Implication of tropical lower stratospheric cooling in recent trends in tropical circulation and deep convective activity

Kodera, Kunihiko; Eguchi, Nawo; Ueyama, Rei; Kuroda, Yoji; Kobayashi, Chiaki; Funatsu, Beatriz M.; Claud, Chantal

doi:10.5194/acp-19-2655-2019

Cited by 9 publications

(5 citation statements)

References 63 publications

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“…8 can be partially attributed to the underestimation of diabatic heat in the reanalysis data set over the tropical convective regions. Kodera et al (2019) shows that convection in Sahel is extremely deep with strong updraft. Deep convection tends to occur in a narrow region.…”

Section: Discussionmentioning

confidence: 99%

“…The Sahel owes its distinct rainy (June-September) and dry (October-May) seasons to the West African monsoon (e.g., Nicholson 2013). Convection in the rainy season is extremely deep (Kodera et al 2019), and it fluctuates widely from year to year (e.g., Nicholson and Palao 1993). Furthermore, the Sahel region is close to the climatological subtropical westerly jet, which can play a role in a waveguide for a teleconnection pattern (Hoskins and Ambrizzi 1993).…”

Section: Introductionmentioning

confidence: 99%

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Possible semi-circumglobal teleconnection across Eurasia driven by deep convection over the Sahel

2021

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The Sahel region, located between the tropical rainforests of Africa and the Sahara Desert, has rainfall that varies widely from year to year, associated with extremely deep convection. This deep convection, strongly heated by water vapor condensation, suggests the possibility of exerting a remote influence on mid- and high-latitude climate similar to the well-known influences of tropical oceanic convection on global climate. Here we investigate the possibility that deep convection over the Sahel initiates a semi-circumglobal teleconnection extending to eastern Eurasia. Statistical analysis and numerical experiments support the possible existence of this teleconnection at an interannual time scale. We propose that the anomalous heat source due to deep convection over the Sahel in the late monsoon season influences meandering of the mid-latitude jet stream over Europe through the combination of a Matsuno-Gill response and advection of absolute vorticity. This subtropical jet meander may in turn drive an eastward propagation of a Rossby wave across Eurasia as far as East Asia. Because deep convection over other subtropical land areas may exert a similar remote influence upon extratropical extreme weather, further studies of the influence of overland convection may provide us with an expanded comprehension of teleconnections.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Possible semi-circumglobal teleconnection across Eurasia driven by deep convection over the Sahel

2021

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“…The positive OLR anomalies in the SH mainly located north of the HC descending branch of the SH, indicating that the expansion of HC in the SH might slow down in recent decades, which can also be clearly inferred from zonal mean TCC trend in Figure S2f. In addition, the negative OLR anomalies (anomalous ascending motion) over central Africa, Asian summer monsoon regions and the Gulf of Mexico are located north of the climatic mean OLR (250 W⋅m −2 ), which is closely associated with the poleward shift of the deep HC ascending branch in NH caused by the cooling of the equatorial southeastern Pacific Ocean in Figure 13c (Kodera et al ., 2019). However, the anomalous ascending motion moves southward over the Equatorial Central and East Pacific as indicated by the zonal‐mean TCC trend in Figure S2f.…”

Section: Atmospheric Circulation Associated With the Principal Modes mentioning

confidence: 99%

Pairwise‐rotated EOFs of global cloud cover and their linkages to sea surface temperature

