Subsurface Thermal Anomalies Research Articles

A spatiotemporal 3D convolutional neural network model for ENSO predictions: A test case for the 2020/21 La Niña conditions

Many coupled models are unable to accurately depict the multi-year La Niña conditions in the tropical Pacific during 2020–22, which poses a new challenge for real-time El Niño–Southern Oscillation (ENSO) predictions. Yet, the corresponding processes responsible for the multi-year coolings are still not understood well. In this paper, reanalysis products are analyzed to examine the ocean–atmosphere interactions in the tropical Pacific that have led to the evolution of sea surface temperature (SST) in the central-eastern equatorial Pacific, including the strong anomalous southeasterly winds over the southeastern tropical Pacific and the related subsurface thermal anomalies. Meanwhile, a divided temporal and spatial (TS) 3D convolution neural network (CNN) model, named TS-3DCNN, was developed to make predictions of the 2020/21 La Niña conditions; results from this novel data-driven model are compared with those from a physics-based intermediate coupled model (ICM). The prediction results made using the TS-3DCNN model for the 2020–22 La Niña indicate that this deep learning–based model can capture the two-year La Niña event to some extent, and is comparable to the IOCAS ICM; the latter dynamical model yields a successful real-time prediction of the Niño3.4 SST anomaly in late 2021 when it is initiated from early 2021. For physical interpretability, sensitivity experiments were designed and carried out to confirm the dominant roles played by the anomalous southeasterly wind and subsurface temperature fields in sustaining the second-year cooling in late 2021. As a potential approach to improving predictions for diversities of ENSO events, additional studies on effectively combining neural networks with dynamical processes and mechanisms are expected to significantly enhance the ENSO prediction capability.摘要2020–22年间热带太平洋经历了持续性多年的拉尼娜事件, 多数耦合模式都难以准确预测其演变过程, 这为厄尔尼诺-南方涛动(ENSO)的实时预测带来了很大的挑战. 同时, 目前学术界对此次持续性双拉尼娜事件的发展仍缺乏合理的物理解释, 其所涉及的物理过程和机制有待于进一步分析. 本研究利用再分析数据产品分析了热带东南太平洋东南风异常及其引起的次表层海温异常在此次热带太平洋海表温度(SST)异常演变中的作用, 并构建了一个时空分离(Time-Space)的三维(3D)卷积神经网络模型(TS-3DCNN)对此次双拉尼娜事件进行实时预测和过程分析. 通过将TS-3DCNN与中国科学院海洋研究所(IOCAS)中等复杂程度海气耦合模式(IOCAS ICM)的预测结果对比, 表明TS-3DCNN模型对2020–22年双重拉尼娜现象的预测能力与IOCAS ICM相当, 二者均能够从2021年初的初始场开始较好地预测2021年末 El Niño3.4区SST的演变. 此外, 基于TS-3DCNN和IOCAS ICM的敏感性试验也验证了赤道外风场异常和次表层海温异常在2021年末赤道中东太平洋海表二次变冷过程中的关键作用. 未来将神经网络与动力 模式模式间的有效结合, 进一步发展神经网络与物理过程相结合的混合建模是进一步提高ENSO事件预测能力的有效途径.

Impact-induced changes in source depth and volume of magmatism on Mercury and their observational signatures

Mercury’s crust is mostly the result of partial melting in the mantle associated with solid-state convection. Large impacts induce additional melting by generating subsurface thermal anomalies. By numerically investigating the geodynamical effects of impacts, here we show that impact-generated thermal anomalies interact with the underlying convection modifying the source depth of melt and inducing volcanism that can significantly postdate the impact depending on the impact time and location with respect to the underlying convection pattern. We can reproduce the volume and time of emplacement of the melt sheets in the interior of Caloris and Rembrandt if at about 3.7–3.8 Ga convection in the mantle of Mercury was weak, an inference corroborated by the dating of the youngest large volcanic provinces. The source depth of the melt sheets is located in the stagnant lid, a volume of the mantle that never participated in convection and may contain pristine mantle material.

Processes involved in the second-year warming of the 2015 El Niño event as derived from an intermediate ocean model

The tropical Pacific experienced a sustained warm sea surface condition that started in 2014 and a very strong El Nino event in 2015. One striking feature of this event was the horseshoe-like pattern of positive subsurface thermal anomalies that was sustained in the western-central equatorial Pacific throughout 2014–2015. Observational data and an intermediate ocean model are used to describe the sea surface temperature (SST) evolution during 2014–2015. Emphasis is placed on the processes involved in the 2015 El Nino event and their relationships with SST anomalies, including remote effects associated with the propagation and reflection of oceanic equatorial waves (as indicated in sea level (SL) signals) at the boundaries and local effects of the positive subsurface thermal anomalies. It is demonstrated that the positive subsurface thermal anomaly pattern that was sustained throughout 2014–2015 played an important role in maintaining warm SST anomalies in the equatorial Pacific. Further analyses of the SST budget revealed the dominant processes contributing to SST anomalies during 2014–2015. These analyses provide an improved understanding of the extent to which processes associated with the 2015 El Nino event are consistent with current El Nino and Southern Oscillation theories.

