|
|
- Revisiting the equatorial Pacific sea surface temperature response to
global warming-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The relative roles of the oceanic and atmospheric processes in the pattern formation of the equatorial Pacific sea surface temperature (SST) response to global warming is investigated using a set of climate model experiments embedded with a novel partial coupling technique. The modeling results show that the SST response experiences a transition from a La Niña-like warming pattern at the initial stage to an El Niño-like warming pattern at the quasi-equilibrium stage. By decomposing anomalous equatorial Pacific SST into atmosphere thermally forced passive component and ocean dynamically induced active component, it is found that the SST warming pattern at both stages is entirely induced by its active component. Specifically, the meridional and vertical ocean circulation changes play a dominant role in forming the La Niña-like SST warming pattern at the initial stage, and the zonal and meridional ocean circulation changes are responsible for the formation of the El Niño-like SST warming pattern at the quasi-equilibrium stage. In contrast, the passive SST at both stages is characterized by a zonally uniform warming along the equator, which can be explained by a balance between the total effect of the heat transport divergence associated with the mean ocean circulation and the effect of the passive surface heat flux change. In addition, this study finds that it is the slowdown of the Pacific subtropical cells during the transition period that controls the evolution of the equatorial SST warming pattern by changing the meridional and vertical ocean heat transports.
PubDate: 2023-12-02
- Impact of initializing the soil with a thermally and hydrologically
balanced state on subseasonal predictability-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Accurate soil moisture initial conditions in dynamical subseasonal forecast systems are known to improve the temperature forecast skill regionally, through more realistic water and energy fluxes at the land-atmosphere interface. Recently, results from a multi-model coordinated experiment have provided evidence of the primal contribution of the initial surface and subsurface soil temperature over the Tibetan Plateau for capturing a hemispheric scale atmopsheric teleconnection leading to improved subseasonal forecasts. Yet, both the soil temperature and water content are key components of the soil enthalpy and we hypothesize that properly initializing one of them without modifying the other in a consistent manner can alter the soil thermal equilibrium, thereby potentially reducing the benefit of land initial conditions on subsequent atmospheric forecasts. This study builds on the protocol of the above-mentioned multi-model experiment, by testing three different land initialization strategies in an Earth system model. Results of this pilot study suggest that a better mass and energy balance in land initial conditions of the Tibetan Plateau triggers a wave train which propagates through the northern hemisphere mid-latitudes, resulting in an improved large scale circulation and temperature anomalies over multiple regions of the globe. While this study is based on a single case, it strongly advocates for enhanced attention towards preserving the soil energy equilibrium at initialization to make the most of land as a driver of atmospheric extended-range predictability.
PubDate: 2023-12-02
- Future risk of decadal megadrought events over eastern China based on
IPO-constrained precipitation-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract A reliable projection of future risk of decadal megadrought is crucial to adaption and mitigation over eastern China in future climate changes. However, it’s difficult to forecast the time of megadrought, which is dominated by internal variability of the model. Using a 50-member ensemble of simulations from the Community Earth System Model Version 2 Large Ensemble (CESM2-LE), it is found that, under the medium-high emission scenario (i.e., SSP3-7.0), internal variability account for all the uncertainty of decadal precipitation variability over eastern China, and the interdecadal Pacific oscillation (IPO) could contribute about 30% to the internal uncertainty during future period (2021–2080). Finally, an emergent constraint based on IPO phase is applied to reduce the uncertainty of simulated precipitation and to forecast the future megadrought risk. The constrained precipitation changes show that northern China will experience a high megadrought risk in the 2050s–2060s, and Yangtze River Valley will experience a high megadrought risk in the 2030s–2040s. These will have great benefit to specific strategies of social infrastructure in the future.
