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Abstract
There was no single relationship between mean temperature and the variability of temperature in the years 1876–1975 in Europe and North America, nor did the variability of precipitation in North America necessarily increase when the temperature decreased
Abstract
There was no single relationship between mean temperature and the variability of temperature in the years 1876–1975 in Europe and North America, nor did the variability of precipitation in North America necessarily increase when the temperature decreased
Abstract
During 24 years when the 700 mb winter mean temperature dropped over most of the hemisphere north of 20°N, the biggest falls were in the belt of strongest baroclinity and were simultaneous with a southward movement and strengthening of the peak in total meridional eddy transport of sensible heat. These changes were accompanied by a southward displacement of the region of most frequent storm tracks at the surface and by compatible trends in surface mean temperature and sea level pressure. At middle latitudes the layer between surface and 700 mb destabilized, while in the arctic it stabilized as the surface temperature over a large part of the polar cap fell more than the 700 mb temperature.
A comparison with the Southern Hemisphere showed that local temperature trends in the antarctic also take place on the scale of long waves, that they are as large as those in the Northern Hemisphere and that a zonally averaged trend is not necessary the same in summer and winter. The net transport of sensible heat by stationary waves is much smaller in the Southern than in the Northern Hemisphere, and changes in stationary wave transport in the Southern Hemisphere are therefore not likely to contribute much to large changes in the net poleward transport of sensible heat by waves. This is connected with the observation that the stationary waves in temperature and pressure are nearly in phase over the almost continuous water surface in southern temperate latitudes.
Abstract
During 24 years when the 700 mb winter mean temperature dropped over most of the hemisphere north of 20°N, the biggest falls were in the belt of strongest baroclinity and were simultaneous with a southward movement and strengthening of the peak in total meridional eddy transport of sensible heat. These changes were accompanied by a southward displacement of the region of most frequent storm tracks at the surface and by compatible trends in surface mean temperature and sea level pressure. At middle latitudes the layer between surface and 700 mb destabilized, while in the arctic it stabilized as the surface temperature over a large part of the polar cap fell more than the 700 mb temperature.
A comparison with the Southern Hemisphere showed that local temperature trends in the antarctic also take place on the scale of long waves, that they are as large as those in the Northern Hemisphere and that a zonally averaged trend is not necessary the same in summer and winter. The net transport of sensible heat by stationary waves is much smaller in the Southern than in the Northern Hemisphere, and changes in stationary wave transport in the Southern Hemisphere are therefore not likely to contribute much to large changes in the net poleward transport of sensible heat by waves. This is connected with the observation that the stationary waves in temperature and pressure are nearly in phase over the almost continuous water surface in southern temperate latitudes.
Abstract
The local temperature trends in summer are not so obviously associated with advection changes as are those in winter. This appears to be due to weaker temperature contrasts at middle and high latitudes in summer combined with a smaller amplitude of the mean waves. A larger share of the total variance in the trend of sea level pressure is accounted for by the shorter waves than in winter. Local temperature changes are as big in summer as in winter in many places at middle latitudes, whereas in the arctic they are appreciably smaller. The zonally averaged trends in summer are larger at middle than at high latitudes, which is the reverse of winter. The sign of the zonally averaged temperature changes differs from one latitude belt to another as in winter, and the sign at a given latitude is not necessarily the same in both seasons. In contrast with winter, the sensible heat transport by mean waves in the sea level pressure in summer plays an insignificant part in causing trends in the zonally averaged temperature.
Abstract
The local temperature trends in summer are not so obviously associated with advection changes as are those in winter. This appears to be due to weaker temperature contrasts at middle and high latitudes in summer combined with a smaller amplitude of the mean waves. A larger share of the total variance in the trend of sea level pressure is accounted for by the shorter waves than in winter. Local temperature changes are as big in summer as in winter in many places at middle latitudes, whereas in the arctic they are appreciably smaller. The zonally averaged trends in summer are larger at middle than at high latitudes, which is the reverse of winter. The sign of the zonally averaged temperature changes differs from one latitude belt to another as in winter, and the sign at a given latitude is not necessarily the same in both seasons. In contrast with winter, the sensible heat transport by mean waves in the sea level pressure in summer plays an insignificant part in causing trends in the zonally averaged temperature.
