We show that gender diversity in corporate boards could improve firm value because of the contributions that women make to the board. Prior studies examine valuation effects of gender-diverse boards ...and reach mixed conclusions. To help resolve this conundrum, we consider how gender diversity could affect firm value, that is, what mechanisms could explain how female directors benefit corporate board performance. We hypothesize and provide evidence that women directors contribute to boards by offering specific functional expertise, often missing from corporate boards. The additional expertise increases board heterogeneity which Kim and Starks (2015) show can increase firm value.
The authors analyze the column-integrated moist static energy budget over the region of the tropical Indian Ocean covered by the sounding array during the Cooperative Indian Ocean Experiment on ...Intraseasonal Variability in the Year 2011 (CINDY2011)/Dynamics of the Madden-Julian Oscillation (DYNAMO) field experiment in late 2011. The analysis is performed using data from the sounding array complemented by additional observational datasets for surface turbulent fluxes and atmospheric radiative heating. The entire analysis is repeated using the ECMWF Interim Re-Analysis (ERA-Interim). The roles of surface turbulent fluxes, radiative heating, and advection are quantified for the two MJO events that occurred in October and November using the sounding data; a third event in December is also studied in the ERA-Interim data. These results are consistent with the view that the MJO's moist static energy anomalies grow and are sustained to a significant extent by the radiative feedbacks associated with MJO water vapor and cloud anomalies and that propagation of the MJO is associated with advection of moist static energy. Both horizontal and vertical advection appear to play significant roles in the events studied here. Horizontal advection strongly moistens the atmosphere during the buildup to the active phase of the October event when the low-level winds switch from westerly to easterly. Horizontal advection strongly dries the atmosphere in the wake of the active phases of the November and December events as the westerlies associated with off-equatorial cyclonic gyres bring subtropical dry air into the convective region from the west and north. Vertical advection provides relative moistening ahead of the active phase and drying behind it, associated with an increase of the normalized gross moist stability.
A linear wave theory for the Madden-Julian oscillation (MJO), previously developed by Sobel and Maloney, is extended upon in this study. In this treatment, column moisture is the only prognostic ...variable and the horizontal wind is diagnosed as the forced Kelvin and Rossby wave responses to an equatorial heat source/sink. Unlike the original framework, the meridional and vertical structure of the basic equations is treated explicitly, and values of several key model parameters are adjusted, based on observations. A dispersion relation is derived that adequately describes the MJO's signal in the wavenumber-frequency spectrum and defines the MJO as a dispersive equatorial moist wave with a westward group velocity. On the basis of linear regression analysis of satellite and reanalysis data, it is estimated that the MJO's group velocity is ~40% as large as its phase speed. This dispersion is the result of the anomalous winds in the wave modulating the mean distribution of moisture such that the moisture anomaly propagates eastward while wave energy propagates westward. The moist wave grows through feedbacks involving moisture, clouds, and radiation and is damped by the advection of moisture associated with the Rossby wave. Additionally, a zonal wavenumber dependence is found in cloud-radiation feedbacks that cause growth to be strongest at planetary scales. These results suggest that this wavenumber dependence arises from the nonlocal nature of cloud-radiation feedbacks; that is, anomalous convection spreads upper-level clouds and reduces radiative cooling over an extensive area surrounding the anomalous precipitation.
The Madden–Julian oscillation (MJO), the dominant mode of tropical intraseasonal variability, provides a major source of tropical and extratropical predictability on a subseasonal time scale. This ...study conducts a quantitative evaluation of the MJO prediction skill in state-of-the-art operational models, participating in the subseasonal-to-seasonal (S2S) prediction project. The relationship of MJO prediction skill with model biases in the mean moisture fields and in the longwave cloud–radiation feedbacks is also investigated.
The S2S models exhibit MJO prediction skill out to a range of 12 to 36 days. The MJO prediction skills in the S2S models are affected by both the MJO amplitude and phase errors, with the latter becoming more important at longer forecast lead times. Consistent with previous studies, MJO events with stronger initial MJO amplitude are typically better predicted. It is found that the sensitivity to the initial MJO phase varies notably from model to model.
In most models, a notable dry bias develops within a few days of forecast lead time in the deep tropics, especially across the Maritime Continent. The dry bias weakens the horizontal moisture gradient over the Indian Ocean and western Pacific, likely dampening the organization and propagation of the MJO. Most S2S models also underestimate the longwave cloud–radiation feedbacks in the tropics, which may affect the maintenance of the MJO convective envelope. The models with smaller bias in the mean horizontal moisture gradient and the longwave cloud–radiation feedbacks show higher MJO prediction skills, suggesting that improving those biases would enhance MJO prediction skill of the operational models.