The roles of atmospheric wind and entrained water temperature (Te) in the second-year cooling of the 2010\u201312 La Ni\xf1a event

An intermediate coupled model (ICM) yields a successful real-time prediction of the sea surface temperature (SST) evolution in the tropical Pacific during the 2010–12 La Niña event, whereas many other coupled models fail. It was previously identified that the thermocline effect on the SST (including vertical advection and mixing), as represented by water temperature entrained into the mixed layer (Te) and its relationship with the thermocline fluctuation, is an important factor that affects the second-year cooling in mid-late 2011. Because atmospheric wind forcing is also important to ENSO processes, its role is investigated in this study within the context of real-time prediction of the 2010–12 La Niña event using the ICM in which wind stress anomalies are calculated using an empirical model as a response to SST anomalies. An easterly wind anomaly is observed to persist over the western-central Pacific during 2010–11, which acts to sustain a horse shoe-like Te pattern connecting large negative subsurface thermal anomalies in the central-eastern regions off and on the equator. Sensitivity experiments are conducted using the ICM to demonstrate how its SST predictions are directly affected by the intensity of wind forcing. The second-year cooling in 2011 is not predicted to occur in the ICM if the easterly wind anomaly intensity is weakly represented below certain levels; instead, a surface warming can emerge in 2011, with weak SST variability. The results of the current study indicate that the intensity of interannual wind forcing is equally important to SST evolution during 2010–11 compared with that of the thermocline effect. To correctly predict the observed La Niña conditions in the fall of 2011, the ICM needs to adequately represent the intensity of both the wind forcing and the thermocline effects.

Subsurface absorption of anthropogenic warming of the land surface: The case of the world's largest brickworks (Stewartby, Bedfordshire, UK)

Stewartby works, for a time the world's largest brickworks, began operation around the start of the twentieth century and closed in 2008. Subsurface temperature measurements are available in its vicinity, obtained as part of monitoring of an adjacent landfill in one of the former quarries for the Oxford Clay, which was the raw material for brick manufacture. A striking subsurface temperature anomaly, an increment of ~12°C, was first measured in 2004, and has subsequently decayed over time. The anomaly is centred beneath one of the former brick kilns, which operated between 1935 and 1991. To investigate processes of heat absorption by the shallow subsurface, this anomaly has been modelled as a consequence of conductive heat flow into the ground due to the operation of the ~3000m2 kiln. This modelling indicates that a very large amount of heat energy was transported into the subsurface; we estimate the typical downward surface heat flow during operation of the kiln as ~1Wm−2 and the energy stored in the subsurface beneath it at its time of shutdown as ~6TJ, or ~0.03% of that released by the fuel for heating the kiln, such that the total heat energy stored beneath this multi-kiln site peaked at ~200TJ. The proportion of heat energy transported into the subsurface was relatively low due to the nature of the Oxford Clay, which has a low thermal conductivity (~0.8Wm−1°C−1) and diffusivity (~0.3mm2s−1); in a more conductive lithology it might well have been three times greater. After kiln shutdown this subsurface thermal anomaly began to dissipate by upward heat conduction and release of heat into the atmosphere; at present about half of the peak energy stored remains, decreasing at ~1% per year, the maximum temperature anomaly being currently ~7°C at a depth of ~30m and the typical upward heat flow during this span of time having exceeded the regional ~40mWm−2 background by roughly an order of magnitude. We believe this to be the first documented case whereby a subsurface thermal anomaly associated with operation of industrial plant has been related in detail to the history of site operations. This case study thus bears upon the controversial topic of the development of subsurface heat islands in general, and the associated perturbation of the thermal state of the subsurface as a result of anthropogenic warming of the atmosphere. It has previously been suggested that the worldwide heat gain in the subsurface over recent decades has exceeded that in the atmosphere by a factor of three. We show that this result is subject to some uncertainty, for example because it does not factor in lateral variations in thermal properties. Nonetheless, our case study demonstrates dissipation of a subsurface thermal anomaly by heat transport into the atmosphere. This indicates that warming of the atmosphere will be sustained in the future by dissipation of the large amount of energy stored in pre-existing subsurface thermal anomalies on a global scale, an issue of major societal implications that demands more detailed investigation.