PubDate: 2023-12-01
- Correction: Aspects of potential vorticity circulation in the Northern
Hemisphere: climatology and variation-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
PubDate: 2023-12-01
- Correction to: Quantification of tropical monsoon precipitation changes in
terms of interhemispheric differences in stratospheric sulfate aerosol
optical depth-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
PubDate: 2023-12-01
- Correction to: Characteristics of clustered heavy precipitation events at
Northeast China and associated atmospheric circulations-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
PubDate: 2023-12-01
- Precipitation variability using GPCC data and its relationship with
atmospheric teleconnections in Northeast Brazil-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: The present study investigates the influence of different atmospheric teleconnections on the annual precipitation variability in Northeast Brazil (NEB) based on the annual precipitation data from the Global Precipitation Climatology Center (GPCC) from 1901 to 2013. The objective of this study is to analyze the influence of different atmospheric teleconnections on the total annual precipitation of NEB for the 1901–2013 period, considering the physical characteristics of four subregions, i.e., Mid-north, Backwoods, Agreste, and Forest zone. To analyze the influence of different atmospheric teleconnections, GPCC data were used, and the behavior of the teleconnections was assessed using Pearson correlation coefficient, Rainfall Anomaly Index (RAI), and cross-wavelet analysis. The Pearson correlation was used to analyze the influence on the annual precipitation for the studied region. RAI was used to calculate the frequency of atmospheric patterns and drought episodes. The cross-wavelet analysis was applied to identify similarity signals between precipitation series and atmospheric teleconnections. The results of the Pearson correlation assessed according to Student's t test and cross-wavelet analysis showed that the Atlantic Multidecadal Oscillation (AMO) exerts a more significant influence on the Backwoods region at an interannual scale. In contrast, the Pacific Decadal Oscillation (PDO) exerts greater control over the modulation of the climatic patterns in NEB. The results of the study are insightful and reveal the differential impacts of teleconnections such as the AMO, PDO, MEI, and NAO on precipitation in the four sub-regions of NEB. The Atlantic circulation patterns strongly influence the interannual and interdecadal precipitation in the Agreste, Backwoods, and Mid-north regions, possibly associated with the Intertropical Convergence Zone (ITCZ) position. Finally, this study contributes to understanding internal climatic variability in NEB and planning of water resources and agricultural activities in such a region. Graphic abstract 
PubDate: 2023-12-01
- Continental configuration controls the base-state water vapor greenhouse
effect: lessons from half-land, half-water planets-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The distribution of land and ocean on Earth’s surface shapes the global atmospheric circulation and climate by modulating fluxes of water and energy between the surface and the atmosphere. Here we rearranged land in an idealized climate model to explore the effect of eight simplified continental configurations on global climate, finding several counterintuitive results. The limited capacity of land to hold water and the smaller heat capacity of land compared to ocean—rather than surface albedo differences—are the primary drivers of continental control on global mean temperature. Specifically, the presence of land in certain locations can enhance tropospheric water vapor content, increasing the greenhouse effect and clear-sky shortwave absorption; these effects can warm the planet more than the cooling effect of higher land surface albedos. For example, continental configurations with land in polar regions and large tropical oceans have the warmest, wettest global climates. Configurations with large tropical land masses are not hot desert planets, but have the coolest global climates due to reduced evaporation and thus reduced atmospheric water vapor compared to configurations without land in the tropics. Interactions between the small heat capacity of land and the seasonal cycle can lead to certain continental configurations having even warmer, wetter atmospheres than an aquaplanet. Our results demonstrate that different configurations of land, such as those obtained through past tectonic movement or on rocky exoplanets, set planetary climate through mechanisms beyond those involving surface albedo or orographic effects.
PubDate: 2023-12-01
- Tropical cyclone size asymmetry index and climatology
-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Size of tropical cyclone (TC) is often asymmetric in nature. Yet, there is a lack of systematic, clean, and intuitive definition/expression to specify the asymmetry of TC size. Here, we introduce a novel index, TC size asymmetry index (SAI), which specifies both the degree and pattern of the asymmetry synthetically. In particular, the symbolic form of SAI is vividly designated for identifying the latter. The SAI proposes 1 quasi-symmetric pattern and 28 asymmetric patterns in total. The 41-year (1979–2019) global climatology of SAI shows that the distribution of the degree of TC size asymmetry is trimodal. Elementarily, the degree and pattern of asymmetry are found to be TC intensity, TC movement, time, and space dependent. The introduction of SAI provides an insight into the subject and lays an important foundation for future applications and research. Furthermore, besides meteorology, it could inspire other fields to index the geometric asymmetries of other kinds.
