scholarly journals CARIBIC DOAS observations of nitrous acid and formaldehyde in a large convective cloud

2013 ◽  
Vol 13 (9) ◽  
pp. 24343-24403
Author(s):  
K.-P. Heue ◽  
H. Riede ◽  
D. Walter ◽  
C. A. M. Brenninkmeijer ◽  
T. Wagner ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Detection Limit ◽  
Nitrous Acid ◽  
World Wide ◽  
Marine Boundary Layer ◽  
Convective Cloud ◽  
Observation System ◽  
Oh Radicals ◽  
Actual System ◽  
The World

Abstract. The CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) flying laboratory measures once per month the chemical composition at cruise altitude (10...12 km) during 4 consecutive Lufthansa flights. Here we present a case study of enhanced nitrogen oxides (NOx), nitrous acid (HONO), and formaldehyde (HCHO) in a thunderstorm cloud over the Caribbean islands of Guadeloupe in August 2011. Nitrous acid is an important reservoir gas for OH radicals, and only few observations of HONO at cruise altitude exist. CARIBIC is designed as a long period atmospheric observation system, the actual system has been flying almost monthly since 8 yr now. During this period only very few similar events (one since 2008) were observed. Due to multiple scattering the light path inside clouds is enhanced, thereby lowering the detection limit of the DOAS instrument. Under background conditions the detection limits are 46 ppt for HONO, 387 ppt for \\chem{HCHO}, and 100 ppt for NO2 and are roughly three times lower inside the cloud. Based on radiative transfer simulations we estimate the path length to 90{\\ldots}100 km and the cloud top height to ≈15 km. The inferred mixing ratios of HONO, HCHO and NO2 are 37 ppt, 400 ppt and 170 ppt, respectively. Bromine monoxide (BrO) remained below the detection limit of 1 ppt. Because the uplifted air masses originated from the remote marine boundary layer and lightning was observed in the area by the World Wide Lightning Location Network several hours prior to the measurement, the NO (≈1.5 ppb) enhancement was in all likelihood caused by lightning. The main source for the observed HCHO is probably updraught from the boundary layer, because the chemical formation of formaldehyde due to methane oxidation is too weak. Besides HCHO also CH3OOH and isoprene are considered as precursors. The chemical box model CAABA is used to estimate the \\chem{NO} and HCHO source strengths, which are necessary to explain our measurements. For NO a source strength of 8.25 × 109 molec cm−2 s−1 km−1 is found, which corresponds to the lightning activity as observed by the World Wide Lightning Location network and a lightning emission of 4.2 × 1025 NO molec/flash. The HCHO updraught is of the order of 121 × 109 molec cm−2 s−1 km−1. Also isoprene and CH3OOH as possible HCHO sources were studied and similar source strengths were found.

scholarly journals Is the ocean surface a source of nitrous acid (HONO) in the marine boundary layer?

2021 ◽  
Author(s):  
Leigh Crilley ◽  
Louisa Kramer ◽  
Francis Pope ◽  
Chris Reed ◽  
James Lee ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Nitrous Acid ◽  
Marine Boundary Layer ◽  
Ocean Surface ◽  
Cape Verde ◽  
Formation Mechanisms ◽  
Oh Radicals ◽  
Surface Source ◽  
Global Impacts ◽  
Quantitative Understanding

