scholarly journals Variability of Summer Rainfall in Northeast China and Its Connection with Spring Rainfall Variability in the Huang-Huai Region and Indian Ocean SST

2014 ◽  
Vol 27 (18) ◽  
pp. 7086-7101 ◽  
Author(s):  
Zongting Gao ◽  
Zeng-Zhen Hu ◽  
Jieshun Zhu ◽  
Song Yang ◽  
Rong-Hua Zhang ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Northeast China ◽  
General Circulation ◽  
Tropical Indian Ocean ◽  
Summer Rainfall ◽  
Rainfall Anomaly ◽  
Atmospheric Modeling ◽  
Late Spring ◽  
Local Soil ◽  
The Impact

Abstract In this work, the variability of summer [June–August (JJA)] rainfall in northeast China is examined and its predictors are identified based on observational analyses and atmospheric modeling experiments. At interannual time scales, the summer rainfall anomaly in northeast China is significantly correlated with the rainfall anomaly over the Huang-Huai region (32°–38°N, 105°–120°E) in late spring (April–May). Compared with climatology, an earlier (later) rainy season in the Huang-Huai region favors a wet (dry) summer in northeast China. Also, this connection has strengthened since the late 1970s. In addition to the impact of the sea surface temperature anomaly (SSTA) in the tropical Indian Ocean, the local soil moisture anomalies caused by the rainfall anomaly in the Huang-Huai region in late spring generate summer general circulation anomalies, which contribute to the rainfall anomaly in northeast China. As a result, when compared with the SSTA, the rainfall anomaly in the Huang-Huai region in late spring can be used as another and even better predictor for the summer rainfall anomaly in northeast China. The results from atmospheric general circulation model experiments forced by observed SST confirm the diagnostic results to some extent, including the connection of the rainfall anomaly between the Huang-Huai region in April–May and northeastern China in JJA as well as the influence from SSTA in the tropical Indian Ocean. It is shown that eliminating the internal dynamical processes by using the ensemble mean intensifies the connection, implying that the connection of rainfall variation in the two different seasons/regions may be partially caused by the external forcing (e.g., SSTA in the tropical Indian Ocean).

scholarly journals Impact of the Madden–Julian Oscillation on Summer Rainfall in Southeast China

2009 ◽  
Vol 22 (2) ◽  
pp. 201-216 ◽  
Author(s):  
Lina Zhang ◽  
Bizheng Wang ◽  
Qingcun Zeng
Keyword(s):  
Indian Ocean ◽  
Tropical Indian Ocean ◽  
Summer Rainfall ◽  
Western Pacific ◽  
Madden Julian Oscillation ◽  
Energy Propagation ◽  
Southeast China ◽  
The Indian Ocean ◽  
The Impact ◽  
The Western Pacific

Abstract The impact of the Madden–Julian oscillation (MJO) on summer rainfall in Southeast China is investigated using the Real-time Multivariate MJO (RMM) index and the observational rainfall data. A marked transition of rainfall patterns from being enhanced to being suppressed is found in Southeast China (east of 105°E and south of 35°N) on intraseasonal time scales as the MJO convective center moves from the Indian Ocean to the western Pacific Ocean. The maximum positive and negative anomalies of regional mean rainfall are in excess of 10% relative to the climatological regional mean. Such different rainfall regimes are associated with the corresponding changes in physical fields such as the western Pacific subtropical high (WPSH), moisture, and vertical motions. When the MJO is mainly over the Indian Ocean, the WPSH shifts farther westward, and the moisture and upward motions in Southeast China are increased. In contrast, when the MJO enters the western Pacific, the WPSH retreats eastward, and the moisture and upward motions in Southeast China are decreased. It is suggested that the MJO may influence summer rainfall in Southeast China through remote and local dynamical mechanisms, which correspond to the rainfall enhancement and suppression, respectively. The remote role is the energy propagation of the Rossby wave forced by the MJO-related heating over the Indian Ocean through the low-level westerly waveguide from the tropical Indian Ocean to Southeast China. The local role is the northward shift of the upward branch of the anomalous meridional circulation when the MJO is over the western Pacific, which causes eastward retreat of the WPSH and suppressed moisture transport toward Southeast China.

scholarly journals Seasonality and Dynamics of Atmospheric Teleconnection from the Tropical Indian Ocean and the Western Pacific to West Antarctica

