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- Author or Editor: Tomohiko Tomita x
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Abstract
Using the National Centers for Environmental Predictions (NCEP)–National Center for Atmospheric Research (NCAR) reanalysis, distributions of the heat source Q 1 and moisture sink Q 2 between 50°N and 50°S are determined for a 15-yr period from 1980 to 1994. Heating mechanisms operating in various parts of the world are examined by comparing the horizontal distributions of the vertically integrated heat source 〈Q 1〉 with those of the vertically integrated moisture sink 〈Q 2〉 and outgoing longwave radiation (OLR) flux and by comparing the vertical distributions of Q 1 with those of Q 2.
In northern winter, the major heat sources are located (i) in a broad zone connecting the tropical Indian Ocean, Indonesia, and the South Pacific convergence zone (SPCZ); (ii) over the Congo and Amazon Basins; and (iii) off the east coasts of Asia and North America. In northern summer, the major heat sources are over (i) the Bay of Bengal coast, (ii) the western tropical Pacific, and (iii) Central America. Throughout the year, the South Indian Ocean, eastern parts of the North and South Pacific Oceans, and eastern parts of the North and South Atlantic Oceans remain to be heat sinks. The desert regions such as the Sahara are characterized by large sensible heating near the surface and intense radiative cooling aloft. Over the tropical oceans, heat released by condensation with deep cumulus convection provides the major heat source. The radiative cooling and moistening due to evaporation are dominant features over the subtropical oceans where subsidence prevails. Over the Tibetan Plateau, the profiles of Q 1 and Q 2 show the importance of sensible heating in spring and contributions from the release of latent heat of condensation in summer. Off the east coast of Japan, intense sensible and latent heat fluxes heat and moisten the lower troposphere during winter.
Heat sources in various regions exhibit strong interannual variability. A long (4–5 yr) periodicity corresponding to the variations in OLR and sea surface temperature (SST) is dominant in the equatorial eastern and central Pacific Ocean, while a shorter-period oscillation is superimposed upon the long-period variation over the equatorial Indian Ocean. The interannual variations of 〈Q 1〉, OLR, and SST are strongly coupled in the eastern and central equatorial Pacific. However, the coupling between the interannual variations of 〈Q 1〉 and OLR with those of SST is weak in the equatorial western Pacific and Indian Ocean, suggesting that factors other than the local SST are also at work in controlling the variations of atmospheric convection in these regions.
Abstract
Using the National Centers for Environmental Predictions (NCEP)–National Center for Atmospheric Research (NCAR) reanalysis, distributions of the heat source Q 1 and moisture sink Q 2 between 50°N and 50°S are determined for a 15-yr period from 1980 to 1994. Heating mechanisms operating in various parts of the world are examined by comparing the horizontal distributions of the vertically integrated heat source 〈Q 1〉 with those of the vertically integrated moisture sink 〈Q 2〉 and outgoing longwave radiation (OLR) flux and by comparing the vertical distributions of Q 1 with those of Q 2.
In northern winter, the major heat sources are located (i) in a broad zone connecting the tropical Indian Ocean, Indonesia, and the South Pacific convergence zone (SPCZ); (ii) over the Congo and Amazon Basins; and (iii) off the east coasts of Asia and North America. In northern summer, the major heat sources are over (i) the Bay of Bengal coast, (ii) the western tropical Pacific, and (iii) Central America. Throughout the year, the South Indian Ocean, eastern parts of the North and South Pacific Oceans, and eastern parts of the North and South Atlantic Oceans remain to be heat sinks. The desert regions such as the Sahara are characterized by large sensible heating near the surface and intense radiative cooling aloft. Over the tropical oceans, heat released by condensation with deep cumulus convection provides the major heat source. The radiative cooling and moistening due to evaporation are dominant features over the subtropical oceans where subsidence prevails. Over the Tibetan Plateau, the profiles of Q 1 and Q 2 show the importance of sensible heating in spring and contributions from the release of latent heat of condensation in summer. Off the east coast of Japan, intense sensible and latent heat fluxes heat and moisten the lower troposphere during winter.
Heat sources in various regions exhibit strong interannual variability. A long (4–5 yr) periodicity corresponding to the variations in OLR and sea surface temperature (SST) is dominant in the equatorial eastern and central Pacific Ocean, while a shorter-period oscillation is superimposed upon the long-period variation over the equatorial Indian Ocean. The interannual variations of 〈Q 1〉, OLR, and SST are strongly coupled in the eastern and central equatorial Pacific. However, the coupling between the interannual variations of 〈Q 1〉 and OLR with those of SST is weak in the equatorial western Pacific and Indian Ocean, suggesting that factors other than the local SST are also at work in controlling the variations of atmospheric convection in these regions.
Abstract
In the North Pacific, the wintertime sea surface temperature anomaly (SSTA), which is represented by March (SSTAMar), when the upper-ocean mixed layer depth (h Mar) reaches its maximum, is formed by the anomalous surface forcing from fall to winter (S′). As a parameter of volume, h Mar has a potential to modify the impact of S′ on SSTAMar. Introducing an upper-ocean heat budget equation, the present study identifies the physical relationship among the spatial distributions of h Mar, S′, and SSTAMar.
The long-term mean of h Mar adjusts the spatial distribution of SSTAMar. Without the adjustment, the impact of S′ on SSTAMar is overestimated where the h Mar mean is deep. Since h Mar is partially due to seawater temperature, it leads to nonlinearity between the S′ and the SSTAMar. When the SSTAMar is negative (positive), the sensitivity to S′ is impervious (responsive) with the deepening (shoaling) of the h Mar compared to the linear sensitivity. The thermal impacts from the ocean to the atmosphere might be underestimated under the assumption of the linear relationship.
