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  • 1
    Publication Date: 2019-07-13
    Description: Light absorbing aerosols not only contribute to Earth's radiative balance but also influence regional climate by cooling the surface and warming the atmosphere. Following recent suggestions that organic aerosols (OAs) absorb substantial amount of solar radiation, we examine the role of light absorbing properties of OA on Asian summer monsoon rainfall redistribution using observational data and an atmospheric general circulation model (AGCM) experiment. Results suggest that the enhanced light absorption by OA in Southeast Asia and Northeast Asia are associated with the advance of the Indian summer monsoon in May and the southward shift of East Asian summer monsoon rain band in June. The rainfall redistribution in May is induced by elevated orographic effect with a warm-core upper-level anticyclone and surface warming of 1-2C over the Tibetan Plateau whereas that of the East Asian summer monsoon in June is formed by stable conditions associated with surface cooling and atmospheric warming around 30N.
    Keywords: Earth Resources and Remote Sensing
    Type: GSFC-E-DAA-TN58055 , Journal of Geophysical Research: Atmospheres (e-ISSN 2169-897X); 123; 4; 2244-2255
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  • 2
    Publication Date: 2016-01-12
    Description: The Northern Hemisphere atmospheric blocking is a primary weather and climate system that accompanies extreme cold spells and heat waves. This study assesses effects of the Tibetan Plateau (TP), the largest continental mountain belt, on the blocking frequency (BF) and amplitude (BA) with progressive TP uplift experiments from 0 to 100 % using a coupled atmosphere–ocean general circulation model. The TP uplift increases the annual-mean BF by 3 and 21 % over the Pacific and Atlantic basins, respectively. A particular focus is placed on the seasonally distinct mechanism in the effects of TP uplift on the boreal winter and summer blockings. During winter, the TP uplift increases the BF over the active centers of both ocean basins via amplifying the eddy kinetic energy of stationary waves. On the other hand, in summer, the TP uplift tends to shift the location of BF northward due to notable poleward displacement of the jet stream and transient eddy activities, particularly over the Atlantic. Compared to the considerable BF increase in both seasons, the amplification of BA due to the TP uplift is much stronger in winter than in summer, reaffirming the seasonally varying TP effect on the blocking. Further analyses reveal that in summer, the TP uplift modulates more effectively the jet displacement than its strength, leading more linear northward shift of jet and BF, especially over the Atlantic. This study will contribute to advances in simulation and prediction of atmospheric blocking events. ©2016 Springer-Verlag Berlin Heidelberg
    Print ISSN: 0930-7575
    Electronic ISSN: 1432-0894
    Topics: Geosciences , Physics
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  • 3
    Publication Date: 2015-10-01
    Description: The tropical North Atlantic (TNA) sea surface temperature (SST) has been identified as one of regulators on the boreal summer climate over the western North Pacific (WNP), in addition to SSTs in the tropical Pacific and Indian Oceans. The major physical process proposed is that the TNA warming induces a pair of cyclonic circulation anomaly over the eastern Pacific and negative precipitation anomalies over the eastern to central tropical Pacific, which in turn lead to an anticyclonic circulation anomaly over the western to central North Pacific. This study further demonstrates that the modulation of the TNA warming to the WNP summer climate anomaly tends to be intensified under background of the weakened Atlantic thermohaline circulation (THC) by using a water-hosing experiment. The results suggest that the weakened THC induces a decrease in thermocline depth over the TNA region, resulting in the enhanced sensitivity of SST variability to wind anomalies and thus intensification of the interannual variation of TNA SST. Under the weakened THC, the atmospheric responses to the TNA warming are westward shifted, enhancing the anticyclonic circulation and negative precipitation anomaly over the WNP. This study supports the recent finding that the negative phase of the Atlantic multidecadal oscillation after the late 1960s has been favourable for the strengthening of the connection between TNA SST variability and WNP summer climate and has important implications for seasonal prediction and future projection of the WNP summer climate. ©2014 Springer-Verlag Berlin Heidelberg
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  • 4
    Publication Date: 2015-05-01
    Description: Two principal modes of Northern Hemisphere (NH) wintertime blocking variability are identified to examine the possible relationships between regional blocking activities and to understand how they are linked. The first mode of NH blocking variability is characterized by regional blocking activities including the North Pacific (PA), Greenland, European, and Ural-Siberian regions. There exists dominant PA blocking associated with the negative North Pacific Oscillation (NPO) pattern. The second mode shows a zonally dipole pattern between PA and North Atlantic (AT) blockings. It is more related to AT blocking, such that there is strong coupling with the negative North Atlantic Oscillation (NAO) pattern. Correlation analysis with major climate variability patterns revealed that both the NPO and NAO may modulate the two leading modes of NH blocking variability. Also, the NPO and Arctic Oscillation (AO) can simultaneously be associated with the blocking occurrence over both the PA and AT basins. The negative phase of the NPO (AO) is favorable for the in- phase (out-of-phase) relationship between west of (south of) PA and south of (west of) AT blocking sectors. This occurs because NH blocking occurrence is dependent on the phase of the AO, especially in the negative NPO pattern. If the NPO and AO are in phase (out of phase), NH blocking occurrence is more enhanced (weakened), in particular, having higher frequency over the Pacific and higher (lower) frequency over the Northwest Atlantic. ©2014 Springer-Verlag Berlin Heidelberg
