Ozone plays a very important role in our atmosphere because it protects any living organisms at the Earth's surface against the harmful solar UVB and UVC radiation. In the stratosphere, ozone plays a critical role in the energy budget because it absorbs both solar UV and terrestrial IR radiation. Further, ozone in the tropopause acts as a strong greenhouse gas, and increasing ozone trends at these altitudes contribute to climate change. This review contains a short description of the various techniques that provided atmospheric ozone measurements valuable for long-term trend analysis. The anthropogenic emissions of substances that deplete ozone (chlorine- and bromine-containing volatile gases) have increased from the 1950s until the second half of the 1980s. The most severe consequence of the anthropogenic release of ozone-depleting substances is the “Antarctic ozone hole.” Long-term observations indicate that stratospheric ozone depletion in the southern winter-spring season over Antarctica started in the late 1970s, leading to a strong decrease in October total ozone means. Present values are only approximately half of those observed prior to 1970. In the Arctic, large ozone depletion was observed in winter and spring in some recent years. Satellite and ground-based measurements show no significant trends in the tropics but significant long-term decreasing trends in the northern and southern midlatitudes (of the order of 2–4% per decade in the period from 1970 to 1996 and an acceleration in trends in the 1980s). Ozone at northern midlatitudes decreased by −7.4±2% per decade at 40 km above mean sea level, while ozone loss was small at 30 km. Large trends were found in the lower stratosphere, −5.1±1.8% at 20 km and −7.3±4.6% at 15 km, where the bulk of the ozone resides. The possibility of a reduction in the observed trends has been discussed recently, but it is very hard to distinguish this from the natural variability. As a consequence of the Montreal Protocol process, the emissions of ozone-depleting substances have decreased since the late 1980s. Chlorine is no longer increasing in the stratosphere, although the total bromine amount is still increasing. Considering anthropogenic emissions of substances that deplete ozone, the turnaround in stratospheric ozone trends is expected to take place in the coming years. However, anthropogenic climate change could have a large influence on the future evolution of the Earth's ozone shield.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999RG000059

Ozone trends: A review

Over Arctic sea ice, pressure ridges and floe and melt pond edges all introduce discrete obstructions to the flow of air or water past the ice and are a source of form drag. In current climate models form drag is only accounted for by tuning the air–ice and ice–ocean drag coefficients, that is, by effectively altering the roughness length in a surface drag parameterization. The existing approach of the skin drag parameter tuning is poorly constrained by observations and fails to describe correctly the physics associated with the air–ice and ocean–ice drag. Here, the authors combine recent theoretical developments to deduce the total neutral form drag coefficients from properties of the ice cover such as ice concentration, vertical extent and area of the ridges, freeboard and floe draft, and the size of floes and melt ponds. The drag coefficients are incorporated into the Los Alamos Sea Ice Model (CICE) and show the influence of the new drag parameterization on the motion and state of the ice cover, with the most noticeable being a depletion of sea ice over the west boundary of the Arctic Ocean and over the Beaufort Sea. The new parameterization allows the drag coefficients to be coupled to the sea ice state and therefore to evolve spatially and temporally. It is found that the range of values predicted for the drag coefficients agree with the range of values measured in several regions of the Arctic. Finally, the implications of the new form drag formulation for the spinup or spindown of the Arctic Ocean are discussed.

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Impact of Variable Atmospheric and Oceanic Form Drag on Simulations of Arctic Sea Ice

A study is presented of the seasonal and interannual variability of Arctic sea‐ice extent over the 32‐year period 1953–84. The data set used consists of monthly sea‐ice concentration values given on a 1°‐latitude grid and represents a 7‐year extension of the 25‐year data set analysed by Walsh and Johnson (1979). By focussing attention on the variability in seven distinct subregions that circumscribe the polar region, a number of interesting spatial patterns emerge in the regional seasonal cycles and anomalies of ice coverage. For example, the time‐scale of the smoothed anomaly fluctuations varies from a 4–6 year cycle in the western Arctic (e.g. the Beaufort Sea) to a decadal one in the eastern Arctic (e.g. the Barents Sea). Also, in agreement with earlier studies, a significant out‐of‐phase relationship was found between the 25‐month smoothed anomalies in the Beaufort and Chukchi Sea region and the Greenland Sea. It is proposed that this behaviour is related to atmospheric pressure anomalies ass...

