scholarly journals Land–Ocean Asymmetry of Tropical Precipitation Changes in the Mid-Holocene

2010 ◽  
Vol 23 (15) ◽  
pp. 4133-4151 ◽  
Author(s):  
Yang-Hui Hsu ◽  
Chia Chou ◽  
Kuo-Yen Wei
Keyword(s):  
Austral Summer ◽  
Atmospheric Temperature ◽  
Boreal Summer ◽  
Net Energy ◽  
Current Season ◽  
Tropical Precipitation ◽  
Summer Insolation ◽  
Tropical Sea ◽  
Precipitation Changes ◽  
Insolation Forcing

Abstract A series of model experiments were conducted using an intermediate ocean–atmosphere–land model for a better understanding of a distinct land–sea asymmetry in tropical precipitation differences between the mid-Holocene and preindustrial climates. In austral (boreal) summer, most reduced (enhanced) precipitation occurs over continental convective regions, while most enhanced (reduced) precipitation occurs over oceanic convection zones. This land–sea asymmetry of tropical precipitation is particularly clear in austral summer. During the mid-Holocene, the solar forcing presents both spatial and seasonal asymmetric patterns. While the boreal summer insolation is stronger at high latitudes of the Northern Hemisphere in the mid-Holocene than at present, the austral summer insolation is weaker with a more spatially symmetric distribution about the equator. Because of the slow response time of the ocean to forcing, the direct insolation forcing of the current season is cancelled by the ocean memory of an earlier insolation forcing, which in the case of the mid-Holocene is opposite to the current season insolation forcing. As a result, tropical sea surface temperature variation, as well as the tropical atmospheric temperature and moisture changes, is small, which gives rise to a different precipitation response from under the condition of stronger atmospheric temperature and moisture changes, such as in the case of postindustrial global warming induced by an increased concentration of atmospheric greenhouse gases. Thus, the cancellation between the direct and memory effects of the seasonally asymmetric insolation forcing leaves the net energy into the atmosphere to be responsible for the land–sea asymmetry of tropical precipitation changes.

scholarly journals Weak Southern Hemispheric monsoons during the Last Interglacial period

2020 ◽  
Author(s):  
Nicholas K. H. Yeung ◽  
Laurie Menviel ◽  
Katrin J. Meissner ◽  
Andréa S. Taschetto ◽  
Tilo Ziehn ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Austral Summer ◽  
Hadley Cell ◽  
Boreal Summer ◽  
Interglacial Period ◽  
Last Interglacial ◽  
Inter Tropical Convergence Zone ◽  
High Northern Latitude ◽  
Summer Insolation ◽  
Last Interglacial Period

Abstract. Due to different orbital configurations, high northern latitude boreal summer insolation was higher during the Last Interglacial period (LIG; 129–116 thousand years before present, ka) than during the preindustrial period (PI), while high southern latitude austral summer insolation was lower. The climatic response to these changes is studied here with focus on the southern hemispheric monsoons, by performing an equilibrium experiment of the LIG at 127 ka with the Australian Earth System Model, ACCESS-ESM1.5, as part of the Paleoclimate Model Intercomparison Project 4 (PMIP4). In our simulation, mean surface air temperature increases by 6.5 °C over land during boreal summer between 40° N and 60° N in the LIG compared to PI, leading to a northward shift of the Inter-Tropical Convergence Zone (ITCZ) and a strengthening of the North African and Indian monsoons. Despite 0.4 °C cooler conditions in austral summer in the Southern Hemisphere (0–90° S), annual mean air temperatures are 1.2 °C higher at southern mid-to-high latitudes (40° S–80° S). These differences in temperature are coincident with a large-scale reorganisation of the atmospheric circulation. The ITCZ shifts southward in the Atlantic and Indian sectors during the LIG austral summer compared to PI, leading to increased precipitation over the southern tropical oceans. However, the decline in Southern Hemisphere insolation during austral summer induces a significant cooling over land, which in turn weakens the land-sea temperature contrast, leading to an overall reduction (−20 %) in monsoonal precipitation over the Southern Hemisphere's continental regions. The intensity and areal extent of the Australian, South American and South African monsoons are consistently reduced. This is associated with greater pressure and subsidence over land due to a strengthening of the southern hemispheric Hadley cell during austral summer.