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  • 5
    Publication Date: 2015-04-01
    Description: The quasi-biennial (QB)-type El Niño-Southern Oscillation (ENSO), showing a fast phase transition from El Niño to La Niña, is closely related to the variability of the North Pacific subtropical high (NPSH) and western North Pacific subtropical high (WNPSH) during summer. Here, we show that the NPSH plays a key role in the fast ENSO transition. The QB-type ENSO is associated with both strengthened WNPSH and NPSH during the boreal summer. By contrast, the low-frequency-type ENSO, which occurs in a typical period of 3–7 years, displays an enhanced WNPSH but weakened NPSH. The stronger El Niño tends to generate a more intensified WNPSH from spring to summer, leading to the initial decay of El Niño via the modulation of easterly wind in the western Pacific. On the contrary, the NPSH has greater linkage with the decaying El Niño process after the boreal summer. Therefore, the coupled pattern of WNPSH–NPSH is important in changing ENSO phase from El Niño to La Niña. The NPSH causes sea surface temperature cooling over the subtropical Northeastern Pacific. The resultant subtropical cooling induces anomalous anticyclone west of the reduced heating, which generates the strengthening of trade winds south of the anticyclone. Consequently, this process contributes to tropical central Pacific cooling and the rapid transition of El Niño to La Niña. This study hints that the QB-type ENSO could be significantly linked to a tropics-midlatitudes coupled system such as an in-phase pattern between WNPSH and NPSH. The results are useful for improvement of ENSO prediction. ©2014 Springer-Verlag Berlin Heidelberg
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  • 6
    Publication Date: 2015-04-01
    Description: The moisture supply and El Niño Southern Oscillation (ENSO) characteristics are investigated for different intraseasonal modes of the East Asian summer monsoon (EASM) identified as the Meiyu–Baiu, Changma, post-Changma, and dry-spell modes. The investigation is conducted with a type of artificial neural network known as self-organizing map analysis. The major modes tend to be dominated by the moisture convergence of the moisture budget equation along the rain-band. The Meiyu–Baiu mode is strongly linked to both the anomalous low-level convergence and vertical wind shear, which is related to baroclinic instability with warm air rising and cold air sinking. The Changma mode has a strengthened tropic–subtropics connection along the western north Pacific subtropical high, which induces vertical destabilization and strong convective instability by the low-level warm advection of moisture-laden air and upper-level cold advection of dry air. In late summer, the post-Changma and dry-spell modes are characterized by anomalous southeasterly flow of warm and moist air from western north Pacific monsoon, and low-level easterly flow, respectively. In response to the preceding El Niño, the Meiyu–Baiu and Changma modes occur more frequently, while the post-Changma and dry-spell modes show the opposite. The response to the La Niña exhibits a relatively weak connection, indicating asymmetric response on the preceding ENSO. This prominent difference in response to the ENSO leads to different behaviors of the Indian Ocean and western Pacific thermal state, and consequently, the distinct moisture supply and instability variations for the EASM intraseasonal modes. ©2014 The Author(s)〈br /〉〈br /〉〈a href="http://doi.org/10.1007/s00382-014-2268-4" target="_blank"〉〈img src="http://bib.telegrafenberg.de/typo3temp/pics/f2f773b55e.png" border="0"〉〈/a〉
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  • 7
    Publication Date: 2014-09-01
    Description: Using observations and 1-month lead hindcast data from six coupled atmosphere–ocean climate models, this study investigates the interdecadal change in the leading maximum covariance analysis mode (MCA1) of atmospheric circulation in response to the changes in the El Niño and Southern Oscillation (ENSO) occurred around late 1970s. We focus on boreal winter climate variability and predictability over the North Pacific–North American (NPNA) region using December–January–February prediction initiated from November 1st in the period of 1960–1980 (P1) and 1981–2001 (P2). Observed analysis reveals that ENSO variability, the related tropical convective activity, and thus the MCA1 are considerably enhanced from P1 to P2. As a result, surface climate anomalies over the NPNA are more significantly correlated with the MCA1 in P2 than P1, particularly over North America. The six coupled models and their multi-model ensemble not only are capable of capturing the interdecadal change of the MCA1 and its relationship with surface air temperature and precipitation over the NPNA regions but also have significantly higher forecast skills for the MCA1 and the surface climate anomalies in P2 than P1. However, models have systematic biases in the spatial distribution of the MCA1. It is demonstrated that the interdecadal change in the MCA1 should contribute to the improved forecast skill of the NPNA climate during recent epoch. ©2013 Springer-Verlag Berlin Heidelberg
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  • 8
    Publication Date: 2014-07-01
