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Global sea level provides an important indicator of the state of the warming climate, but changes in regional sea level are most relevant for coastal communities around the world. With improvements to the sea-level observing system, the knowledge of regional sea-level change has advanced dramatically in recent years. Satellite measurements coupled with in situ observations have allowed for comprehensive study and improved understanding of the diverse set of drivers that lead to variations in sea level in space and time. Despite the advances, gaps in the understanding of contemporary sea-level change remain and inhibit the ability to predict how the relevant processes may lead to future change. These gaps arise in part due to the complexity of the linkages between the drivers of sea-level change. Here we review the individual processes which lead to sea-level change and then describe how they combine and vary regionally. The intent of the paper is to provide an overview of the current state of understanding of the processes that cause regional sea-level change and to identify and discuss limitations and uncertainty in our understanding of these processes. Areas where the lack of understanding or gaps in knowledge inhibit the ability to provide the needed information for comprehensive planning efforts are of particular focus. Finally, a goal of this paper is to highlight the role of the expanded sea-level observation network-particularly as related to satellite observations-in the improved scientific understanding of the contributors to regional sea-level change.

Saltwater intrusion is a critical concern for coastal communities due to its impacts on fresh ecosystems and civil infrastructure. Declining recharge and rising sea level are the two dominant drivers of saltwater intrusion along the land‐ocean continuum, but there are currently no global estimates of future saltwater intrusion that synthesize these two spatially variable processes. Here, for the first time, we provide a novel assessment of global saltwater intrusion risk by integrating future recharge and sea level rise while considering the unique geology and topography of coastal regions. We show that nearly 77% of global coastal areas below 60° north will undergo saltwater intrusion by 2100, with different dominant drivers. Climate‐driven changes in subsurface water replenishment (recharge) is responsible for the high‐magnitude cases of saltwater intrusion, whereas sea level rise and coastline migration are responsible for the global pervasiveness of saltwater intrusion and have a greater effect on low‐lying areas. Plain Language Summary: Coastal watersheds around the globe are facing perilous changes to their freshwater systems. Driven by climatic changes in recharge and sea level working in tandem, sea water encroaches into coastal groundwater aquifers and consequently salinizes fresh groundwater, in a process called saltwater intrusion. To assess the vulnerability of coastal watersheds to future saltwater intrusion, we applied projections of sea level and groundwater recharge to a global analytical modeling framework. Nearly 77% of the global coast is expected to undergo measurable salinization by the year 2100. Changes in recharge have a greater effect on the magnitude of salinization, whereas sea level rise drives the widespread extensiveness of salinization around the global coast. Our results highlight the variable pressures of climate change on coastal regions and have implications for prioritizing management solutions. Key Points: First global analysis of future saltwater intrusion vulnerability responding to spatially variable recharge and sea level rise is providedRecharge drives the extreme cases of saltwater intrusion, while sea level rise is responsible for its global pervasivenessNearly 77% of global coastal areas below 60° north will undergo saltwater intrusion by 2100 [ABSTRACT FROM AUTHOR]