Hemispherical Asymmetry of Tropical Precipitation in ECHAM5/MPI-OM during El Niño and under Global Warming

2008 ◽  
Vol 21 (6) ◽  
pp. 1309-1332 ◽  
Author(s):  
Chia Chou ◽  
Jien-Yi Tu
Keyword(s):  
Global Warming ◽  
El Niño ◽  
El Nino ◽  
Hadley Circulation ◽  
Seasonal Migration ◽  
Boreal Summer ◽  
Max Planck ◽  
Tropical Precipitation ◽  
Precipitation Anomalies ◽  
Precipitation Changes

Abstract Similarities and differences between El Niño and global warming are examined in hemispherical and zonal tropical precipitation changes of the ECHAM5/Max Planck Institute Ocean Model (MPI-OM) simulations. Similarities include hemispherical asymmetry of tropical precipitation changes. This precipitation asymmetry varies with season. In the boreal summer and autumn (winter and spring), positive precipitation anomalies are found over the Northern (Southern) Hemisphere and negative precipitation anomalies are found over the Southern (Northern) Hemisphere. This precipitation asymmetry in both the El Niño and global warming cases is associated with the seasonal migration of the Hadley circulation; however, their causes are different. In El Niño, a meridional moisture gradient between convective and subsidence regions is the fundamental basis for inducing the asymmetry. Over the ascending branch of the Hadley circulation, convection is enhanced by less effective static stability. Over the margins of the ascending branch, convection is suppressed by the import of dry air from the descending branch. In global warming, low-level moisture is enhanced significantly due to warmer tropospheric temperatures. This enhances vertical moisture transport over the ascending branch of the Hadley circulation, so convection is strengthened. Over the descending branch, the mean Hadley circulation tends to transport relatively drier air downward, so convection is reduced.

scholarly journals Land–sea temperature contrasts at the Last Interglacial and their impact on the hydrological cycle

2021 ◽  
Vol 17 (2) ◽  
pp. 869-885
Author(s):  
Nicholas King-Hei Yeung ◽  
Laurie Menviel ◽  
Katrin J. Meissner ◽  
Andréa S. Taschetto ◽  
Tilo Ziehn ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Hydrological Cycle ◽  
Austral Summer ◽  
Hadley Cell ◽  
Boreal Summer ◽  
Interglacial Period ◽  
Last Interglacial ◽  
Sea Temperature ◽  
High Northern Latitude ◽  
Summer Insolation

Abstract. Due to different orbital configurations, high northern latitude summer insolation was higher during the Last Interglacial period (LIG; 129–116 thousand years before present, ka) than during the pre-industrial period (PI), while high southern latitude summer insolation was lower. The climatic response to these changes is studied here with focus on the Southern Hemisphere monsoons, by performing an equilibrium experiment of the LIG at 127 ka with the Australian Earth System Model, ACCESS-ESM1.5, as part of the Paleoclimate Model Intercomparison Project 4 (PMIP4). Simulated mean surface air temperature between 40 and 60∘ N over land during boreal summer is 6.5 ∘C higher at the LIG compared to PI, which leads to a northward shift of the Intertropical Convergence Zone (ITCZ) and a strengthening of the North African and Indian monsoons. Despite 0.4 ∘C cooler conditions in austral summer in the Southern Hemisphere (0–90∘ S), annual mean air temperatures are 1.2 ∘C higher at southern mid-latitudes to high latitudes (40–80∘ S). These differences in temperature are coincident with a large-scale reorganisation of the atmospheric circulation. The ITCZ shifts southward in the Atlantic and Indian sectors during the LIG austral summer compared to PI, leading to increased precipitation over the southern tropical oceans. However, weaker Southern Hemisphere insolation during LIG austral summer induces a significant cooling over land, which in turn weakens the land–sea temperature contrast, leading to an overall reduction (−20 %) in monsoonal precipitation over the Southern Hemisphere's continental regions compared to PI. The intensity and areal extent of the Australian, South American and South African monsoons are consistently reduced in LIG. This is associated with greater pressure and subsidence over land due to a strengthening of the Southern Hemisphere Hadley cell during austral summer.

scholarly journals Global carbonyl sulfide (OCS) measured by MIPAS/Envisat during 2002–2012

2016 ◽  
Author(s):  
Norbert Glatthor ◽  
Michael Höpfner ◽  
Adrian Leyser ◽  
Gabriele P. Stiller ◽  
Thomas von Clarmann ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Michelson Interferometer ◽  
Austral Summer ◽  
Emission Spectra ◽  
Set Covering ◽  
Boreal Summer ◽  
Systematic Bias ◽  
High Latitudes ◽  
Data Set ◽  
The Tropics

