Measurements In Polar Regions Research Articles

Retrieving bbp and POC from CALIOP: A deep neural network approach

The CALIOP instrument has demonstrated tremendous potential in terms of oceanic detection. Nighttime measurements from spaceborne lidar increase knowledge of the diurnal variability of ocean optical properties, while measurements in polar regions fill the gaps that passive measurements of ocean color may leave in these areas. However, due to non-ideal instrumental characteristics, errors may occur during retrieval of the ocean optical properties that are derived directly from CALIOP's measured signals. These errors are caused by the transient response (TR) function of the detectors and the polarization crosstalk (CT) between the polarization beam splitters. However, there is no study that integrates and explicitly describes both the required corrections. In addition, the published physics-based methods for retrieving the particulate backscatter coefficient (bbp) from CALIOP use an empirical linear relationship between bbp and the backscatter coefficient at 180° b(π) without considering the spatial and temporal variability associated with the conversion coefficient. In this study, after both effects are eliminated through TR deconvolution and CT correction, an innovative deep neural network (DNN) approach is proposed to retrieve bbp and particulate organic carbon (POC) from CALIOP. The DNN is trained with the CALIOP total ocean column-integrated depolarization ratio and subsurface column-integrated perpendicular backscatter data, which are combined with the collocated daytime MODIS bbp and POC products. Once the DNN has been trained with the daytime MODIS product, measurements can be derived from CALIOP in conditions not covered by MODIS data, such as at night or in polar regions. Compared to published physics-based methods, this approach does not require diffuse attenuation coefficients, nor are additional assumptions regarding the conversion coefficient between bbp and the backscatter coefficient at 180° b(π) necessary. A comparison of global total depolarization ratios, which are calculated before and after TR deconvolution and CT correction, indicates the necessity and efficacy of correction, and the preliminary results show that the oceanic properties derived from CALIOP via this DNN-based approach agree better with the MODIS products than those derived with the traditional physics-based methods. The use of lidar measurements to derive bbp and POC without relying on passively acquired data is of great interest to the ocean color community.

CPUE retrieval from spaceborne lidar data: A case study in the Atlantic bigeye tuna fishing area and Antarctica fishing area

The measurement of Catch Per Unit Effort (CPUE) supports the assessment of status and trends by managers. This proportion of total catch to the harvesting effort estimates the abundance of fishery resources. Marine environmental data obtained by satellite remote sensing are essential in fishing efficiency estimation or CPUE standardization. Currently, remote sensing chlorophyll data used for fisheries resource assessment are mainly from passive ocean color remote sensing. However, high-resolution data are not available at night or in high-latitude areas such as polar regions due to insufficient solar light, clouds, and other factors. In this paper, a CPUE inversion method based on spaceborne lidar data is proposed, which is still feasible for polar regions and at nighttime. First, Atlantic bigeye tuna CPUE was modeled using Cloud aerosol lidar and infrared pathfinder satellite observations (CALIPSO) lidar-retrieved chlorophyll data in combination with sea surface temperature data. The Generalized Linear Model (GLM), Artificial Neural Network (ANN) and Support Vector Machine Methods (SVM) were used for modeling, and the three methods were compared and validated. The results showed that the correlation between predicted CPUE and nominal CPUE was higher for the ANN method, with an R2of 0.34, while the R2was 0.08 and 0.22 for GLM and SVM, respectively. Then, chlorophyll data in the polar regions were derived using CALIPSO diurnal data, and an ANN was used for Antarctic krill. The inversion result performed well, and it showed that the R2of the predicted CPUE to nominal CPUE was 0.92. Preliminary results suggest that (1) nighttime measurements can increase the understanding of the diurnal variability of the upper ocean; (2) CALIPSO measurements in polar regions fill the gap of passive measurements; and (3) comparison with field data shows that ANN-based lidar products perform well, and a neural network approach based on CALIPSO lidar data can be used to simulate CPUE inversions in polar regions.

The representation of solar cycle signals in stratospheric ozone – Part 2: Analysis of global models

Abstract. The impact of changes in incoming solar irradiance on stratospheric ozone abundances should be included in climate simulations to aid in capturing the atmospheric response to solar cycle variability. This study presents the first systematic comparison of the representation of the 11-year solar cycle ozone response (SOR) in chemistry–climate models (CCMs) and in pre-calculated ozone databases specified in climate models that do not include chemistry, with a special focus on comparing the recommended protocols for the Coupled Model Intercomparison Project Phase 5 and Phase 6 (CMIP5 and CMIP6). We analyse the SOR in eight CCMs from the Chemistry–Climate Model Initiative (CCMI-1) and compare these with results from three ozone databases for climate models: the Bodeker Scientific ozone database, the SPARC/Atmospheric Chemistry and Climate (AC&C) ozone database for CMIP5 and the SPARC/CCMI ozone database for CMIP6. The peak amplitude of the annual mean SOR in the tropical upper stratosphere (1–5 hPa) decreases by more than a factor of 2, from around 5 to 2 %, between the CMIP5 and CMIP6 ozone databases. This substantial decrease can be traced to the CMIP5 ozone database being constructed from a regression model fit to satellite and ozonesonde measurements, while the CMIP6 database is constructed from CCM simulations. The SOR in the CMIP6 ozone database therefore implicitly resembles the SOR in the CCMI-1 models. The structure in latitude of the SOR in the CMIP6 ozone database and CCMI-1 models is considerably smoother than in the CMIP5 database, which shows unrealistic sharp gradients in the SOR across the middle latitudes owing to the paucity of long-term ozone measurements in polar regions. The SORs in the CMIP6 ozone database and the CCMI-1 models show a seasonal dependence with enhanced meridional gradients at mid- to high latitudes in the winter hemisphere. The CMIP5 ozone database does not account for seasonal variations in the SOR, which is unrealistic. Sensitivity experiments with a global atmospheric model without chemistry (ECHAM6.3) are performed to assess the atmospheric impacts of changes in the representation of the SOR and solar spectral irradiance (SSI) forcing between CMIP5 and CMIP6. The larger amplitude of the SOR in the CMIP5 ozone database compared to CMIP6 causes a likely overestimation of the modelled tropical stratospheric temperature response between 11-year solar cycle minimum and maximum by up to 0.55 K, or around 80 % of the total amplitude. This effect is substantially larger than the change in temperature response due to differences in SSI forcing between CMIP5 and CMIP6. The results emphasize the importance of adequately representing the SOR in global models to capture the impact of the 11-year solar cycle on the atmosphere. Since a number of limitations in the representation of the SOR in the CMIP5 ozone database have been identified, we recommend that CMIP6 models without chemistry use the CMIP6 ozone database and the CMIP6 SSI dataset to better capture the climate impacts of solar variability. The SOR coefficients from the CMIP6 ozone database are published with this paper.

