Regime Change of the Boreal Summer Hadley Circulation and Its Connection with the Tropical SST

2011 ◽  
Vol 24 (15) ◽  
pp. 3867-3877 ◽  
Author(s):  
Ran Feng ◽  
Jianping Li ◽  
Jincheng Wang
Keyword(s):  
High Frequency ◽  
Regime Change ◽  
Hadley Circulation ◽  
Warm Pool ◽  
Boreal Summer ◽  
Tropical Atlantic ◽  
Asymmetric Mode ◽  
Pacific Warm Pool ◽  
Highly Correlated ◽  
Relationship Of

Abstract The year-to-year variability of the boreal summer [June–August (JJA)] Hadley circulation (HC) is dominated by an asymmetric mode centered in the Northern Hemisphere (AMN) and a quasi-symmetric mode centered at 5°N (QSM). The regime change of the JJA HC is revealed by the phase reversal of the time series of the AMN, showing significant weakening of the northern part of the JJA HC and a reversed seesaw relationship of the zonal-mean updraft over 10°–20°N and around the equator. This transition is accompanied by the southward retreat of the HC core and is well correlated with the weakening of tropical summer monsoons. The strong warming trends of the sea surface temperature over the tropical Atlantic and Indo–west Pacific warm pool play an important role in the regime change of the JJA HC. The high-frequency interannual variability of the JJA HC, however, is mainly featured by the QSM and is highly correlated with the Niño-3.4 index, implying that ENSO’s influence is mainly on the high-frequency interannual time scale.

scholarly journals Long-Term Variation of the Principal Mode of Boreal Spring Hadley Circulation Linked to SST over the Indo-Pacific Warm Pool

2013 ◽  
Vol 26 (2) ◽  
pp. 532-544 ◽  
Author(s):  
Juan Feng ◽  
Jianping Li ◽  
Fei Xie
Keyword(s):  
Meridional Circulation ◽  
Hadley Circulation ◽  
Warming Trend ◽  
Warm Pool ◽  
Asymmetric Mode ◽  
Principal Mode ◽  
Boreal Spring ◽  
Pacific Warm Pool ◽  
Term Variation

Abstract The variability of the boreal spring [March–May (MAM)] Hadley circulation (HC) is investigated, focusing on the long-term variation of the first principal mode for 1951–2008, which is an equatorially asymmetric mode (AM) with the rising branch located around 10°S. This mode explains about 70% of the variance of the MAM HC and shows an obvious upward trend and thus contributes to the strengthening of the MAM HC. The robust warming trends of sea surface temperature (SST) over the Indo-Pacific warm pool (IPWP) play an essential role in the variations of the MAM HC. When SST over the IPWP is warm, anomalous meridional circulation is induced with descending branches located in regions 30°–20°S and 5°–15°N and rising motion located near 10°S. The anomalous rising south of the equator is due to the inhomogeneous warming of SST over the IPWP. SST within the IPWP in the Southern Hemisphere shows a larger warming trend than that in the Northern Hemisphere. The position of the anomalous convergence associated with SST variations over the IPWP is aligned with the maximum meridional gradient of zonal mean SST, resulting in an equatorially asymmetric meridional circulation. This point is further established in theoretical analyses. However, the meridional SST gradient within the IPWP shows a decreasing trend, suggesting the associated anomalous meridional circulation intensifies, which in turn explains the strengthening of the MAM HC. Under this scenario, the accompanied descent in the regions of 30°–20°S and 5°–15°N is enhanced, implying a frequent drought in these regions during MAM.

Subseasonal SST Variability in the Tropical Eastern North Pacific during Boreal Summer

2008 ◽  
Vol 21 (17) ◽  
pp. 4149-4167 ◽  
Author(s):  
Eric D. Maloney ◽  
Dudley B. Chelton ◽  
Steven K. Esbensen
Keyword(s):  
Costa Rica ◽  
Warm Pool ◽  
Boreal Summer ◽  
Sst Variability ◽  
East Pacific ◽  
Pacific Warm Pool ◽  
Northern Edge ◽  
Precipitation Anomalies ◽  
Sst Anomalies ◽  
Costa Rica Dome

