Changes In Cyclone Activity Research Articles

СВЯЗЬ МОРСКОГО ВОЛНЕНИЯ С ЦИКЛОНИЧЕСКОЙ АКТИВНОСТЬЮ В АТМОСФЕРЕ СЕВЕРНОГО ПОЛУШАРИЯ ПО ДАННЫМ РЕАНАЛИЗА ERA5

Based on the ERA5 reanalysis data for the period 1979-2021, the authors have quantified the seasonal and regional connections between significant wave heights and changes in cyclone activity in the atmosphere of the Northern Hemisphere. The contribution of extratropical cyclones to the formation of the corresponding features and variations of sea waves is evaluated. The maxima of the extreme sea wave occurrence frequency in winter and summer corresponds to sea areas with an increased frequency of cyclones, in particular, over the Pacific and Atlantic oceans. It has been found that the contribution of extratropical cyclones to the generation of significant wave heights reaches 70% in winter and 50% in summer. The largest contribution is associated with intense cyclones: 90% in winter and 40% in summer.

Changes in Cyclone Activity and Precipitation in the Extratropical Latitudes of the Northern Hemisphere in Recent Decades According to ERA5 Reanalysis

Changes in Cyclone Activity and Precipitation in the Extratropical Latitudes of the Northern Hemisphere in Recent Decades According to ERA5 Reanalysis

Changes in the Surface Wind Associated with Atmospheric Cyclones at Extra-Tropical Latitudes of the Northern Hemisphere in Recent Decades

We obtained quantitative estimates of seasonal and regional features and changes in cyclone activity in the atmosphere of the Northern Hemisphere and determined the contribution of extratropical cyclones to the formation of corresponding features and changes in the surface wind, using ERA5 reanalysis data for recent decades (1979–2021). According to these estimates, the contribution of extratropical cyclones to surface wind speeds in the regions of their high occurrence reaches 60% in winter and 50% in summer. The strongest contribution is related to intense cyclones: about 60% in winter and about 25% in summer.

Декомпозиция временного ряда величины рН поверхностных вод глубоководной части Черного моря по архивным данным второй половины XX века

Based on the archival data of the Institute of Natural and Technical Systems for the period from 1956 to 1996 the decomposition of the time series of the pH value of the surface layer of the deep-water part of the Black Sea was carried out with subsequent extrapolation until 2010. The analysis shows that the reconstructed time series is divided into two time interval trends with different sign and data quality: from 1956 to 1976 and from 1977 to 1996. The presence of these two fundamentally different time periods is largely due to the method for determining the pH value. Until about the mid-1970s the pH value in the Black Sea was determined mainly by the colorimetric method with an accuracy of tenths of pH, i.e. with a high error. In subsequent years, the potentiometric method began to be widely used, the accuracy of which is an order of magnitude higher. Therefore, further in the work, the second time period is analyzed – since 1977. In the time course of pH, a regular seasonal variation, interannual quasicyclic components of variability with periods of about 6.7 and 2.5 years, and a significant negative linear trend are identified. It is most likely that the main reason for the quasiperiodic variability of pH in the upper layer of the open part of the Black Sea on an interannual scale is related to variations in atmospheric precipitation caused by changes in cyclonic activity in the Atlantic-European sector, including the Black Sea region, in different phases of climatic modes in the ocean-atmosphere system (such as, in particular, NAO). The highlighted tendency of the pH value since 1977 indicates the acidification of the upper layer of the Black Sea waters, with an average rate of about 0.013pH units / 10 years. This corresponds to the rate of increase in acidity of surface waters in other regions of the World Ocean. Expedition data from 2010 confirm the validity of the extrapolation performed.