Biomineralization through microbially or enzymatically induced calcium carbonate precipitation (MICP/EICP) by urea hydrolysis has been widely investigated for various engineering applications. ...Empirical correlations relating the amount of mineral precipitation to engineering properties like strength, stiffness, or permeability show large variations, which can be partly attributed to the pore‐scale characteristics of the precipitated minerals. This study aimed to gain insight into the precipitation kinetics and pore‐scale characteristics of calcium carbonate minerals through time lapse imaging of a transparent microfluidic chip, which was flushed 10 times with a reactive solution to stimulate EICP. An image processing algorithm was developed to detect the individual precipitated minerals and separate them from the grains and trapped air. Statistical analysis was performed to quantify the number and size distribution of precipitated minerals during each treatment cycle and the cumulative volume, surface area, bulk precipitation rate, nucleation rate, and supersaturation were calculated and compared with a simple numerical model and more complex theory on precipitation kinetics. The analysis showed that results were significantly affected by the assumed particle shape. The supersaturation, which controls the crystal nucleation and growth rates, was shown to be a function of the hydrolysis rate, the kinetic order and growth rate constant, and available surface area for mineral growth. Possible explanations for observed discrepancies between observations and theory, including diffusion limitations, the presence of inhibiting compounds, local pore clogging or observation bias, and limitations of the methodology, are discussed.
Key Points
Image processing of a microfluidic chip experiment provides insights on the pore‐scale characteristics of biominerals in porous media
The results of image analysis are significantly affected by the assumed particle shape, being cylindrical or semispherical
Observed cumulative crystal volume, bulk precipitation rate, number of crystals, and crystal size distribution deviate from expected values
Eastward propagation of the Madden‐Julian Oscillation (MJO) detours the Maritime Continent (MC) region southward during austral summer, exhibiting enhanced convective activity preferentially in the ...southern part of the MC area with much weaker anomalies in the central MC area. Column‐integrated moist static energy budget of the MJO is analyzed to understand the processes responsible for the MJO detouring. Results show that zonal and meridional moisture advection is the essential process to the MJO detouring, causing the difference between the southern and central MC regions in the moisture recharge before and during the MJO onset. Further analysis reveals that moisture advection by MJO perturbation winds acting upon the background moisture gradient has the dominant contribution to the regional contrast between the central and southern MC areas. The zonal moisture advection is greater in the southern MC region because the zonal gradient of the background moisture field is much steeper in the southern MC area than in the central MC area. The onset of the Australian monsoon in austral summer contributes to the establishment of the sharp zonal moisture gradient in the southern MC region. The meridional moisture advection is weaker in the central MC area because meridional wind anomalies associated with the MJO vary regionally, presumably through interactions with the topography and land‐sea contrast.
Key Points
Column‐integrated moist static energy budget of the MJO is analyzed to understand the processes responsible for the MJO detouring
Horizontal moisture advection is the essential process to the detouring, causing the difference between the southern and central MC regions
Zonal moisture advection by MJO winds acting upon the background moisture gradient has a large regional contrast between the two regions
Many climate models struggle with a poor simulation of the Madden‐Julian Oscillation (MJO), especially its propagation across the Maritime Continent (MC). This study quantitatively evaluates the ...robustness of MJO propagation over the MC in climate models that participated in Coupled Model Intercomparison Project Phase 5 (CMIP5) and Phase 6 (CMIP6) with a newly developed MC propagation metric. The results show that the CMIP6 models simulate MJO propagation over the MC more realistically than the CMIP5 models. Lower free‐tropospheric moisture budget analysis highlights that the greater horizontal moisture advection is responsible for the enhanced MJO propagation over the MC. The increase in horizontal moisture advection in the CMIP6 models is mainly attributed to the steeper horizontal mean state moisture gradient around the MC, which is associated with the reduction of the equatorial dry bias.
Plain Language Summary
The Madden‐Julian Oscillation (MJO), planetary‐scale eastward propagating tropical convective cloud clusters coupled with large‐scale circulation, is the dominant mode of intraseasonal variability in the tropics and thereby influences a wide range of weather and climate phenomena. Unfortunately, however, many contemporary climate models struggle to simulate a realistic MJO propagation across the Maritime Continent, and this common bias had persisted over the previous generations of the Coupled Model Intercomparison Project (CMIP). We show that, in the newly released CMIP Phase 6 (CMIP6) models, the simulation of the MJO propagation is significantly improved when compared to their predecessors—CMIP Phase 5 (CMIP5) models. The improvement in the MJO simulation is mainly due to the reduction of the dry bias that many CMIP5 models exhibit over the Indo‐Pacific Warm Pool region.