Abstract. We present a global OCS data set covering the period June 2002 to April 2012, derived from FTIR limb emission spectra measured with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on the ENVISAT satellite. The vertical resolution is 4–5 km in the height region 6–15 km and 15 km at 40 km altitude. The total estimated error amounts to 40–50 pptv between 10 and 20 km and to 120 pptv at 40 km altitude. MIPAS OCS data show no systematic bias with respect to balloon observations, with deviations mostly below ±50 pptv. However, they are systematically higher than the OCS volume mixing ratios of the ACE-FTS instrument on SCISAT, with maximum deviations of up to 100 pptv in the altitude region 13–16 km. The data set of MIPAS OCS exhibits only moderate interannual variations and low interhemispheric differences. Average concentrations at 10 km altitude range from 480 pptv at high latitudes to 500–510 pptv in the tropics and at northern mid-latitudes. Seasonal variations at 10 km altitude amount up to 35 pptv in the northern and up to 15 pptv in the southern hemisphere. Northern hemispheric OCS abundances at 10 km altitude peak in June in the tropics and around October at high latitudes, while the respective southern hemispheric maxima were observed in July and in November. Global OCS distributions at 250 hPa (~ 10–11 km) show enhanced values at low latitudes, peaking during boreal summer above the western Pacific and the Indian Ocean, which indicates oceanic release. Further, a region of depleted OCS amounts extending from Brazil to central and southern Africa was detected at this altitude, which is most pronounced in austral summer. This depletion is related to seasonally varying vegetative uptake by the tropical forests. Typical signatures of biomass burning like the southern hemispheric biomass burning plume are not visible in MIPAS data, indicating that this process is only a minor source of tropospheric OCS. At the 150 hPa level (~ 13–14 km) enhanced amounts of OCS were also observed inside the Asian Monsoon Anticyclone, but this enhancement is not especially outstanding as compared to other low latitude regions at the same altitude. At the 80 hPa level (~ 17–18 km) equatorward transport of mid-latitude air masses containing lower OCS amounts around the summertime anticyclones was observed. A significant trend could not be detected in tropospheric MIPAS OCS amounts, which points to globally balanced sources and sinks.

scholarly journals Ice-driven CO<sub>2</sub> feedback on ice volume

2006 ◽  
Vol 2 (1) ◽  
pp. 43-55 ◽  
Author(s):  
W. F. Ruddiman
Keyword(s):  
Geographic Origin ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Early Pleistocene ◽  
Schematic Model ◽  
Co2 Response ◽  
Ice Volume ◽  
Summer Insolation ◽  
Northern Summer ◽  
Insolation Forcing

Abstract. The origin of the major ice-sheet variations during the last 2.7 million years is a long-standing mystery. Neither the dominant 41 000-year cycles in δ18O/ice-volume during the late Pliocene and early Pleistocene nor the late-Pleistocene oscillations near 100 000 years is a linear ("Milankovitch") response to summer insolation forcing. Both responses must result from non-linear behavior within the climate system. Greenhouse gases (primarily CO2) are a plausible source of the required non-linearity, but confusion has persisted over whether the gases force ice volume or are a positive feedback. During the last several hundred thousand years, CO2 and ice volume (marine δ18O) have varied in phase at the 41 000-year obliquity cycle and nearly in phase within the ~100 000-year band. This timing rules out greenhouse-gas forcing of a very slow ice response and instead favors ice control of a fast CO2 response. In the schematic model proposed here, ice sheets responded linearly to insolation forcing at the precession and obliquity cycles prior to 0.9 million years ago, but CO2 feedback amplified the ice response at the 41 000-year period by a factor of approximately two. After 0.9 million years ago, with slow polar cooling, ablation weakened. CO2 feedback continued to amplify ice-sheet growth every 41 000 years, but weaker ablation permitted some ice to survive insolation maxima of low intensity. Step-wise growth of these longer-lived ice sheets continued until peaks in northern summer insolation produced abrupt deglaciations every ~85 000 to ~115 000 years. Most of the deglacial ice melting resulted from the same CO2/temperature feedback that had built the ice sheets. Several processes have the northern geographic origin, as well as the requisite orbital tempo and phasing, to be candidate mechanisms for ice-sheet control of CO2 and their own feedback.

A Consolidated CLIPER Model for Improved August–September ENSO Prediction Skill

10.1175/813.1 ◽  
2004 ◽  
Vol 19 (6) ◽  
pp. 1089-1105 ◽  
Author(s):  
Benjamin Lloyd-Hughes ◽  
Mark A. Saunders ◽  
Paul Rockett
Keyword(s):  
Prediction Model ◽  
Seasonal Prediction ◽  
Boreal Summer ◽  
Northwest Pacific ◽  
Tropical Precipitation ◽  
Spring Predictability Barrier ◽  
Forecast Models ◽  
Hurricane Activity ◽  
Initial Results ◽  
Enso Indices