Migration of black-naped terns in contrasted cyclonic conditions

Cyclones are currently increasing in frequency and intensity across the tropical regions, and such changes in cyclonic activity can adversely impact tropical marine ecosystems. To examine the potential effects of these changes on marine migrations, we tracked the annual at-sea distribution of black-naped terns from Okinawa Islands, southwest Japan (26.5° N; 127.9° E). Using light-based geolocation loggers, we compared the migration chronology of six terns between 4 years of contrasted conditions regarding cyclones (regionally called typhoons). Shortly after breeding (30 August ± 13.9 days), the birds undertook their migration across the Philippine Sea to coastal regions of Borneo and Sulawesi Islands, and seemed able to avoid or cross the storm systems. The two birds tracked in years of medium–high typhoon activity (2012–2014) seemed to target a stopover area in the northern Philippines several days after a typhoon hit. By contrast, in 2017, no strong typhoon hit in August and the four study birds showed later departure by 23.8 days, but moved significantly quicker, with little or no stopover. Arrival date at the wintering site was similar among years (1 October ± 3.5 days). Terns thus show remarkable variability in their migration chronology, presumably linked with annual storm frequency. However, the limits to this variability are currently unknown. Further, if individuals respond to environmental cues to time their migration to potentially benefit from lagged optimal feeding conditions en route, it is likely that the increase of back-to-back cyclonic events in the region may reduce the benefits of such a strategy for surface-feeding predators.

Towards modelling the future risk of cyclone wave damage to the world's coral reefs.

Tropical cyclones generate extreme waves that can damage coral reef communities. Recovery typically requires up to a decade, driving the trajectory of coral community structure. Coral reefs have evolved over millennia with cyclones. Increasingly, however, processes of recovery are interrupted and compromised by additional pressures (thermal stress, pollution, diseases, predators). Understanding how cyclones interact with other pressures to threaten coral reefs underpins spatial prioritization of conservation and management interventions. Models that simulate coral responses to cumulative pressures often assume that the worst cyclone wave damage occurs within ~100km of the track. However, we show major coral loss at exposed sites up to 800km from a cyclone that was both strong (high sustained wind speeds >=33m/s) and big (widespread circulation >~300km), using numerical wave models and field data from northwest Australia. We then calculate the return time of big and strong cyclones, big cyclones of any strength and strong cyclones of any size, for each of 150 coral reef ecoregions using a global data set of past cyclones from 1985 to 2015. For the coral ecoregions that regularly were exposed to cyclones during that time, we find that 75% of them were exposed to at least one cyclone that was both big and strong. Return intervals of big and strong cyclones are already less than 5years for 13 ecoregions, primarily in the cyclone-prone NW Pacific, and less than 10years for an additional 14 ecoregions. We identify ecoregions likely at higher risk in future given projected changes in cyclone activity. Robust quantification of the spatial distribution of likely cyclone wave damage is vital not only for understanding past coral response to pressures, but also for predicting how this may change as the climate continues to warm and the relative frequency of the strongest cyclones rises.

Atmospheric moisture transport and the decline in Arctic Sea ice

AbstractThis article contains a review of the transport of moisture to the Arctic and its effect on Arctic Sea Ice Extent (SIE). The review includes a synthesis of our knowledge regarding the main sources supplying moisture to the Arctic, the changes experienced over the last few decades due to variations in the transport of moisture, the factors that control interannual variability, and the inherent contrast in the mechanisms related to the effect of changes in moisture transport on SIE in the Arctic. We note that the precise identification of the moisture sources for the Arctic depends both on the definition of the Arctic region itself and on the approach used to identify the sources, with the remote regions over the extratropical Atlantic and Pacific Oceans being universally important, as are some continental areas over Siberia and North America. This review also reaffirms the absence of any clear agreement regarding the trends in atmospheric moisture transport to the Arctic, and highlights discrepancies between different data sets and approaches in the quantification of moisture transport, implying that its long‐term impact on the intensification of the hydrological cycle in the Arctic remains unclear. We confirm the influence of the major modes of climate variability, planetary circulation patterns, and the changes in cyclonic activity in the variability of moisture transport to the Arctic. We reaffirm that the effect of moisture transport on the Arctic SIE through changes in humidity, cloud cover, and precipitation over the Arctic is a complex scientific problem that requires further detailed study over the decades to come, and we propose some important challenges for future research.This article is categorized under: Paleoclimates and Current Trends > Modern Climate Change

