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Observations of anthropogenic global warming

Archive for July, 2010

Papers on Hadley Cell expansion

Posted by Ari Jokimäki on July 27, 2010

This is a list of papers on Hadley Cell expansion due to global warming. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (April 1, 2012): Zhou et al. (2011) added. Thanks to Barry for pointing this out in the discussion of another list.

Recent trends of the tropical hydrological cycle inferred from Global Precipitation Climatology Project and International Satellite Cloud Climatology Project data – Zhou et al. (2011) “Scores of modeling studies have shown that increasing greenhouse gases in the atmosphere impact the global hydrologic cycle; however, disagreements on regional scales are large, and thus the simulated trends of such impacts, even for regions as large as the tropics, remain uncertain. The present investigation attempts to examine such trends in the observations using satellite data products comprising Global Precipitation Climatology Project precipitation and International Satellite Cloud Climatology Project cloud and radiation. Specifically, evolving trends of the tropical hydrological cycle over the last 20–30 years were identified and analyzed. The results show (1) intensification of tropical precipitation in the rising regions of the Walker and Hadley circulations and weakening over the sinking regions of the associated overturning circulation; (2) poleward shift of the subtropical dry zones (up to 2° decade−1 in June-July-August (JJA) in the Northern Hemisphere and 0.3–0.7° decade−1 in June-July-August and September-October-November in the Southern Hemisphere) consistent with an overall broadening of the Hadley circulation; and (3) significant poleward migration (0.9–1.7° decade−1) of cloud boundaries of Hadley cell and plausible narrowing of the high cloudiness in the Intertropical Convergence Zone region in some seasons. These results support findings of some of the previous studies that showed strengthening of the tropical hydrological cycle and expansion of the Hadley cell that are potentially related to the recent global warming trends.” Zhou, Y. P., K.-M. Xu, Y. C. Sud, and A. K. Betts (2011), Recent trends of the tropical hydrological cycle inferred from Global Precipitation Climatology Project and International Satellite Cloud Climatology Project data, J. Geophys. Res., 116, D09101, doi:10.1029/2010JD015197 [Full text]

Cause of the widening of the tropical belt since 1958 – Lu et al. (2009) “Previous studies have shown that the width of the tropical belt has been increasing since at least the late 1970s based on a variety of metrics. One such metric, the frequency of occurrence of a high-altitude tropopause characteristic of the tropics, is used here to show that the observed widening of the tropics can be accurately replicated by an atmospheric general circulation model forced by the observed evolution of global SST and sea ice distributions as well as the direct radiative effects from both natural and anthropogenic sources. Contrasting this simulation with one forced by the observed SST and sea ice distributions alone reveals that the widening trend can be attributed entirely to direct radiative forcing, in particular those related to greenhouse gases and stratospheric ozone depletion. SST forcing causes no significant change in the width of the tropics, and even a contraction in some seasons.” [Full text] [Citation: Lu, J., C. Deser, and T. Reichler (2009), Cause of the widening of the tropical belt since 1958, Geophys. Res. Lett., 36, L03803, doi:10.1029/2008GL036076.]

Hadley Cell Widening: Model Simulations versus Observations – Johanson & Fu (2009) “Observations show that the Hadley cell has widened by about 2°–5° since 1979. This widening and the concomitant poleward displacement of the subtropical dry zones may be accompanied by large-scale drying near 30°N and 30°S. Such drying poses a risk to inhabitants of these regions who are accustomed to established rainfall patterns. Simple and comprehensive general circulation models (GCMs) indicate that the Hadley cell may widen in response to global warming, warming of the west Pacific, or polar stratospheric cooling. The combination of these factors may be responsible for the recent observations. But there is no study so far that has compared the observed widening to GCM simulations of twentieth-century climate integrated with historical changes in forcings. Here the Hadley cell widening is assessed in current GCMs from historical simulations of the twentieth century as well as future climate projections and preindustrial control runs. The authors find that observed widening cannot be explained by natural variability. This observed widening is also significantly larger than in simulations of the twentieth and twenty-first centuries. These results illustrate the need for further investigation into the discrepancy between the observed and simulated widening of the Hadley cell.” [Full text] [Citation: Johanson, Celeste M., Qiang Fu, 2009: Hadley Cell Widening: Model Simulations versus Observations. Journal of Climate, 22, 2713-2725.]