Abstract Boreal summer intraseasonal (30–90-day time scale) sea surface temperature (SST) variability in the east Pacific warm pool is examined using Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) sea surface temperatures during 1998–2005. Intraseasonal SST variance maximizes at two locations in the warm pool: in the vicinity of 9°N, 92°W near the Costa Rica Dome and near the northern edge of the warm pool in the vicinity of 19°N, 108°W. Both locations exhibit a significant spectral peak at 50–60-day periods, time scales characteristic of the Madden–Julian oscillation (MJO). Complex empirical orthogonal function (CEOF) and spectra coherence analyses are used to show that boreal summer intraseasonal SST anomalies are coherent with precipitation anomalies across the east Pacific warm pool. Spatial variations of phase are modest across the warm pool, although evidence exists for the northward progression of intraseasonal SST and precipitation anomalies. Intraseasonal SSTs at the north edge of the warm pool lag those in the vicinity of the Costa Rica Dome by about 1 week. The MJO explains 30%–40% of the variance of intraseasonal SST anomalies in the east Pacific warm pool during boreal summer. Peak-to-peak SST variations of 0.8°–1.0°C occur during MJO events. SST is approximately in quadrature with MJO precipitation, with suppressed (enhanced) MJO precipitation anomalies leading positive (negative) SST anomalies by 7–10 days. Consistent with the CEOF and coherence analyses, MJO-related SST and precipitation anomalies near the Costa Rica Dome lead those at the northern edge of the warm pool by about 1 week.

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 Impact of the Indo-Pacific Warm Pool on the Hadley, Walker, and Monsoon Circulations

Atmosphere ◽  
2020 ◽  
Vol 11 (10) ◽  
pp. 1030
Author(s):  
Hye-Ryeom Kim ◽  
Kyung-Ja Ha ◽  
Suyeon Moon ◽  
Hyoeun Oh ◽  
Sahil Sharma
Keyword(s):  
Dominant Role ◽  
Hadley Circulation ◽  
Walker Circulation ◽  
Warming Trend ◽  
Warm Pool ◽  
Vital Role ◽  
Natural Variability ◽  
Natural Mode ◽  
Monsoon Circulation ◽  
Pacific Warm Pool

The Indo-Pacific warm pool (IPWP) is enclosed by a 28 °C isotherm and plays a vital role in controlling atmospheric circulations. However, the effects of changes in regional warm pool sea surface temperatures (SSTs) remain unexplored. We divided the IPWP into the Indian and Pacific sectors and distinguished their responses to natural variability and global warming. Furthermore, we examined the impacts of the interannual variability (IAV) in warm pool SST on the tropical Hadley, Walker, and monsoon circulations. The Hadley circulation was affected by warm pool SST warming, i.e., warmer SSTs over the warm pool strengthened the upward branch of Hadley circulation, whereas the downward branch was respectively weakened and strengthened in the Northern and Southern Hemispheres. Walker circulation was strengthened (weakened) in the warming (natural) mode. Consequently, the Walker circulation is weakened since the natural variability of warm pool SST plays a more dominant role rather than the warming trend of SSTs over the warm pool. Furthermore, our analysis displays that warm pool warming has little impact on the monsoon circulation. Our findings highlight the different roles of the IAV of warm pool regions in each tropical circulation as part of the warming trend and natural variability.

scholarly journals Influence of the Madden–Julian Oscillation and Caribbean Low-Level Jet on East Pacific Easterly Wave Dynamics

2018 ◽  
Vol 75 (4) ◽  
pp. 1121-1141 ◽  
Author(s):  
Justin W. Whitaker ◽  
Eric D. Maloney
Keyword(s):  
Warm Pool ◽  
Central American ◽  
Madden Julian Oscillation ◽  
Easterly Waves ◽  
Low Level ◽  
East Pacific ◽  
Pacific Warm Pool ◽  
Low Level Jet ◽  
Favorable Conditions ◽  
Relationship Of