Abstract. Nitrous acid, HONO, is a key net photolytic precursor to OH radicals in the atmospheric boundary later. As OH is the dominant atmospheric oxidant, driving the removal of many primary pollutants and the formation of secondary species, a quantitative understanding of HONO sources is important to predict atmospheric oxidising capacity. While a number of HONO formation mechanisms have been identified, recent work has ascribed significant importance to the dark, ocean-surface mediated conversion of NO2 to HONO in the coastal marine boundary layer. In order to evaluate the role of this mechanism, here we analyse measurements of HONO and related species obtained at two contrasting coastal locations – Cape Verde (Atlantic Ocean), representative of the clean remote tropical marine boundary layer, and Weybourne (United Kingdom), representative of semi-polluted Northern European coastal waters. As expected, higher average concentrations of HONO (70 ppt) were observed in marine air for the more anthropogenically influenced Weybourne location compared to Cape Verde (HONO < 5 ppt). At both sites, the approximately constant HONO/NO2 ratio at night pointed to a low importance for the dark ocean-surface mediated conversion of NO2 into HONO, whereas the midday maximum in the HONO/NO2 ratios indicated significant contributions from photo-enhanced HONO formation mechanisms (or other sources). We obtained an upper limit to the rate coefficient of dark ocean-surface HONO-to-NO2 conversion of CHONO = 0.0011 ppb hr−1 from the Cape Verde observations; this is a factor of 5 lower than the slowest rate reported previously. These results point to significant geographical variation in the predominant HONO formation mechanisms in marine environments and indicate that caution is required when extrapolating the importance of such mechanisms from individual study locations to assess regional and/or global impacts on oxidising capacity. As a significant fraction of atmospheric processing occurs in the marine boundary layer, particularly in the tropics, better constraint of the possible ocean surface source of HONO is important for a quantitative understanding of chemical processing of primary trace gases in the global atmospheric boundary layer and associated impacts upon air pollution and climate.

scholarly journals CARIBIC DOAS observations of nitrous acid and formaldehyde in a large convective cloud

2014 ◽  
Vol 14 (13) ◽  
pp. 6621-6642 ◽  
Author(s):  
K.-P. Heue ◽  
H. Riede ◽  
D. Walter ◽  
C. A. M. Brenninkmeijer ◽  
T. Wagner ◽  
...  
Keyword(s):  
Nitrous Acid ◽  
World Wide ◽  
Convective Cloud ◽  
Global Scale ◽  
Box Model ◽  
Convective System ◽  
Mixing Ratios ◽  
The World ◽  
Tropopause Region

Abstract. The chemistry in large thunderstorm clouds is influenced by local lightning-NOx production and uplift of boundary layer air. Under these circumstances trace gases like nitrous acid (HONO) or formaldehyde (HCHO) are expected to be formed or to reach the tropopause region. However, up to now only few observations of HONO at this altitude have been reported. Here we report on a case study where enhancements in HONO, HCHO and nitrogen oxides (NOx) were observed by the CARIBIC flying laboratory (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container). The event took place in a convective system over the Caribbean Sea in August 2011. Inside the cloud the light path reaches up to 100 km. Therefore the DOAS instrument on CARIBIC was very sensitive to the tracers inside the cloud. Based on the enhanced slant column densities of HONO, HCHO and NO2, average mixing ratios of 37, 468 and 210 ppt, respectively, were calculated. These data represent averages for constant mixing ratios inside the cloud. However, a large dependency on the assumed profile is found; for HONO a mixing ratio of 160 ppt is retrieved if the total amount is assumed to be situated in the uppermost 2 km of the cloud. The NO in situ instrument measured peaks up to 5 ppb NO inside the cloud; the background in the cloud was about 1.3 ppb, and hence clearly above the average outside the cloud (≈ 150 ppt). The high variability and the fact that the enhancements were observed over a pristine marine area led to the conclusion that, in all likelihood, the high NO concentrations were caused by lighting. This assumption is supported by the number of flashes that the World Wide Lightning Location Network (WWLLN) counted in this area before and during the overpass. The chemical box model CAABA is used to estimate the NO and HCHO source strengths which are necessary to explain our measurements. For NO a source strength of 10 × 109 molec cm−2 s−1 km−1 is found, which corresponds to the lightning activity as observed by the World Wide Lightning Location network, and lightning emissions of 5 × 1025 NO molec flash−1 (2.3–6.4 × 1025). The uncertainties are determined by a change of the input parameters in the box model, the cloud top height and the flash density. The emission rate per flash is scaled up to a global scale and 1.9 (1.4–2.5) tg N a−1 is estimated. The HCHO updraught is of the order of 120 × 109 molec cm−2 s−1 km−1. Also isoprene and CH3OOH as possible HCHO sources are discussed.

scholarly journals Is the ocean surface a source of nitrous acid (HONO) in the marine boundary layer?