Application of superconducting integrated receiver in the TELIS instrument for the spectroscopic study of atmosphere

A superconducting integrated receiver (SIR) (superheterodyne receiver) is developed for detection of radiation in a frequency range of 450–650 GHz. The SIR is used as a detector in the Terahertz Limb Sounder (TELIS) instrument that is mounted on a high-altitude balloon for the study of the atmospheric composition in the terahertz frequency range using limb sounding. The TELIS instrument and its detectors are described, and several results of the measurements in Polar Regions in 2009–2014 are presented

Sensitivity studies for a space-based methane lidar mission

Abstract. Methane is the third most important greenhouse gas in the atmosphere after water vapour and carbon dioxide. A major handicap to quantify the emissions at the Earth's surface in order to better understand biosphere-atmosphere exchange processes and potential climate feedbacks is the lack of accurate and global observations of methane. Space-based integrated path differential absorption (IPDA) lidar has potential to fill this gap, and a Methane Remote Lidar Mission (MERLIN) on a small satellite in polar orbit was proposed by DLR and CNES in the frame of a German-French climate monitoring initiative. System simulations are used to identify key performance parameters and to find an advantageous instrument configuration, given the environmental, technological, and budget constraints. The sensitivity studies use representative averages of the atmospheric and surface state to estimate the measurement precision, i.e. the random uncertainty due to instrument noise. Key performance parameters for MERLIN are average laser power, telescope size, orbit height, surface reflectance, and detector noise. A modest-size lidar instrument with 0.45 W average laser power and 0.55 m telescope diameter on a 506 km orbit could provide 50-km averaged methane column measurement along the sub-satellite track with a precision of about 1% over vegetation. The use of a methane absorption trough at 1.65 μm improves the near-surface measurement sensitivity and vastly relaxes the wavelength stability requirement that was identified as one of the major technological risks in the pre-phase A studies for A-SCOPE, a space-based IPDA lidar for carbon dioxide at the European Space Agency. Minimal humidity and temperature sensitivity at this wavelength position will enable accurate measurements in tropical wetlands, key regions with largely uncertain methane emissions. In contrast to actual passive remote sensors, measurements in Polar Regions will be possible and biases due to aerosol layers and thin ice clouds will be minimised.

What controls photochemical NO and NO2 production from Antarctic snow? Laboratory investigation assessing the wavelength and temperature dependence

Laboratory experiments were conducted to determine the wavelength and temperature dependence of NO and NO2 release from Antarctic snow. This photochemically driven process has been observed during recent field measurements in polar regions. In this work the photochemical production of NO and NO2 was reproduced under laboratory conditions with NO2 dominating the production. The wavelength of incident light was varied over the range 295–385 nm. We observed a λ dependence where NO and NO2 release ceases when the snow was illuminated with λ > 345 nm. Comparing these data with the aqueous absorption cross section of the nitrate ion (NO3−) indicates that NO3− is the precursor N‐oxide species, which is photolyzed in snow. The temperature of the experimental system was varied over the range 253–243 K with no effect on NO and NO2 production. The occurrence of these photochemical processes followed by release to the atmosphere will impact the chemistry of the boundary layer over any snow‐covered region. In addition, understanding these processes is essential for accurate ice core interpretation.

Physical nature of a new cross‐field current‐driven instability in the lower ionosphere

The physical nature of a new instability predicted earlier in the framework of a kinetic theory [Dimant and Sudan, 1995a, b, c] is clarified by using a simple fluid model. It is associated with ohmic heating of electrons by the modulated electric field. Temperature modulations lead to the instability via two independent mechanisms. One mechanism consists in the reversal of the sign of pressure perturbations, and the other is associated with perturbations of the electron Pedersen conductivity due to the temperature dependence of the electron‐neutral collision frequency. The instability gives rise to the excitation of sufficiently long waves (several meters and longer) in the upper D/lower E regions. The unstable zone covers two broad ranges of flow angles around the bisectors between the directions of the ambient electric field ±E0 and the E0 × B drift. The data available from rocket measurements in polar regions indicate possible evidence for the new instability.