Based on latest estimates (e.g., https://sealevel.nasa.gov), global mean sea level has risen nearly 100 mm since 1993. However, the rate of rise has not been constant in space or time and recent observations (since ∼ 2008) reveal pronounced regional acceleration in the Gulf of Mexico (GoM). Here we use model solutions and observational data to identify the physical mechanisms responsible for enhanced rates of coastal sea‐level rise in this region. We quantify the effect of offshore subsurface ocean warming on coastal sea‐level rise and its relationship to regional hypsometry, the distribution of ocean area with depth. Using an Estimating the Circulation and Climate of the Ocean (ECCO) state estimate, we establish that coastal sea‐level changes at the 10‐year timescale are largely the result of changes in regional ocean mass, reflected in ocean bottom pressure. These coastal bottom pressure changes reflect both net mass flux into the Gulf, as well as internal mass redistribution within the Gulf, which can be understood as an isostatic ocean response to subsurface warming. We test the relationships among coastal sea‐level, bottom pressure, and subsurface warming identified in ECCO using observations from satellite gravimetry, altimetry, tide gauges, and Argo floats. Estimates of mass redistribution explain a significant fraction of coastal sea‐level trends observed by tide gauges. For instance, at St. Petersburg, Florida, this mass redistribution mechanism accounts for >50% of the coastal sea‐level trend observed between 2008 and 2017. This study thus elucidates a physical mechanism whereby coastal sea‐level responds to open‐ocean subsurface density change. Plain Language Summary: We investigate drivers of coastal sea‐level rise in the GoM. Using both model output and observational data we consider the relationship between warming of the ocean at depths below the surface and away from the coast and sea‐level rise at the coast. Changes in ocean bottom pressure throughout the GoM over recent decadal periods reveal a redistribution of water from deeper to shallower regions that coincides with warming throughout the water column. This analysis incorporates observations of coastal sea‐level from tide gauges along the US GoM coast, ocean temperature and salinity from profiling floats, ocean bottom pressures from satellite gravimetry, and sea surface height from satellite altimetry. Results reveal that offshore warming below the surface contributes importantly to coastal sea‐level rise. Its relative contribution is greater in the eastern Gulf, where rates of vertical land motion are smaller than in the western Gulf. Key Points: Recently observed sea‐level trends along the US Gulf coast are consistent with higher future sea‐level rise scenariosSubsurface ocean warming has caused mass redistribution within the Gulf of Mexico (GoM) contributing to positive coastal sea‐level trendsMass redistribution within and mass import into the GoM explain a dominant fraction of eastern Gulf trends in sea‐level [ABSTRACT FROM AUTHOR]

Interannual sea‐level variations between the United States (U.S.) Northeast and Southeast Coasts separated by Cape Hatteras are significantly less correlated than those within their respective sectors, but the cause is poorly understood. Here we investigate atmospheric forcing mechanisms that affect the interannual sea‐level co‐variability between these two sectors using an adjoint reconstruction and decomposition approach in the framework of Estimating the Circulation and Climate of the Ocean (ECCO) ocean state estimate. We compare modeled and observed sea‐level changes at representative locations in each sector: Nantucket Island, Massachusetts for the Northeast and Charleston, South Carolina for the Southeast. The adjoint reconstruction and decomposition approach used in this work allows for identification and quantification of the causal mechanisms responsible for observed coastal sea‐level variability. Coherent sea‐level variations in Nantucket and Charleston arise from nearshore wind stress anomalies north of Cape Hatteras and buoyancy forcing, especially from the subpolar North Atlantic, while offshore wind stress anomalies, in contrast, reduce co‐variability. Offshore wind stress contributes much more to interannual sea‐level variation at Charleston than at Nantucket, causing incoherent sea level variations between the two locations. Buoyancy forcing anomalies south of Charleston, including over the Florida shelf, the Gulf of Mexico, and the Caribbean Sea, also reduce co‐variability because they induce sea‐level responses at Charleston but not Nantucket. However, the relative impact of buoyancy forcing on interannual sea‐level co‐variability between the two sectors is much smaller than that of offshore wind stress. Plain Language Summary: The magnitude of year‐to‐year sea‐level variations along the East Coast of the United States (U.S.) can be comparable to that of global mean sea‐level rise over a few decades. These year‐to‐year sea‐level variations contribute to more frequent nuisance floods that affect coastal communities. Year‐to‐year sea‐level variations between the U.S. Northeast and Southeast Coasts separated by Cape Hatteras are significantly less correlated than those within the respective sectors. Understanding causal mechanisms affecting the coherence of year‐to‐year sea‐level variations in the two sectors would help improve sea‐level predictions. Our study attributes year‐to‐year sea‐level variations at Charleston and Nantucket, proxy locations for the U.S. Southeast and Northeast Coasts, to wind and buoyancy forcing (air‐sea heat exchange and precipitation/evaporation at sea surface that both affect seawater buoyancy). We find that nearshore winds north of Cape Hatteras and buoyancy forcing both cause coherent year‐to‐year sea‐level variations between Nantucket and Charleston. Offshore winds affect much more year‐to‐year sea‐level variation at Charleston than that at Nantucket. Offshore winds are the major factor causing less correlated year‐to‐year sea‐level variations between Nantucket and Charleston. Warming/cooling of water south of Charleston affects sea‐level variations at Charleston, but not at Nantucket. However, this effect is smaller than that of the offshore wind. Key Points: Nearshore winds north of Cape Hatteras and buoyancy forcing cause coherent interannual sea‐level variations between Nantucket and CharlestonOffshore winds contribute much more to interannual sea‐level variation at Charleston than to that at NantucketOffshore winds are the major factor causing incoherent interannual sea‐level variations between Nantucket and Charleston [ABSTRACT FROM AUTHOR]