Widening of the tropical belt in a changing climate – Seidel et al. (2008) A review article. “Some of the earliest unequivocal signs of climate change have been the warming of the air and ocean, thawing of land and melting of ice in the Arctic. But recent studies are showing that the tropics are also changing. Several lines of evidence show that over the past few decades the tropical belt has expanded. This expansion has potentially important implications for subtropical societies and may lead to profound changes in the global climate system. Most importantly, poleward movement of large-scale atmospheric circulation systems, such as jet streams and storm tracks, could result in shifts in precipitation patterns affecting natural ecosystems, agriculture, and water resources. The implications of the expansion for stratospheric circulation and the distribution of ozone in the atmosphere are as yet poorly understood. The observed recent rate of expansion is greater than climate model projections of expansion over the twenty-first century, which suggests that there is still much to be learned about this aspect of global climate change.” [Full text (same link as the abstract link)] [Citation: Dian J. Seidel, Qiang Fu, William J. Randel & Thomas J. Reichler, Widening of the tropical belt in a changing climate, Nature Geoscience 1, 21 - 24 (2008), doi:10.1038/ngeo.2007.38.]

Observed poleward expansion of the Hadley circulation since 1979 – Hu & Fu (2007) “Using three meteorological reanalyses and three outgoing long-wave radiation (OLR) datasets, we show that the Hadley circulation has a significant expansion of about 2 to 4.5 degrees of latitude since 1979. The three reanalyses all indicate that the poleward expansion of the Hadley circulation in each hemisphere occurs during its summer and fall seasons. Results from the OLR datasets do not have such seasonality. The expansion of the Hadley circulation implies a poleward expansion of the band of subtropical subsidence, leading to enhanced mid-latitude tropospheric warming and poleward shifts of the subtropical dry zone. This would contribute to an increased frequency of midlatitude droughts in both hemispheres.” [Full text] [Citation: Hu, Y. and Fu, Q.: Observed poleward expansion of the Hadley circulation since 1979, Atmos. Chem. Phys., 7, 5229-5236, doi:10.5194/acp-7-5229-2007, 2007.]

Recent widening of the tropical belt: Evidence from tropopause observations – Seidel & Randel (2007) “Radiosonde measurements and reanalysis data are used to examine long-term changes in tropopause behavior in the subtropics. Tropopause heights in the subtropics exhibit a bimodal distribution, with maxima in occurrence frequency above 15 km (characteristic of the tropical tropopause) and below 13 km (typical of the extratropical tropopause). Both the radiosonde and reanalysis data show that the frequency of occurrence of high tropopause days in the subtropics of both hemispheres has systematically increased during the past few decades, so that tropical characteristics occur more frequently in recent years. This behavior is consistent with a widening of the tropical belt, and the data indicate an expansion of about 5–8° latitude during 1979–2005.” [Full text] [Citation: Seidel, D. J., and W. J. Randel (2007), Recent widening of the tropical belt: Evidence from tropopause observations, J. Geophys. Res., 112, D20113, doi:10.1029/2007JD008861.]

Annular modes and Hadley cell expansion under global warming – Previdi & Liepert (2007) “Projections of 21st century climate from the latest state-of-the-art climate models consistently call for a poleward expansion of the tropical Hadley cell (HC) and subtropical dry zones (SDZ) in response to increasing levels of atmospheric greenhouse gases. We find that approximately half of the model-simulated HC and SDZ expansion during the next hundred years can be explained by positive trends in the Northern Hemisphere and Southern Hemisphere annular modes (NAM and SAM), implying a close connection between changes in the tropical and extratropical atmospheric circulation. The link between NAM and SAM variability and the SDZ expansion suggests that future changes in the hydrologic cycle are likely to be strongly influenced by atmospheric dynamics.” [Citation: Previdi, M., and B. G. Liepert (2007), Annular modes and Hadley cell expansion under global warming, Geophys. Res. Lett., 34, L22701, doi:10.1029/2007GL031243.]