PubDate: 2023-12-01
- Characteristics of clustered heavy precipitation events at Northeast China
and associated atmospheric circulations-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Heavy precipitation events can exert greater impact than general precipitation on the economy, ecology, and people’s livelihoods. Based on CN05.1 daily precipitation data and the NCEP/NCAR global daily reanalysis dataset, this study analyzes the characteristics of clustered heavy precipitation (CHP) events during summer in Northeast China (NEC) during 1961–2020, with consideration of associated atmospheric circulations and moisture transport. Results indicate that CHP events occurred mainly during midsummer, especially in July. Both the frequency and the intensity of CHP events decrease after the mid-1970s, increase after the early 1980s, and then diminish again after the 2000s. The CHP events occur in association with an anomalous lower-tropospheric cyclone centered over NEC, northward and westward shifts of the western North Pacific subtropical high in the middle troposphere, and northward shift of an intensified westerly jet in the upper troposphere, in conjunction with strengthened local convective motion. Additionally, the net moisture budget begins to increase 2 days before the occurrence of CHP and peaks 6 h earlier than the CHP. Further results indicate that net moisture influx across the southern boundary of NEC made a dominant contribution to the net moisture budget. The results of this study have importance regarding the prediction of CHP events over NEC.
PubDate: 2023-12-01
- Projected trends in hydro-climatic extremes in small-to-mid-sized
watersheds in eastern Nepal based on CMIP6 outputs-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Quantifying the extent of change in climatic and hydrological variables in the past and the future is essential for climate change-resilient development, especially in the climate change sensitive region of Nepal. This paper analyzed future climatic trends and extremes, historical hydrological extremes and their linkage with historical precipitation extremes, and discussed the impacts of climate change on various sectors in the less-studied Small and Medium-sized Eastern River Basins (SMERB) of Nepal. Applying an ensemble of five Coupled Model Intercomparison Project phase 6 (CMIP6) global climate models (GCMs), we evaluated 10 precipitation and 13 temperature extreme indices using Climpact2 for the historical (1979–2020), near-future (2021–2045), mid-future (2046–2070) and far-future (2071–2100) under two Shared Socioeconomic Pathway (SSP), SSP245 and SSP585. Hydrological extreme indices were assessed using Indicators of Hydrologic Alteration tool. Projected climate revealed significant increase (9–73%) in annual and seasonal rainfall except winter; frequent intense rainfall extremes but prolonged dry spells; significant increasing minimum and maximum temperature trends (0.4–5 °C); rise in extreme heat events; increasing minimum and maximum discharge extreme trends in most hydrological stations; as well as strong association between maximum 1 day precipitation (Rx1day) and 1 day max flow for all stations. Growing dry periods but intense rainfall in few wet days, coupled with warming pattern all-over SMERB with frequent extreme events indicate high risk for future climate-related disasters. The harsher climate will potentially have damaging implications, especially in climate-induced disasters, food security, and water and sanitation infrastructure.
PubDate: 2023-12-01
- Using simplified linear and nonlinear models to assess ENSO-modulated MJO
teleconnections-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Simple dynamical models are used to understand fundamental processes of how ENSO modulates subseasonal teleconnections associated with tropical imprints of the MJO by stripping away complex phenomena. Both a dry linear baroclinic model and a dry nonlinear baroclinic model are employed to (1) assess how much of the MJO teleconnection pattern in a particular ENSO phase can be captured by linear and nonlinear dynamics and (2) analyze the role of the ENSO-modulated MJO forcing and base state in reproducing the teleconnection patterns. The modeling experiments reveal that linear dynamics are sufficient in capturing differences between the Northern Hemisphere teleconnections associated with the MJO during El Niño and La Niña. Nonlinear dynamics modestly capture more of the Northern Hemisphere MJO teleconnection pattern, particularly over North America, suggesting the teleconnection response over North America is more complex. The teleconnection patterns are sensitive to changes in both the ENSO background state and the domain of the monthly MJO-associated forcing. A Rossby wave source diagnosis is applied to further understand the underlying mechanisms. Further, a series of experiments swapping MJO forcings during El Niño events versus La Niña events with an ENSO-neutral base state and vice versa show that the MJO forcing has a larger influence over the teleconnection pattern than the base state. Therefore, the modulation of the MJO convection by ENSO dominates the ENSO-phase-dependent changes to the Northern Hemisphere teleconnection pattern. These modeling experiments highlight that MJO teleconnections must be considered in the context of the ongoing ENSO event.