Anthropogenic effects on the subsurface thermal and groundwater environments in Osaka, Japan and Bangkok, Thailand

Anthropogenic effects in both Osaka and Bangkok were evaluated to compare the relationships between subsurface environment and the development stage of both cities. Subsurface thermal anomalies due to heat island effects were found in both cities. The Surface Warming Index (SWI), the departure depth from the steady geothermal gradient, was used as an indicator of the heat island effect. SWI increases (deeper) with the magnitude of heat island effect and the elapsed time starting from the surface warming. Distributions of subsurface thermal anomalies due to the heat island effect agreed well with the distribution of changes in air temperature due to the same process, which is described by the distribution of population density in both Osaka and Bangkok. Different time lags between groundwater depression and subsidence in the two cities was found. This is attributed to differences in hydrogeologic characters, such as porosity and hydraulic conductivity. We find that differences in subsurface degradations in Osaka and Bangkok, including subsurface thermal anomalies, groundwater depression, and land subsidence, depends on the difference of the development stage of urbanization and hydrogeological characters.

Integrated research on subsurface environments in Asian urban areas

The RIHN project “Human impacts on urban subsurface environments” aims to suggest improved development plans of urban centers for human well-being. This will be done by examining reconstructed past changes in urban environments, and by developing integrated nature-social models. Subsurface environmental indicators are developed from the points of view of: (1) human activities; (2) climate change; and (3) character of urban development and social policies. Water, heat, and material environments and transport vectors are being evaluated by a number of different approaches. Some of these include investigating changes in groundwater resources using satellite observations, reconstructing effects of climate change and urbanization using subsurface thermal regimes, and evaluating past contamination patterns from preserved subsurface records. In this overview paper, we describe the current status of urbanization in Asia, subsurface water conditions, material and contaminant transport to surface waters by groundwater, and subsurface thermal anomalies due to the heat island effect. The rapid pace of urbanization in Asia requires that we develop a better understanding of how to deal with environmental impacts, both above and below ground.

Northwest Africa upwelling and the Atlantic climate variability

Summer Subtropical North Atlantic (SNA) Sea Surface Temperature (SST) anomalies have recently been connected to winter atmospheric variability in the Atlantic European sector. Wind‐induced surface heat flux changes are believed to be the major cause of SNA SST anomalies. However, the impact of coastal upwelling off northwest Africa, on SNA SST variability has been overlooked. Since the area is known to have a richer dynamical behavior than other regions of the central SNA, subsurface thermal anomalies are included in our analysis. Results show that this upwelling region affects significantly the patterns of co‐variability between climatically relevant variables, suggesting that more intricate processes may be involved in generating surface anomalies that, in turn, may influence the European sector climate variability.

Effects of hydrogeological and climate change on the subsurface thermal regime in the Sendai Plain

We estimated the effects of hydrogeological and surface temperature warming on subsurface thermal regime from the temperature–depth profiles and hydrological data of groundwater quality both in the quaternary and tertiary systems in the Sendai Plain as a preliminary step toward reconstruction of climate changes. Annual mean air temperature in the plain has increased about 1.5 °C in the last 70 years and this surface warming resulted in low or negative thermal gradient. However, anomaly of thermal gradient was recognized in not all temperature–depth profiles. Groundwater chemical compositions and stable isotope data (δD and δ 18O) show that the groundwater flow system has marked difference between those of tertiary and quaternary systems. Calculated results of three dimensional groundwater flow and heat transport model ensure the above hypothesis and shows that thermal gradient changes at close to basement of the quaternary system. The differences in groundwater flow systems are expressed as subsurface thermal gradient anomalies in the temperature–depth profiles in the Sendai Plain. Furthermore, one-dimensional numerical analyze including the effect of surface warming indicates that calculated profile has departure from steady state line at depths in 60–80 m agree well with observed one.

Role of off‐equatorial subsurface anomalies in initiating the 1991–1992 El Niño as revealed by the National Centers for Environmental Prediction ocean reanalysis data

