Shear and Convective Turbulence in a Model of Thermohaline Intrusions

2007 ◽  
Vol 37 (10) ◽  
pp. 2534-2549 ◽  
Author(s):  
Rachael D. Mueller ◽  
William D. Smyth ◽  
Barry Ruddick
Keyword(s):  
Shear Instability ◽  
Convective Turbulence ◽  
Convective Mixing ◽  
Independent Laboratory ◽  
Numerical Studies ◽  
Thermohaline Intrusions ◽  
In Situ Observations ◽  
Parameter Values

Abstract Thermohaline interleaving is an important mechanism for laterally fluxing salt, heat, and nutrients between water masses. Interleaving is driven by a release of potential energy resulting from the differing diffusivities of heat and salt in seawater. The flows are composed of stacked intrusions that flux more and less buoyant water in opposite directions. In this paper, the role of shear instability caused by this juxtaposed motion is investigated. The model described in Walsh and Ruddick is modified to include both the effects of shear-induced turbulence and an improved convective mixing parameterization. Shear and convective mixing play a similar and significant role in interleaving dynamics. In the absence of either instability, cross-front fluxes are increased by approximately 30%. While in situ observations of horizontal diffusivity resulting from interleaving are not yet precise enough to calibrate the parameterizations independently, parameter values based on independent laboratory and numerical studies lead to diffusivity predictions that are within the error of the observations.

scholarly journals The role of DYNAMO in situ observations in improving NASA CERES-like daily surface and atmospheric radiative flux estimates

2017 ◽  
Vol 4 (4) ◽  
pp. 164-183 ◽  
Author(s):  
Hailan Wang ◽  
Wenying Su ◽  
Norman G. Loeb ◽  
Deepthi Achuthavarier ◽  
Siegfried D. Schubert
Keyword(s):  
Radiative Flux ◽  
In Situ Observations

Solar Orbiter observations of magnetic Kelvin-Helmholtz waves in the solar wind

2021 ◽  
Author(s):  
Rungployphan Kieokaew ◽  
Benoit Lavraud ◽  
David Ruffolo ◽  
William Matthaeus ◽  
Yan Yang ◽  
...  
Keyword(s):  
Solar Wind ◽  
Heliospheric Current Sheet ◽  
Shear Instability ◽  
Slow Solar Wind ◽  
Flow Shear ◽  
In Situ Observations ◽  
Set Up ◽  
Nonlinear Shear ◽  
Wind Source

<p>The Kelvin-Helmholtz instability (KHI) is a nonlinear shear-driven instability that develops at the interfaces between shear flows in plasmas. KHI is ubiquitous in plasmas and has been observed in situ at planetary interfaces and at the boundaries of coronal mass ejections in remote-sensing observations. KHI is also expected to develop at flow shear interfaces in the solar wind, but while it was hypothesized to play an important role in the mixing of plasmas and exciting solar wind fluctuations, its direct observation in the solar wind was still lacking. We report first in-situ observations of ongoing KHI in the solar wind using Solar Orbiter during its cruise phase. The KHI is found in a shear layer in the slow solar wind near the Heliospheric Current Sheet. We find that the observed conditions satisfy the KHI onset criterion from linear theory and the steepening of the shear boundary layer is consistent with the development of KH vortices. We further investigate the solar wind source of this event to understand the conditions that support KH growth. In addition, we set up a local MHD simulation using the empirical values to reproduce the observed KHI. This observed KHI in the solar wind provides robust evidence that shear instability develops in the solar wind, with obvious implications in the driving of solar wind fluctuations and turbulence. The reasons for the lack of previous such measurements are also discussed.</p>

scholarly journals Role of Convective Precipitation in the Relationship between Subdaily Extreme Precipitation and Temperature

