C-Cosine Functions and the Abstract Cauchy Problem, I

AbstractIfAis the generator of an exponentially boundedC-cosine function on a Banach spaceX, then the abstract Cauchy problem (ACP) forAhas a unique solution for every pair (x,y) of initial values from (λ−A)−1C(X). The main result is a characterization of the generator of aC-cosine function, which may not be exponentially bounded and may have a nondensely defined generator, in terms of the associated ACP

Multi-satellite altimetry and GOCE geoid based surface and subsurface currents in the Mediterranean Sea

Peer ReviewedPostprint (published version

Determination and Characterization of 20th Century Global Sea Level Rise

The Report describes the PhD dissertation research completed by Chung-Yen Kuo on November, 2005, supervised by C.K. Shum and other PhD Committee Members including Douglas Alsdorf, Michael Bevis, Laury Miller, and Yuchan Yi.This research is supported by grants from NOAA under NA16RG2252, NA86RG0053 (R/CE-5) and NA030AR4170060 (R/CE-8), and NASA's Ocean and Ice, Cryosphere, Physical Oceanography and Interdisciplinary Science Programs (NNG04GA53G, NAG5-9335, NAG5-12585, JPL- 1265252).Sea level rise has been widely recognized as a measurable signal and as one of the consequences of a possible anthropogenic (human-induced) effect on global climate change. The small rate of sea level rise, 1–2 mm/yr during the last century [Church et al., 2001, Chapter 11, Changes in Sea Level, in the Third Assessment Report (TAR) of the Intergovernmental Panel for Climate Change (IPCC), Working Group I, Houghton et al., 2001], could only be partially explained by a number of competing geophysical processes, each of which is a complex process within the Earth-atmosphere-ocean-cryosphere-hydrosphere system. In particular, the observed 20th Century sea level rise rate of 1.84±0.35 mm/yr [Douglas, 2001; Peltier, 2001] could not explain up to one half of the predicted 20th Century global sea level rise based on the IPCC TAR estimate of 1.1 mm/yr (0.6 mm/yr of melted water from ice sheets and glaciers, and 0.5 mm/yr from the steric effect in the ocean) [Church et al., 2001] and remains an enigma [Munk, 2002]. The quest to resolve the controversy [Meier and Wahr, 2002] and to further understand sea level change [Chao et al., 2002] is well underway including efforts being conducted during the current IPCC Fourth Assessment Report (FAR), 2003–2007. In this study, we provide a determination of the 20th Century (1900–2002) global sea level rise, the associated error budgets, and the quantifications or characterization of various geophysical sources of the observed sea level rise, using data and geophysical models. We analyzed significant geographical variations of global sea level change including those caused by the steric component (heat and salinity) in the ocean, and sea level redistribution resulting from ice sheets and glacier melting in consequence of self gravitation, and the effects of glacial isostatic adjustment (GIA) since the Pleistocene affecting sea level signals in the observations. In particular, relative sea level data from up to 651 global long-term (longest record is 150 years) tide gauges from Permanent Service for Mean Sea Level (PSMSL) and other sources, and geocentric sea level data from multiple satellite radar altimetry (1985–2005) have been used to determine and characterize the 20th Century global sea level rise. Altimeter and selected tide gauge data have been used for sea level determination, accounting for relative biases between different altimeters and offsets between the tide gauges, effects of thermosteric sea level variations, vertical motions affecting tide gauge sea level measurements, sea level redistribution due to ice melt resulting from self gravitation, and barotropic ocean response due to atmospheric forcing. This study is also characterized by the role of the polar ocean in the global sea level study and addressing the question whether there is a detectable acceleration of sea level rise during the last decade. Vertical motions have been estimated by combining geocentric sea level measurements from satellite altimetry (TOPEX/POSEIDON, T/P) and long-term relative (crustfixed) sea level records from global tide gauges using the Gauss-Markov model with stochastic constraints. The