Atmosphere ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 849
Author(s):  
Hyun-Ju Lee ◽  
Emilia-Kyung Jin
Keyword(s):  
Indian Ocean ◽  
Rossby Wave ◽  
Tropical Indian Ocean ◽  
Western Pacific ◽  
Tropical Region ◽  
Formation Mechanisms ◽  
West Antarctica ◽  
Background Flow ◽  
The Impact ◽  
The Western Pacific

The global impact of the tropical Indian Ocean and the Western Pacific (IOWP) is expected to increase in the future because this area has been continuously warming due to global warming; however, the impact of the IOWP forcing on West Antarctica has not been clearly revealed. Recently, ice loss in West Antarctica has been accelerated due to the basal melting of ice shelves. This study examines the characteristics and formation mechanisms of the teleconnection between the IOWP and West Antarctica for each season using the Rossby wave theory. To explicitly understand the role of the background flow in the teleconnection process, we conduct linear baroclinic model (LBM) simulations in which the background flow is initialized differently depending on the season. During JJA/SON, the barotropic Rossby wave generated by the IOWP forcing propagates into the Southern Hemisphere through the climatological northerly wind and arrives in West Antarctica; meanwhile, during DJF/MAM, the wave can hardly penetrate the tropical region. This indicates that during the Austral winter and spring, the IOWP forcing and IOWP-region variabilities such as the Indian Ocean Dipole (IOD) and Indian Ocean Basin (IOB) modes should paid more attention to in order to investigate the ice change in West Antarctica.

An Enhanced Influence of Tropical Indian Ocean on the South Asia High after the Late 1970s

2012 ◽  
Vol 25 (20) ◽  
pp. 6930-6941 ◽  
Author(s):  
Xia Qu ◽  
Gang Huang
Keyword(s):  
Indian Ocean ◽  
South Asia ◽  
Tropical Indian Ocean ◽  
Tropospheric Temperature ◽  
Decadal Change ◽  
The South ◽  
South Asia High ◽  
The Impact ◽  
Change In Mean ◽  
Sst Anomalies

Abstract The tropical Indian Ocean (TIO)’s influence on the South Asia high (SAH)’s intensity experiences a decadal change in the late 1970s; after (before) the decadal shift, the influence is significant (insignificant). The present study investigates the role of tropospheric temperature in relaying the impact of sea surface temperature (SST) to the SAH and the change in the TIO’s influence. During the two epochs, the local tropospheric temperature responses to the TIO warming are distinct—more significant during the second epoch. It is inferred that this change may be responsible for the strengthening of the TIO’s influence on the SAH. Encouragingly, the ensemble simulations accurately capture the time of the decadal change, indicating that the enhanced influence is attributed to the SST forcing. There are two possible reasons for the change in the TIO–SAH relationship. The first reason is the change in the locations of the SST anomalies in the TIO. During the second epoch, positive SST anomalies lie in the Indian Ocean warm pool. Through the background vigorous convection and moist adjustment, the SST anomalies affect largely the tropospheric temperature and thus the SAH. The second reason is the decadal change in mean SST and the SST variability. During the recent decades, both the background SST and the variability of the TIO SST increase, which enhance the influence of the SST anomalies on the atmosphere. The influence of the remote oceanic forcing on the enhanced TIO–SAH relationship and its comparison with the contribution of the TIO SST are also discussed.

scholarly journals Impacts of Late-Spring North Eurasian Soil Moisture Variation on Summer Rainfall Anomalies in Northern East Asia

2021 ◽  
Author(s):  
Yinghan Sang ◽  
Hong-Li Ren ◽  
Yi Deng ◽  
Xiaofeng Xu ◽  
Xueli Shi ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Temperature Gradient ◽  
East Asia ◽  
Summer Rainfall ◽  
Low Pressure ◽  
Late Spring ◽  
Boreal Summer ◽  
Pressure Center ◽  
North Eurasia ◽  
The Impact