Expansion of the Hadley cell under global warming – Lu et al. (2007) “A consistent weakening and poleward expansion of the Hadley circulation is diagnosed in the climate change simulations of the IPCC AR4 project. Associated with this widening is a poleward expansion of the subtropical dry zone. Simple scaling analysis supports the notion that the poleward extent of the Hadley cell is set by the location where the thermally driven jet first becomes baroclinically unstable. The expansion of the Hadley cell is caused by an increase in the subtropical static stability, which pushes poleward the baroclinic instability zone and hence the outer boundary of the Hadley cell.” [Full text] [Citation: Lu, J., G. A. Vecchi, and T. Reichler (2007), Expansion of the Hadley cell under global warming, Geophys. Res. Lett., 34, L06805, doi:10.1029/2006GL028443.]

Width of the Hadley cell in simple and comprehensive general circulation models – Frierson et al. (2007) “The width of the Hadley cell is studied over a wide range of climate regimes using both simple and comprehensive atmospheric general circulation models. Aquaplanet, fixed sea surface temperature lower boundary conditions are used in both models to study the response of the Hadley cell width to changes in both global mean temperature and pole-to-equator temperature gradient. The primary sensitivity of both models is a large expansion of the Hadley cell with increased mean temperature. The models also exhibit a smaller increase in width with temperature gradient. The Hadley cell widths agree well with a scaling theory by Held which assumes that the width is determined by the latitude where baroclinic eddies begin to occur. As surface temperatures are warmed, the latitude of baroclinic instability onset is shifted poleward due to increases in the static stability of the subtropics, which is increased in an atmosphere with higher moisture content.” [Full text] [Citation: Frierson, D. M. W., J. Lu, and G. Chen (2007), Width of the Hadley cell in simple and comprehensive general circulation models, Geophys. Res. Lett., 34, L18804, doi:10.1029/2007GL031115.]

Enhanced Mid-Latitude Tropospheric Warming in Satellite Measurements – Fu et al. (2006) “The spatial distribution of tropospheric and stratospheric temperature trends for 1979 to 2005 was examined, based on radiances from satellite-borne microwave sounding units that were processed with state-of-the-art retrieval algorithms. We found that relative to the global-mean trends of the respective layers, both hemispheres have experienced enhanced tropospheric warming and stratospheric cooling in the 15 to 45° latitude belt, which is a pattern indicative of a widening of the tropical circulation and a poleward shift of the tropospheric jet streams and their associated subtropical dry zones. This distinctive spatial pattern in the trends appears to be a robust feature of this 27-year record.” [Full text] [Citation: Qiang Fu, Celeste M. Johanson, John M. Wallace, Thomas Reichler, Enhanced Mid-Latitude Tropospheric Warming in Satellite Measurements, Science 26 May 2006: Vol. 312. no. 5777, p. 1179, DOI: 10.1126/science.1125566.]

Recent behavior of the Hadley cell and tropical thermodynamics in climate models and reanalyses – Mitas & Clement (2006) “The behavior of the Hadley cell and the thermodynamic structure of the tropical atmosphere is analyzed over the period 1979–2000 in climate models and reanalyses. Significant trends in the strength of the Hadley cell are present in reanalyses that are not reproduced by models. Analysis of the thermodynamic structure also shows significant discrepancies between models and reanalyses, the former show warming aloft and increased static stability while the latter show a cooling trend and decreased static stability in the tropical mid-troposphere. Additional energy balance analysis reveals that models and reanalyses have a fundamentally different balance between diabatic heating, circulation and thermodynamic structure over the period 1979–2000. Uncertainties in the observations of tropospheric temperatures as well as potential biases and errors in the climate models raise questions about the true long-term behavior of the thermodynamic structure of the tropical troposphere and the Hadley cell.” [Full text] [Citation: Mitas, C. M., and A. Clement (2006), Recent behavior of the Hadley cell and tropical thermodynamics in climate models and reanalyses, Geophys. Res. Lett., 33, L01810, doi:10.1029/2005GL024406.]