Abstract The east Pacific warm pool exhibits basic-state variability associated with the Madden–Julian oscillation (MJO) and Caribbean low-level jet (CLLJ), which affects the development of easterly waves (EWs). This study compares and contrasts composite changes in the background environment, eddy kinetic energy (EKE) budgets, and EW tracks during MJO and CLLJ events. While previous studies have shown that the MJO influences jet activity in the east Pacific, the influence of the MJO and CLLJ on the east Pacific and EWs is not synonymous. The CLLJ is a stronger modulator of the ITCZ than the MJO, while the MJO has a more expansive influence on the northeastern portion of the basin. Anomalous low-level westerly MJO and CLLJ periods are associated with favorable conditions for EW development paralleling the Central American coast, contrary to previous findings about the relationship of the CLLJ to EWs. Easterly MJO and CLLJ periods support enhanced ITCZ EW development, although the CLLJ is a greater modulator of EW tracks in this region, which is likely associated with stronger moisture and convection variations and their subsequent influence on the EKE budget. ITCZ EW growth during easterly MJO periods is more reliant on barotropic conversion than during strong CLLJ periods, when eddy available potential energy (EAPE)-to-EKE conversion associated with ITCZ convection is more important. Thus, the influence of these phenomena on east Pacific EWs should be considered distinct.

scholarly journals Anvil Characteristics as Seen by C-POL during the Tropical Warm Pool International Cloud Experiment (TWP-ICE)

2008 ◽  
Vol 136 (1) ◽  
pp. 206-222 ◽  
Author(s):  
Kaycee Frederick ◽  
Courtney Schumacher
Keyword(s):  
Deep Convection ◽  
Warm Pool ◽  
Radar Data ◽  
Strong Positive Correlation ◽  
Monsoon Period ◽  
Rain Area ◽  
Strong Negative Correlation ◽  
Areal Coverage ◽  
Pacific Warm Pool ◽  
Relationship Of

Abstract The Tropical Pacific Warm Pool International Cloud Experiment (TWP-ICE) took place in Darwin, Australia, in early 2006. C-band radar data were used to characterize tropical anvil (i.e., thick, nonprecipitating cloud associated with deep convection) areal coverage, height, and thickness during the monthlong field campaign. The morphology, evolution, and longevity of the anvil were analyzed, as was the relationship of the anvil to the rest of the precipitating system. The anvil was separated into mixed (i.e., echo base below 6 km) and ice-only categories. The average areal coverage for each anvil type was between 4% and 5% of the radar grid. Ice anvil thickness averaged 2.8 km and mixed anvil thickness averaged 6.7 km. Areal peaks show that mixed anvil typically formed out of the stratiform rain region. Peak production in ice anvil usually followed the mixed anvil peak by 1–3 h. Anvil typically lasted 4–10 h after the initial convective rain area peak. TWP-ICE experienced three distinct regimes: an active monsoon, a dry monsoon, and a break period. During the experiment (except the active monsoon period) there was a strong negative correlation between ice anvil thickness and ice anvil height, a strong positive correlation between ice anvil area and thickness, and a greater variance in ice anvil bottom than ice anvil top. These results have important implications for understanding how anvil affects the tropical atmosphere.

scholarly journals Autonomic effects on the spectral analysis of heart rate variability after exercise

2009 ◽  
Vol 297 (4) ◽  
pp. H1421-H1428 ◽  
Author(s):  
Jason Ng ◽  
Sri Sundaram ◽  
Alan H. Kadish ◽  
Jeffrey J. Goldberger
Keyword(s):  
Frequency Domain ◽  
High Frequency ◽  
Frequency Domain Analysis ◽  
Mean Square ◽  
Rr Intervals ◽  
Autonomic Blockade ◽  
Frequency Components ◽  
Highly Correlated ◽  
Relationship Of ◽  
The Relationship

Although frequency-domain analysis of heart rate variability (HRV) has been performed in the setting of exercise and recovery from exercise, the relationship of specific frequency components to sympathetic and parasympathetic inputs has not been validated in this setting. The aim of this study is to evaluate the relationship of frequency components of HRV to sympathetic and parasympathetic modulation in the setting of recovery after exercise using selective autonomic blockade. Normal subjects ( n = 27, 17 men, 53 ± 7 yr old) underwent bicycle stress testing on four separate days. On day 1, a baseline study without autonomic blockade was performed. On days 2 through 4, either β-adrenergic, parasympathetic, or double blockade was administered during exercise and completed 3 min before recovery. Continuous ECG was recorded for 5 min starting from the end of exercise. Time- and frequency-domain measures of HRV were computed for each of the five 1-min segments of RR intervals. Parasympathetic blockade significantly decreased all the HRV measures compared with baseline ( P < 0.02 for all). Root mean square of successive differences of RR intervals (rMSSD) was increased by β-adrenergic blockade ( P < 0.0002). All the HRV measures except rMSSD showed increases with time after the first minute of recovery. The low frequency-to-high frequency ratio did not respond to autonomic blockade or to recovery time, consistent with the expected changes in sympathovagal influence. Root mean square (detrended SD) and rMSSD were highly correlated with the square root of the total power ( r = 0.96) and high-frequency power ( r = 0.95), respectively. Although there are marked reductions in the frequency-domain measures in recovery versus rest, the fluctuations in the low- and high-frequency bands respond to autonomic blockade in the expected fashion. Time-domain measures of HRV were highly correlated with frequency-domain measures and therefore provide a computationally more efficient assessment of autonomic influences during recovery from exercise that is less susceptible to anomalies of frequency-domain analysis.