The National Centers for Environmental Prediction ocean reanalysis data for 1980–1995 have been analyzed along mean constant density surfaces (mean isopycnals) in order to describe better and understand the three‐dimensional space‐time evolution of the 1991–1992 El Niño event in the tropical Pacific. The major finding is of a well‐defined, shallow pathway of off‐equatorial temperature anomalies along the Pacific North Equatorial Countercurrent (NECC) associated with the onset phase of the event. This pathway originates from the western boundary off the equator in the Northern Hemisphere along 6°–10°N and then basically follows the mean circulation eastward and upward along the NECC path toward the central basin. Along this pathway, temperature anomalies show coherent phase relationships off and on the equator and in surface and subsurface layers, respectively. A sequence of events is described that lead to E1 Niño conditions in the tropical Pacific Ocean. Beginning in early 1989, a positive temperature anomaly progressed coherently eastward along the NECC path off the equator toward the central basin, finally making its way equatorward with the expected mean circulation in late 1990. As the thermocline shoals eastward and upward along the NECC, in due course the progressing subsurface anomaly outcropped near the date line off the equator and initiated and sustained a midbasin warm sea surface temperature (SST) anomaly during the period from late 1990 through early 1991. This SST anomaly induced westerly wind anomalies over the western tropical Pacific, favoring Ekman convergence onto the equator. These anomalous surface currents advected these initially subsurface‐produced SST anomalies equatorward. Subsequently, these SST and wind anomalies were coupled, which resulted in a large‐scale relaxation of the trade winds over the western and central tropical basin, generating eastward currents that transported water mass eastward along the equator. These results are markedly different from the delayed oscillator physics in that the major role can be played by advection and outcropping of off‐equatorial subsurface thermal anomalies along the shallow NECC pathway, not necessarily involving the western boundary reflection of equatorial Rossby waves.

Interannual and decadal variability of the subsurface thermal structure in the Pacific Ocean: 1961-90

Heat content anomalies are analyzed to understand subsurface variability on both aparticular focus on the evolving basinwide patterns and oceanic connections between the extratropics and tropics. Various analyses indicate two distinct modes, one interannual and the other decadal, that involve the tropics and the North Pacific subtropical gyre, respectively. Interannual variability is associated with El Nino in the tropics, with a prominent “see-saw” pattern alternately on and off the equator, and in the east and west, respectively. The interannual cycle features a coherent propagation of subsurface signals around the tropical Pacific, eastward along the equator but westward off the equator at 10–15 °N. Decadal signals are dominant in the subtropics and midlatitudes but also have a tropical component that appears to be independent of interannual variations. An oceanic connection can be seen between subsurface anomalies in the midlatitudes, in the subtropics and tropics on decadal time scales. Subsurface thermal anomalies associated with midlatitude decadal variability can propagate through the subtropics into the tropics, which may modulate the intensity of interannual variability in the tropics. For example, in the middle and late 1970s, a significant warm temperature anomaly appeared to penetrate into the western and central tropics at depth, warming the tropical upper ocean and depressing the thermocline. During the development of El Nino, therefore, an extratropically preconditioned subsurface state (e.g., an enhanced positive heat content anomaly) in the western and central tropical Pacific would favor a warmer sea surface temperature anomaly in the eastern equatorial Pacific, potentially increasing the intensity of ocean-atmosphere coupling. These changes in the thermocline structure and possibly in the coupling strength can further alter the very character of tropical air-sea interactions. This may help to explain decadal variability of El Nino evolution in the tropical Pacific as observed in the 1980s. Our subsurface variability analysis presents observational evidence for the detailed space-time structure of decadal oceanic links between the extratropics and the tropics.

The onset of the 1991–92 El Niño event in the tropical Pacific Ocean: The NECC subsurface pathway

Based on the NCEP ocean re‐analysis data, the three‐dimensional co‐evolution of the tropical Pacific climate system is examined to explain the onset of the 1991–92 El Niño event. A logical sequence is discovered that links subsurface and surface temperature anomalies off and on the equator in the western and central Pacific. Along the North Equatorial Countercurrent (NECC) path, subsurface temperature anomalies propagated coherently eastward from the western boundary in mid‐1989 to the date line in mid‐1990, at a speed of about 10–20 cm−1. As the thermocline shoals eastward along the NECC, the subsurface anomalies outcropped in the regions near the date line, initiating warm sea surface temperature (SST) anomalies which further amplified while advectively extending into the equatorial wave guide. These subsurface‐induced SST anomalies could then trigger local coupled air‐sea interactions producing atmospheric‐oceanic anomalies that developed and evolved in 1991, thus setting onset conditions for the 1991–92 El Niño. These results differ markedly from the delayed oscillator physics in that a major role can be played by the eastward advection of off‐equatorial subsurface thermal anomalies and their outcropping along the NECC subsurface pathways, not necessarily involving wave reflections along the western boundary for triggering El Niño. This mechanism explains well the observed, otherwise unaccounted for, surface warming near the date line during late 1989 and early 1990.

Subcutaneous temperatures: a method of noninvasive sensing.

A new method of noninvasive sensing of the subsurface temperature distribution in human and animal tissue is described. Thermal radiation emitted from subsurface depths of several centimeters can be detected with microwave receivers. Temperature sensitivity of order 0.1 degree C and spatial resolution of approximately 1 by 2 centimeters have been obtained. Measurements demonstrating the technique, with feline and human tissue, are reported. A potential medical application is the detection of subsurface thermal anomalies such as malignant tumors and regions of vascular insufficiency.