2017 ◽  
Vol 30 (23) ◽  
pp. 9527-9537 ◽  
Author(s):  
In-Hong Park ◽  
Seung-Ki Min
Keyword(s):  
South Korea ◽  
Extreme Precipitation ◽  
Physical Effect ◽  
Convective Precipitation ◽  
Statistical Effect ◽  
Convective Process ◽  
In Situ Observations ◽  
The Relationship

On a subdaily time scale, the intensities of extreme precipitation are observed to increase with temperature at a rate exceeding water vapor constraints determined by the Clausius–Clapeyron (C-C) relationship. This so-called super C-C scaling has been suggested to occur as a result of 1) the statistical effect that involves the transition of precipitation types from stratiform to convective events and 2) the physical effect by which the convective process itself can overcome the thermodynamic limitation. This study examines these two mechanisms for the super C-C relationship using in situ observations in South Korea for a recent 35-yr period, focusing on the role of convective rainfall. Scaling results show that hourly extreme precipitation undergoes a transition from a C-C rate to a super C-C rate at around 20°C, supporting the statistical effect. The transition temperature observed in South Korea is, however, much higher than in European regions (12°C), which seems to be due to the climatologically lower frequency of convective events in South Korea than in Europe. Nevertheless, the threshold fraction of convective precipitation when the scaling transition starts to occur is found to very similar between two regions, around 0.2, indicating the important role of convective events in shaping the scaling. On the other hand, convective extreme precipitation alone exhibits a super C-C scaling, suggesting that the physical effect is also at work in South Korea. Also, the scaling shows a robust peaklike shape with maximum precipitation intensity near 24°C, which is closely linked with moisture limitation at high temperature, supporting the previous findings.

scholarly journals The 25-Day-Period Large-Scale Oscillations in the Argentine Basin Revisited

2005 ◽  
Vol 35 (8) ◽  
pp. 1473-1479 ◽  
Author(s):  
Chang-Kou Tai ◽  
Lee-Lueng Fu
Keyword(s):  
Simulation Study ◽  
Large Scale ◽  
Space Time ◽  
Sea Surface ◽  
Time Sampling ◽  
Numerical Studies ◽  
In Situ Observations ◽  
Ocean Topography ◽  
Argentine Basin

Abstract From sea surface height measurements made by the Ocean Topography Experiment (TOPEX)/Poseidon satellite, Fu et al. found and described large-scale oscillations at the period of 25 days in the Argentine Basin of the South Atlantic Ocean. These oscillations were previously hinted at by in situ observations. Only the extensive space–time sampling capability of TOPEX/Poseidon, however, was able to give a complete description of the phenomenon as a counterclockwise-rotating dipole centered at 45°S, 317°E over the Zapiola Rise. Fu et al. also undertook theoretical and numerical studies to suggest that the phenomenon is a resonantly excited barotropic normal mode of the locally closed f/H contour. In a simulation study, however, they also found that the space–time smoothing scheme employed would probably lower the amplitude of the estimated phenomenon by 30%–40%. By reprocessing the data using a different method and showing the amplitude to be almost 2 times as large, in this note it is confirmed that this is indeed the case. The original 5-yr study has also been extended to nearly 10 yr, demonstrating that the same phenomenon has persisted for almost 10 yr.

scholarly journals Fingerprints of a riming event on cloud radar Doppler spectra: observations and modeling

2015 ◽  
Vol 15 (20) ◽  
pp. 28619-28658 ◽  
Author(s):  
H. Kalesse ◽  
W. Szyrmer ◽  
S. Kneifel ◽  
P. Kollias ◽  
E. Luke
Keyword(s):  
Supercooled Liquid ◽  
Relative Role ◽  
Traditional Use ◽  
Radar Observations ◽  
Atmospheric Radiation Measurement ◽  
In Situ Observations ◽  
Air Motion ◽  
Biogenic Aerosols

