A New Normal for the Sea Ice Index

The NSIDC Sea Ice Index is a popular data product that shows users how ice extent and concentration have changed since the beginning of the passive microwave satellite record in 1978. It shows time series of monthly ice extent anomalies rather than actual extent values, in order to emphasize the information the data are carrying. Along with the time series, an image of average extent for the previous month is shown as a white field, with a pink line showing the median extent for that month. These are updated monthly; corresponding daily products are updated daily

Anomalous Variability in Antarctic Sea Ice Extents During the 1960s With the Use of Nimbus Data

The Nimbus I, II, and III satellites provide a new opportunity for climate studies in the 1960s. The rescue of the visible and infrared imager data resulted in the utilization of the early Nimbus data to determine sea ice extent. A qualitative analysis of the early NASA Nimbus missions has revealed Antarctic sea ice extents that are signicant larger and smaller than the historic 1979-2012 passive microwave record. The September 1964 ice mean area is 19.7x10 km +/- 0.3x10 km. This is more the 250,000 km greater than the 19.44x10 km seen in the new 2012 historic maximum. However, in August 1966 the maximum sea ice extent fell to 15.9x10 km +/- 0.3x10 km. This is more than 1.5x10 km below the passive microwave record of 17.5x10 km set in September of 1986. This variation between 1964 and 1966 represents a change of maximum sea ice of over 3x10 km in just two years. These inter-annual variations while large, are small when compared to the Antarctic seasonal cycle

Anomalous Variability in Antarctic Sea Ice Extents During the 1960s With the Use of Nimbus Data

The Nimbus I, II, and III satellites provide a new opportunity for climate studies in the 1960s. The rescue of the visible and infrared imager data resulted in the utilization of the early Nimbus data to determine sea ice extent. A qualitative analysis of the early NASA Nimbus missions has revealed Antarctic sea ice extents that are significant larger and smaller than the historic 1979-2012 passive microwave record. The September 1964 ice mean area is 19.7x10(exp 6) sq. km +/- 0.3x10(exp 6) sq. km. This is more the 250,000 sq. km greater than the 19.44x10(exp 6) sq. km seen in the new 2012 historic maximum. However, in August 1966 the maximum sea ice extent fell to 15.9x10(exp 6) sq. km +/- 0.3x10(exp 6) sq. km. This is more than 1.5x10(exp 6) sq. km below the passive microwave record of 17.5x10(exp 6) sq. km set in September of 1986. This variation between 1964 and 1966 represents a change of maximum sea ice of over 3x10(exp 6) sq. km in just two years. These inter-annual variations while large, are small when compared to the Antarctic seasonal cycle

Verification of a New NOAA/NSIDC Passive Microwave Sea-Ice Concentration Climate Record

A new satellite-based passive microwave sea-ice concentration product developed for the National Oceanic and Atmospheric Administration (NOAA)Climate Data Record (CDR) programme is evaluated via comparison with other passive microwave-derived estimates. The new product leverages two well-established concentration algorithms, known as the NASA Team and Bootstrap, both developed at and produced by the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC). The sea ice estimates compare well with similar GSFC products while also fulfilling all NOAA CDR initial operation capability (IOC) requirements, including (1) self describing file format, (2) ISO 19115-2 compliant collection-level metadata,(3) Climate and Forecast (CF) compliant file-level metadata, (4) grid-cell level metadata (data quality fields), (5) fully automated and reproducible processing and (6) open online access to full documentation with version control, including source code and an algorithm theoretical basic document. The primary limitations of the GSFC products are lack of metadata and use of untracked manual corrections to the output fields. Smaller differences occur from minor variations in processing methods by the National Snow and Ice Data Center (for the CDR fields) and NASA (for the GSFC fields). The CDR concentrations do have some differences from the constituent GSFC concentrations, but trends and variability are not substantially different

Assessing the Potential of Enhanced Resolution Gridded Passive Microwave Brightness Temperatures for Retrieval of Sea Ice Parameters

A new enhanced resolution gridded passive microwave brightness temperature (TB) product is used to estimate sea ice concentration and motion. The effective resolution of the TBs is found to be roughly twice that of the standard 25 km resolution, though the gridded resolution of the distributed product is higher. Enhanced resolution sea ice concentrations from the Bootstrap algorithm show more detail in the sea ice, including relatively small open water regions within the ice pack. Sea ice motion estimates from the enhanced resolution TBs using a maximum cross-correlation method show a smoother motion circulation pattern; in comparison to buoys, RMS errors are 15&ndash;20% lower than motion estimates from the standard resolution fields and the magnitude of the bias is smaller as well. The enhanced resolution product includes other potentially beneficial characteristics, including twice-daily grids based on local time of day and a complete timeseries of data from nearly all multi-channel passive microwave radiometers since 1978. These enhanced resolution TBs are potential new source for long-term records of sea ice concentration, motion, age, melt, as well as salinity and ocean-atmosphere fluxes.&nbsp;</div