Abstract This paper reports findings from a diagnostic and modeling analysis that investigates the impact of the late-spring soil moisture anomaly over North Eurasia on the boreal summer rainfall over northern East Asia (NEA). Soil moisture in May in the region from the Kara-Laptev Sea coasts to Central Siberian Plateau is found to be negatively correlated with the summer rainfall from Mongolia to Northeast China. The atmospheric circulation anomalies associated with the anomalously dry soil are characterized by a pressure dipole with the high-pressure center located over North Eurasia and the low-pressure center over NEA, where an anomalous lower-level moisture convergence occurs, favoring rainfall formation. Diagnoses and Modeling experiments demonstrate that the effect of the spring low soil moisture over North Eurasia may persist into the following summer through modulating local surface latent and sensible heat fluxes, increasing low-level air temperature at higher latitudes, and effectively reducing the meridional temperature gradient. The weakened temperature gradient could induce the decreased zonal wind and the generation of a low-pressure center over NEA, associated with a favorable condition of local synoptic activity. The above relationships and mechanisms are vice versa for the prior wetter soil and decreased NEA rainfall. These findings suggest that soil moisture anomalies over North Eurasia may act as a new precursor providing an additional predictability source for better predicting the summer rainfall in NEA.

The Fingerprint of Indian Ocean Rain and River Water in Salinity and Circulation

2021 ◽  
Author(s):  
Vinu Valsala
Keyword(s):  
Indian Ocean ◽  
General Circulation ◽  
Climate Models ◽  
Transport Model ◽  
Tropical Indian Ocean ◽  
Quasi Equilibrium ◽  
Tracer Transport ◽  
Tropical Ocean ◽  
Cumulative Impact ◽  
Circulation Anomalies

Abstract Per unit area of the tropical Indian Ocean receives the world’s largest tropical ocean rain and river runoff (RRW). The 3-dimensional spreading of RRW entering the tropical Indian Ocean and associated salinity and circulation anomalies are explored for 60 years using ocean reanalysis data tailored to a tracer transport model. Over 60 years, the cumulative impact of RRW entering the tropical Indian Ocean is to freshen the Indian Ocean basin as large as 2-0.1 p.s.u from the surface to 500m. The RRW has propagated to a vast extent of the Atlantic and Pacific Oceans via general circulation pathways. A quasi-equilibrium model of accumulation of RRW over the tropical Indian Ocean suggests that it induces clockwise geostrophic currents from the Bay of Bengal to the Arabian Sea over 0-500m depths, a net inter-basin transport tendency of 0.8±0.14 Sv year-1. The study implies that coupled climate models with apparent precipitation biases may miscalculate such salinity and circulation anomalies due to RRW and aggravating biases in simulated climate dynamics.

Recent Atmospheric Variability at Kibo Summit, Kilimanjaro, and Its Relation to Climate Mode Activity

2018 ◽  
Vol 31 (10) ◽  
pp. 3875-3891 ◽  
Author(s):  
Emily Collier ◽  
Thomas Mölg ◽  
Tobias Sauter
Keyword(s):  
Indian Ocean ◽  
Current Knowledge ◽  
Southern Oscillation ◽  
Strong Association ◽  
Atmospheric Modeling ◽  
High Mountain ◽  
Atmospheric Variability ◽  
Rain Season ◽  
The Indian Ocean ◽  
The Impact

Abstract Accurate knowledge of the impact of internal atmospheric variability is required for the detection and attribution of climate change and for interpreting glacier records. However, current knowledge of such impacts in high-mountain regions is largely based on statistical methods, as the observational data required for process-based assessments are often spatially or temporally deficient. Using a case study of Kilimanjaro, 12 years of convection-permitting atmospheric modeling are combined with an 8-yr observational record to evaluate the impact of climate oscillations on recent high-altitude atmospheric variability during the short rains (the secondary rain season in the region). The focus is on two modes that have a well-established relationship with precipitation during this season, El Niño–Southern Oscillation and the Indian Ocean zonal mode, and demonstrate their strong association with local and mesoscale conditions at Kilimanjaro. Both oscillations correlate positively with humidity fluctuations, but the association is strongest with the Indian Ocean zonal mode in the air layers near and above the glaciers because of changes in zonal circulation and moisture transport, emphasizing the importance of the moisture signal from this basin. However, the most anomalous conditions are found during co-occurring positive events because of the combined effects of the (i) extended positive sea surface temperature anomalies, (ii) enhanced atmospheric moisture capacity from higher tropospheric temperatures, (iii) most pronounced weakening of the subsiding branch of the Indian Ocean Walker circulation over East Africa, and (iv) stronger monsoonal moisture fluxes upstream from Kilimanjaro. This study lays the foundation for unraveling the contribution of climate modes to observed changes in Kilimanjaro’s glaciers.