Abstract. Radar Doppler spectra measurements are exploited to study a riming event when precipitating ice from a seeder cloud sediments through a supercooled liquid water (SLW) layer. The observations were collected during the deployment of the Atmospheric Radiation Measurement Program's (ARM) mobile facility AMF2 at Hyytiälä, Finland during the BAECC (Biogenic Aerosols – Effects on Clouds and Climate Snowfall Experiment) field campaign. The presented analysis of the height evolution of the radar Doppler spectra is a state-of-the-art retrieval with profiling cloud radars in SLW layers beyond the traditional use of spectral moments. Dynamical effects are taken into account by following the particle population evolution along slanted tracks that are caused by horizontal advection of the cloud under wind shear conditions. In the SLW layer, the identified liquid peak is used as an air motion tracer to correct the Doppler spectra for vertical air motion and the ice peak is used to study the radar profiles of rimed particles. A 1-D steady-state bin microphysical model is constrained using the SLW and air motion profiles and cloud top radar observations. The observed radar moment profiles of the rimed snow can be simulated reasonably well by the model, but not without making several assumptions about the ice particle concentration and the relative role of deposition and aggregation. This suggests that in-situ observations of key ice properties are needed to complement the profiling radar observations before process-oriented studies can effectively evaluate ice microphysical parameterizations.

scholarly journals Analysis of the Khmer Walled Defensive System of Vimayapura (Phimai City, Thailand): Symbolism or Military Effectiveness?

MANUSYA ◽  
2020 ◽  
Vol 23 (2) ◽  
pp. 253-285
Author(s):  
Víctor Lluís Pérez Garcia
Keyword(s):  
City Centre ◽  
Military Effectiveness ◽  
Archaeological Remains ◽  
Theoretical Level ◽  
In Situ Observations ◽  
The City

This article analyses the walled defensive system of the Khmer city centre of Vimayapura (modern Phimai, Thailand) to evaluate the theoretical level of military effectivity of both the walls and the moats against potential attackers, considering their technical characteristics and the enemy’s weapons. We also study the layout of the urban enceinte, the constructive material, the gateways as well as weakness and strengths of the stronghold and the symbolic, monumental and ornamental functions in the overall role of the walls. Based on comparisons with similar cases, as well as in situ observations of the archaeological remains and a bibliographical research, our study reveals that the stonewalls were not designed primarily to resist military attacks. Instead, the army, the moat, and possibly the embankments and/or palisades would have been the first lines of defence of the city.

scholarly journals The changing role of organic nitrates in the removal and transport of NO<sub><i>x</i></sub>

2020 ◽  
Vol 20 (1) ◽  
pp. 267-279 ◽  
Author(s):  
Paul S. Romer Present ◽  
Azimeh Zare ◽  
Ronald C. Cohen
Keyword(s):  
Air Pollution ◽  
The United States ◽  
Ozone Production ◽  
Organic Nitrates ◽  
Nox Emissions ◽  
Direct Formation ◽  
In Situ Observations ◽  
Changing Role

Abstract. A better understanding of the chemistry of nitrogen oxides (NOx) is crucial to effectively reducing air pollution and predicting future air quality. The response of NOx lifetime to perturbations in emissions or in the climate system is set in large part by whether NOx loss occurs primarily by the direct formation of HNO3 or through the formation of alkyl and multifunctional nitrates (RONO2). Using 15 years of detailed in situ observations, we show that in the summer daytime continental boundary layer the relative importance of these two pathways can be well approximated by the relative likelihood that OH will react with NO2 or instead with a volatile organic compound (VOC). Over the past decades, changes in anthropogenic emissions of both NOx and VOCs have led to a significant increase in the overall importance of RONO2 chemistry to NOx loss. We find that this shift is associated with a decreased effectiveness of NOx emissions reductions on ozone production in polluted areas and increased transport of NOx from source to receptor regions. This change in chemistry, combined with changes in the spatial pattern of NOx emissions, is observed to be leading to a flatter distribution of NO2 across the United States, potentially transforming ozone air pollution from a local issue into a regional one.

Sign in / Sign up

Export Citation Format

Share Document