The daily rise and fall of the tides are intimately familiar to those living on the coast. However, due to sea‐level rise, what communities in the United States now experience as the highest, lowest, and average water levels on a typical day no longer corresponds to the official definitions of high tide, low tide, and mean sea level, respectively. Water levels now regularly exceed official high tide along parts of the Chesapeake Bay, Gulf Coast, and Puerto Rico. In other words, yesterday's high tide is becoming today's new normal. This demonstrates how sea‐level rise is radically redefining the American shore. Plain Language Summary: Due to sea‐level rise, coastal elevations that we once knew as marking the highest water level over a typical daily tidal cycle now correspond more closely to the average level of the sea: yesterday's high tide is becoming today's new normal. This illustrates how profoundly sea‐level rise is altering how we live, work, and play by the sea. Key Points: Sea‐level rise is altering how we live, work, and play by the seaElevations that marked high tide only decades ago are now closer to mean sea levelThis has implications for transportation, construction, and policy [ABSTRACT FROM AUTHOR]

Terrestrial water storage (TWS) anomalies derived from the Gravity Recovery and Climate Experiment (GRACE) mission have been useful for several earth science applications, ranging from global earth system science studies to regional water management. However, the relatively short record of GRACE has limited its use in understanding the climate-driven interannual-to-decadal variability in TWS. Targeting these timescales, we used the novel method of cyclostationary empirical orthogonal functions (CSEOFs) and the common modes of variability of TWS with precipitation and temperature to reconstruct the TWS record of 1979–2020. Using the same common modes of variability, we also provide a realistic, time-varying uncertainty estimate of the reconstructed TWS. The interannual variability in the resulting TWS record is consistent in space and time, and links the global variations in TWS to the regional ones. In particular, we highlight improvements in the representation of ENSO variability when compared to other available TWS reconstructions. [ABSTRACT FROM AUTHOR]