study provided a demonstration of improved vertical motion solutions in semienclosed seas and lakes, including Fennoscandia and the Great Lakes region, showing excellent agreement with independent GPS observed radial velocities, or with predictions from GIA models. In general, the estimated uncertainty of the observed vertical motion is <0.5 mm/yr, significantly better than other studies. Finally, improved algorithms to account for nonlinear vertical motions caused by other geodynamic processes than GIA including post-seismic deformations, have been developed and applied to tectonically active regions such as Alaska and compared well with GPS velocities and other studies. This novel technique could potentially provide improved vertical motion globally where long-term tide gauge records exist. The thermosteric sea level trend of the upper (0–500 m) layers of the ocean accounts for about 70% of the variations when deeper ocean (0–3000 m) is considered using the World Ocean Altas 2001 (WOA01). The estimated global thermosteric sea level trend of 0.33 mm/yr (0–500 m) and 0.43 mm/yr (0–3000 m) agrees well with other studies [Levitus et al., 2005; Ishii et al., 2005]. A detailed analysis using in situ temperature and salinity data from the Ocean Station Data (OSD), in the Eastern Pacific (where the in situ data are more abundant) is conducted to assess the contributions of respective roles of thermal and salinity effects on sea level changes. The analysis indicates that the estimated thermosteric sea level trends integrated from 0–500 m and from 0–1000 m depths using OSD are almost identical at ~0.64 mm/yr in the Eastern Pacific ocean. In this region, the halosteric (salinity) sea level trend is small, at the 0.04 mm/yr level for both the 0–500 m and 0–1000 m cases. The result is consistent with Miller and Douglas [2004], which analyzed data from selected oceanic regions including the Eastern Pacific, Eastern Atlantic, and Caribbean. In general, observed sea level (from tide gauges or altimetry) and thermosteric sea level are highly correlated except in regions of high mesoscale variability. A detailed comparison of the estimated thermosteric sea level trends with the observed sea level trend near proximities of global tide gauges (~50 years, 1950–2004, up to 597 sites) indicates that the thermosteric sea level trends account for 36% and 68% of the observed global sea level trend, for the 0–500 m and 0–3000 m cases, respectively, indicating the importance of deeper ocean thermal effects. Comparison of global thermosteric sea level trend with altimetry observed sea level trends indicates that the results are dependant on data spans used: thermosteric sea level trend (0–500 m) accounts for over 81% of total observed sea level using T/P altimetry during 1993–2003, while accounts for only 26% when data span extends to 1985–2005 using multiple altimetry. The primary reason is the presence of long-period oceanic variability (interannual, decadal or longer) in trend estimates causing inconsistent conclusions. Comparison of thermosteric sea level trend with sea level observed by selected tide gauges reaches different conclusions depending on the choice and number of tide gauges (1955–1996) used: thermosteric sea level trend (0–3000 m) accounts for over 88% of the observed sea level from 27 tide gauges, while it accounts for only 38% if 515 tide gauges are used. A study using temporal gravity field measurements observed by the Gravity Recovery and Climate Experiment (GRACE) in terms of oceanic mass variations at long-wavelength (>800 km) and monthly sampling demonstrates its potential use, when combined with satellite altimetry, to improve steric sea level trend estimates over the Southern Ocean, where the OSD is extremely sparse or non-existent. The global (covering within ±81°.5 latitude) sea level trend (corrected for IB) observed by multiple satellite altimetry (GEOSAT, ERS-1, T/P, ERS-2, GFO, JASON and ENVISAT, data covering 1985–2002 except for 1988–1991), and by ~530 tide gauges are 2.8±0.5 mm/yr (corrected for GIA geoid effect) and 2.7±0.4 mm/yr, respectively, indicating excellent agreement. The observed sea level trend using multiple satellite altimeters covering 1985–2004 is 2.9±0.5 mm/yr, although the data span is still too short to yield reliable trend estimates. The