Modification of upper-ocean temperature structure by subsurface mixing in the presence of strong salinity stratification

Author Posting. © The Oceanography Society, 2016. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 29, no. 2 (2016): 62–71, doi:10.5670/oceanog.2016.39.The Bay of Bengal has a complex upper-ocean temperature and salinity structure that is, in places, characterized by strong salinity stratification and multiple inversions in temperature. Here, two short time series from continuously profiling floats, equipped with microstructure sensors to measure subsurface mixing, are used to highlight implications of complex hydrography on upper-ocean heat content and the evolution of sea surface temperature. Weak mixing coupled with the existence of subsurface warm layers suggest the potential for storage of heat below the surface mixed layer over relatively long time scales. On the diurnal time scale, these data demonstrate the competing effects of surface heat flux and subsurface mixing in the presence of thin salinity-stratified mixed layers with temperature inversions. Pre-existing stratification can amplify the sea surface temperature response through control on the vertical extent of heating and cooling by surface fluxes. In contrast, subsurface mixing entrains relatively cool water during the day and relatively warm water during the night, damping the response to daytime heating and nighttime cooling at the surface. These observations hint at the challenges involved in improving monsoon prediction at longer, intraseasonal time scales as models may need to resolve upper-ocean variability over short time and fine vertical scales.This work was funded by Office of Naval Research grants N00014-14-1-0236 (ELS, JNM), N00014-13-1-0483 (DLR), N00014-13-1- 0453 (JTF), and N00014-12-1-0938 (SKV, AG)

The global monsoon system: research and forecast

The main objective of this workshop was to provide a forum for discussion between researchers and forecasters on the current status of monsoon forecasting and on priorities and opportunities for monsoon research. WMO hopes that through this series of quadrennial workshops, the following goals can be accomplished: (a) to update forecasters on the latest reseach findings and forecasting technology; (b) to update researchers on monsoon analysis and forecasting; (c) to identify basic and applied research priorities and opportunities; (d) to identify opportunities and priorities for acquiring observations; (e) to discuss the approach of a web-based training document in order to update forecasters on developments of direct relevance to monsoon forecasting

The First Pan-WCRP Workshop on Monsoon Climate Systems: Toward Better Prediction of the Monsoons

In 2004 the Joint Scientific Committee (JSC) that provides scientific guidance to the World Climate Research Programme (WCRP) requested an assessment of (1) WCRP monsoon related activities and (2) the range of available observations and analyses in monsoon regions. The purpose of the assessment was to (a) define the essential elements of a pan-WCRP monsoon modeling strategy, (b) identify the procedures for producing this strategy, and (c) promote improvements in monsoon observations and analyses with a view toward their adequacy, and addressing any undue redundancy or duplication. As such, the WCRP sponsored the ''1st Pan-WCRP Workshop on Monsoon Climate Systems: Toward Better Prediction of the Monsoons'' at the University of California, Irvine, CA, USA from 15-17 June 2005. Experts from the two WCRP programs directly relevant to monsoon studies, the Climate Variability and Predictability Programme (CLIVAR) and the Global Energy and Water Cycle Experiment (GEWEX), gathered to assess the current understanding of the fundamental physical processes governing monsoon variability and to highlight outstanding problems in simulating the monsoon that can be tackled through enhanced cooperation between CLIVAR and GEWEX. The agenda with links to the presentations can be found at: http://www.clivar.org/organization/aamon/WCRPmonsoonWS/agenda.htm. Scientific motivation for a joint CLIVAR-GEWEX approach to investigating monsoons includes the potential for improved medium-range to seasonal prediction through better simulation of intraseasonal (30-60 day) oscillations (ISO's). ISO's are important for the onset of monsoons, as well as the development of active and break periods of rainfall during the monsoon season. Foreknowledge of the active and break phases of the monsoon is important for crop selection, the determination of planting times and mitigation of potential flooding and short-term drought. With a few exceptions simulations of ISO are typically poor in all classes of modeling. Observational and modeling studies indicate that the diurnal cycle of radiative heating and surface fluxes over the ocean are rectified on to the intraseasonal timescale indicating that a synergistic approach to studying monsoon variability is necessary. The diurnal cycle of precipitation and clouds, which directly influence the radiative heating and surface fluxes, are also poorly represented in global models, especially. Thus, it is anticipated that improving the simulation of the diurnal cycle of precipitation and clouds in global models will contribute to an improved ability to simulate ISOs. Improved understanding and simulation of the diurnal cycle is also important since it influences low-levels jets and the associated transport of moisture as well as the rainfall over regions of complex topography

Intraseasonal Variability: Processes, Predictability and Prospects for Prediction