2021 ◽  
Vol 21 (24) ◽  
pp. 18213-18225
Author(s):  
Leigh R. Crilley ◽  
Louisa J. Kramer ◽  
Francis D. Pope ◽  
Chris Reed ◽  
James D. Lee ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Nitrous Acid ◽  
Marine Boundary Layer ◽  
Ocean Surface ◽  
Cape Verde ◽  
Formation Mechanisms ◽  
Oh Radicals ◽  
Surface Source ◽  
Quantitative Understanding

Abstract. Nitrous acid, HONO, is a key net photolytic precursor to OH radicals in the atmospheric boundary layer. As OH is the dominant atmospheric oxidant, driving the removal of many primary pollutants and the formation of secondary species, a quantitative understanding of HONO sources is important to predict atmospheric oxidising capacity. While a number of HONO formation mechanisms have been identified, recent work has ascribed significant importance to the dark, ocean-surface-mediated conversion of NO2 to HONO in the coastal marine boundary layer. In order to evaluate the role of this mechanism, here we analyse measurements of HONO and related species obtained at two contrasting coastal locations – Cabo Verde (Atlantic Ocean, denoted Cape Verde herein), representative of the clean remote tropical marine boundary layer, and Weybourne (United Kingdom), representative of semi-polluted northern European coastal waters. As expected, higher average concentrations of HONO (70 ppt) were observed in marine air for the more anthropogenically influenced Weybourne location compared to Cape Verde (HONO < 5 ppt). At both sites, the approximately constant HONO/NO2 ratio at night pointed to a low importance for the dark, ocean-surface-mediated conversion of NO2 into HONO, whereas the midday maximum in the HONO/NO2 ratios indicated significant contributions from photo-enhanced HONO formation mechanisms (or other sources). We obtained an upper limit to the rate coefficient of dark, ocean-surface HONO-to-NO2 conversion of CHONO = 0.0011 ppb h−1 from the Cape Verde observations; this is a factor of 5 lower than the slowest rate reported previously. These results point to significant geographical variation in the predominant HONO formation mechanisms in marine environments and indicate that caution is required when extrapolating the importance of such mechanisms from individual study locations to assess regional and/or global impacts on oxidising capacity. As a significant fraction of atmospheric processing occurs in the marine boundary layer, particularly in the tropics, better constraint of the possible ocean surface source of HONO is important for a quantitative understanding of chemical processing of primary trace gases in the global atmospheric boundary layer and associated impacts upon air pollution and climate.

scholarly journals Concentrations of OH and HO<sub>2</sub> radicals during NAMBLEX: measurements and steady state analysis

2005 ◽  
Vol 5 (6) ◽  
pp. 12403-12464 ◽  
Author(s):  
S. C. Smith ◽  
J. D. Lee ◽  
W. J. Bloss ◽  
G. P. Johnson ◽  
D. E. Heard
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Detection Limit ◽  
Diurnal Variation ◽  
Marine Boundary Layer ◽  
Chemical Conversion ◽  
Early Morning ◽  
Research Station ◽  
Solar Noon ◽  
Mean Concentration

Abstract. OH and HO2 concentrations were measured simultaneously at the Mace Head Atmospheric Research Station in the summer of 2002 during the NAMBLEX (North Atlantic Marine Boundary Layer EXperiment) field campaign. OH was measured by laser-induced fluorescence employing the FAGE (Fluorescence Assay by Gas Expansion) technique, with a mean daytime detection limit of 2.7×105 molecule cm−3 (5 min acquisition period; signal-to-noise ratio = 1). HO2 was detected as OH following its chemical conversion through addition of NO, with a mean detection limit of 4.4×106 molecule cm−3. The diurnal variation of OH was measured on 24 days, and that of HO2 on 17 days. The local solar noon OH concentrations ranged between (3–8)×106 molecule cm−3, with a 24 h mean concentration of 9.1×105 molecule cm−3. The local solar noon HO2 concentrations were (0.9–2.1)×108 molecule cm−3 (3.5–8.2 pptv), with a 24 h mean concentration of 4.2×107 molecule cm−3. HO2 radicals in the range (2–3)×107 molecule cm−3 were observed at night. During NAMBLEX, a comprehensive suite of supporting measurements enabled a detailed study of the behaviour of HOx radicals under primarily clean marine conditions. Case study periods highlight the typical radical levels observed under different conditions. Steady state expressions are used to calculate OH and HO2 concentrations and to evaluate the effect of different free-radical sources and sinks. The diurnally averaged calculated to measured OH ratio was 1.04±0.36, but the ratio displays a distinct diurnal variation, being less than 1 during the early morning and late afternoon/evening, and greater than 1 in the middle of the day. For HO2 there was an overprediction, with the agreement between calculated and measured concentrations improved by including reaction with measured IO and BrO radicals and uptake to aerosols. Increasing the concentration of IO radicals included in the calculations to above that measured by a DOAS instrument with an absorption path located mainly over the ocean, reflecting the domination of the inter-tidal region as an iodine source at Mace Head, led to further improvement. The results are compared with previous measurements at Mace Head, and elsewhere in the remote marine boundary layer.