multiple altimeter data sets allow coverage in the polar oceans, as opposed to only using data from T/P (coverage within ±66°), and have a longer data span (~19 years versus 10 year for T/P). The data have been calibrated against each other and with tide gauge data for robust determination of their relative biases with respect to T/P. The 20th Century (1900–2002) global sea level trend determined from 651 tide gauge stations is 1.6±0.4 mm/yr, while the trend estimate for the last 50 years (1948–2002) is similar, but used 620 tide gauges. The atmospheric effect via the barotropic IB correction (globally averaged at ~0.11 mm/yr and over 50 years at global tide gauge locations) to sea level (tide gauges or altimetry) observations is warranted as it reduces variances of the data and causes improved agreements between altimetry and tide gauge sea level data. The multiple altimeter data allows sea level studies in the Arctic and Sub-Arctic Oceans, which have been less studied. The sea level trend in the Sub-Arctic Ocean, bounded by latitude 55°N–82°N and longitude 315°E–60°E, is estimated at 1.8 mm/yr using primarily ERS-1 and ERS-2 altimetry, which have been calibrated by TOPEX/POSEIDON in the lower latitude (±66° latitude) oceans and remove constant offsets and a latitude-dependent bias. The sea level trend can mostly be explained by atmospheric forcing and thermosteric effects. In the Arctic Ocean, sea level trend during 1948–2002 is estimated at 1.9–2.0 mm/yr using tide gauges after correction of land motion using different GIA models. After applying the inverted barometric (IB) correction, the sea level rate reduces to 1.5–1.6 mm/yr, indicating that the barotropic response of the ocean contributes significantly more to the sea level trend in the Arctic Ocean than for the global ocean. In an attempt to estimate the global sea level trend and to quantify some of the known contributions in the 20th Century using data from sparsely distributed long-term tide gauges and ~20 years of satellite altimetry, we assume that the spatial patterns of sea level trends from melt water sources (Antarctica, Greenland and mountain glaciers), the thermosteric effects, and geoid change and land uplift due to GIA are known, while their magnitudes are unknown. We ignored contributions from fresh water imbalances due to continental hydrological processes [Milly et al., 2003; Ngo-Duc et al., 2005], human-impoundment of water in reservoirs or lakes [Chao et al., 1994; Sahagian et al., 1994] and other effects, including permafrost melt [Zhang et al., 2005]. Using two different estimators, the Weighted Least Squares (WLS) and the Elementwise- Weighted Total Least Squares (EW-TLS), and using long-term tide gauges and satellite altimetry, we estimate the respective contributions of each of the sources to the global sea level rise. The EW-TLS technique is found to be more stable while the WLS technique produces solutions with larger error of ~0.3 mm/yr in a simulated study. The EW-TLS solution yields the estimated 20th Century (1900–2002) sea level trend contributions by melt water from the Antarctic and Greenland ice sheets and mountain glaciers to be 0.80±0.14 mm/yr, 0.56±0.12 mm/yr and 0.31±0.08 mm/yr, respectively; the estimated contribution from the thermosteric effect is 0.06±0.04 mm/yr, and the estimated scale of the GIA (ICE-4G) model to correct tide gauge sea level data is 1.27±0.08, indicating that the correction should be higher by 27%. The resulting 20th Century (1900–2002) globally averaged sea level trend is estimated to be 1.73±0.42 mm/yr (95% confidence or 2s) after summing the above forcing factors. The estimate of the resulting last 50 year (1948–2002) global sea level trend is 1.74±0.48 mm/yr (95% confidence or 2s). Finally, we address the issue of whether the sea level trend acceleration is detectable. An analysis indicates that the minimum data span to obtain a stable rate of sea level trend from 27 selected tide gauges [Douglas, 2001] is 20 years or more, while one should use a 30-year or longer data span to derive a stable thermosteric sea level trend from WOA01. It is concluded that, with 95% confidence, there is no statistically significant evidence of sea level acceleration during 1900–2000 from tide gauge data, and during 1950-2000 from thermosteric data. The estimated 