Analyses of the oceanic heat content during 1980–2014 and satellite‐era cyclones over Bay of Bengal

Bay of Bengal (BoB) is one of the most cyclone prone regions in the world. Cyclones receive energy from warm ocean surface waters and the change in cyclone activity generally depends on the change in heat energy available in the upper ocean. Here, we use satellite‐based Modern Era Retrospective‐analysis for Research and Applications dataset, and reanalysis of Simple Ocean Data Assimilation (SODA) and European Centre for Medium‐range Weather Forecasts–Ocean ReAnalysis System 4 (ECMWF–ORAS4) to analyse the oceanic heat content (OHC) and heat flux to identify sources of the additional heat input in the region during the period 1980–2014. It has been observed that during 1999–2014, heat energy is mainly stored in the southern and northwestern parts of the bay and it shows an increasing trend in both regions. In the analysis of OHC, the European Centre for Medium‐range Weather Forecasts (ECMWF) data show a trend of −0.87 × 1018 J/month during 1980–1998 and 7.58 × 1018 J/month during 1999–2014 whereas, the SODA data show a trend of 0.94 × 1018 J/month during 1980–1998 and 5.25 × 1018 J/month during 1999–2014. It is found that many cyclones are seeded in the southeastern bay and intensified over the northwestern bay, consistent with the increase in cyclone heat potential and the upper ocean heat content (UOHC) in those regions. The heat flux in the bay is primarily governed by the heat entering the eastern side and leaving through the western side. In 1999–2014, the incoming heat flux along the eastern boundary has increased significantly (from 0.18 × 1012 to 0.57 × 1012 W/month), indicating that more heat enters the region. Furthermore, a significant reduction in the outgoing heat flux along the western boundary has also been found from the analysis. These processes trap the heat and thereby contributing to the increase in OHC in the bay. The heat flux through the bay is mainly linked with conditions prevailing over Pacific Ocean, such as, the heat influx of BoB decreases during El‐Nino and increases during La‐Nina years.

Changes in Winter North Atlantic Extratropical Cyclones in High-Resolution Regional Pseudo–Global Warming Simulations

The present study investigates changes in the location, frequency, intensity, and dynamical processes of North Atlantic extratropical cyclones with warming consistent with the IPCC Fifth Assessment Report (AR5) representative concentration pathway 8.5 (RCP8.5) scenario. The modeling, analysis, and prediction (MAP) climatology of midlatitude storminess (MCMS) feature-tracking algorithm was utilized to analyze 10 cold-season high-resolution atmospheric simulations over the North Atlantic region in current and future climates. Enhanced extratropical cyclone activity is most evident in the northeast North Atlantic and off the U.S. East Coast. These changes in cyclone activity are offset from changes in eddy kinetic energy and eddy heat flux. Investigation of the minimum SLP reached at each grid point reveals a lack of correspondence between the strongest events in the current and future simulations, indicating the future simulations produced a different population of storms. Examination of the percent change of storms in the storm-track region shows a reduction in the number of strong storms (i.e., those reaching a minimum SLP perturbation of at least −51 hPa). Storm-relative composites of strong and moderate storms show an increase in precipitation, associated with enhanced latent heat release and strengthening of the 900–700-hPa layer-average potential vorticity (PV). Other structural changes found for cyclones in a future climate include weakened upper-level PV for strong storms and a weakened near-surface potential temperature anomaly for moderate storms, demonstrating a change in storm dynamics. Furthermore, the impacts associated with extratropical cyclones, such as strong near-surface winds and heavy precipitation, strengthen and become more frequent with warming.