Projected Changes in Mean and Extreme Precipitation in Africa under Global Warming. Part II: East Africa

2011 ◽  
Vol 24 (14) ◽  
pp. 3718-3733 ◽  
Author(s):  
Mxolisi E. Shongwe ◽  
Geert Jan van Oldenborgh ◽  
Bart van den Hurk ◽  
Maarten van Aalst
Keyword(s):  
Indian Ocean ◽  
East Africa ◽  
Extreme Precipitation ◽  
General Circulation ◽  
Tropical Indian Ocean ◽  
General Circulation Models ◽  
Rate Of Change ◽  
Intergovernmental Panel ◽  
Eastern Hemisphere ◽  
Short Rains

Abstract Probable changes in mean and extreme precipitation in East Africa are estimated from general circulation models (GCMs) prepared for the Intergovernmental Panel on Climate Change Fourth Assessment Report (AR4). Bayesian statistics are used to derive the relative weights assigned to each member in the multimodel ensemble. There is substantial evidence in support of a positive shift of the whole rainfall distribution in East Africa during the wet seasons. The models give indications for an increase in mean precipitation rates and intensity of high rainfall events but for less severe droughts. Upward precipitation trends are projected from early this (twenty first) century. As in the observations, a statistically significant link between sea surface temperature gradients in the tropical Indian Ocean and short rains (October–December) in East Africa is simulated in the GCMs. Furthermore, most models project a differential warming of the Indian Ocean during boreal autumn. This is favorable for an increase in the probability of positive Indian Ocean zonal mode events, which have been associated with anomalously strong short rains in East Africa. On top of the general increase in rainfall in the tropics due to thermodynamic effects, a change in the structure of the Eastern Hemisphere Walker circulation is consistent with an increase in East Africa precipitation relative to other regions within the same latitudinal belt. A notable feature of this change is a weakening of the climatological subsidence over eastern Kenya. East Africa is shown to be a region in which a coherent projection of future precipitation change can be made, supported by physical arguments. Although the rate of change is still uncertain, almost all results point to a wetter climate with more intense wet seasons and less severe droughts.

scholarly journals Explorations of the Annual Mean Heat Budget of the Tropical Indian Ocean. Part II: Studies with a Simplified Ocean General Circulation Model

2007 ◽  
Vol 20 (13) ◽  
pp. 3229-3248 ◽  
Author(s):  
Rui-Jin Hu ◽  
J. Stuart Godfrey
Keyword(s):  
Indian Ocean ◽  
General Circulation ◽  
Heat Budget ◽  
Tropical Indian Ocean ◽  
Open Boundary ◽  
Western Boundary ◽  
Diapycnal Mixing ◽  
Depth Estimate ◽  
Minimum Depth ◽  
One Year

Abstract Present-day OGCMs give low values of annual mean net heat flux (AMNHF) in the tropical Indian Ocean, compared to climatologies. AMNHF generation is examined in an open-boundary model of this region with realistic coastlines. In the first two of three experiments only annual mean wind stresses were applied so that a modified form of the “minimum depth criterion” of the previous paper would be applicable. Area-integrated AMNHF was well below observed values, despite the fact that western boundary inflow was substantially deeper and colder than was expected from the modified minimum depth estimate. The model showed large “spikes” in the gradient of “depth-integrated steric height” (DISH) along the western boundary, coinciding with coastline steps (which were absent in the previous paper). Most diapycnal entrainment occurred next to the coast, near these steps. In a third experiment a seasonal cycle of wind stress was added to the same annual mean. Annual mean diapycnal mixing and entrainment increased and the western boundary inflow deepened, resulting in substantially greater AMNHF for the same annual mean Ekman transports. However, area-integrated AMNHF was still well below the mean of directly observed surface fluxes. The recirculation around the “Great Whirl” doubled, permitting more cold water crossing the equator in one year to mix with recirculated water generated in a previous year. Entrainment up to the surface thus went by stages, over more than one year. The increased Great Whirl was related to stronger annual mean curls of nonlinear terms in the momentum equation, while the deeper entrainment was caused by stronger annual mean diapycnal mixing. In all experiments, diapycnal mixing was primarily due to the “flux corrected transport” (FCT) advective scheme, which in effect replaces spurious convective overturn by numerical diffusion. More research is needed to solve such problems, but sensitivity of AMNHF in OGCMs to time-varying forcing—due to seasonal, intraseasonal, or baroclinic instability—may offer a new source of climate predictability.