Abstract A prime challenge for ENSO seasonal forecast models is to predict boreal summer ENSO conditions at lead. August–September ENSO has a strong influence on Atlantic hurricane activity, Northwest Pacific typhoon activity, and tropical precipitation. However, summer ENSO skill is low due to the spring predictability barrier between March and May. A “consolidated” ENSO–climatology and persistence (CLIPER) seasonal prediction model is presented to address this issue with promising initial results. Consolidated CLIPER comprises the ensemble of 18 model variants of the statistical ENSO–CLIPER prediction model. Assessing August–September ENSO skill using deterministic and probabilistic skill measures applied to cross-validated hindcasts from 1952 to 2002, and using deterministic skill measures applied to replicated real-time forecasts from 1900 to 1950, shows that the consolidated CLIPER model consistently outperforms the standard CLIPER model at leads from 2 to 6 months for all the main ENSO indices (3, 3.4, and 4). The consolidated CLIPER August–September 1952–2002 hindcast skill is also positive to 97.5% confidence at leads out to 4 months (early April) for all ENSO indices. Optimization of the consolidated CLIPER model may lead to further skill improvements.

scholarly journals Relationship between the Hadley Circulation and Different Tropical Meridional SST Structures during Boreal Summer

2018 ◽  
Vol 31 (16) ◽  
pp. 6575-6590 ◽  
Author(s):  
Juan Feng ◽  
Jianping Li ◽  
Feifei Jin ◽  
Sen Zhao ◽  
Jianlei Zhu
Keyword(s):  
Asian Summer Monsoon ◽  
Hadley Circulation ◽  
Dominant Mode ◽  
Boreal Summer ◽  
Sst Variability ◽  
Warming Pattern ◽  
Leading Mode ◽  
Asian Summer ◽  
Tropical Sea ◽  
Relationship Of

Abstract The relationship of the Hadley circulation (HC) to different tropical sea surface temperature (SST) meridional structures during boreal summer is investigated over the period of 1979–2016. After decomposing the variations of the HC into the equatorially asymmetric HC (HEA), zonal-mean equatorially asymmetric SST (SEA), equatorially symmetric HC (HES), and equatorially symmetric SST (SES) components, the ratio of the HEA associated with SEA with respect to the HES associated with SES is around 2 across multiple reanalyses, which is a smaller ratio than in the annual and seasonal cycle. The reduced ratio of the HC to SST is due to the regional SST variation in the Asian summer monsoon (ASM) domain. The first leading mode (EOF1) of the regional SST variability in the ASM domain is dominated by a homogeneous warming pattern. This pattern is associated with an equatorially asymmetric HC, but it has an opposite direction to the climatological HEA and so weakens the HEA. The second dominant mode has an El Niño–like pattern, which resembles the distribution of the principal mode of the SST in the non-ASM region. Both modes are responsible for the variation of HES. However, the SST EOF1 in the ASM domain displays a significant upward trend, favoring a suppressed HEA, and leading to the smaller ratio of the HC to SST during boreal summer. Moreover, the variation of the SST EOF1 is closely linked with the intensity of the ASM, highlighting the potential modulation by the ASM of the relation between the HC and SST during boreal summer.

scholarly journals Thermodynamic and dynamic responses of the hydrological cycle to solar dimming

2016 ◽  
Author(s):  
Jane E. Smyth ◽  
Rick D. Russotto ◽  
Trude Storelvmo
Keyword(s):  
Hydrological Cycle ◽  
Global Climate ◽  
Hadley Circulation ◽  
Climate Impacts ◽  
Dynamic Responses ◽  
Tropical Precipitation ◽  
Solar Geoengineering ◽  
Intercomparison Project ◽  
Rainfall Anomalies ◽  
Precipitation Changes

Abstract. The fundamental role of the hydrological cycle in the global climate system motivates thorough evaluation of its responses to climate change and mitigation. The Geoengineering Model Intercomparison Project (GeoMIP) is a global collaboration that aims to assess the climate impacts of solar geoengineering, a proposal to counteract global warming with a reduction of incoming solar radiation. We assess the mechanisms underlying the rainfall response to a simplified simulation of solar dimming in the suite of GeoMIP models and identify robust features. While solar geoengineering restores preindustrial temperatures, the global hydrology is altered. Tropical precipitation changes dominate the response across the model suite. The models indicate a range of possibilities for the hydrological response, and in most cases, both thermodynamic and non-thermodynamic mechanisms drive precipitation minus evaporation changes in the geoengineered simulations relative to the preindustrial. Shifts of the Hadley circulation cells cause greater rainfall anomalies than local changes in relative humidity or the Clausius-Clapeyron scaling of precipitation minus evaporation. The variations among models in the movement of the intertropical convergence zone highlights the need for cautious consideration and continued study before any implementation of solar geoengineering.

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