    Description: The Indian Ocean sea surface temperature (SST) variability has been represented with the two dominant variability modes: the Indian Ocean basin-wide (IOBW) and dipole (IOD) modes. Here we investigate future changes of the two modes together with mean state and El Niño and Southern Oscillation (ENSO) relationship under the anthropogenic global warming using 20 coupled models that participated in the phase five of Coupled Model Intercomparison Project by comparing the historical run from 1950 to 2005 and the RCP 4.5 run from 2050 to 2099. The five best models are selected based on the evaluation of the 20 models’ performances in simulating the two modes and Indian Ocean basic state for the latest 56 years. They are capable of capturing the IOBW and IOD modes in their spatial distribution, seasonal cycle, major periodicity, and relationship with ENSO to some extent. The five best models project the significant changes in the Indian Ocean mean state and variability including the two dominant modes in the latter part of twenty-first century under the anthropogenic warming scenario. First, the annual mean climatological SST displays an IOD-like pattern change over the Indian Ocean with enhanced warming in the northwestern Indian Ocean and relatively weaker warming off the Sumatra–Java coast. It is also noted that the monthly SST variance is increased over the eastern and southwestern Indian Ocean. Second, the IOBW variability on a quasi-biennial time scale will be enhanced due to the strengthening of the ENSO–IOBW mode relationship although the total variance of the IOBW mode will be significantly reduced particularly during late summer and fall. The enhanced air-sea coupling over the Indian-western Pacific climate in response to El Nino activity in the future projection makes favorable condition for a positive IOD while it tends to derive relatively cold temperature over the eastern Indian Ocean. This positive IOD-like ENSO response weakens the relationship between the eastern Indian Ocean and El Nino while strengthens the relationship with western Indian Ocean. Third, the IOD mode, intrinsic coupled mode of the Indian Ocean may not be changed appreciably under the anthropogenic global warming. ©2013 The Author(s)〈br /〉〈br /〉〈a href="http://doi.org/10.1007/s00382-013-2002-7" target="_blank"〉〈img src="http://bib.telegrafenberg.de/typo3temp/pics/f2f773b55e.png" border="0"〉〈/a〉
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  • 9
    Publication Date: 2014-05-01
    Description: The interdecadal and the interannual variability of the global monsoon (GM) precipitation over the area which is chosen by the definition of Wang and Ding (Geophys Res Lett 33: L06711, 2006 ) are investigated. The recent increase of the GM precipitation shown in previous studies is in fact dominant during local summer. It is evident that the GM monsoon precipitation has been increasing associated with the positive phase of the interdecadal Pacific oscillation in recent decades. Against the increasing trend of the GM summer precipitation in the Northern Hemisphere, its interannual variability has been weakened. The significant change-point for the weakening is detected around 1993. The recent weakening of the interannual variability is related to the interdecadal changes in interrelationship among the GM subcomponents around 1993. During P1 (1979–1993) there is no significant interrelationship among GM subcomponents. On the other hand, there are significant interrelationships among the Asian, North American, and North African summer monsoon precipitations during P2 (1994–2009). It is noted that the action center of the interdecadal changes is the Asian summer (AS) monsoon system. It is found that during P2 the Western North Pacific summer monsoon (WNPSM)-related variability is dominant but during P1 the ENSO-related variability is dominant over the AS monsoon region. The WNPSM-related variability is rather related to central-Pacific (CP) type ENSO rather than the eastern-Pacific (EP) type ENSO. Model experiments confirm that the CP type ENSO forcing is related to the dominant WNPSM-related variability and can be responsible for the significant interrelationship among GM subcomponents. ©2013 Springer-Verlag Berlin Heidelberg
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  • 10
    Publication Date: 2013-08-01
    Description: Efforts have been made to appreciate the extent to which we can predict the dominant modes of December–January–February (DJF) 2 m air temperature (TS) variability over the Asian winter monsoon region with dynamical models and a physically based statistical model. Dynamical prediction was made on the basis of multi-model ensemble (MME) of 13 coupled models with the November 1 initial condition for 21 boreal winters of 1981/1982–2001/2002. Statistical prediction was performed for 21 winters of 1981/1982–2001/2002 in a cross-validated way and for 11 winters of 1999/2000–2009/2010 in an independent verification. The first four observed modes of empirical orthogonal function analysis of DJF TS variability explain 69 % of the total variability and are statistically separated from other higher modes. We identify these as predictable modes, because they have clear physical meaning and the MME reproduces them with acceptable criteria. The MME skill basically originates from the models’ ability to capture the predictable modes. The MME shows better skill for the first mode, represented by a basin-wide warming trend, and for second mode related to the Arctic Oscillation. However, the statistical model better captures the third and fourth modes, which are strongly related to El Niño and Southern Oscillation (ENSO) variability on interannual and interdecadal timescales, respectively. Independent statistical forecasting for the recent 11-year period further reveals that the first and fourth modes are highly predictable. The second and third modes are less predictable due to lower persistence of boundary forcing and reduced potential predictability during the recent years. In particular, the notable decadal change in the monsoon–ENSO relationship makes the statistical forecast difficult. ©2012 The Author(s)〈br /〉〈br /〉〈a href="http://doi.org/10.1007/s00382-012-1588-5" target="_blank"〉〈img src="http://bib.telegrafenberg.de/typo3temp/pics/f2f773b55e.png" border="0"〉〈/a〉
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