scholarly journals Nitrous acid in marine boundary layer over eastern Bohai Sea, China: Characteristics, sources, and implications

2019 ◽  
Vol 670 ◽  
pp. 282-291 ◽  
Author(s):  
Liang Wen ◽  
Tianshu Chen ◽  
Penggang Zheng ◽  
Lin Wu ◽  
Xinfeng Wang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Nitrous Acid ◽  
Bohai Sea ◽  
Marine Boundary Layer

scholarly journals A box model study on photochemical interactions between VOCs and reactive halogen species in the marine boundary layer

2004 ◽  
Vol 4 (7) ◽  
pp. 1961-1987 ◽  
Author(s):  
K. Toyota ◽  
Y. Kanaya ◽  
M. Takahashi ◽  
H. Akimoto
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Box Model ◽  
Chemical Mechanism ◽  
Oh Radicals ◽  
Halogen Chemistry ◽  
Reactive Halogen Species ◽  
Oceanic Emissions ◽  
Chemical Scheme ◽  
Halogen Species

Abstract. A new chemical scheme is developed for the multiphase photochemical box model SEAMAC (size-SEgregated Aerosol model for Marine Air Chemistry) to investigate photochemical interactions between volatile organic compounds (VOCs) and reactive halogen species in the marine boundary layer (MBL). Based primarily on critically evaluated kinetic and photochemical rate parameters as well as a protocol for chemical mechanism development, the new scheme has achieved a near-explicit description of oxidative degradation of up to C3-hydrocarbons (CH4, C2H6, C3H8, C2H4, C3H6, and C2H2) initiated by reactions with OH radicals, Cl- and Br-atoms, and O3. Rate constants and product yields for reactions involving halogen species are taken from the literature where available, but the majority of them need to be estimated. In particular, addition reactions of halogen atoms with alkenes will result in forming halogenated organic intermediates, whose photochemical loss rates are carefully evaluated in the present work. Model calculations with the new chemical scheme reveal that the oceanic emissions of acetaldehyde (CH3CHO) and alkenes (especially C3H6) are important factors for regulating reactive halogen chemistry in the MBL by promoting the conversion of Br atoms into HBr or more stable brominated intermediates in the organic form. The latter include brominated hydroperoxides, bromoacetaldehyde, and bromoacetone, which sequester bromine from a reactive inorganic pool. The total mixing ratio of brominated organic species thus produced is likely to reach 10-20% or more of that of inorganic gaseous bromine species over wide regions over the ocean. The reaction between Br atoms and C2H2 is shown to be unimportant for determining the degree of bromine activation in the remote MBL. These results imply that reactive halogen chemistry can mediate a link between the oceanic emissions of VOCs and the behaviors of compounds that are sensitive to halogen chemistry such as dimethyl sulfide, NOx, and O3 in the MBL.

scholarly journals A 2-year record of atmospheric mercury species at a background Southern Hemisphere station on Amsterdam Island

2014 ◽  
Vol 14 (20) ◽  
pp. 11461-11473 ◽  
Author(s):  
H. Angot ◽  
M. Barret ◽  
O. Magand ◽  
M. Ramonet ◽  
A. Dommergue
Keyword(s):  
Detection Limit ◽  
Indian Ocean ◽  
Southern Hemisphere ◽  
Marine Boundary Layer ◽  
Atmospheric Mercury ◽  
Southern Indian Ocean ◽  
Observation System ◽  
Mercury Species ◽  
Data Set ◽  
Back Trajectories