Abstract
For each grid point (5° latitude by 5° longitude) and each season, the long-term mean sea-level pressure (1899–1972) and its standard deviation were found, using a data set compiled by NCAR. Individual deviations from the mean greater than three standard deviations were compared with nearby station data from World Whether Records. Some deviations were found in the sea-level pressure data and not in the station pressure data. Comparison was made between the NCAR sea-level pressure data set and the United Kingdom Meteorological Office data set; large differences are found since 1940 when the data acts started using different sources.
Abstract
For each grid point (5° latitude by 5° longitude) and each season, the long-term mean sea-level pressure (1899–1972) and its standard deviation were found, using a data set compiled by NCAR. Individual deviations from the mean greater than three standard deviations were compared with nearby station data from World Whether Records. Some deviations were found in the sea-level pressure data and not in the station pressure data. Comparison was made between the NCAR sea-level pressure data set and the United Kingdom Meteorological Office data set; large differences are found since 1940 when the data acts started using different sources.
Abstract
The sign of the weighted temperature change over two periods (1950–64, 1942–72) for 15°–80°N was determined by the change in the polar region in spring and autumn, as it was in winter but not in summer. Each of the four seasons shows a different distribution of zonally averaged temperature changes.
Abstract
The sign of the weighted temperature change over two periods (1950–64, 1942–72) for 15°–80°N was determined by the change in the polar region in spring and autumn, as it was in winter but not in summer. Each of the four seasons shows a different distribution of zonally averaged temperature changes.
Abstract
We have demonstrated that regional temperature trends at the surface in winter are connected with circulation changes on the scale of long waves, and that within a given period the trends change sign both with longitude and with latitude. Since the biggest zonally averaged temperature trends north of about 50°N in our samples exceed the biggest zonally averaged trends over the rest of the Northern Hemisphere by a factor of seven to eight, and since the sign of the zonally averaged trends is not uniform, the sign of the average trend over the subpolar and polar regions in winter becomes decisive for the sign of the average temperature trend of the hemisphere.
An important difference between a period when the average temperature of the Northern Hemisphere increased (1900–1941) and one when it decreased (1942–1972), was in the amount of sensible heat transported poleward by the, mean eddies north of the latitude of maximum transport (based on maps of sea level pressure). While the higher latitudes warmed, the poleward transport north of about 55°N (and thus the convergence of heat over the polar cap) was larger than during the period of cooling. This difference was associated with a stronger meridional circulation around the Icelandic low and on the east side of the Siberian high during the warming than during the cooling
The trend of the zonally averaged poleward transport by the mean eddies at sea level, which was positive during the warming and negative during the cooling, amounted at each latitude to a very small fraction of the quantity transported across that latitude.
Abstract
We have demonstrated that regional temperature trends at the surface in winter are connected with circulation changes on the scale of long waves, and that within a given period the trends change sign both with longitude and with latitude. Since the biggest zonally averaged temperature trends north of about 50°N in our samples exceed the biggest zonally averaged trends over the rest of the Northern Hemisphere by a factor of seven to eight, and since the sign of the zonally averaged trends is not uniform, the sign of the average trend over the subpolar and polar regions in winter becomes decisive for the sign of the average temperature trend of the hemisphere.
An important difference between a period when the average temperature of the Northern Hemisphere increased (1900–1941) and one when it decreased (1942–1972), was in the amount of sensible heat transported poleward by the, mean eddies north of the latitude of maximum transport (based on maps of sea level pressure). While the higher latitudes warmed, the poleward transport north of about 55°N (and thus the convergence of heat over the polar cap) was larger than during the period of cooling. This difference was associated with a stronger meridional circulation around the Icelandic low and on the east side of the Siberian high during the warming than during the cooling
The trend of the zonally averaged poleward transport by the mean eddies at sea level, which was positive during the warming and negative during the cooling, amounted at each latitude to a very small fraction of the quantity transported across that latitude.
Abstract
We have tested three methods of estimating the level of a coming season's mean temperature at a station where the statistical association between two selected seasons is as high as one can expect in extratropical regions. The methods are contingency tables, regression equations, and the use of the last few decades if there is a trend at the station which will separate the mean of these decades a fair distance from the long-term mean. A moderate amount of skill was achieved, but the degree of seasonal association in our test case was exceptionally high, and generally these methods will provide only a small improvement over a probability based on knowing only the observed frequency distribution.