Seasonal patterns and trends of fastest 2‐min winds at coastal stations in the conterminous USA

ABSTRACTWeather extremes have a substantial societal impact, particularly in increasingly densely populated coastal areas. This research uses ‘fastest 2‐min wind’ records at land‐based coastal automated weather stations in the conterminous United States to characterize seasonal patterns of ‘extreme’ wind speed. The records also are examined for evidence of trends in the fastest winds that may be indicative of changes in cyclone activity over the available period of record (13–19 years).Fastest 2‐min winds at stations along the Pacific, western Gulf, and northern Atlantic coasts have a winter maximum and a summer minimum, similar to the seasonal variation in mean wind speeds. In contrast, the fastest winds at southern Atlantic and eastern Gulf coast stations show a winter minimum and a summer maximum that is opposite what is observed for mean speeds. Over the period of available record, many coastal stations show positive trends in the fastest 2‐min wind speeds in winter, spring and summer. Negative trends are most frequent in the autumn. On an annual basis, the trends in fastest 2‐min winds are consistent with the results of satellite‐derived near‐coastal oceanic wind speed assessments. Examination of daily weather maps and synoptic composites supports the interpretation that extratropical cyclone activity is the primary driver of the fastest wind speeds at most stations, with tropical systems and mesoscale features such as thunderstorms producing some of the fastest winds during the summer and autumn.

Projected Atlantic hurricane surge threat from rising temperatures

Detection and attribution of past changes in cyclone activity are hampered by biased cyclone records due to changes in observational capabilities. Here, we relate a homogeneous record of Atlantic tropical cyclone activity based on storm surge statistics from tide gauges to changes in global temperature patterns. We examine 10 competing hypotheses using nonstationary generalized extreme value analysis with different predictors (North Atlantic Oscillation, Southern Oscillation, Pacific Decadal Oscillation, Sahel rainfall, Quasi-Biennial Oscillation, radiative forcing, Main Development Region temperatures and its anomaly, global temperatures, and gridded temperatures). We find that gridded temperatures, Main Development Region, and global average temperature explain the observations best. The most extreme events are especially sensitive to temperature changes, and we estimate a doubling of Katrina magnitude events associated with the warming over the 20th century. The increased risk depends on the spatial distribution of the temperature rise with highest sensitivity from tropical Atlantic, Central America, and the Indian Ocean. Statistically downscaling 21st century warming patterns from six climate models results in a twofold to sevenfold increase in the frequency of Katrina magnitude events for a 1 °C rise in global temperature (using BNU-ESM, BCC-CSM-1.1, CanESM2, HadGEM2-ES, INM-CM4, and NorESM1-M).

Homogeneous record of Atlantic hurricane surge threat since 1923

Detection and attribution of past changes in cyclone activity are hampered by biased cyclone records due to changes in observational capabilities. Here we construct an independent record of Atlantic tropical cyclone activity on the basis of storm surge statistics from tide gauges. We demonstrate that the major events in our surge index record can be attributed to landfalling tropical cyclones; these events also correspond with the most economically damaging Atlantic cyclones. We find that warm years in general were more active in all cyclone size ranges than cold years. The largest cyclones are most affected by warmer conditions and we detect a statistically significant trend in the frequency of large surge events (roughly corresponding to tropical storm size) since 1923. In particular, we estimate that Katrina-magnitude events have been twice as frequent in warm years compared with cold years (P < 0.02).