Abstract. Although essential to fully understand the cycling of mercury at the global scale, mercury species records in the Southern Hemisphere are scarce. Under the framework of the Global Mercury Observation System (GMOS) project, a monitoring station has been set up on Amsterdam Island (37°48´ S, 77°34´ E) in the remote southern Indian Ocean. For the first time in the Southern Hemisphere, a 2-year record of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particle-bound mercury (PBM) is presented. GEM concentrations were remarkably steady (1.03 ± 0.08 ng m−3) while RGM and PBM concentrations were very low and exhibited a strong variability (mean: 0.34 pg m−3, range: < detection limit–4.07 pg m−3; and mean: 0.67 pg m−3, range: < detection limit–12.67 pg m−3, respectively). Despite the remoteness of the island, wind sector analysis, air mass back trajectories and the observation of radonic storms highlighted a long-range contribution from the southern African continent to the GEM and PBM budgets from July to September during the biomass burning season. Low concentrations of GEM were associated with southerly polar and marine air masses from the remote southern Indian Ocean. This unique data set provides new baseline GEM concentrations in the Southern Hemisphere midlatitudes while mercury speciation along with upcoming wet deposition data will help to improve our understanding of the mercury cycle in the marine boundary layer.

scholarly journals Concentrations of OH and HO<sub>2</sub> radicals during NAMBLEX: measurements and steady state analysis

2006 ◽  
Vol 6 (5) ◽  
pp. 1435-1453 ◽  
Author(s):  
S. C. Smith ◽  
J. D. Lee ◽  
W. J. Bloss ◽  
G. P. Johnson ◽  
T. Ingham ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Detection Limit ◽  
Diurnal Variation ◽  
Marine Boundary Layer ◽  
Chemical Conversion ◽  
Early Morning ◽  
Research Station ◽  
Solar Noon ◽  
Mean Concentration

Abstract. OH and HO2 concentrations were measured simultaneously at the Mace Head Atmospheric Research Station in the summer of 2002 during the NAMBLEX (North Atlantic Marine Boundary Layer EXperiment) field campaign. OH was measured by laser-induced fluorescence employing the FAGE (Fluorescence Assay by Gas Expansion) technique, with a mean daytime detection limit of 2.7×105 molecule cm−3 (5 min acquisition period; signal-to-noise ratio = 1). HO2 was detected as OH following its chemical conversion through addition of NO, with a mean detection limit of 4.4×106 molecule cm−3. The diurnal variation of OH was measured on 24 days, and that of HO2 on 17 days. The local solar noon OH concentrations ranged between (3–8)×106 molecule cm−3, with a 24 h mean concentration of 9.1×105 molecule cm−3. The local solar noon HO2 concentrations were (0.9–2.1)×108 molecule cm−3 (3.5–8.2 pptv), with a 24 h mean concentration of 4.2×107 molecule cm−3 (1.6 pptv). HO2 radicals in the range (2–3)×107 molecule cm−3 were observed at night. During NAMBLEX, a comprehensive suite of supporting measurements enabled a detailed study of the behaviour of HOx radicals under primarily clean marine conditions. Steady state expressions are used to calculate OH and HO2 concentrations and to evaluate the effect of different free-radical sources and sinks. The diurnally averaged calculated to measured OH ratio was 1.04±0.36, but the ratio displays a distinct diurnal variation, being less than 1 during the early morning and late afternoon/evening, and greater than 1 in the middle of the day. For HO2 there was an overprediction, with the agreement between calculated and measured concentrations improved by including reaction with measured IO and BrO radicals and uptake to aerosols. Increasing the concentration of IO radicals included in the calculations to above that measured by a DOAS instrument with an absorption path located mainly over the ocean, reflecting the domination of the inter-tidal region as an iodine source at Mace Head, led to further improvement. The results are compared with previous measurements at Mace Head, and elsewhere in the remote marine boundary layer.

scholarly journals A box model study on photochemical interactions between VOCs and reactive halogen species in the marine boundary layer