Abstract
We have tested three methods of estimating the level of a coming season's mean temperature at a station where the statistical association between two selected seasons is as high as one can expect in extratropical regions. The methods are contingency tables, regression equations, and the use of the last few decades if there is a trend at the station which will separate the mean of these decades a fair distance from the long-term mean. A moderate amount of skill was achieved, but the degree of seasonal association in our test case was exceptionally high, and generally these methods will provide only a small improvement over a probability based on knowing only the observed frequency distribution.
Abstract
The standard deviations of mean sea-level pressure in January are compared for five discrete 16-year periods between 1901 and 1980. The changes from one period to another are large and larger in the North Atlantic than in the North Pacific Ocean. The differences between the periods are associated with variations in the position and central pressure of the Aleutian and Icelandic lows. There is no consistent link between the two lows as their central pressure varied in parallel till the late 1930s and oppositely thereafter.
Abstract
The standard deviations of mean sea-level pressure in January are compared for five discrete 16-year periods between 1901 and 1980. The changes from one period to another are large and larger in the North Atlantic than in the North Pacific Ocean. The differences between the periods are associated with variations in the position and central pressure of the Aleutian and Icelandic lows. There is no consistent link between the two lows as their central pressure varied in parallel till the late 1930s and oppositely thereafter.
Abstract
Observations of monthly mean sea level pressure, surface air temperature, and 500 mb and 300 mb geopotential heights and temperatures are used to study trends in the Southern Hemisphere from 1951–81.
The winter mean sea level pressure fell over the Indian/Atlantic half of the hemisphere from the 1950s to the 1960s, and rose over the other half. Generally, these trends reversed from the 1960s to the 1970s. The trends are equivalent barotropic.
The trends of temperatures are often regionally dependent. There was a significant warming over Antarctica from the 1960s to 1970s at all upper levels except for a small area on the Indian Ocean side.
Abstract
Observations of monthly mean sea level pressure, surface air temperature, and 500 mb and 300 mb geopotential heights and temperatures are used to study trends in the Southern Hemisphere from 1951–81.
The winter mean sea level pressure fell over the Indian/Atlantic half of the hemisphere from the 1950s to the 1960s, and rose over the other half. Generally, these trends reversed from the 1960s to the 1970s. The trends are equivalent barotropic.
The trends of temperatures are often regionally dependent. There was a significant warming over Antarctica from the 1960s to 1970s at all upper levels except for a small area on the Indian Ocean side.
Abstract
In the tropics of the Southern Hemisphere the zonal wind in the troposphere above the 500-mb level has a well defined half-yearly oscillation with westerly maxima (easterly minima) in May and November. It is demonstrated that the oscillation is associated with second harmonics of opposite phase in the temperature above the equator and in the subtropics. The temperature oscillations are tentatively explained as being the result of an intensification of vertical motions from autumn to winter. The half-yearly temperature oscillations reverse phase near the tropopause, and again near the 50-mb level. Above this level they are thus in the same phase as in the upper troposphere. The phase reversals imply that the second harmonic of the zonal component of the thermal wind likewise changes phase twice.
A marked longitudinal asymmetry is observed with the oscillations being considerably stronger in the Eastern than in the Western Hemisphere.
Abstract
In the tropics of the Southern Hemisphere the zonal wind in the troposphere above the 500-mb level has a well defined half-yearly oscillation with westerly maxima (easterly minima) in May and November. It is demonstrated that the oscillation is associated with second harmonics of opposite phase in the temperature above the equator and in the subtropics. The temperature oscillations are tentatively explained as being the result of an intensification of vertical motions from autumn to winter. The half-yearly temperature oscillations reverse phase near the tropopause, and again near the 50-mb level. Above this level they are thus in the same phase as in the upper troposphere. The phase reversals imply that the second harmonic of the zonal component of the thermal wind likewise changes phase twice.
A marked longitudinal asymmetry is observed with the oscillations being considerably stronger in the Eastern than in the Western Hemisphere.