Dong

et al. 2020

Intl Journal of Climatology

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Sea surface temperature (SST) could significantly affect the dynamic and thermodynamic conditions of the atmospheric circulation and consequently the cloud variations. Here we use several different satellite records to extract the spatial‐time modes of total cloud cover (TCC) by employing a pairwise rotation of Empirical Orthogonal Function analysis. The results show that the first two principal oscillation modes of TCC are closely associated with the Central Pacific El Niño Southern Oscillation (CP ENSO) and Eastern Pacific (EP) ENSO during the 1980s–2000s, while the ENSO‐like mode of TCC can provide an evident contribution to the TCC change during the 2000s–2010s. In CP El Niño, the cloud vertical structure decomposed from CloudSat observations shows an increase of cloud occurrence frequency near the equator and around 40°, and a decrease around 10° in both hemispheres, suggesting a symmetric tightening of Hadley cell (HC). In addition, cloud occurrence frequency increases around 180°, which is accompanied by an eastward shift of Walker circulation (WC). In EP El Niño, TCC increases (decreases) over the Equatorial Eastern Pacific (Western Pacific warm pool), and decreases asymmetrically over the subtropical Pacific Ocean, indicating a weakening of WC and an asymmetric tightening of HC, respectively. The different responses of circulation and clouds to CP and EP El Niño highlight the nonlinearity of El Niño SST forcing. We also construct a trend mode of TCC to investigate cloud long‐term responses to SST warming by transferring the linear trends of the rest modes to a specific mode. The principal components (PCs) of TCC trend modes are strongly correlated with global‐mean SST (GSST) with correlation a coefficient of about 0.60 during the 1980s–2000s and 0.45 during the 2000s–2010s, suggesting a continued influence of global SST warming on TCC. The global TCC change is mainly influenced by the combined effects of Atlantic Multi‐decadal Oscillation (AMO), Pacific Decadal Oscillation (PDO) and Indian Ocean Dipole (IOD). The variation about the trend mode of TCC is closely associated with PDO and IOD.

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“…Many studies of ASM variability and trends have focused on near-surface fields such as rainfall and low-level temperatures or winds (e.g., Kajikawa et al 2012;Preethi et al 2017;Kodera et al 2019;Brönnimann et al 2016;Wu et al 2020;and references therein), and some suggest a trend toward earlier monsoon onset in spring, with possible relationships to anthropogenic forcing (e.g., Kajikawa et al 2012;Bollasina et al 2013Bollasina et al , 2014Bombardi et al 2020). Near-surface metrics have been linked to the upper-level circulation, with, for example, westward and northward trends in the UT anticyclonic circulation associated with corresponding interannual variability in surface conditions (e.g., Preethi et al 2017), links between interannual variability in ASM precipitation onset and tropopause variations (e.g., Ravindra Babu et al 2019), and evidence of UT subtropical jet changes (weakening or latitude changes) associated with earlier monsoon onset (e.g., Samanta et al 2020;Wu et al 2020).…”

Section: Introductionmentioning

confidence: 99%

A Moments View of Climatology and Variability of the Asian Summer Monsoon Anticyclone

et al. 2021

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A comprehensive investigation of the climatology of and interannual variability and trends in the Asian summer monsoon anticyclone (ASMA) is presented, based on a novel area and moments analysis. Moments include centroid location, aspect ratio, angle, and “excess kurtosis” (measuring how far the shape is from elliptical) for an equivalent ellipse with the same area as the ASMA. Key results are robust among the three modern reanalyses studied. The climatological ASMA is nearly elliptical, with its major axis aligned along its centroid latitude and a typical aspect ratio of ~5–8. The ASMA centroid shifts northward with height, northward and westward during development, and in the opposite direction as it weakens. New evidence finding no obvious climatological bimodality in the ASMA reinforces similar suggestions from previous studies using modern reanalyses. Most trends in ASMA moments are not statistically significant. ASMA area and duration, however, increased significantly during 1979–2018; the 1958–2018 record analyzed for one reanalysis suggests that these trends may have accelerated in recent decades. ASMA centroid latitude is significantly positively (negatively) correlated with subtropical jet core latitude (altitude), and significantly negatively correlated with concurrent ENSO; these results are consistent with and extend previous work relating monsoon intensity, ENSO, and jet shifts. ASMA area is significantly positively correlated with the MEI ENSO index two months previously. These results improve our understanding of the ASMA using consistently defined diagnostics of its size, geometry, interannual variability, and trends that have not previously been analyzed.

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Implication of tropical lower stratospheric cooling in recent trends in tropical circulation and deep convective activity

Cited by 9 publications

References 63 publications

Possible semi-circumglobal teleconnection across Eurasia driven by deep convection over the Sahel

Possible semi-circumglobal teleconnection across Eurasia driven by deep convection over the Sahel

Pairwise‐rotated EOFs of global cloud cover and their linkages to sea surface temperature

A Moments View of Climatology and Variability of the Asian Summer Monsoon Anticyclone

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