scholarly journals Explorations of the Annual Mean Heat Budget of the Tropical Indian Ocean. Part I: Studies with an Idealized Model

2007 ◽  
Vol 20 (13) ◽  
pp. 3210-3228 ◽  
Author(s):  
J. Stuart Godfrey ◽  
Rui-Jin Hu ◽  
Andreas Schiller ◽  
R. Fiedler
Keyword(s):  
Indian Ocean ◽  
Lower Limit ◽  
General Circulation ◽  
Heat Budget ◽  
Tropical Indian Ocean ◽  
General Circulation Models ◽  
Heat Fluxes ◽  
Ekman Transport ◽  
Western Boundary ◽  
Northern Boundary

Abstract Annual mean net heat fluxes from ocean general circulation models (OGCMs) are systematically too low in the tropical Indian Ocean, compared to observations. In the models, only some of the geostrophic inflow replacing southward Ekman outflow is colder than the minimum sea surface temperature (MINSST). Observed heat fluxes imply that much more inflow is colder than MINSST. Since inflow below MINSST can only join the surface Ekman transport after diathermal warming, the OGCMs must underestimate diathermal effects. A crude analog of the annual mean Indian Ocean heat budget was generated, using a rectangular box model with a deep “Indo–Pacific” gap at 7°–10°S in its eastern side. Wind stress was zonal and proportional to the Coriolis parameter, so Ekman transport was spatially constant and equaled Sverdrup transport. For three experiments, zonally integrated Ekman transport was steady and southward at 10 Sv (Sv ≡ 106 m3 s−1). In steady state, a 10 Sv “Indonesian Throughflow” fed a northward western boundary current of 10 Sv, which turned eastward along the northern boundary at 10°N to feed the southward Ekman transport. Most diathermal mixing occurred within an intense eddy in the northwest corner. Some of the geostrophic inflow was at temperatures colder than MINSST (found at the northeast corner of the eddy); it must warm to MINSST via diathermal mixing. Northern boundary upwelling exceeded the 10-Sv Ekman transport. The excess warms as it recirculates around the eddy, apparently supplying the heat to warm inflow below MINSST. In an experiment using the “flux-corrected transport” (FCT) scheme, diathermal mixing occurred in the strongly sheared currents around the eddy. However the Richardson number never became low enough to drive strong diathermal mixing, perhaps because (like that of other published models) the present model’s vertical resolution was too coarse. In three experiments, the dominant mixing was caused by horizontal diffusion, spurious convective overturn, and numerical mixing invoked by the FCT scheme, respectively. All three mixing mechanisms are physically suspect; such model problems (if widespread) must be resolved before the mismatch between observed and modeled heat fluxes can be addressed. However, the fact that the density profile at the western boundary must be hydrostatically stable places a lower limit on the area-integrated heat fluxes. Results from the three main experiments—and from many published OGCMs—are quite close to this lower limit.

scholarly journals Predictions of Indian Ocean SST Indices with a Simple Statistical Model: A Null Hypothesis

2009 ◽  
Vol 22 (18) ◽  
pp. 4930-4938 ◽  
Author(s):  
Dietmar Dommenget ◽  
Malte Jansen
Keyword(s):  
Indian Ocean ◽  
Statistical Model ◽  
General Circulation Model ◽  
Null Hypothesis ◽  
General Circulation ◽  
Circulation Model ◽  
Tropical Indian Ocean ◽  
Model Studies ◽  
Sst Variability ◽  
The Indian Ocean

Abstract Several recent general circulation model studies discuss the predictability of the Indian Ocean dipole (IOD) mode, suggesting that it is predictable because of coupled ocean–atmosphere interactions in the Indian Ocean. However, it is not clear from these studies how much of the predictability is due to the response to El Niño. It is shown in this note that a simple statistical model that treats the Indian Ocean as a red noise process forced by tropical Pacific SST shows forecast skills comparable to those of recent general circulation model studies. The results also indicate that some of the eastern tropical Indian Ocean SST predictability in recent studies may indeed be beyond the skill of the simple model proposed in this note, indicating that dynamics in the Indian Ocean may have caused this improved predictability in this region. The model further indicates that the IOD index may be the least predictable index of Indian Ocean SST variability. The model is proposed as a null hypothesis for Indian Ocean SST predictions.

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