20th Century global sea level rise is compared with the more recently estimated total geophysical effects contributing to global sea level rise of 1.41–1.53 mm/yr, which include the sum of the steric effect (~0.4 mm/yr) [e.g., Levitus et al., 2005; Antonov et al., 2005], mountain glacier melting (~0.51 mm/yr) [e.g., Arendt et al., 2002; Dyurgerov and Meier, 2005; Raper and Braithwaite, 2005; and others], ice sheet mass imbalance (~0.45 mm/yr) [e.g., Krabill et al., 2004, Rignot et al., 2005, Thomas et al., 2005], hydrological imbalance (~0.0–0.12 mm/yr) [Milly et al., 2003, Ngo-Duc et al., 2005], and anthropogenic effect (~0.05 mm/yr) [Dork Sahagian, pers. comm.]. This study (1.74±0.48 mm/yr) reduces the existing discrepancy [Chruch et al., 2001] to 0.21–0.33 mm/yr between the total observed and predicted contributions to 20th Century global sea level rise. However, the estimated individual contributions of the ice sheet imbalance and the oceanic steric effect remain significantly different from the current results from observations, and not much progress has been made since the last IPCC study on the effect of hydrologic imbalance and anthropogenic causes. Much future work remains to improve our understanding of the complex processes governing global sea level changes

Determination and Characterization of 20th Century Global Sea Level Rise

The Report describes the PhD dissertation research completed by Chung-Yen Kuo on November, 2005, supervised by C.K. Shum and other PhD Committee Members including Douglas Alsdorf, Michael Bevis, Laury Miller, and Yuchan Yi.This research is supported by grants from NOAA under NA16RG2252, NA86RG0053 (R/CE-5) and NA030AR4170060 (R/CE-8), and NASA's Ocean and Ice, Cryosphere, Physical Oceanography and Interdisciplinary Science Programs (NNG04GA53G, NAG5-9335, NAG5-12585, JPL- 1265252).Sea level rise has been widely recognized as a measurable signal and as one of the consequences of a possible anthropogenic (human-induced) effect on global climate change. The small rate of sea level rise, 1–2 mm/yr during the last century [Church et al., 2001, Chapter 11, Changes in Sea Level, in the Third Assessment Report (TAR) of the Intergovernmental Panel for Climate Change (IPCC), Working Group I, Houghton et al., 2001], could only be partially explained by a number of competing geophysical processes, each of which is a complex process within the Earth-atmosphere-ocean-cryosphere-hydrosphere system. In particular, the observed 20th Century sea level rise rate of 1.84±0.35 mm/yr [Douglas, 2001; Peltier, 2001] could not explain up to one half of the predicted 20th Century global sea level rise based on the IPCC TAR estimate of 1.1 mm/yr (0.6 mm/yr of melted water from ice sheets and glaciers, and 0.5 mm/yr from the steric effect in the ocean) [Church et al., 2001] and remains an enigma [Munk, 2002]. The quest to resolve the controversy [Meier and Wahr, 2002] and to further understand sea level change [Chao et al., 2002] is well underway including efforts being conducted during the current IPCC Fourth Assessment Report (FAR), 2003–2007. In this study, we provide a determination of the 20th Century (1900–2002) global sea level rise, the associated error budgets, and the quantifications or characterization of various geophysical sources of the observed sea level rise, using data and geophysical models. We analyzed significant geographical variations of global sea level change including those caused by the steric component (heat and salinity) in the ocean, and sea level redistribution resulting from ice sheets and glacier melting in consequence of self gravitation, and the effects of glacial isostatic adjustment (GIA) since the Pleistocene affecting sea level signals in the observations. In particular, relative sea level data from up to 651 global long-term (longest record is 150 years) tide gauges from Permanent Service for Mean Sea Level (PSMSL) and other sources, and geocentric sea level data from multiple satellite radar altimetry (1985–2005) have been used to determine and characterize the 20th Century global sea level rise. Altimeter and selected tide gauge data have been used for sea level determination, accounting for relative biases between different altimeters and offsets between the tide gauges, effects of thermosteric sea level