Sea‐level rise is an important indicator of ongoing climate change and well observed by satellite altimetry. However, observations from conventional altimetry degrade at the coast where regional sea‐level changes can deviate from the open‐ocean and impact local communities. With the 2018 launch of the laser altimeter onboard ICESat‐2, new high‐resolution observations of ice, land, and ocean elevations are available. Here we assess the potential benefits of sea level measured by ICESat‐2 by comparing to data from Jason‐3 and tide gauges. We find good agreement in the linear rates computed from the independent observations, with an absolute average residual of 3.60 ± 0.03 cm yr−1 between global ICESat‐2 and Jason‐3 observations at a 1° posting. The recent La Niña is clearly evident in ICESat‐2 observations, as well as small‐scale features. By demonstrating the quality of the ICESat‐2‐measured sea level, we provide support for integrating it into the existing suite of sea‐level observations. Plain Language Summary: Sea levels are rising globally due to human induced climate change. However, local sea levels that impact coastal communities often differ from the global increase, sometimes by a factor of 2 or more. Unfortunately, measuring sea level along the coast can be challenging, as radar satellites are primarily designed for the open ocean. Additionally, direct measurements from tide gauge stations are typically spaced far apart, and thus don't adequately represent the full range of changes that occur along the coast. In 2018, NASA launched the ICESat‐2 satellite which carries a laser instrument capable of measuring sea level much closer to the coast than existing radar satellites. Here we assess how well ICESat‐2 data measures coastal sea level by comparing it to data from the radar satellite Jason‐3 and tide gauges measurements. We find good agreement in recent sea‐level changes computed from both data sources. Large‐scale climate patterns, such as the recent La Niña, as well as small‐scale oceanic features like currents are clearly evident in the ICESat‐2 data. These results support the idea that ICESat‐2 measurements can be integrated into the existing suite of sea‐level observations and serve as an additional tool for addressing ongoing sea‐level rise. Key Points: High spatial resolution sea‐level observations from ICESat‐2 are available over the global oceansSea‐level trends computed from ICESat‐2 observations agree with independent measurements from radar altimetry and tide gaugesUncertainty on the estimated trends is expected to decrease by an order of magnitude in 5 years through averaging [ABSTRACT FROM AUTHOR]

The global water cycle is generally viewed as the cycling of water masses among the land, ocean, and atmosphere. This cycling predominantly occurs at the annual time scale and between land and ocean, constituting the seasonal global water cycle. NASA's Gravity Recovery and Climate Experiment (GRACE) and GRACE‐Follow On missions can directly observe the seasonal global water cycle and describe the changes in its intensity. We present seasonal amplitudes of the global land water and ocean mass anomalies between 04/2002 and 11/2020. We find that the average seasonal amplitude is 17.0 ± 0.6 mm sea level equivalent (SLE), and its interannual variability (σ = 1.1 mm SLE) is comparable to the long‐term trends in the land and ocean masses. We investigate two periods of rapid amplification and deamplification during which the amplitude changed as much as 29%, and find that changes in hydroclimatology in certain land regions modulate the seasonal global water cycle. Plain Language Summary: The global water cycle is generally viewed as the cycling of water among the land, ocean, and atmosphere. By observing the changes in the water mass, NASA's Gravity Recovery and Climate Experiment (GRACE) and GRACE‐Follow On missions are capable of measuring the global water cycle, and its changes, directly. The largest portion of the cycling occurs between global land and global ocean at the annual time scale, constituting the seasonal global water cycle. We present the amplitude of this cycling, its year‐to‐year changes that describe the changes in the intensity of the seasonal global water cycle, and the regions contributing to it. Key Points: The seasonal amplitude of global ocean and land water mass describes the seasonal global water cycle and is a metric of its strengthThe seasonal amplitude varies interannually with magnitude comparable to the long‐term trend in global ocean massHydrological changes in specific land regions are most responsible for these year‐to‐year variations [ABSTRACT FROM AUTHOR]

The 25‐year record of satellite altimeter‐measured sea level has led to improvements in the understanding of sea level change on both regional and global scales. However, the extent to which the pattern of regional sea level rise measured by altimeters is representative of the forced sea level response remains an open question. Internal variability both contributes to regional sea level changes on short time scales and masks the pattern of forced trend and acceleration associated with anthropogenic global warming. Recent studies have demonstrated that the forced trend pattern of regional rise has begun to emerge, although there has been no assessment of a possible associated acceleration. Here, the regional acceleration pattern is estimated from the altimeter sea level record and assessed with regard to the influence of internal variability. While the dominant features in the acceleration pattern can be attributed to internal variability, there is an indication that the forced acceleration pattern may emerge as the record continues to lengthen. Key Points: Internal variability is removed from the satellite altimeter record, and the impact on trends and accelerations is assessedFor most locations, a significant acceleration or deceleration still has not emerged, despite removing some amount of internal variabilityMany of the large‐amplitude signals have been removed, narrowing the range of accelerations that could be associated with a forced response [ABSTRACT FROM AUTHOR]