PubDate: 2023-12-01
- Attribution of the December 2013 extreme rainfall over the Pearl River
Delta to anthropogenic influences-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract During 14 to 17 December 2013, the Pearl River Delta (PRD) in South China received its largest wintertime 4-day precipitation of above 100 mm since 1998, due to strong cold air intrusion. Here we investigate the extent to which such extreme rainfall can be attributed to human activities, by carrying out Weather Research and Forecasting (WRF) model multi-physics integrations at a convection-permitting resolution. The factual WRF runs were conducted using the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA)-Interim as boundary and initial conditions, and the counterfactual runs by the same ERA-Interim forcing with human influences removed. The latter was deduced by subtracting the Coupled Model Intercomparison Project Phase 5 (CMIP5) historical-natural from the historical run outputs. Results show that the 4-day mean rainfall could increase by 11% for 1.2 K near-surface warming on average under human-induced thermodynamic forcing in relation to humidity changes, whereas it increases by 17% for 2 K warming under all forcing (i.e., including dynamic forcing associated with wind circulation changes), which is nearly the Clausius–Clapeyron rate. Moreover, the former and latter forcing can intensify the 95th percentile daily rainfall by ~ 13% and ~ 19%, respectively, suggesting that human-caused dynamic forcing can further exacerbate the thermodynamic-driven rainfall enhancement in this event. Indeed, there is stronger land-sea thermal contrast with anomalous low-level southerly winds and convergence in coastal South China under all forcing. The frontal system and ascending motion are therefore intensified, resulting in even stronger rain rates than under thermodynamic forcing. Moisture budget analysis reveals that the dynamic component accounts for most of the increase in 4-day mean rainfall while the thermodynamic contribution is negligible under all forcing. Our findings highlight the salient role of dynamic effects on intensifying PRD’s extreme rainfall in wintertime.
PubDate: 2023-12-01
- Characterization of precipitation and temperature equilibrium and its
driving forces in the Yangtze river basin under climate change-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Global warming has severely affected the climate in the Yangtze River Basin (YRB), resulting in complex and varying meteorological and hydrological processes. Therefore, identifying the effects of climate change in the YRB is important for characterizing the affected meteorological and hydrological processes. In this study, the characteristics of climate equilibrium were analyzed and the natural drivers of climate change in the YRB were explored using precipitation and temperature data from 1961 to 2018. The major findings can be summarized as follows. (1) Significant spatial and temporal differences in precipitation and temperature occurred. For example, annual precipitation showed a decreasing trend in the middle reaches but a significant increasing trend in the headwaters area and lower reaches. Between 1981 and 2001, annual precipitation and temperature exhibited overall increasing trends as well as abrupt changes. (2) Temporal changes in precipitation were primarily low in the middle and lower reaches and high in the headwater region of the YRB, although a low precipitation concentration degree (CD) occurred in summer in the upper reaches. High temperature changes over time mainly occurred in the headwater region of the YRB, although a high temperature CD occurred in winter in the northern parts. (3) Different teleconnection indices affected precipitation and temperature in different seasons. In particular, the Niño 3.4, North Atlantic Oscillation, and North Pacific Index had a significant influence on precipitation and temperature. This study provides critical information for revealing the changes in meteorological and hydrological processes and potential influencing factors in the YRB.
PubDate: 2023-12-01
- The improvements of sea surface temperature simulation over China Offshore
Sea in present climate from CMIP5 to CMIP6 models-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract By using the 43 Historical experiments from phase 6 of the Coupled Model Intercomparison Project (CMIP6) and 45 Historical experiments from phase 5 of CMIP (CMIP5) for the period of 1950–2005, we comprehensively assess the improvements in simulating the spatial pattern, warming trend, climatology and interannual variation of sea surface temperature (SST) in China offshore sea (COS) from CMIP5 to CMIP6 models. Both CMIP6 multi-model ensemble mean (CMIP6 MME) and CMIP5 multi-model ensemble mean (CMIP5 MME) well simulated the spatial pattern of climatological-mean COS SST, but they tend to underestimate the warming trends of COS SST at both seasonal and interannual timescales, which is due to the low estimations of SST warming rate before the late 1970s, particularly for the CMIP6 models. Nevertheless, both the simulated trend biases and inter-model uncertainties are reduced from CMIP5 to CMIP6 models during the period 1979–2005. Compared to the simulated annual-mean and seasonal-mean COS SST in the CMIP5 models, the inter-model uncertainties and cold biases of SST simulated by the CMIP6 models have been significantly reduced, particularly for the autumn-mean and summer-mean SST. Similarly, the CMIP6 models perform better than the CMIP5 models in simulating the interannual variation of COS SST, as evidenced by a much lower interannual variability skill score over the South China Sea and Huang&Bo China Sea. Furthermore, more than 60% of CMIP6 models perform better than their counterpart CMIP5 models in simulating the spatial patterns and interannual variations of annual-mean and seasonal-mean COS SST based on the rank of individual models performance and comprehensive ranking measure ordering. Additionally, the insignificant improvement of the evident warm bias in the East China Sea during winter and spring and cold bias in the Huang&Bo China Sea during spring and summer from CMIP5 to CMIP6 models is primarily associated with the defect of the ocean dynamical processes.