variations, vertical motions affecting tide gauge sea level measurements, sea level redistribution due to ice melt resulting from self gravitation, and barotropic ocean response due to atmospheric forcing. This study is also characterized by the role of the polar ocean in the global sea level study and addressing the question whether there is a detectable acceleration of sea level rise during the last decade. Vertical motions have been estimated by combining geocentric sea level measurements from satellite altimetry (TOPEX/POSEIDON, T/P) and long-term relative (crustfixed) sea level records from global tide gauges using the Gauss-Markov model with stochastic constraints. The study provided a demonstration of improved vertical motion solutions in semienclosed seas and lakes, including Fennoscandia and the Great Lakes region, showing excellent agreement with independent GPS observed radial velocities, or with predictions from GIA models. In general, the estimated uncertainty of the observed vertical motion is <0.5 mm/yr, significantly better than other studies. Finally, improved algorithms to account for nonlinear vertical motions caused by other geodynamic processes than GIA including post-seismic deformations, have been developed and applied to tectonically active regions such as Alaska and compared well with GPS velocities and other studies. This novel technique could potentially provide improved vertical motion globally where long-term tide gauge records exist. The thermosteric sea level trend of the upper (0–500 m) layers of the ocean accounts for about 70% of the variations when deeper ocean (0–3000 m) is considered using the World Ocean Altas 2001 (WOA01). The estimated global thermosteric sea level trend of 0.33 mm/yr (0–500 m) and 0.43 mm/yr (0–3000 m) agrees well with other studies [Levitus et al., 2005; Ishii et al., 2005]. A detailed analysis using in situ temperature and salinity data from the Ocean Station Data (OSD), in the Eastern Pacific (where the in situ data are more abundant) is conducted to assess the contributions of respective roles of thermal and salinity effects on sea level changes. The analysis indicates that the estimated thermosteric sea level trends integrated from 0–500 m and from 0–1000 m depths using OSD are almost identical at ~0.64 mm/yr in the Eastern Pacific ocean. In this region, the halosteric (salinity) sea level trend is small, at the 0.04 mm/yr level for both the 0–500 m and 0–1000 m cases. The result is consistent with Miller and Douglas [2004], which analyzed data from selected oceanic regions including the Eastern Pacific, Eastern Atlantic, and Caribbean. In general, observed sea level (from tide gauges or altimetry) and thermosteric sea level are highly correlated except in regions of high mesoscale variability. A detailed comparison of the estimated thermosteric sea level trends with the observed sea level trend near proximities of global tide gauges (~50 years, 1950–2004, up to 597 sites) indicates that the thermosteric sea level trends account for 36% and 68% of the observed global sea level trend, for the 0–500 m and 0–3000 m cases, respectively, indicating the importance of deeper ocean thermal effects. Comparison of global thermosteric sea level trend with altimetry observed sea level trends indicates that the results are dependant on data spans used: thermosteric sea level trend (0–500 m) accounts for over 81% of total observed sea level using T/P altimetry during 1993–2003, while accounts for only 26% when data span extends to 1985–2005 using multiple altimetry. The primary reason is the presence of long-period oceanic variability (interannual, decadal or longer) in trend estimates causing inconsistent conclusions. Comparison of thermosteric sea level trend with sea level observed by selected tide gauges reaches different conclusions depending on the choice and number of tide gauges (1955–1996) used: thermosteric sea level trend (0–3000 m) accounts for over 88% of the observed sea level from 27 tide gauges, while it accounts for only 38% if 515 tide gauges are used. A study using temporal gravity field measurements observed by the Gravity Recovery and Climate Experiment (GRACE) in terms of oceanic mass variations at long-wavelength (>800 km) and monthly sampling demonstrates its potential use, when combined with