Longitude

About: Longitude is a research topic. Over the lifetime, 2260 publications have been published within this topic receiving 54988 citations. The topic is also known as: angle of longitude.

Causes of change in Northern Hemisphere winter meridional winds and regional hydroclimate

Abstract: Improved mechanistic understanding of greenhouse gas-induced change in Northern Hemisphere atmospheric circulation reveals a tendency of models to overestimate future mid-winter rainfall along the North American west coast. A critical aspect of human-induced climate change is how it will affect precipitation around the world. Broadly speaking, warming increases atmospheric moisture holding capacity, intensifies moisture transports and makes sub-tropical dry regions drier and tropical and mid-to-high-latitude wet regions wetter1,2. Extra-tropical precipitation patterns vary strongly with longitude, however, owing to the control exerted by the storm tracks and quasi-stationary highs and lows or stationary waves. Regional precipitation change will, therefore, also depend on how these aspects of the circulation respond. Current climate models robustly predict a change in the Northern Hemisphere (NH) winter stationary wave field that brings wetting southerlies to the west coast of North America, and drying northerlies to interior southwest North America and the eastern Mediterranean3,4,5. Here we show that this change in the meridional wind field is caused by strengthened zonal mean westerlies in the sub-tropical upper troposphere, which alters the character of intermediate-scale stationary waves. Thus, a robust and easily understood model response to global warming is the prime cause of these regional wind changes. However, the majority of models probably overestimate the magnitude of this response because of biases in their climatological representation of the relevant waves, suggesting that winter season wetting of the North American west coast will be notably less than projected by the multi-model mean.

Annual, quasi-biennial, and El Niño-Southern Oscillation (ENSO)time-scale variations in equatorial total ozone

Abstract: Equatorial total ozone variations with time scales of annual, quasi-biennial, and about 4-year periodicities are described by paying attention to their longitudinal structure. Analyses are made for 11 years from 1979 to 1989, using the global total ozone data derived from the total ozone mapping spectrometer on board the Nimbus 7 satellite. Over the equator an annual cycle in total ozone is conspicuous. Zonal mean values are maximum around September and minimum around January. The longitudinal structure shows a zonal wavenumber 1 pattern with minimum values around 140°E to the date line all year-round, indicating a close relationship to a region where the convective cloud activity is vigorous. By removing the climatological annual cycle from the original data, there appears the quasi-biennial oscillation in total ozone. This variation is characterized by zonally uniform phase changes and is strongly coupled with the quasi-biennial oscillation of the equatorial zonal wind in the lower stratosphere. Moreover, subtracting zonal mean values from the anomaly data mentioned above, we see an east-west seesaw variation with a nodal longitude around the date line. This east-west variation, having a characteristic time scale of about 4 years, is clearly related to the El Nino and the Southern Oscillation cycle. During El Nino events the longitudinal anomaly field in total ozone is positive in the western Pacific and negative in the eastern Pacific; the anomaly pattern is reversed during anti-El Nino events. Because the active region of convective clouds is located relatively in the eastern Pacific sector during El Nino events, it is suggested that the stronger upwelling and the higher tropopause associated with the convective cloud activity bring about less total ozone.

Seasonal estimates of global atmospheric sea‐salt distributions

Abstract: Seasonal estimates of sea-salt aerosol particle concentration distributions 15 m above the sea are presented on global contour maps. Measured data from a variety of sources relating atmospheric sea-salt concentration to wind speed have been combined, yielding relationships of form C = exp (as + b), where C is sea-salt concentration in micrograms per cubic meter and s is the horizontal wind speed in meters per second. These relationships, coupled with a Gaussian wind speed frequency distribution, allow us to calculate the atmospheric sea-salt concentration accounting for the variance about mean wind speeds. We use monthly wind mean speed and variance information in 5° × 5° latitude/longitude squares over the world ocean to estimate the global sea-salt aerosol particle mass distribution. The atmospheric sea-salt concentrations in the northern hemisphere marine troposphere display a substantial seasonal dependence. The 3-month seasonal average sea-salt concentrations in this region differ by a factor of 2–3 between the boreal winter and summer, and the highest values are between 40 and 49 μg m−3. The seasonal variability of atmospheric sea-salt concentrations in the high-latitude southern hemisphere is much less than that in the northern hemisphere, varying by less than a factor of 2 between the austral winter and summer, and again the highest values are about 45 μg m−3. The equatorial areas have uniformly lower atmospheric sea-salt concentrations than the high-latitude regions. The monsoonal winds over the Indian Ocean produce sea-salt concentrations in excess of 40 μg m−3 for the 3-month boreal summer average.

Ocean circulation variations associated with the Antarctic Circumpolar Wave

Abstract: Altimeter data analysis indicates persistent sea surface height (SSH) anomalies propagating eastward about the Antarctic continent. The spatial and temporal characteristics match variations in the atmosphere and sea surface temperature (SST) that are associated with the Antarctic Circumpolar Wave (ACW). During the observation time period, the SSH appears quasiperiodic with a dominant 4 year period and 180° longitude wavelength. Thus, the SSH signature of the ACW appears as two anomalies on opposite sides of the Antarctic continent propagating eastward at 10 cm/s. The SSH response to observed wind forcing agrees in terms of amplitude and phase with simple quasigeostrophic dynamics.