Satellite altimetry reveals substantial decadal variability in sea level ζ across the tropical Pacific during 1993–2015. An ocean state estimate that faithfully reproduces the observations is used to elucidate the origin of these low‐frequency tropical Pacific ζ variations. Analysis of the hydrostatic equation reveals that recent decadal ζ changes in the tropical Pacific are mainly thermosteric in nature, related to changes in upper‐ocean heat content. A forcing experiment performed with the numerical model suggests that anomalous wind stress was an important driver of the relevant heat storage and thermosteric variation. Closed budget diagnostics further clarify that the wind‐stress‐related thermosteric ζ variation resulted from the joint actions of large‐scale ocean advection and local surface heat flux, such that advection controlled the budget over shorter, intraseasonal to interannual time scales, and local surface heat flux became increasingly influential at longer decadal periods. In particular, local surface heat flux was important in contributing to a recent reversal of decadal ζ trends in the tropical Pacific. Contributions from local surface heat flux partly reflect damping latent heat flux tied to wind‐stress‐driven sea‐surface‐temperature variations. Key Points: Sea level in the western tropical North Pacific and eastern and central equatorial Pacific underwent decadal variation over 1993–2015This decadal variation reflects ocean heat storage related to ocean heat transport and local surface heat flux due to anomalous wind stressContributions from air‐sea heat exchange arise from latent heat flux associated with wind‐stress‐related sea‐surface temperature changes [ABSTRACT FROM AUTHOR]

The continuous and near‐global coverage of satellite altimeters has provided an improved understanding of sea level rise on both global and regional scales. With its relatively short record, however, questions have persisted regarding how well satellite‐measured trends reflect the trends associated with forced or anthropogenic forcing. Masking the forced sea level rise in the altimeter record is the presence of unaccounted‐for, naturally occurring variability. Here, a combined approach using models and observations is used to attribute a portion of the satellite‐measured sea level record to natural variability. The agreement between the observations and models makes clear the quality of current models and their ability to realistically capture sea level variability. This paper shows a regional trend pattern where the influence of natural variability has been reduced, providing a clearer picture of how anthropogenic forcing may impact sea level arise around the globe. Key Points: A combined approach using models and observations is used to attribute satellite‐measured sea level to natural variabilityThe agreement of the observations and models provides an assessment of current models and their ability to capture sea level variabilityA clearer picture of how anthropogenic forcing may impact sea level arise is obtained after removing natural variability [ABSTRACT FROM AUTHOR]

Since the advent of the modern satellite altimeter era, the understanding of the sea level has increased dramatically. The satellite altimeter record, however, dates back only to the 1990s. The tide gauge record, on the other hand, extends through the 20th century but with poor spatial coverage when compared to the satellites. Many studies have been conducted to create a dataset with the spatial coverage of the satellite datasets and the temporal length of the tide gauge records by finding novel ways to combine the satellite data and tide gauge data in what is known as sea level reconstruction. However, most of the reconstructions of sea level were conducted on a global scale, leading to reduced accuracy on regional levels, especially when there are relatively few tide gauges. The seas around the Korean Peninsula are one such area with few tide gauges before 1960. In this study, new methods are proposed to reconstruct past sea level around the Korean Peninsula. Using spatial patterns obtained from a cyclostationary empirical orthogonal function decomposition of satellite data, we reconstruct sea level over the period from 1900 to 2014. Sea surface temperature data and altimeter data are used simultaneously in the reconstruction process, leading to an elimination of reliance on tide gauge data. Although we did not use the tide gauge data in the reconstruction process, the reconstructed sea level has a better agreement with the tide gauge observations in the region than previous studies that incorporated the tide gauge data. This study demonstrates a reconstruction technique that can potentially be used at regional levels, with particular emphasis on areas with poor tide gauge coverage. [ABSTRACT FROM AUTHOR]