satellite altimetry, to improve steric sea level trend estimates over the Southern Ocean, where the OSD is extremely sparse or non-existent. The global (covering within ±81°.5 latitude) sea level trend (corrected for IB) observed by multiple satellite altimetry (GEOSAT, ERS-1, T/P, ERS-2, GFO, JASON and ENVISAT, data covering 1985–2002 except for 1988–1991), and by ~530 tide gauges are 2.8±0.5 mm/yr (corrected for GIA geoid effect) and 2.7±0.4 mm/yr, respectively, indicating excellent agreement. The observed sea level trend using multiple satellite altimeters covering 1985–2004 is 2.9±0.5 mm/yr, although the data span is still too short to yield reliable trend estimates. The multiple altimeter data sets allow coverage in the polar oceans, as opposed to only using data from T/P (coverage within ±66°), and have a longer data span (~19 years versus 10 year for T/P). The data have been calibrated against each other and with tide gauge data for robust determination of their relative biases with respect to T/P. The 20th Century (1900–2002) global sea level trend determined from 651 tide gauge stations is 1.6±0.4 mm/yr, while the trend estimate for the last 50 years (1948–2002) is similar, but used 620 tide gauges. The atmospheric effect via the barotropic IB correction (globally averaged at ~0.11 mm/yr and over 50 years at global tide gauge locations) to sea level (tide gauges or altimetry) observations is warranted as it reduces variances of the data and causes improved agreements between altimetry and tide gauge sea level data. The multiple altimeter data allows sea level studies in the Arctic and Sub-Arctic Oceans, which have been less studied. The sea level trend in the Sub-Arctic Ocean, bounded by latitude 55°N–82°N and longitude 315°E–60°E, is estimated at 1.8 mm/yr using primarily ERS-1 and ERS-2 altimetry, which have been calibrated by TOPEX/POSEIDON in the lower latitude (±66° latitude) oceans and remove constant offsets and a latitude-dependent bias. The sea level trend can mostly be explained by atmospheric forcing and thermosteric effects. In the Arctic Ocean, sea level trend during 1948–2002 is estimated at 1.9–2.0 mm/yr using tide gauges after correction of land motion using different GIA models. After applying the inverted barometric (IB) correction, the sea level rate reduces to 1.5–1.6 mm/yr, indicating that the barotropic response of the ocean contributes significantly more to the sea level trend in the Arctic Ocean than for the global ocean. In an attempt to estimate the global sea level trend and to quantify some of the known contributions in the 20th Century using data from sparsely distributed long-term tide gauges and ~20 years of satellite altimetry, we assume that the spatial patterns of sea level trends from melt water sources (Antarctica, Greenland and mountain glaciers), the thermosteric effects, and geoid change and land uplift due to GIA are known, while their magnitudes are unknown. We ignored contributions from fresh water imbalances due to continental hydrological processes [Milly et al., 2003; Ngo-Duc et al., 2005], human-impoundment of water in reservoirs or lakes [Chao et al., 1994; Sahagian et al., 1994] and other effects, including permafrost melt [Zhang et al., 2005]. Using two different estimators, the Weighted Least Squares (WLS) and the Elementwise- Weighted Total Least Squares (EW-TLS), and using long-term tide gauges and satellite altimetry, we estimate the respective contributions of each of the sources to the global sea level rise. The EW-TLS technique is found to be more stable while the WLS technique produces solutions with larger error of ~0.3 mm/yr in a simulated study. The EW-TLS solution yields the estimated 20th Century (1900–2002) sea level trend contributions by melt water from the Antarctic and Greenland ice sheets and mountain glaciers to be 0.80±0.14 mm/yr, 0.56±0.12 mm/yr and 0.31±0.08 mm/yr, respectively; the estimated contribution from the thermosteric effect is 0.06±0.04 mm/yr, and the estimated scale of the GIA (ICE-4G) model to correct tide gauge sea level data is 1.27±0.08, indicating that the correction should be higher by 27%. The resulting 20th Century (1900–2002) globally averaged sea level trend is estimated to be 1.73±0.42 mm/yr (95% confidence or 2s) after summing the above forcing factors. The estimate