Key Points
A metric indicating the robustness of MJO propagation across the MC is developed and applied to 30 CMIP5 and 34 CMIP6 models
CMIP6 models represent MJO propagation over the MC more realistically than the CMIP5 models
The improvement in MJO propagation is due to the steepening of the mean state moisture gradient around the MC
The Madden-Julian Oscillation (MJO) is the most dominant mode of subseasonal variability in the tropics, characterized by an eastward-moving band of rain clouds. The MJO modulates the El Niño ...Southern Oscillation
, tropical cyclones
and the monsoons
, and contributes to severe weather events over Asia, Australia, Africa, Europe and the Americas. MJO events travel a distance of 12,000-20,000 km across the tropical oceans, covering a region that has been warming during the twentieth and early twenty-first centuries in response to increased anthropogenic emissions of greenhouse gases
, and is projected to warm further. However, the impact of this warming on the MJO life cycle is largely unknown. Here we show that rapid warming over the tropical oceans during 1981-2018 has warped the MJO life cycle, with its residence time decreasing over the Indian Ocean by 3-4 days, and increasing over the Indo-Pacific Maritime Continent by 5-6 days. We find that these changes in the MJO life cycle are associated with a twofold expansion of the Indo-Pacific warm pool, the largest expanse of the warmest ocean temperatures on Earth. The warm pool has been expanding on average by 2.3 × 10
km
(the size of Washington State) per year during 1900-2018 and at an accelerated average rate of 4 × 10
km
(the size of California) per year during 1981-2018. The changes in the Indo-Pacific warm pool and the MJO are related to increased rainfall over southeast Asia, northern Australia, Southwest Africa and the Amazon, and drying over the west coast of the United States and Ecuador.
Basinwide convective anomalies over the Indian Ocean (IO) associated with the Madden–Julian oscillation (MJO) sometimes propagate eastward and reach the west Pacific (WP), but sometimes do not. ...Long-term observations and reanalysis products are used to investigate the difference between the propagating and nonpropagating MJO events. IO convection onset events associated with the MJO are grouped into three categories based on the strengths of the simultaneous dry anomalies over the eastern Maritime Continent and WP. The IO convection anomaly preferentially makes eastward propagation and reaches the WP when the dry anomaly is stronger.
Analysis of the column-integrated moist static energy (MSE) budget shows that horizontal advection moistens the atmosphere to the east of the positive MSE anomaly associated with the active convection over the IO and is of sufficient magnitude to explain the eastward propagation of the positive MSE anomaly. Interpretation is complicated, however, by lack of closure in the MSE budget. A residual term, of smaller but comparable magnitude to the horizontal advection, also moistens the column to the east of the positive MSE anomaly. Nonetheless, the authors decompose the horizontal advection term into contributions from different scales and find that a dominant contribution is from free-tropospheric meridional advection by the intraseasonal time scale wind anomalies. The positive meridional advection in between the convective and dry anomalies is induced by the anomalous poleward flow, which is interpreted as part of the Rossby wave response to the dry anomaly. The poleward flow advects the climatological MSE, which peaks at the equator, and moistens to the east of IO convective anomaly.
The literature often holds that, in salt marshes, surface elevation mediates the depth, duration, and frequency of submergence, thereby constituting the fundamental factor of plant species ...distribution and most other environmental variables. However, such an elevation-centered view has not been fully tested in a temporal sense; it is still unclear whether elevation is also a significant control on the rate of changes in species composition over time. In the Skallingen salt marsh of the Danish Wadden Sea, this question was evaluated along two elevation gradients where distinct physical and ecological processes operate: a gradient across a marsh platform and the other across creek bars. The rate of vegetation dynamics was measured as the Euclidean distance between two positions of the same plot, each representing two different points in time, in a two-dimensional diagram produced by nonmetric multidimensional scaling. Results showed that the rate of vegetation dynamics did not show any significant relationships with surface elevation across either marsh platform or tidal creeks (R ² less than 0.04). This suggests that, other than elevation, some biological factors, such as the presence of keystone species and the initial species composition, control patterns of vegetation change in the marsh. This logic leads to a point that hydrological effects (e.g., inundation frequency and duration), often represented by surface elevation, are not necessarily overriding factors of rates of changes in species composition in backbarrier marshes like Skallingen. The conventional elevation-centered perspective may be an oversimplification of the biological and environmental variability of salt marshes.
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