During the last ice age there were several quasi-periodic abrupt warming events. The climatic effects of the so-called Dansgaard-Oeschger (DO) events were felt globally, although the North Atlantic experienced the largest and most abrupt temperature anomalies. Similar but weaker oscillations also took place during the interglacial period. This paper proposes an auto-oscillatory mechanism between sea ice and convective deep water formation in the north Atlantic as the source of the persistent cycles. A simple dynamical model is constructed by coupling and slightly modifying two existing models of ocean circulation and sea ice. The model exhibits mixed mode oscillations, consisting of decadal scale small amplitude oscillations, and a large amplitude relaxation fluctuation. The decadal oscillations occur due to the insulating effect of sea ice and leads to periodic ventilation of heat from the polar ocean. Gradually an instability builds up in the polar column and results in an abrupt initiation of convection and polar warming. The unstable convective state relaxes back to the small amplitude oscillations from where the process repeats in a self-sustained manner. Freshwater pulses mimicking Heinrich events cause the oscillations to be grouped into packets of progressively weaker fluctuations, as also observed in the proxy records. Modulation of this stable oscillation mechanism by freshwater and insolation variations could account for the distribution and pacing of DO and Bond events. Physical aspects of the system such as sea ice extent and oceanic advective flow rates could determine the characteristic 1,500 year timescale of DO events.
The last glacial period was punctuated by a series of abrupt climate shifts, the so-called Dansgaard-Oeschger (DO) events. The frequency of DO events varied in time, supposedly because of changes in background climate conditions. Here, the influence of external forcings on DO events is investigated with statistical modelling. We assume two types of simple stochastic dynamical systems models (double-well potential-type and oscillator-type), forced by the northern hemisphere summer insolation change and/or the global ice volume change. The model parameters are estimated by using the maximum like…
We propose a conceptual model which generates abrupt climate changes akin to Dansgaard-Oeschger events. In the model these abrupt climate changes are not triggered by external perturbations but rather emerge in a dynamic self-consistent model through complex interactions of the ocean, the atmosphere and an intermittent process. The abrupt climate changes are caused in our model by intermittencies in the sea-ice cover. The ocean is represented by a Stommel two-box model, the atmosphere by a Lorenz-84 model and the sea-ice cover by a deterministic approximation of correlated additive and multipl…
The climate record preserved in polar glaciers, mountain glaciers, and widespread cave deposits shows repeated occurrence of abrupt global transitions between cold/dry stadial and warm/wet interstadial states during glacial periods. These abrupt transitions occur on millennial time scale and in the absence of any known global-scale forcing. Here a theory is advanced implicating a feedback between atmospheric dust and the hydrological cycle in producing these abrupt transitions. Calculations are performed using a radiative-convective model that includes the interaction of aerosols with radiatio…
This paper is a case study of horizontal atmospheric rolls that formed over the Black Sea on 16 August 2007. The rolls were discovered in WRF modeling results for a mesoscale cyclone that originated over the sea on 15 August 2007. The roll formation mechanisms, such as Rayleigh-Benard convective instability, dynamic instability, advection and stretching of vertical velocity field inhomogeneities, are considered. It is shown that indeed convective instability played an important role in the roll formation but dynamic instability did not occur. In order to distinguish other possible mechanisms o…
This paper presents an assessment of the new Geostationary Operational Environmental Satellite (GOES) imager channel 3 - 4 brightness temperature difference (BTD) product for two early cold season severe convective storm events that occurred over the Mid-Atlantic region on 17 November and 1 December 2010. Both of these events involved squall lines that produced strong downbursts as they tracked over the Tidal Potomac River and Chesapeake Bay regions. It has been found recently that the BTD between GOES infrared channel 3 (water vapor) and channel 4 (thermal infrared) can highlight regions wher…
We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the …
Vertically 0.042-m-spaced moored high-resolution temperature sensors are used for detailed internal wave-turbulence monitoring near Texel North Sea and Wadden Sea beaches on calm summer days. In the maximum 2 m deep waters irregular internal waves are observed supported by the density stratification during day-times warming in early summer, outside the breaking zone of <0.2 m surface wind waves. Internal-wave-induced convective overturning near the surface and shear-driven turbulence near the bottom are observed in addition to near-bottom convective overturning due to heating from below. Small…
Formation and evolution of turbulence in convectively unstable internal solitary waves of depression shoaling over gentle slopes in the South China Sea
Cornell University（康奈尔大学）；University of Washington（华盛顿大学）；University of Waterloo（滑铁卢大学）；Wandering Wakhs Research（Wandering Wakhs 研究）
The mechanism that causes an interdecadal oscillation in a coarse resolution sector ocean model forced by mixed boundary conditions is studied. The oscillation is characterized by large fluctuations in convective activity and air/sea heat exchange on a decadal time scale. When the convective activity is large, a strengthening of the southeastward surface flow advects more relatively fresh water from the northwestern part of the basin into the convective area, which reduces the convective activity. Similarly, when the convective activity is small, the flow of relatively fresh water is weak, whi…