PubDate: 2023-12-01
- On the simulations of latent heat flux over the Indian Ocean in CMIP6
models-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The historical simulations of latent heat flux (LHF) over the Indian Ocean (IO) region in 46 climate models participating in the phase 6 of Coupled Model Intercomparison Project (CMIP6) have been evaluated against the ERA5 dataset for the period 1975–2014. The multimodel mean (MMM) captures the observed spatial pattern of LHF climatological mean state to a great extent, but there are large biases in magnitude, especially over the region north of 20 °S and south of 40 °S, and these biases are common to more than 70% of the individual CMIP6 models. The origins of these biases are due to overestimated surface winds and vertical humidity gradients in the models. The simulated trend values of LHF are largely underestimated and are highly inconsistent in individual models. The basin-wide increase of surface saturation specific humidity ( \({Q}_{s}\) ) is largely compensated by a similar increase in near-surface saturation specific humidity ( \({Q}_{a}\) ) trend, which leads to reduced vertical humidity gradient for the latent heat transfer to take place at the air-sea interface. The long-term trend of sea surface temperature (SST) and \({Q}_{s}\) are found to be reasonable in CMIP6 models. One of the reasons for the underestimated LHF trend in CMIP6 models is the faster rate of increase of \({Q}_{a}\) and very slow rate of increase of surface wind speed compared to the ERA5 dataset.
PubDate: 2023-12-01
- Mid-Holocene precipitation variations in the Luoyang Basin within the
Central Plains of China: a pollen-based reconstruction-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract In the context of ongoing global warming, understanding the East Asian Summer Monsoon (EASM) dynamics is of great significance for predicting future climate changes. This study reconstructed the mid-Holocene precipitation variations on the basis of pollen data obtained from Taojiacun section in the Luoyang Basin within the Central Plains of China. Our research results show that the region experienced three dry intervals during the data-covering period (~ 8.08 to ~ 4.76 cal. kyr BP): ~8.08 to ~ 7.35, ~ 6.42 to ~ 5.59, and ~ 4.94 to ~ 4.76 cal. kyr BP. The intervened were two wet intervals: ~7.35 to ~ 6.42 and ~ 5.59 to ~ 4.94 cal. kyr BP. The chronological correspondence between drier (wetter) intervals in the Luoyang Basin and warmer (cooler) intervals in the western Tropical Pacific implies that the north-south shifts of the Western Pacific Subtropical High (WPSH), driven by the western Tropical Pacific Sea Surface Temperature (SST), regulated the positions of the EASM-related rain-belt during the data-covering period. We compared the mean annual precipitation (Pann) sequence from Taojiacun section with those from the southern and northern neighboring areas. With a full consideration of chronological uncertainties and sampling resolution differences, it can be generalized that those drier (wetter) intervals in the Luoyang Basin within the Central Plains of China were broadly correspondent with those drier (wetter) intervals expressed in the sequences of the southern neighboring areas (i.e., the middle and lower reaches of the Yangtze River with an addition of the Huai River Basin). It means that the changes in precipitation in the Central Plains was most likely coincident with that in the southern neighboring areas during the data-covering period (~ 8.08 to ~ 4.76 cal. kyr BP).