Climate of West Antarctica and Influence of Marine Air Intrusions*

Abstract High-resolution numerical weather forecasts from the Antarctic Mesoscale Prediction System (AMPS) archive are used to investigate the climate of West Antarctica (WA) during 2006–07. A comparison with observations from West Antarctic automatic weather stations confirms the skill of the model at simulating near-surface variables. AMPS cloud cover is also compared with estimates of monthly cloud fractions over Antarctica derived from spaceborne lidar measurements, revealing close agreement between both datasets. Comparison with 20-yr averages from the Interim ECMWF Re-Analysis (ERA-Interim) dataset demonstrates that the 2006–07 time period as a whole is reflective of the West Antarctic climate from the last two decades. On the 2006–07 annual means computed from AMPS forecasts, the most salient feature is a tongue-shaped pattern of higher cloudiness, accumulation, and 2-m potential temperature stretching over central WA. This feature is caused by repeated intrusions of marine air inland linked to the sustained cyclonic activity in the Ross and western Amundsen Seas. It is further enhanced by the ice sheet’s topography and by the mid–low-tropospheric wind flow on either side of the central ice divide. Low pressures centered over the Ross Sea (as opposed to the Bellingshausen Sea) are found to be most effective in conveying heat and moisture into WA. This study offers a perspective on how recent and projected changes in cyclonic activity in the South Pacific sector of the Southern Ocean may affect the climate and surface mass balance of WA.

Response of Northern Hemisphere extratropical cyclone activity and associated precipitation to climate change, as represented by the Community Climate System Model

The projected effects of rising CO2 levels on Northern Hemisphere extratropical cyclone activity and cyclone‐associated precipitation are examined for September–May, using output from version 3 of the Community Climate System Model (CCSM3). A cyclone identification algorithm was applied to a five member ensemble of CCSM3 20th and 21st century output, along with a method of isolating precipitation produced by each cyclone. Mean seasonal statistics describing cyclone activity and the character of associated precipitation were calculated over several study regions for 20 a periods. The dominant change in cyclone activity is a marked midlatitude decrease in frequency during autumn, winter, and spring. Few significant shifts in storm tracks or cyclone intensity were identified. Total daily precipitation from these events is found to increase into the 21st century, largely because of increases in available atmospheric moisture with rising temperatures. This thermodynamic increase in precipitation leads to large rises in total seasonal cyclone‐associated precipitation over high latitudes, while over midlatitudes the thermodynamic increase is offset by the dynamic effect associated with decreased cyclone frequency.

European cyclone track analysis based on ECMWF ERA‐40 data sets

AbstractChanges in large‐scale circulation patterns over the North‐Atlantic‐European region are presented and analyzed for the 20th century. First, changes in decadal frequency of Hess‐Brezowsky macrocirculation patterns (MCP) are evaluated for the period between 1881 and 2000. Frequency of several MCP types increased or decreased considerably during these 120 years, which may be explained by large‐scale changes in circulation characteristics, e.g. by changes in cyclone activity in the different regions. Therefore, cyclone center identification and cyclone tracks and intensity analysis have been accomplished on the basis of the European Centre for Medium‐range Weather Forecast (ECMWF) reanalysis data sets (ERA‐40) on a 2.5° horizontal resolution grid for the period between 1957 and 2002. Results suggest that both the number of midlatitude cyclones and the cyclone activity increased considerably in the North‐Atlantic‐European region, especially in the northwestern part of the domain. Copyright © 2006 Royal Meteorological Society.

Assessment of winter cyclone activity in a transient ECHAM4-OPYC3 GHG experiment

Winter cyclone activity over the Northern Hemisphere is investigated in an ECHAM4/OPYC3 greenhouse gas scenario simulation. The goal of this investigation is to identify changes in cyclone activity associated with increasing concentrations. To this aim, two 50-year time periods are analysed, one representing present day climate conditions and the other a perturbed climate when CO2 concentrations exceed twice the present concentrations. Cyclone activity is assessed using an automatic algorithm, which identifies and tracks cyclones based on sea level pressure fields. The algorithm detects not only large and long living cyclones over the main ocean basins, but also their smaller counterparts in secondary storm track regions like the Mediterranean Basin. For the present climate, results show a good agreement with NCEP-reanalysis, provided that the spectral and time resolutions of the reanalysis are reduced to those available for the model. Several prominent changes in cyclone activity are observed for the scenario period in comparison to the present day climate, especially over the main ocean basins. A significant decrease of overall cyclone track density is found between 35 and 55 degrees North, together with a small increase polewards. These changes result from two different signals for deep and medium cyclones: for deep cyclones (core pressure below 990 hPa) there is a poleward shift in the greenhouse gas scenario, while for medium cyclones (core pressure between 990 and 1010 hPa) a general decrease in cyclone counts is found. The same kind of changes (a shift for intense cyclones and an overall decrease for the weaker ones) are detected when distinguishing cyclones from their intensity, quantified in terms of ∇2p. Thus, the simulated changes can not solely be attributed to alterations in mean sea level pressure. Instead, corresponding increases in upper-tropospheric baroclinicity suggest more favourable conditions for the development of stronger systems at higher latitudes, especially at the delta regions of the North Atlantic and the North Pacific storm tracks.