Assessment of the Stability of Passive Microwave Brightness Temperatures for NASA Team Sea Ice Concentration Retrievals

Gridded passive microwave brightness temperatures (TB) from special sensor microwave imager and sounder (SSMIS) instruments on three different satellite platforms are compared in different years to investigate the consistency between the sensors over time. The orbits of the three platforms have drifted over their years of operation, resulting in changing relative observing times that could cause biases in TB estimates and near-real-time sea ice concentrations derived from the NASA Team algorithm that are produced at the National Snow and Ice Data Center. Comparisons of TB histograms and concentrations show that there are small mean differences between sensors, but variability within an individual sensor is much greater. There are some indications of small changes due to orbital drift, but these are not consistent across different frequencies. Further, the overall effect of the drift, while not definitive, is small compared to the intra- and interannual variability in individual sensors. These results suggest that, for near-real-time use, the differences in the sensors are not critical. However, for long-term time series, even the small biases should be corrected for. The strong day-to-day, seasonal, and interannual variability in TB distributions indicate that time-varying algorithm coefficients in the NASA team algorithm would lead to improved, more consistent sea ice concentration estimates.</div

The Spectral Energy Distribution of CO lines in M82

We present an analysis of the excitation conditions of the molecular gas in the streamers and the outflow of M82 based on observations obtained at the IRAM 30m telescope. Our analysis of J=1-0 and J=2-1 transitions of CO and 13CO and the CO(3-2) line in 13 regions outside the central starburst disk shows that the gas density within the streamer/outflow system is about an orderof magnitude lower (n(H2) ~ 10^3 cm^-3) than in the central molecular disk. We have used an LVG model and data from the literature to constrain the flux density in each CO transition (the `CO line SED') arising from the streamer/outflow system and the central starburst disk itself. Globally, we find that the CO flux density up to the J=3-2 line is dominated by the diffuse outer regions while lines above the J=5-4 transition are almost exclusively emitted by the central starburst disk. We compare the CO line SED of M82 to CO observations of galaxies at high redshift and suggest that small high-J/low-J CO flux density ratios (observed in some of these sources) are not necessarily caused by a different excitation of the central molecular gas concentration, but may result from an additional, more extended and diffuse gas reservoir around these systems, reminiscent of the situation in M82.Comment: 12 pages, 7 figures, accepted by A&

Computing and Representing Sea Ice Trends: Toward a Community Consensus

Estimates of the recent decline in Arctic Ocean summer sea ice extent can vary due to differences in sea ice data sources, in the number of years used to compute the trend, and in the start and end years used in the trend computation. Compounding such differences, estimates of the relative decline in sea ice cover (given in percent change per decade) can further vary due to the choice of reference value (the initial point of the trend line, a climatological baseline, etc.). Further adding to the confusion, very often when relative trends are reported in research papers, the reference values used are not specified or made clear. This can lead to confusion when trend studies are cited in the press and public reports

A Blended Sea Ice Concentration Product from AMSR2 and VIIRS

An effective blended Sea-Ice Concentration (SIC) product has been developed that utilizes ice concentrations from passive microwave and visible/infrared satellite instruments, specifically the Advanced Microwave Scanning Radiometer-2 (AMSR2) and the Visible Infrared Imaging Radiometer Suite (VIIRS). The blending takes advantage of the all-sky capability of the AMSR2 sensor and the high spatial resolution of VIIRS, though it utilizes only the clear sky characteristics of VIIRS. After both VIIRS and AMSR2 images are remapped to a 1 km EASE-Grid version 2, a Best Linear Unbiased Estimator (BLUE) method is used to combine the AMSR2 and VIIRS SIC for a blended product at 1 km resolution under clear-sky conditions. Under cloudy-sky conditions the AMSR2 SIC with bias correction is used. For validation, high spatial resolution Landsat data are collocated with VIIRS and AMSR2 from 1 February 2017 to 31 October 2019. Bias, standard deviation, and root mean squared errors are calculated for the SICs of VIIRS, AMSR2, and the blended field. The blended SIC outperforms the individual VIIRS and AMSR2 SICs. The higher spatial resolution VIIRS data provide beneficial information to improve upon AMSR2 SIC under clear-sky conditions, especially during the summer melt season, as the AMSR2 SIC has a consistent negative bias near and above the melting point.</div