PubDate: 2023-12-01
- Relationships among Arctic warming, sea-ice loss, stability, lapse rate
feedback, and Arctic amplification-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The Arctic warms much faster than other places under increasing greenhouse gases, a phenomenon known as Arctic amplification (AA). Arctic positive lapse-rate feedback (LRF) and oceanic heating induced by sea-ice loss have been considered as major causes of Arctic warming and AA, and Arctic high atmospheric stability has been considered as a key factor for the occurrence of the bottom-heavy warming profile and thus positive LRF in the Arctic. Here we analyze model simulations with and without large AA and sea-ice loss and long-term changes in ERA5 reanalysis data to examine the relationships among Arctic sea-ice loss, stability, LRF, Arctic warming, and AA. Results show that the Arctic bottom-heavy warming profile and the resultant positive LRF are produced primarily by increased oceanic heating of the air due to sea-ice loss in Arctic winter, rather than high atmospheric stability. Without the oceanic heating induced by sea-ice loss, most Arctic climate feedbacks weaken greatly, and all other processes can only produce slightly enhanced surface warming and thus weak positive LRF under stable Arctic air. A non-convective Arctic environment allows the oceanic heating to warm near-surface air more than the upper levels, resulting in large positive LRF that roughly doubles the surface warming compared with the case without the LRF. We conclude that enhanced cold-season oceanic heating due to sea-ice loss is the primary cause of Arctic large positive LRF, which in turn allows the surface heating to produce more Arctic warming and large AA.
PubDate: 2023-12-01
- ENSO phase space dynamics with an improved estimate of the thermocline
depth-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract The recharge oscillator model of the El Niño Southern Oscillation (ENSO) describes the ENSO dynamics as an interaction between the eastern tropical Pacific sea surface temperatures (T) and subsurface heat content (thermocline depth; h), defining a dynamical cycle with different phases. h is often approximated on the basis of the depth of the 20 °C isotherm (Z20). In this study we will address how the estimation of h affects the representation of ENSO dynamics. We will compare the ENSO phase space with h estimated based on Z20 and based on the maximum gradient in the temperature profile (Zmxg). The results illustrate that the ENSO phase space is much closer to the idealised recharge oscillator model if based on Zmxg than if based on Z20. Using linear and non-linear recharge oscillator models fitted to the observed data illustrates that the Z20 estimate leads to artificial phase dependent structures in the ENSO phase space, which result from an in-phase correlation between h and T. Based on the Zmxg estimate the ENSO phase space diagram show very clear non-linear aspects in growth rates and phase speeds. Based on this estimate we can describe the ENSO cycle dynamics as a non-linear cycle that grows during the recharge and El Nino state, and decays during the La Nina states. The most extreme ENSO states are during the El Nino and discharge states, while the La Nina and recharge states do not have extreme states. It further has faster phase speeds after the El Nino state and slower phase speeds during and after the La Nina states. The analysis suggests that the ENSO phase speed is significantly positive in all phases, suggesting that ENSO is indeed a cycle. However, the phase speeds are closest to zero during and after the La Nina state, indicating that the ENSO cycle is most likely to stall in these states.
PubDate: 2023-12-01
- Seasonal predictable signals of east Asian summer monsoon rainfall in
existing monsoon indices-
Free pre-print version: Loading...
Rate this result:
What is this?
Please help us test our new pre-print finding feature by giving the pre-print link a rating.
A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract East Asian summer monsoon indices (EASMIs) have been widely used to investigate the variability and predictability of the East Asian summer monsoon rainfall (EASMR). However, the ability of existing EASMIs remains unclear to represent the interannual variability of the EASMR in predictable (P-) and unpredictable (U-) components. Based on a (co-)variance decomposition method, the fractional variance explained by a single EASMI has the highest value of 22% in both P- and U-components. A set of the best three EASMIs, together with the linear trend, is linearly independent of each other and can explain a large percentage of EASMR variance in P-component (54%). This set of EASMIs captures the main predictive circulation features in the corresponding EASMR P-modes, i.e., a low-level Philippine Sea (anti-)cyclone and an upper-level zonal wind tripole pattern for P-mode1, an East China Sea (anti-)cyclone for P-mode2, and a west–east pressure dipole pattern for P-mode3. In addition, they also have the major predictable sources from the predictors of their corresponding P-modes, i.e., the decaying and developing El Niño–Southern Oscillation, the spring Arctic Oscillation, the spring sea surface temperatures over the western North Pacific, tropical and southern Atlantic, southern Indian and Arctic oceans. By considering the predictable and unpredictable components, this work not only improves our knowledge of the physical meanings and the potential limitations of the existing EASMIs, but also helps us in selecting the most appropriate EASMIs when focusing on the issue of seasonal forecasting.
PubDate: 2023-12-01
|
Hybrid journal (It can contain Open Access articles)