Convective storms are one of the severe weather hazards found during the warm season. Doppler weather radar is the only operational instrument that can frequently sample the detailed structure of convective storm which has a small spatial scale and short lifetime. For the challenging task of short-term convective storm forecasting, 3-D radar images contain information about the processes in convective storm. However, effectively extracting such information from multisource raw data has been problematic due to a lack of methodology and computation limitations. Recent advancements in deep learni…
Plankton dynamics depend in a complex manner on a variety of physical phenomena, according to both experimental and numerical data. In particular, experimental field studies have highlighted the relation between phytoplankton survival and turbulent upwelling and downwelling from thermal convection. Recent numerical works have also shown the importance of accounting for advective transport by persistent structures in simulation models. In nutrient-rich polar marine environments phytoplankton blooms are critically limited by light availability under ice-covered waters. Such heterogeneity of the …
A Multivariable Approach to the Regional Calibration of the Galvez Davison Index across Mexico Climate Regimes
Instituto de Astronomía y Meteorología (IAM), Departamento de Física, Centro Universitario de Ciencias Exactas e Ingenierías (CUCEI), Universidad de Guadalajara（瓜达拉哈拉大学）；Agencia Mexicana de Meteorología y Geociencias (GEOSMET)（墨西哥气象与地球科学署）；Centro de Investigaciones sobre Desertificación, Consejo Superior de Investigaciones Científicas (CIDE, CSIC-UV-GVA)（西班牙国家研究委员会沙漠化研究中心）；Unidad Académica de Estudios Territoriales Yucatán (UAETY), Instituto de Geografía, Universidad Nacional Autónoma de México (UNAM)（墨西哥国立自治大学）；Colorado State University（科罗拉多州立大学）；University of Valladolid（巴利亚多利德大学）；Agencia Estatal de Meteorología (AEMET)（西班牙国家气象局）；Complutense University of Madrid（马德里康普顿斯大学）
On small scales, the tropical atmosphere tends to be either moist or very dry. This defines two states that, on large scales, are separated by a sharp margin, well-identified by the anti-mode of the bimodal tropical column water vapor distribution. Despite recent progress in understanding physical processes governing the spatio-temporal variability of tropical water vapor, the behavior of this margin remains elusive, and we lack a simple framework to understand the bimodality of tropical water vapor in observations. Motivated by the success of coarsening theory in explaining bimodal distributi…
MLS and CALIPSO Evidence for a Warm-Pool Transition in Tropical Convective Moistening and Cloud Ice
Pacific Academy（太平洋学院）；Joint Institute for Regional Earth System Science & Engineering, University of California, Los Angeles（区域地球系统科学与工程联合研究所，加州大学洛杉矶分校）；Department of Atmospheric and Oceanic Sciences, Fudan University（大气与海洋科学系，复旦大学）；Environmental Sciences Department, University of California, Riverside（环境科学系，加州大学河滨分校）；State Key Laboratory of Regional Environment and Sustainability, School of Environment, Tsinghua University（区域环境可持续性国家重点实验室，环境学院，清华大学）；Department of Climate and Energy Systems Engineering, Ewha Womans University（气候与能源系统工程系，梨花女子大学）
Using the well-known Z-R power law, Z = A R^b, A-b parameters derived from a single disdrometer are readily found and can provide useful information to study rainfall drop size distributions (DSDs). However, large variations in values are often seen when comparing A-b sets from various researchers. Values of b typically range from 1.25 to 1.55 for both stratiform and convective events. The values of A approximately fall into three groups: 150 to 200 for convective, 200 to 400 for stratiform, and 400 to 500 for convective. Computing the A-b parameters using the gamma DSD, coupled with a modifie…
Bayesian Deep Learning for Convective Initiation Nowcasting Uncertainty Estimation
Department of Meteorology and Atmospheric Science, The Pennsylvania State University, University Park, Pennsylvania（气象学与大气科学系，宾夕法尼亚州立大学，大学公园，宾夕法尼亚州）；National Center for Atmospheric Research, Boulder, Colorado（国家大气研究中心，博尔德，科罗拉多）；Institute for Computational and Data Sciences, The Pennsylvania State University, University Park, Pennsylvania（计算与数据科学研究所，宾夕法尼亚州立大学，大学公园，宾夕法尼亚州）；Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, Pennsylvania（土木与环境工程系，宾夕法尼亚州立大学，大学公园，宾夕法尼亚州）
Turbulent and internal wave motions are important for the exchange of momentum, heat and suspended matter in the deep-sea which is generally stably stratified in density. Turbulence-generation models involve shear of vertical current differences that deforms the stratified waters, and convection that is drive by (unstable) buoyancy. Shear-generation is found more general in the well-stratified ocean-interior, while convection is known to occur near the sea-surface, e.g. via nighttime cooling. Far below the surface, the Western-Mediterranean Sea is very weakly stratified and offers opportunity …
We present a detailed analysis of the temperature statistics in an oceanographic observational dataset. The data are collected using a moored array of thermistors, 100 m tall and starting 5 m above the bottom, deployed during four months above the slopes of a Seamount in the north-eastern Atlantic Ocean. Turbulence at this location is strongly affected by the semidiurnal tidal wave. Mean stratification is stable in the entire dataset. We compute structure functions, of order up to 10, of the distributions of temperature increments. Strong intermittency is observed, in particular, during the do…
The influence of the Madden Julian Oscillation (MJO) on the precipitation extremes in Indonesia during the rainy season (October to April) has been evaluated using the daily station rain gauge data and the gridded Asian Precipitation Highly Resolved Observational Data Integration Toward Evaluation of Water Resources (APHRODITE) from 1987 to 2017 for different phases of the MJO. The results show that MJO significantly modulates the frequency of extreme precipitation events in Indonesia, with the magnitude of the impact varying across regions. Specifically, the convectively active (suppressed) M…