Observed Changes in Cyclone Activity in Canada and Their Relationships to Major Circulation Regimes

Abstract This study assessed the climate and trend of cyclone activity in Canada using mainly the occurrence frequency of cyclone deepening events and deepening rates, which were derived from hourly mean sea level pressure data observed at 83 Canadian stations for up to 50 years (1953–2002). Trends in the frequency of cyclone activity were estimated by logistic regression analysis, and trends of seasonal extreme cyclone intensity, by linear regression analysis. The results of trend analysis show that, among the four seasons, winter cyclone activity has shown the most significant trends. It has become significantly more frequent, more durable, and stronger in the lower Canadian Arctic, but less frequent and weaker in the south, especially along the southeast and southwest coasts. Winter cyclone deepening rates have increased in the zone around 60°N but decreased in the Great Lakes area and southern Prairies–British Columbia. However, extreme winter cyclone activity seems to have experienced a weaker increase in northwest-central Canada but a stronger decline in the Great Lakes area and in southern Prairies. The results also show more frequent summer cyclone activity with slower deepening rates on the east coast, as well as less frequent cyclone activity with faster deepening rates in the Great Lakes area in autumn. Cyclone activity in Canada was found to be closely related to the North Atlantic Oscillation (NAO), the Pacific Decadal Oscillation (PDO), and El Niño–Southern Oscillation (ENSO). Overall, cyclone activity in Canada is most closely related to the NAO. The simultaneous NAO index explains about 44% (41%) of the winter (autumn) cyclone activity variance in the east coast, 31% of winter cyclone activity variance in the 60°–70°N zone, and 17% of autumn cyclone activity variance in the Great Lakes area. Also, in several regions (e.g., the east coast, the southwest, and the 60°–70°N zone) up to 15% of the seasonal cyclone activity variance can be explained by the NAO/PDO/ENSO index one–three seasons earlier, which is useful for seasonal forecasting.

Possible Change of Extratropical Cyclone Activity due to Enhanced Greenhouse Gases and Sulfate Aerosols—Study with a High-Resolution AGCM