Since the advent of the modern satellite altimeter era, the understanding of the sea level has increased dramatically. The satellite altimeter record, however, dates back only to the 1990s. The tide gauge record, on the other hand, extends through the 20th century, but with poor spatial coverage when compared to the satellites. Many studies have been conducted to extend the spatial resolution of the satellite data into the past by finding novel ways to combine the satellite data and tide gauge data in what are known as sea level reconstructions. However, most of the reconstructions of sea level were conducted on a global scale, leading to reduced accuracy on regional levels, particularly where there are relatively few tide gauges. The sea around the Korean Peninsula is one such area with few tide gauges prior to 1960. In this study, new methods are proposed to reconstruct the past sea level and project the future sea level around the Korean Peninsula. Using spatial patterns obtained from a cyclo-stationary empirical orthogonal function decomposition of satellite data, we reconstruct sea level over the time period from 1900 to 2014. Sea surface temperature data and altimeter data are used simultaneously in the reconstruction process, leading to an elimination of reliance on tide gauge data. Although the tide gauge data was not used in the reconstruction process, the reconstructed results showed better agreement with the tide gauge observations in the region than previous studies that incorporated the TG data. This study demonstrates a reconstruction technique that can be used on regional levels, with particular emphasis on areas with poor tide gauge coverage. [ABSTRACT FROM AUTHOR]

Sea ice loss is proposed as a primary reason for the Arctic amplification, although the physical mechanism of the Arctic amplification and its connection with sea ice melting is still in debate. In the present study, monthly ERAInterim reanalysis data are analyzed via cyclostationary empirical orthogonal function analysis to understand the seasonal mechanism of sea ice loss in the Arctic Ocean and the Arctic amplification. While sea ice loss is widespread over much of the perimeter of the Arctic Ocean in summer, sea ice remains thin in winter only in the Barents-Kara seas. Excessive turbulent heat flux through the sea surface exposed to air due to sea ice reduction warms the atmospheric column. Warmer air increases the downward longwave radiation and subsequently surface air temperature, which facilitates sea surface remains to be free of ice. This positive feedback mechanism is not clearly observed in the Laptev, East Siberian, Chukchi, and Beaufort seas, since sea ice refreezes in late fall (November) before excessive turbulent heat flux is available for warming the atmospheric column in winter. A detailed seasonal heat budget is presented in order to understand specific differences between the Barents-Kara seas and Laptev, East Siberian, Chukchi, and Beaufort seas. [ABSTRACT FROM AUTHOR]

While global mean sea level rise (SLR) and acceleration (SLA) are indicators of climate change and are informative regarding the current state of the climate, assessments of regional and local SLR are essential for policy makers responding to, and preparing for, changes in sea level. In this work, three acceleration detection techniques are used to demonstrate the robust SLA in the China Seas. Interannual to multidecadal sea level variations (periods >2 years), which are mainly related to natural internal climate variability and significantly affect estimation of sea level acceleration, are removed with empirical mode decomposition (EMD) analysis prior to the acceleration determination. Consistent SLAs of 0.085 ± 0.020 mm± yr-2 (1950-2013) and 0.074 ± 0.032 mm± yr-2 (1959-2013) in regional tide gauge records are shown to result from the three applied approaches in the Bohai Sea (BS) and East China Sea (ECS), respectively. The SLAs can be detected in records as short as 20 years if long-term sea level variability is adequately removed. The spatial distribution of SLA derived from a sea level reconstruction shows significant SLA in the BS, Yellow Sea (YS) and Yangtze River Estuary. [ABSTRACT FROM AUTHOR]

The article highlights the significance of vertical land motion (VLM) in understanding sea level rise in New York City due to climate change. It discusses how subsidence and uplift in various areas of the city can impact coastal resilience efforts and the need for precise, high-resolution estimates of VLM to inform adaptation strategies.

