouds, and govern their lifetime as well as their microphysical properties influencing the precipitation and also the radiative budget (aerosol indirect effect), e.g., Lohmann and Feichter (2005). The ice phase in mixed-phase clouds is of crucial importance, as 30 % of the tropical rain forms via the ice phase (Lau and Wu, 2003).…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, aerosols play a major role in the formation of clouds, and govern their lifetime as well as their microphysical properties influencing the precipitation and also the radiative budget (aerosol indirect effect), e.g., Lohmann and Feichter (2005). The ice phase in mixed-phase clouds is of crucial importance, as 30 % of the tropical rain forms via the ice phase (Lau and Wu, 2003). Ice crystals in the atmosphere form via two pathways: homogeneous and heterogeneous nucleation.…”

Section: Introductionmentioning

confidence: 99%

Ice nuclei properties within a Saharan dust event at the Jungfraujoch in the Swiss Alps

et al. 2011

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Abstract.The new portable ice nucleation chamber (PINC) developed by the Institute for Atmospheric and Climate Sciences of ETH Zurich was operated during two measurement campaigns at the high alpine research station Jungfraujoch situated at 3580 m a.s.l, in March and June 2009. During this time of the year, a high probability of Saharan dust events (SDE) at the Jungfraujoch has been observed. We used an impactor with a cutoff size of 1 µm aerodynamic diameter and operated the system at −31 • C and relative humidities of 127 % and 91 % with respect to ice and water, respectively. Investigation of the ambient number concentration of ice nuclei (IN) in the deposition nucleation mode and during a SDE in the free troposphere is reported. The results discussed in this paper are the first continuous IN measurements over a period of several days at the Jungfraujoch. The average IN concentration found during the campaign in March was 8 particles per liter whereas during the campaign in June, the average number concentration was higher up to 14 particles per liter. Two SDEs were detected on 15 and 16 June 2009. Our measurements show that the SDEs had IN number concentration up to several hundreds per liter. We found the best correlation between the number concentration of the larger particle fraction measured by an optical particle counter and the IN number concentration during a Saharan dust event. This correlation factor is higher for particles larger than 0.5 µm meaning that a higher concentration of larger particles induced higher IN number concentration. No correlation could be found between the black carbon mass concentration and the variations in IN number concentration.

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Warm rain processes over tropical oceans and climate implications

Cited by 197 publications

References 16 publications

Robust Hadley Circulation changes and increasing global dryness due to CO ₂ warming from CMIP5 model projections

Robust Hadley Circulation changes and increasing global dryness due to CO ₂ warming from CMIP5 model projections

Droplet growth in warm turbulent clouds

Ice nuclei properties within a Saharan dust event at the Jungfraujoch in the Swiss Alps

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Warm rain processes over tropical oceans and climate implications

Cited by 197 publications

References 16 publications

Robust Hadley Circulation changes and increasing global dryness due to CO 2 warming from CMIP5 model projections

Robust Hadley Circulation changes and increasing global dryness due to CO 2 warming from CMIP5 model projections

Droplet growth in warm turbulent clouds

Ice nuclei properties within a Saharan dust event at the Jungfraujoch in the Swiss Alps

Contact Info

Product

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Robust Hadley Circulation changes and increasing global dryness due to CO ₂ warming from CMIP5 model projections

Robust Hadley Circulation changes and increasing global dryness due to CO ₂ warming from CMIP5 model projections