2003 ◽  
Vol 3 (5) ◽  
pp. 4549-4632 ◽  
Author(s):  
K. Toyota ◽  
Y. Kanaya ◽  
M. Takahashi ◽  
H. Akimoto
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Box Model ◽  
Chemical Mechanism ◽  
Oh Radicals ◽  
Halogen Chemistry ◽  
Reactive Halogen Species ◽  
Oceanic Emissions ◽  
Chemical Scheme ◽  
Halogen Species

Abstract. A new chemical scheme is developed for the multiphase photochemical box model SEAMAC (size-SEgregated Aerosol model for Marine Air Chemistry) to investigate photochemical interactions between volatile organic compounds (VOCs) and reactive halogen species in the marine boundary layer (MBL). Based primarily on critically evaluated kinetic and photochemical rate parameters as well as a protocol for chemical mechanism development, the new scheme has achieved a near-explicit treatment of oxidative degradation of up to C3-hydrocarbons CH4, C2H6, C3H8, C2H4, C3H6, and C2H2) initiated by reactions with OH radicals, Cl- and Br-atoms, and O3. Rate constants and product yields for reactions involving halogen species are taken from the literature where available, but the majority of them need to be estimated. In particular, addition reactions of halogen atoms with alkenes will result in the formation of halogenated organic intermediates, whose photochemical loss rates are carefully evaluated in the present work. Model calculations with the new chemical scheme reveal that the oceanic emissions of acetaldehyde (CH3CHO) and alkenes (especially C3H6) are important factors for regulating reactive halogen chemistry in the MBL by promoting the conversion of Br atoms into HBr or more stable brominated intermediates in the organic form. The latter include brominated hydroperoxides, bromoacetaldehyde, and bromoacetone, which sequester bromine from reactive inorganic pool. The total mixing ratio of brominated organic species thus produced is likely to reach 10-20% or more of that of inorganic gaseous bromine species over wide regions over the ocean. On the other hand, the reaction between Br atoms and C2H2 is unimportant for determining the degree of bromine activation in the remote MBL. It is suggested that peroxyacetic acid formed via CH3CHO oxidation is one of the important chemical agents for triggering autocatalytic halogen release from sea-salt aerosols. These results imply that reactive halogen chemistry can mediate a link between the oceanic emissions of VOCs and the behaviors of compounds that are sensitive to halogen chemistry such as dimethyl sulfide, NOx, and O3 in the MBL.

scholarly journals Marine Boundary Layer Height Obtained by New Numerical Regularization Method Based on GPS Radio Occultation Data

Sensors ◽  
2020 ◽  
Vol 20 (17) ◽  
pp. 4762
Author(s):  
Jianyin Zhou ◽  
Jie Xiang ◽  
Sixun Huang
Keyword(s):  
Boundary Layer ◽  
Standard Deviation ◽  
Marine Boundary Layer ◽  
Convective Cloud ◽  
Ocean Currents ◽  
Free Atmosphere ◽  
Layer Height ◽  
Boundary Layer Height ◽  
Occultation Data ◽  
Numerical Regularization

The boundary layer height (BLH) determines the interface between the lower and the free atmosphere, and it is a key variable in numerical simulations and aerosol and environmental pollution studies. This article proposes a novel method in conjunction with numerical regularization to analyze the climate characteristics of the marine boundary layer height (MBLH) using 2007–2011 GPS-RO data from the COSMIC mission. The MBLH corresponds to the smallest gradient, which is calculated using the numerical regulation method where the regulation parameters are determined by the double-parameter model function method. The results reveal the relationship between the MBLH and ocean currents for the first time. A low MBLH is associated with cold seasons and seas where cold ocean currents prevail whereas a high MBLH is related to warm seasons and seas where warm currents prevail. This correlation was validated by comparing the obtained results with different occultation data including atmprf and echprf, which also showed that atmprf is more sensitive to convective cloud top capture. To test the credibility of the results, the standard deviation was used to express the MBLH confidence level. The results show that the standard deviation of the MBLH was highest in low latitudes and lowest in the middle and high latitudes. Furthermore, we analyzed the trends in interannual MBLH variations, which display significant seasonal variations and spatial distributions that correspond with the current and subsolar point. Finally, we conducted a case study in the South China Sea, and identified a distinctive seasonal change and interannual decline in MBLH.

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