The tropical atmospheric conveyor belt: a Lagrangian perspective of the large-scale tropical circulation

2020 ◽  
Author(s):  
Dana Raiter ◽  
Eli Galanti ◽  
Yohai Kaspi
Keyword(s):  
Large Scale ◽  
Meridional Circulation ◽  
Hadley Circulation ◽  
Warm Pool ◽  
Conveyor Belt ◽  
Jet Stream ◽  
Tropical Circulation ◽  
Pacific Warm Pool ◽  
Actual Movement ◽  
The Tropics

&lt;div&gt; &lt;div&gt;The Hadley circulation (HC) is a key element of the climate system. It is traditionally defined as the zonally averaged meridional circulation in the tropics, therefore treated as a zonally symmetric phenomenon. However, differences in temperature between land and sea cause zonal asymmetries on Earth, dramatically affecting the circulation. The longitudinal dependence of the HC evokes questions about where and when the actual large scale tropical circulation occurs. In this study, we look into the connection between the longitudinally dependent HC and the actual large scale movement of air in the tropics using a coupled Eulerian and Lagrangian approach. Decomposing the velocity field, we identify the components affecting the actual circulation. In addition, we calculate trajectories of air parcels to analyze the actual movement. We propose an alternative definition for the circulation, that describes the actual path of air parcels in the tropics, as a tropical conveyor belt. The Indo-Pacific warm pool is the driver of the circulation, where air converges and ascends, then moves westward and poleward before entering the jet stream, moving eastward with it, eventually beginning its descent near the Americas. Furthermore, using an idealized moist GCM, we explore how tropical asymmetries affect the circulation and discuss the possible mechanisms controlling the tropical conveyor belt.&lt;/div&gt; &lt;/div&gt;

scholarly journals Increased Chances of Drought in Southeastern Periphery of the Tibetan Plateau Induced by Anthropogenic Warming

2017 ◽  
Vol 30 (16) ◽  
pp. 6543-6560 ◽  
Author(s):  
Shuangmei Ma ◽  
Tianjun Zhou ◽  
Oliver Angélil ◽  
Hideo Shiogama
Keyword(s):  
Climate Change ◽  
Tibetan Plateau ◽  
Climate Models ◽  
Hadley Circulation ◽  
Warm Pool ◽  
Severe Drought ◽  
The Tibetan Plateau ◽  
Ensemble Simulations ◽  
Pacific Warm Pool ◽  
Drought Conditions

The southeastern periphery of the Tibetan Plateau (SEPTP) was hit by an extraordinarily severe drought in the autumn of 2009. Overall, the SEPTP has been gripped by a sustained drought for six consecutive years. To better understand the physical causes of these types of severe and frequent droughts and thus to improve their prediction and enhance the ability to adapt, many research efforts have been devoted to the disastrous droughts in the SEPTP. Nonetheless, whether the likelihood and strength of the severe droughts in the SEPTP, such as that in the autumn of 2009, have been affected by anthropogenic climate change remains unknown. This study first identifies the atmospheric circulation regime responsible for the SEPTP droughts and then explores how human-induced climate change has affected the severe droughts in the SEPTP. It is found that the drought conditions in the SEPTP have been driven by the Indian–Pacific warm pool (IPWP) sea surface temperature (SST) through strengthening of the local Hadley circulation and anomalously cyclonic motion over the South China Sea. Ensemble simulations of climate models demonstrate a robust increase in the dry and warm meteorological conditions seen during the 2009 SEPTP autumn drought due to anthropogenic global warming. Given that warming is expected to continue into the future, these results suggest that it is likely that drought conditions will become more common in the SEPTP.

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