Liquid crystal drops dispersed in a continuous phase of silicone oil are generated with a narrow distribution in droplet size in microfluidic devices both above and below the nematic-to-isotropic transition temperature. Our experiments show that the surface properties of the channels can be critical for droplet formation. We observe different dynamics in liquid crystal droplet generation and coalescence, and distinct droplet morphology on altering the microchannel surface energy. This is explained by the thermodynamic description of the wetting dynamics of the system. The effect of the nematic-to-isotropic transition on the formation of liquid crystal droplets is also observed and related to the capillary number. We also investigate how the nematic droplet size varies with the flow rate ratio and compare this behaviour with a Newtonian reference system. The effect of the defect structures of the nematic liquid crystal can lead to distinctly different scaling of droplet size in comparison with the Newtonian system. When the nematic liquid crystal phase is stretched into a thin filament before entering the orifice, different defect structures and numbers of defect lines can introduce scatter in the drop size. Capillary instabilities in thin nematic liquid crystal filament have an additional contribution from anisotropic effects such as surface gradients of bending stress, which can provide extra instability modes compared with that of isotropic fluids. [ABSTRACT FROM AUTHOR]

The regional sea level variability in the Bohai Sea (BS), Yellow Sea (YS) and East China Sea (ECS) is investigated based on tide gauge, satellite altimeter data and an independent oceanic general circulation model for the Earth Simulator (OFES) model outputs. It is found that atmospheric forcing significantly affects local sea level variability in the BS and YS and local sea level variability at the Southern ECS is highly correlated with along-shore currents. Particularly, the annual sea level fluctuations potentially change inundation risk and the frequency and magnitude of flooding in regions with high annual sea level. Hence, the cyclostationary empirical orthogonal function (CSEOF) analysis is carried out to investigate the variations of annual sea level cycle amplitude. Similar spatial distribution characteristics of annual sea level amplitude fluctuations are presented from satellite altimeter data and model outputs. The variability of annual sea level amplitude estimated from the satellite altimeter data agrees well with that from the tide gauge data, and positively (negatively) correlates with Southern Oscillation Index (Pacific Decadal Oscillation). The OFES model, however, underestimates the fluctuation of the annual cycle. After removing the annual signal, the low-passed (i.e., 13-month running mean) tide gauge data shows high correlations with SOI and PDO on time scales over 8 years in the BS and ECS. [ABSTRACT FROM AUTHOR]

In this paper, we focus on the isotropic-to-nematic phase transition in a liquid-crystal droplet. We present the results of an experiment to measure the growth of the nematic phase within an isotropic phase liquid-crystal droplet. Experimentally, we observe two primary phase transition regimes. At short time scales, our experimental results (R(t) approximately t0.51) show good agreement with a Stefan-type model of the evolution of the nematic phase within the isotropic phase of a liquid crystal. As time progresses, the growth of the nematic phase is restricted by increased confinement of the droplet boundary. During this stage of growth, the nematic phase grows at a slower rate of R(t) approximately t0.31. The slower growth at later stages might be due to a variety of factors such as confinement-induced latent heat reduction; a change of defect strength during its evolution; or interactions between the defect and the interface between the liquid crystal and oil or between adjacent defects. The presence of two growth regimes is also consistent with the molecular simulations of Bradac et al. (Bradac, Z.; Kralj, S.; Zumer, S. Phys. Rev. E 2002, 65, 021705) who identify an early stage domain regime and a late stage confinement regime. For the domain and confinement regimes, Bradac et al. (Bradac, Z.; Kralj, S.; Zumer, S. Phys. Rev. E 2002, 65, 021705) obtained growth exponents of 0.49 +/- 0.05 and 0.25 +/- 0.05. These are remarkably close to the values 0.51 and 0.31 observed in our experiments.