The intraseasonal Oscillation (ISO) is a very strong and coherent mode of variability observed in the Earths climate. Rainfall variability in the intraseasonal timescale is particularly strong in the Tropics and it directly interacts with the South Asian monsoon during boreal summer and with the Australian monsoon during winter. A detailed analysis of the horizontal and vertical structure of the ISO during both summer and winter is presented in this work considering the coupled ocean-atmosphere system. In addition, the role of the intraseasonal variability of the Southeast Asian monsoon is studied in detail. From the applications point of view, the intraseasonal time scale is arguably the most important period of variability. However, extended forecasting of intraseasonal activity has proven to be a difficult task for the state of the art numerical models. In order to improve the forecasts of the ISO activity over the Southeast Asian monsoon region, a physically based empirical scheme was designed. The scheme uses wavelet banding to separate the predictand and predictors into physically significant bands where linear regression followed by recombination of the bands is used to generate the forecast. Results of the empirical scheme suggest that isolating the evolution of the intraseasonal signal from higher frequency variability and noise improve the skill of the prediction. The hypothesis is that a similar phenomenon occurs in numerical models: The strong intraseasonal signal is eroded by high frequency errors due to the model parameterizations, especially in convection. To evaluate the hypothesis, a coupled ocean-atmosphere model was run in ensemble mode for 30 day periods initialized daily for 20 days before to 20 days after major intraseasonal oscillations, allowing the examination of the skill of the model relative to the phase of the oscillation. The results, which confirm the previous hypothesis, represent well the observations for about 7 days after which the magnitude of the errors is greater than the signal itself. An integration scheme was developed for the coupled ocean-atmosphere general circulation model in order to mimic the philosophy of the empirical scheme and use for 30-day forecasts. The propagation features associated to ISO activity are improved.Ph.D.Committee Chair: Dr. Peter J. Webster; Committee Member: Dr. Judith A. Curry; Committee Member: Dr. Predrag Cvitanovic; Committee Member: Dr. Robert Dickinson; Committee Member: Dr. Robert X. Blac

Progress in understanding of Indian Ocean circulation, variability, air-sea exchange and impacts on biogeochemistry

Over the past decade, our understanding of the Indian Ocean has advanced through concerted efforts toward measuring the ocean circulation and air–sea exchanges, detecting changes in water masses, and linking physical processes to ecologically important variables. New circulation pathways and mechanisms have been discovered that control atmospheric and oceanic mean state and variability. This review brings together new understanding of the ocean–atmosphere system in the Indian Ocean since the last comprehensive review, describing the Indian Ocean circulation patterns, air–sea interactions, and climate variability. Coordinated international focus on the Indian Ocean has motivated the application of new technologies to deliver higher-resolution observations and models of Indian Ocean processes. As a result we are discovering the importance of small-scale processes in setting the large-scale gradients and circulation, interactions between physical and biogeochemical processes, interactions between boundary currents and the interior, and interactions between the surface and the deep ocean. A newly discovered regional climate mode in the southeast Indian Ocean, the Ningaloo Niño, has instigated more regional air–sea coupling and marine heatwave research in the global oceans. In the last decade, we have seen rapid warming of the Indian Ocean overlaid with extremes in the form of marine heatwaves. These events have motivated studies that have delivered new insight into the variability in ocean heat content and exchanges in the Indian Ocean and have highlighted the critical role of the Indian Ocean as a clearing house for anthropogenic heat. This synthesis paper reviews the advances in these areas in the last decade

Assessing the role of local air–sea interaction over the South Asia region in simulating the Indian Summer Monsoon (ISM) using the new earth system model RegCM-ES