Arctic Sea‐Ice extent and anomalies, 1953–1984

Arctic winter, spring and autumn surface air temperature (SAT) anomalies and associated sea level pressure (SLP) fields have decidedly different spatial patterns at the beginning of the 21st century (2000–2007) compared to most of the 20th century; we suggest calling this recent interval the Arctic warm period. For example, spring melt date as measured at the North Pole Environmental Observatory (2002–2007) is 7 d earlier than the records from the Russian North Pole stations (1937–1987) and statistically different at the 0.05 level. The 20th century was dominated by the two main climate patterns, the Arctic Oscillation/Northern Annular Mode (AO/NAM) and the Pacific North American-like (PNA∗) pattern. The predominately zonal winds associated with the positive phases of these patterns contribute to warm anomalies in the Arctic primarily over their respective Eastern and Western Hemisphere land areas, as in 1989–1995 and 1977–1987. In contrast, SAT in winter (DJF) and spring (MAM) for 2000–2007 show an Arctic-wide SAT anomaly of greater than +1.0◦C and regional hot spots over the central Arctic of greater than +3.0◦C. Unlike the AO and PNA∗, anomalous geostrophic winds for 2000–2007 often tended to blow toward the central Arctic, a meridional wind circulation pattern. In spring 2000–2005, these winds were from the Bering Sea toward the North Pole, whereas in 2006–2007 they were mostly from the eastern Barents Sea. A meridional pattern was also seen in the late 1930s with anomalous winter (DJFM) SAT, at Spitzbergen, of greater than +4◦C. Both periods suggest natural atmospheric advective contributions to the hot spots with regional loss of sea ice. Recent warm SAT anomalies in autumn are consistent with climate model projections in response to summer reductions in sea ice extent. The recent dramatic loss of Arctic sea ice appears to be due to a combination of a global warming signal and fortuitous phasing of intrinsic climate patterns.

The Recent Arctic Warm Period

Progress in the study and management of river ice jams

A major impetus for scientific studies of climate change in the Arctic Ocean has been the reduction in the areal extent and thickness of its sea ice cover. An extended measurement record of the horizontal dimensions of this ice cover is available for the full Arctic Ocean Basin based upon a record compiled from more than 30 years of relatively continuous satellite based measurements. Unfortunately, data accumulations for the ice cover’s vertical dimension, ie, sea ice thickness, tend to be limited to data sets with durations no longer than 15 years, reflecting underlying greater measurement difficulties. Moreover, the longest duration ice thickness data collection efforts have been confined only to two specific portions of the Basin, namely, Fram Strait and the Canadian sector of the Beaufort Sea. Elsewhere, the available data sets are either of notably shorter duration or non-existent.Upward-looking sonar (ULS) has been and continues to be the primary source of data with volumes and accuracy sufficient f...

Advances in upward looking sonar technology for studying the processes of change in Arctic Ocean ice climate

Scientific and engineering studies of polar and marginal ice zones require detailed information on sea ice thickness and topography. Accurate information on sea ice thickness and topography data is required for basic ice-covered ocean studies and, increasingly, for addressing important navigation-, offshore structure design/safety- and climate change-issues. Since the early 1990's, upward-looking sonar (ULS) instrumentation have been developed and applied to provide under-ice topography data with high horizontal and vertical spatial resolution. Such internal recording ULS instruments, or ice profilers, are typically operated from the seafloor on taut line mooring systems. The ASL Model IPS4 Ice Profiler, which has been widely used in studies of the Arctic Ocean, as well as in numerous seasonal ice zones and in the Southern Ocean, is being upgraded to allow much expanded data storage capacity (from 69 Mbytes to 1-8 Gigabytes) and 16 bit A/D resolution for ice ranges and other parameters. With typical ping rates of 0.5 or 1 Hz, the enhanced capability of the Ice Profiler provides very high resolution measurements of ice keel drafts and the under-ice topography of sea-ice keel features. The Ice Profiler is often used in conjunction with an Acoustic Doppler Current Profiler which provides direct measurements of ice velocity. The combination of high resolution ice draft time series with ice velocities allows for computation of quasi-spatial ice drafts as a function of horizontal distance. The results from the first deployment of an upgraded Ice Profiler, operated just off the Confederation Bridge in Northumberland Strait, from November 2006 to April 2007, are presented and compared with the results of previous sea ice studies at the same location. The much larger onboard data capacity allows for realization of multiple targets for each ping and, on a subsampled basis, offers data on acoustic backscatter returns over the complete water column. This additional information is being analyzed to examine the nature and cause of occasional false target returns. In past measurement campaigns, there have been episodic occurrences of deep targets detected which are not consistent with sea ice features that can be reasonably expected to occur in Northumberland Strait. These features are often associated with occurrences of the largest (spring) tidal currents, leading to the hypothesis that these anomalous targets may be associated with velocity shears in the water column resulting from strong tidal flows past the bridge support structures. Based on these analyses, improvements to the target detection algorithm are being developed and tested.