To investigate the possible impacts of enhanced greenhouse gases and sulfate aerosols on extratropical cyclone activity, two 20-yr time-slice experiments—the control run and the global warming run—are performed with a high-resolution AGCM (T106) of the Japan Meteorological Agency. In the control run, the atmosphere is forced by the observed SST and sea ice of 1979–98 and present-day CO2 and sulfate aerosol concentrations. In the global warming run, the atmosphere is forced by the observed SST and sea ice of 1979–98 plus the monthly mean anomalies of SST and sea ice at about the year 2050 obtained from a transient climate change experiment with the Geophysical Fluid Dynamics Laboratory (GFDL) coupled ocean–atmosphere model with a low resolution of R15. The equivalent amounts of CO2 and sulfate aerosol concentrations at about the year 2050 as used in the GFDL R15 model are prescribed. First, the performance of the high-resolution AGCM (T106) in reproducing the extratropical cyclone activity of both hemispheres in the control run is examined—by comparing the cyclone activities simulated in the AGCM and those analyzed from the NCEP–NCAR reanalysis data of the same period from 1979 to 1998. An objective cyclone identification and tracking algorithm is used to analyze the cyclone activity. The results show that the model can reproduce the cyclone activity reasonably well. Second, the possible change in cyclone activity due to enhanced greenhouse gases and sulfate aerosols is examined. The main results are summarized as follows. 1) The total cyclone density (number of cyclones in a 4.5° × 4.5° area per season) tends to decrease significantly in the midlatitudes of both of the Northern and Southern Hemispheres during the December–January–February (DJF) and June–July–August (JJA) seasons. The decrease of cyclone density in the midlatitudes of both of the Northern and Southern Hemispheres in the DJF season is about 7%. In the JJA season, the decreases of cyclone density in the Northern and Southern Hemispheres' midlatitudes are about 3% and 10%, respectively. 2) Although weak and medium-strength cyclones decrease, the density of strong cyclones increases by more than 20% in the Northern Hemisphere in JJA and in the Southern Hemisphere in both DJF and JJA. 3) The density of strong cyclones in the Northern Hemisphere summer (JJA) increases over the eastern coasts of Asia and North America. In the Southern Hemisphere, the density of strong cyclones increases over the circumpolar regions around Antarctica in both summer (DJF) and winter (JJA) seasons. The density of strong cyclones also increases over the southeastern coasts of South Africa and South America. Finally, the possible reasons for the change in cyclone activity due to enhanced greenhouse gases and sulfate aerosols are examined. It is shown that the changes in the extratropical cyclone activity are closely linked to the changes in the baroclinicity in the lower troposphere, which are mainly related to the changes in the horizontal and vertical temperature distributions in the atmosphere due to enhanced greenhouse gases and sulfate aerosols. It is shown that, in the Northern Hemisphere midlatitudes, the decrease of baroclinicity is mainly caused by the decrease of meridional temperature gradient, while in the Southern Hemisphere midlatitudes, the decrease of baroclinicity is mainly caused by the increase of static stability caused by the enhanced greenhouse gases and sulfate aerosols.

The influence of the Andes mountains on the South American low‐level flow

A dry, hydrostatic, three‐dimensional primitive equation model is used to evaluate the mechanical effect of the Andes mountains on the South American low‐level flow (LLF). The model simulations reproduce the evolution of a baroclinic wave over the continent under winter and summer conditions. In both seasons as a consequence of the interaction between the basic flow and the Andes, northerly LLF was reproduced east of the Andes which resembles the main characteristics of the observed flow. Moreover, seasonal changes of cyclone activity have a significant impact on the location of maximum LLF and its alignment, which exhibits a NW‐SE orientation during winter and more meridional orientation in the warm season.

Surface energy budget over the central Arctic Ocean during late summer and early freeze‐up

During the Arctic Ocean Expedition 1996 we measured radiative, turbulent, and conductive heat fluxes from late summer to early freeze‐up, over the Norwegian Sea into the Arctic Ocean to latitude 88°N, mainly in air that had spent several days over the pack ice. In summer the net radiation was positive, on average +26 W m−2, where the leads contributed more than the ice floes. Clouds had a cooling net effect. During the freeze‐up period the net radiation was dominated by the ice floes, on average −8 W m−2, with a warming cloud net effect. The turbulent fluxes were on average small and unable to balance the net radiation, except during cyclone activity, when the total turbulent heat fluxes averaged to +11 W m−2. During the freeze‐up period the conductive heat flux averaged to −4 W m−2. In summer, melting of ice must largely have caused the average positive residual (+21±5 W m−2). During the freeze‐up period the average negative residual (−7±3 W m−2) must result from formation of new ice and oceanic turbulent/convective fluxes in the leads. There was a diurnal cycle in net radiation both in summer (17 W m−2 average amplitude) and the freeze‐up period (8 W m−2). The turbulent sensible heat flux (average amplitude ∼5 W m−2), as well as the turbulent latent heat flux (1 W m−2 in summer) and conductive flux in the ice (2.5 W m−2 during the freeze‐up) responded to this. These results emphasize the high sensitivity of the heat and radiation budget balances to changes in cyclone activity, leads, and clouds.