of the resulting last 50 year (1948–2002) global sea level trend is 1.74±0.48 mm/yr (95% confidence or 2s). Finally, we address the issue of whether the sea level trend acceleration is detectable. An analysis indicates that the minimum data span to obtain a stable rate of sea level trend from 27 selected tide gauges [Douglas, 2001] is 20 years or more, while one should use a 30-year or longer data span to derive a stable thermosteric sea level trend from WOA01. It is concluded that, with 95% confidence, there is no statistically significant evidence of sea level acceleration during 1900–2000 from tide gauge data, and during 1950-2000 from thermosteric data. The estimated 20th Century global sea level rise is compared with the more recently estimated total geophysical effects contributing to global sea level rise of 1.41–1.53 mm/yr, which include the sum of the steric effect (~0.4 mm/yr) [e.g., Levitus et al., 2005; Antonov et al., 2005], mountain glacier melting (~0.51 mm/yr) [e.g., Arendt et al., 2002; Dyurgerov and Meier, 2005; Raper and Braithwaite, 2005; and others], ice sheet mass imbalance (~0.45 mm/yr) [e.g., Krabill et al., 2004, Rignot et al., 2005, Thomas et al., 2005], hydrological imbalance (~0.0–0.12 mm/yr) [Milly et al., 2003, Ngo-Duc et al., 2005], and anthropogenic effect (~0.05 mm/yr) [Dork Sahagian, pers. comm.]. This study (1.74±0.48 mm/yr) reduces the existing discrepancy [Chruch et al., 2001] to 0.21–0.33 mm/yr between the total observed and predicted contributions to 20th Century global sea level rise. However, the estimated individual contributions of the ice sheet imbalance and the oceanic steric effect remain significantly different from the current results from observations, and not much progress has been made since the last IPCC study on the effect of hydrologic imbalance and anthropogenic causes. Much future work remains to improve our understanding of the complex processes governing global sea level changes

Phosphorous Diffuser Diverged Blue Laser Diode for Indoor Lighting and Communication.

An advanced light-fidelity (Li-Fi) system based on the blue Gallium nitride (GaN) laser diode (LD) with a compact white-light phosphorous diffuser is demonstrated for fusing the indoor white-lighting and visible light communication (VLC). The phosphorous diffuser adhered blue GaN LD broadens luminescent spectrum and diverges beam spot to provide ample functionality including the completeness of Li-Fi feature and the quality of white-lighting. The phosphorous diffuser diverged white-light spot covers a radiant angle up to 120(o) with CIE coordinates of (0.34, 0.37). On the other hand, the degradation on throughput frequency response of the blue LD is mainly attributed to the self-feedback caused by the reflection from the phosphor-air interface. It represents the current state-of-the-art performance on carrying 5.2-Gbit/s orthogonal frequency-division multiplexed 16-quadrature-amplitude modulation (16-QAM OFDM) data with a bit error rate (BER) of 3.1 × 10(-3) over a 60-cm free-space link. This work aims to explore the plausibility of the phosphorous diffuser diverged blue GaN LD for future hybrid white-lighting and VLC systems

Present-Day Lake Level Variation from Envisat Altimetry over the Northeastern Qinghai-Tibetan Plateau: Links with Precipitation and Temperature

Lakes in permafrost regions are highly sensitive to changes in air temperature, snowmelt, and soil frost. In particular, the Qinghai-Tibetan Plateau (QTP) is one of the most sensitive regions in the world influenced by global climate change. In this study, we use retracked Enivsat radar altimeter measurements to generate water level change time series over Lake Qinghai and Lake Ngoring in the northeastern QTP and examine their relationships with precipitation and temperature changes. The response of water levels in Lake Qinghai and Lake Ngoring is positive with regards to precipitation amount. There is a negative relationship between water level and temperature change. These findings further the idea that the arid and high-elevation lakes in the northeastern QTP are highly sensitive to climate variations. Water level increases in Lake Qinghai in winter may indicate inputs of subsurface water associated with freeze-thaw cycles in the seasonally frozen ground and the active layer