openThe understanding and prediction of the monsoon variability over South Asia region is one of the biggest challenges for climatologist and meteorologist today. The Indian Summer Monsoon (ISM) has different temporal and spatial scales of variability and it is mainly driven by strong air sea interactions. In this thesis we evaluate the performance of the new regional Earth System Model (ESM) RegCM-ES in reproducing the main characteristics of the ISM rainfall (ISMR). We performed two sets of simulations, one with the new RegCM-ES and another with the stand-alone version of the atmospheric component i.e. the regional climate model (RCM) RegCM4. RegCM-ES is composed mainly by three components, the RegCM4, the ocean model MITgcm and the hydrological model HD. Another experiment, performed using RegCM-ES with a more high-resolution hydrological model implemented ad hoc for this study, has been added to this two set of experiments. The climatological mean state of the monsoon is well represented by mostly all the experiments although not with the same skills. The most interesting results are observed in simulating the variability of the monsoon and here we highlight some of them. The intraseasonal northward(eastward) propagation of the convection has been analysed using lag/lead map of the regressed anomalies as a function of latitudes(longitudes). The two propagations are better reproduced by the set of ESM simulations thanks to the role of the air-sea coupling. For what concerns the interannual variability (IAV) of the ISMR the air-sea coupling plays an important role. The time series of simulated anomalies by RCM exhibit no correlation with the observed anomalies obtained from the dataset of the Indian Meteorological Department (IMD). On the other hand, the corresponding ESM simulations exhibits good skills in reproducing the IAV of ISMR and good correlation coefficients are observed with IMD. One new finding of this study is a new source of predictability with one-year lag for the ISMR. It is well known that El Niño Southern Oscillation (ENSO) plays a quite important role in modulating the precipitation over most of the intertropical belt and over the South Asia region. As seen in previous findings, the response of the ISMR to ENSO can be delayed of two seasons through the contribution of different air-sea coupled mechanisms as the decrease of Western Arabian Sea Upwellingthe Indo-western Pacific ocean capacitor and the Indo-Tropical northwest Pacific ocean-atmosphere interaction. Our findings extend and confirm the possibility that this response may have a longer feedback time, a year or so. The coupled simulations are used to explain the mechanism and investigate the models response. They appear quite similar to those proposed in the previous studies but further investigations are needed to understand more in deep the phenomena involved. The role of the new hydrological model (CHyM) implemented inside RegCM-ES on the ISMR is also investigated. Due to the main role that the freshwater discharge plays on the formation of a shallow mixed layer depth on the Bay of Bengal that influences the air-sea coupling and the formation of deep convection over this area, the correct estimation of the freshwater discharge is quite important. Although the new hydrological model produces a more realistic annual cycle of the discharge (verified only for a limited set of data due to the lack of observations over this region), this doesn't seem to have a relevant effect on both the mean climatological state of the monsoon and in its variability. A possible explanation for this comes from a missing representation of the barrier layer (BL) in the Bay of Bengal (BoB) due to many different reasons. Two of them are a not enough resoluted ocean model as well as a too strong wind stress forcing that doesn’t allow the formation of the BL.SCIENZE DELLA TERRA E MECCANICA DEI FLUIDIopenDI SANTE, FabioDI SANTE, Fabi

Modern Climatology - Full Text

Climatology, the study of climate, is no longer regarded as a single discipline that treats climate as something that fluctuates only within the unchanging boundaries described by historical statistics. The field has recognized that climate is something that changes continually under the influence of physical and biological forces and so, cannot be understood in isolation but rather, is one that includes diverse scientific disciplines that play their role in understanding a highly complex coupled “whole system” that is the Earth’s climate. The modern era of climatology is echoed in this book. On the one hand it offers a broad synoptic perspective but also considers the regional standpoint as it is this that affects what people need from climatology, albeit water resource managers or engineers etc. Aspects on the topic of climate change – what is often considered a contradiction in terms – is also addressed. It is all too evident these days that what recent work in climatology has revealed carries profound implications for economic and social policy; it is with these in mind that the final chapters consider acumens as to the application of what has been learned to date. This book is divided into four sections that cover sub-disciplines in climatology. The first section contains four chapters that pertain to synoptic climatology, i.e., the study of weather disturbances including hurricanes, monsoon depressions, synoptic waves, and severe thunderstorms; these weather systems directly impact humanity. The second section on regional climatology has four chapters that describe the climate features within physiographically defined areas. The third section is on climate change which involves both past (paleoclimate) and future climate: The first two chapters cover certain facets of paleoclimate while the third is centered towards the signals (observed or otherwise) of climate change. The fourth and final section broaches the sub-discipline that is often referred to as applied climatology; this represents the important goal of all studies in climatology–one that affects modes of living. Here, three chapters are devoted towards the application of climatological research that might have useful application for operational purposes in industrial, manufacturing, agricultural, technological and environmental affairs. Please click here to explore the components of this work.https://digitalcommons.usu.edu/modern_climatology/1014/thumbnail.jp

Modelling the Madden Julian Oscillation

The MJO has long been an aspect of the global climate that has provided a tough test for the climate modelling community. Since the 1980s there have been numerous studies of the simulation of the MJO in atmospheric general circulation models (GCMs), ranging from Hayashi and Golder (1986, 1988) and Lau and Lau (1986), through to more recent studies such as Wang and Schlesinger (1999) and Wu et al. (2002). Of course, attempts to reproduce the MJO in climate models have proceeded in parallel with developments in our understanding of what the MJO is and what drives it. In fact, many advances in understanding the MJO have come through modeling studies. In particular, failure of climate models to simulate various aspects of the MJO has prompted investigations into the mechanisms that are important to its initiation and maintenance, leading to improvements both in our understanding of, and ability to simulate, the MJO. The initial focus of this chapter will be on modeling the MJO during northern winter, when it is characterized as a predominantly eastward propagating mode and is most readily seen in observations. Aspects of the simulation of the MJO will be discussed in the context of its sensitivity to the formulation of the atmospheric model, and the increasing evidence that it may be a coupled ocean-atmosphere phenomenon. Later, we will discuss the challenges regarding the simulation of boreal summer intraseasonal variability, which is more complex since it is a combination of the eastward propagating MJO and the northward propagation of the tropical convergence zone. Finally some concluding remarks on future directions in modeling the MJO and its relationship with other timescales of variability in the tropics will be made