Has the Hadley cell been strengthening in recent decades? – Mitas & Clement (2005) “The intensity and structure of the Northern Hemisphere DJF Hadley cell as depicted in various commonly used data sets are examined. We find that the NCEP/NCAR and ECMWF reanalyses show a statistically significant intensification of their Hadley circulation throughout their periods. In marked contrast the NCEP-DOE reanalysis does not show any discernible trend over its period. Furthermore, the Hadley cell structure differs substantially from the other two reanalyses. We also examine a data set of global rawinsonde observations in which the Hadley cell shows no intensification. Finally, we investigate the Hadley cell simulated by an atmospheric GCM. The ensemble mean shows a statistically significant intensification, though it is smaller in magnitude than the reanalyses. We conclude that the two major reanalyses appear to be in agreement on the strengthening of the Hadley cell in recent decades. However, discrepancies among data sets do raise questions about the robustness of this strengthening.” [Full text] [Citation: Mitas, C. M., and A. Clement (2005), Has the Hadley cell been strengthening in recent decades?, Geophys. Res. Lett., 32, L03809, doi:10.1029/2004GL021765.]

Evidence for Strengthening of the Tropical General Circulation in the 1990s – Chen et al. (2002) “Satellite observations suggest that the thermal radiation emitted by Earth to space increased by more than 5 watts per square meter, while reflected sunlight decreased by less than 2 watts per square meter, in the tropics over the period 1985-2000, with most of the increase occurring after 1990. By analyzing temporal changes in the frequency of occurrence of emitted thermal and reflected solar fluxes, the effects of El Niño-Southern Oscillation are minimized, and an independent longer-time-scale variation of the radiation budget is identified. Similar analyses of upper tropospheric humidity, cloud amount, surface air temperature, and vertical velocity confirm that these flux changes are associated with a decadal-time-scale strengthening of the tropical Hadley and Walker circulations. Equatorial convective regions have intensified in upward motion and moistened, while both the equatorial and subtropical subsidence regions have become drier and less cloudy.” [Full text] [Citation: Science 1 February 2002, Vol. 295. no. 5556, pp. 838 - 841, DOI: 10.1126/science.1065835.]

Posted in AGW evidence | 3 Comments »

Go to Hot Topic and…

Posted by Ari Jokimäki on July 15, 2010

…give your support to John Abraham.

I think Monckton is going for the good old there’s-no-such-thing-as-bad-publicity…

Posted in Climate claims | Leave a Comment »

Wiley Interdisciplinary Reviews: Climate Change

Posted by Ari Jokimäki on July 10, 2010

Lately I have gotten familiar with the climate science journals as I have been writing some news pieces to Finnish people. One of the journals I have noticed is from Wiley Interscience and it is called “Wiley Interdisciplinary Reviews: Climate Change”. This journal publishes all kinds of review articles on issues relating to climate. For an amateur like me, review articles are very important. They are scientific articles but yet they are written in a language that an amateur can understand. Sure there are occasions when even a review article goes too complicated for me but still they usually are very readable.

This Wiley Interscience journal has just started – it only has two issues published. First issue contains papers from Judith Lean (“Cycles and trends in solar irradiance and climate”) and Spencer Weart (“The idea of anthropogenic global climate change in the 20th century”). There are lot of other interesting papers too in that issue.

Second issue has Peter Stott et al’s “Detection and attribution of climate change: a regional perspective” among others. The early view articles (at the time of the writing) has David Frank et al’s “A noodle, hockey stick, and spaghetti plate: a perspective on high-resolution paleoclimatology” and J. Annan’s “Bayesian approaches to detection and attribution”. Even deniers are kept happy as there’s Roger Pielke Jr’s “The Carbon Economy and Climate Mitigation: an editorial essay”. I wrote in Finnish about the Piquet’s “Linking climate change, environmental degradation, and migration: a methodological overview” and I’m sure that I will use many of the articles published in this journal in the future. They have one important thing why I’m especially interested in this journal – they offer all of their articles for free to everyone (edited to add: I thank Wiley Interscience for that) (edited to add 2: it seems that issue 1 papers are not freely available but they must be purchased).

If you are interested in climate science, I suggest you dig into the papers published by this journal. I know I will.

Posted in Climate science | 7 Comments »

 
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