Abstract
In the North Pacific, the wintertime sea surface temperature anomaly (SSTA), which is represented by March (SSTAMar), when the upper-ocean mixed layer depth (h Mar) reaches its maximum, is formed by the anomalous surface forcing from fall to winter (S′). As a parameter of volume, h Mar has a potential to modify the impact of S′ on SSTAMar. Introducing an upper-ocean heat budget equation, the present study identifies the physical relationship among the spatial distributions of h Mar, S′, and SSTAMar.
The long-term mean of h Mar adjusts the spatial distribution of SSTAMar. Without the adjustment, the impact of S′ on SSTAMar is overestimated where the h Mar mean is deep. Since h Mar is partially due to seawater temperature, it leads to nonlinearity between the S′ and the SSTAMar. When the SSTAMar is negative (positive), the sensitivity to S′ is impervious (responsive) with the deepening (shoaling) of the h Mar compared to the linear sensitivity. The thermal impacts from the ocean to the atmosphere might be underestimated under the assumption of the linear relationship.
Abstract
Early summer climate in the western North Pacific is largely represented by the baiu phenomenon. The meridional fluctuations of the baiu front on interannual time scales and the associated large-scale circulations are examined using the empirical orthogonal function (EOF) analysis and composite or correlation analyses based on the EOF time coefficients.
The first EOF mode indicates a 5- or 6-yr low-frequency fluctuation (LF mode) appearing south of 35°N. The development is concurrent with horseshoe sea surface temperature anomalies (SSTAs) in the entire tropical Pacific that are associated with the El Niño–Southern Oscillation (ENSO). SSTAs in the western North Pacific control the anomalous southward expansion of the baiu front through a modification of the convection at around 20°–35°N. The LF mode is negatively correlated with the south-southeast Asian summer monsoon.
The second EOF mode is characterized by a meridional seesawlike fluctuation with a node at around 28°N and a time scale of biennial oscillation (BO mode). The horseshoe SSTAs again control the anomalous meridional circulations, but with a different spatial phase through a convection off the Philippines. The spatial phase difference between the two horseshoe patterns is about 90° in both the zonal and meridional directions. The BO mode is negatively correlated with the tropical western North Pacific monsoon.
SSTAs associated with the BO mode tend to be confined to the tropical western Pacific, while the signals of the LF mode extend rather broadly in the tropical Pacific–Indian Ocean sector, suggesting that the tropical BO is an aborted ENSO in the tropical central–western Pacific. The spatial phase of horseshoe SSTAs adjusts the interannual variability of the meridional fluctuation of the baiu front in the western North Pacific.
Abstract
Early summer climate in the western North Pacific is largely represented by the baiu phenomenon. The meridional fluctuations of the baiu front on interannual time scales and the associated large-scale circulations are examined using the empirical orthogonal function (EOF) analysis and composite or correlation analyses based on the EOF time coefficients.
The first EOF mode indicates a 5- or 6-yr low-frequency fluctuation (LF mode) appearing south of 35°N. The development is concurrent with horseshoe sea surface temperature anomalies (SSTAs) in the entire tropical Pacific that are associated with the El Niño–Southern Oscillation (ENSO). SSTAs in the western North Pacific control the anomalous southward expansion of the baiu front through a modification of the convection at around 20°–35°N. The LF mode is negatively correlated with the south-southeast Asian summer monsoon.
The second EOF mode is characterized by a meridional seesawlike fluctuation with a node at around 28°N and a time scale of biennial oscillation (BO mode). The horseshoe SSTAs again control the anomalous meridional circulations, but with a different spatial phase through a convection off the Philippines. The spatial phase difference between the two horseshoe patterns is about 90° in both the zonal and meridional directions. The BO mode is negatively correlated with the tropical western North Pacific monsoon.
SSTAs associated with the BO mode tend to be confined to the tropical western Pacific, while the signals of the LF mode extend rather broadly in the tropical Pacific–Indian Ocean sector, suggesting that the tropical BO is an aborted ENSO in the tropical central–western Pacific. The spatial phase of horseshoe SSTAs adjusts the interannual variability of the meridional fluctuation of the baiu front in the western North Pacific.
Abstract
Gradual cooling in the evening forms a wintertime nocturnal urban heat island. This work, with a mesoscale model involving urban canopy physics, is an examination of how four thermal and geometric controls—anthropogenic heat QF , heat capacity C, thermal conductivity k, and sky-view factor ψs —modify the rate of surface air temperature changes ΔT/Δt. In particular, the time dependence is diagnosed through numerical experiments. The controls QF and k are major agents in the evening, when QF changes the evening ΔT/Δt linearly and k is logarithmic. The effects of C and ψs are large in the morning and in the afternoon with those of k. The impact of QF is, however, substantial only in the evening. Because the time dependence of C and k is different, the thermal inertia used as a parameter in the urban climate studies should be divided into two parameters: C and k. To improve the thermal environment in urban areas, the modification of QF and k could be effective.
Abstract
Gradual cooling in the evening forms a wintertime nocturnal urban heat island. This work, with a mesoscale model involving urban canopy physics, is an examination of how four thermal and geometric controls—anthropogenic heat QF , heat capacity C, thermal conductivity k, and sky-view factor ψs —modify the rate of surface air temperature changes ΔT/Δt. In particular, the time dependence is diagnosed through numerical experiments. The controls QF and k are major agents in the evening, when QF changes the evening ΔT/Δt linearly and k is logarithmic. The effects of C and ψs are large in the morning and in the afternoon with those of k. The impact of QF is, however, substantial only in the evening. Because the time dependence of C and k is different, the thermal inertia used as a parameter in the urban climate studies should be divided into two parameters: C and k. To improve the thermal environment in urban areas, the modification of QF and k could be effective.