Improvements in Upward Looking Sonar-Based Sea-Ice Measurements: A Case Study for 2007 Ice Features in Northumberland Strait, Canada

Iceberg models, as presently used in applications off the eastern coast of Canada, are described and summarized. These models can be divided into short, intermediate, and long-term categories, which are associated with: close-in ice management (within 30 km of drill sites); regional iceberg distribution forecasts, and; generalized 3 to 6 month advanced predictions of iceberg severity, respectively. Short- and intermediate-term models are usually further subdivided according to the underlying approach as dynamical, statistical or kinematic. The key features of major modelling category status are given below.

Iceberg Movement Prediction off the Canadian East Coast

A new underwater acoustic instrument for river ice studies has been designed, developed, and deployed in the Peace River in Northern Alberta, which is hydraulically regulated by upstream hydroelectric projects. The data is being collected to support studies related to ice jam occurrences and hydropower operations during the winter. An upward looking sonar instrument was deployed for the 2004-2005 ice season. From the acoustic backscatter returns of the transmitted acoustic pulses, the sonar instrument measured the distance to the water surface or the underside of floating ice at the surface. The instrument also had the capability to record the profile of acoustic backscatter returns through the river water column. The instrument provided valuable insights into numerous freeze-up, midwinter and spring ice processes difficult or impossible to obtain by other methods. These processes included formation of frazil in suspension, development of frazil ice pans, anchor ice formation/detection, formation of the river ice cover including highly dynamic freeze-up events, changes in the river ice cover over the winter, undercover ice transport and, finally, thermal break-up. 1.0 Introduction The Peace River in northern British Columbia and Alberta is regulated by the WAC Bennett and Peace Canyon dams (Figure 1.1.1). During the winter, flow releases have to be managed to reduce the potential for ice jamming and subsequent flooding that can occur under a variety of environmental conditions. At particular risk is the Town of Peace River, Alberta about 375 km downstream from the hydroelectric facilities. These management efforts require better understandings of river ice processes, including calibration of computer ice models. The collection of field data is useful for meeting these management requirements as well as for providing baseline data for ongoing evaluations and for assessing potential development of the Dunvegan Hydroelectric Project about 100 km upstream of the Town of Peace River. The Shallow Water Ice Profiling Sonar (SWIPS) unit, which was central to 2004-2005 field measurement campaign, was deployed near the Town of Peace River (Figure 1.1.1) to investigate ice processes at a location where such processes could have near-maximal impact on overall Peace River management. The chosen site was also logistically convenient, as close proximity to the town site allowed for both frequent site visits and use of other data being collected in surrounding areas. 1.1 Measurement Objectives Measurements of ice processes occurring in the water layer and/or below the uppermost ice surface have been rarely reported upon in the …

Instrument for detecting freeze-up, mid-winter and break-up ice processes in rivers

The new upward looking sonar instrument was deployed on the riverbed in November 2005 and 2006. The instrument package contained a 545 KHz sonar transducer, as well as temperature-, 2-axis tiltand pressuresensors as well as onboard heaters to prevent anchor ice formation. The original instrument deployed in October 2004 and November 2005 was a 235 KHz unit. The sonar instruments measure the distance to the water surface or the undersides of drifting or stationary ice. By computing the difference between the acoustically-derived distance to the ice and an independently measured water level, the draft of the floating ice can be determined at one second sampling intervals. The instruments can also record the profile of acoustic backscatter returns through the body of the river water column allowing detection of the presence and depth of suspended frazil ice. The higher frequency of the second generation unit was intended to facilitate detection of smaller particles of frazil ice.

John R. Marko

Papers

Advances in upward looking sonar technology for studying the processes of change in Arctic Ocean ice climate

Improvements in Upward Looking Sonar-Based Sea-Ice Measurements: A Case Study for 2007 Ice Features in Northumberland Strait, Canada

Iceberg Movement Prediction off the Canadian East Coast

Instrument for detecting freeze-up, mid-winter and break-up ice processes in rivers

Instrument for Detecting Suspended and Surface Ice Runs in Rivers