Interannual signals in length of day and atmospheric angular momentum

Atmospheric angular momentum (AAM) and length of day (LOD) series are investigated for their characteristics on interannual time scales during the half-century period 1949 to 1998. During this epoch, the interannual variability in LOD can be separated naturally into three bands: a quasi-biennial, a triennial-quadrennial and one at six-seven years. The atmosphere appears to excite the first two bands, while it does not contribute to the last. Considering the quasi-biennial (QB) band alone, the atmosphere appears to excite most of its signal in LOD, but it arises from separate fluctuations with stratospheric and tropospheric origin. Thus, although close in frequency, stratospheric and tropospheric processes differ in their amplitude and phase variability. The time shift can be noted especially during the strong El Niño events of 1982/83 and 1997/98 when both processes have positive phase and thus combine to help produce particularly strong peak in AAM and LOD. In addition, we have reconfirmed the downward propagation in the stratosphere and upward propagation in the troposphere of AAM observed in earlier studies for other variables. In the triennial-quadrennial (TQ) band, time-variable spectral analyses reveal that LOD and AAM contain strong variability, with periods shorter than four years before 1975 and longer thereafter. This signal originates mainly within the troposphere and propagates upwards from the lower to the higher layers of the troposphere. According to a zonal analysis, an equatorial poleward mode, strongly linked to the SOI, explains more than 60% of the total variability at these ranges. In addition, this study also indicates that an equatorward mode, originating within polar latitudes, explains, on average, more than 15% of the triennial-quadrennial oscillation (TQO) variability in AAM, and up to 30% at certain epochs. Finally, a six year period in LOD noted in earlier studies, as well as in lengthier series covering much of the century, is found to be absent in atmospheric excitations, and it is thus likely to arise from mantle/core interactions.     

Analyses of zonal atmospheric excitation functions and their correlation with polar motion excitation functions

The atmospheric influence on the Earths, rotation can be described by the effective atmospheric angular momentum (EAAM) functions. In this study we focus on the analysis of short period variations of the equatorial components of the zonal EAAM excitation functions ₁ and ₂ and their influence on similar variations of polar motion. The global objective analysis data of the Japanese Meteorological Agency for the period 1986–1992 were used to compute the EAAM excitation functions in different latitude belts. Time- and latitude-variable amplitude spectra of variations of these functions with periods shorter than 150 days, containing pressure, pressure with the inverted barometric correction, and wind terms were computed. The spectra show distinct latitude and time variations of the prograde and retrograde oscillations which reach their maxima mainly in mid-latitudes. Prograde and retrograde oscillations with periods of about 40–60 days and about 110–120 days are seen in the spectra of pressure terms of the equatorial components of the zonal EAAM excitation functions. Additionally, correlation coefficients and cross-spectra between variations of the geodetic polar motion and equatorial components of the zonal EAAM excitation functions were computed to identify the latitude belts of the globe over which atmospheric circulation changes are correlated mostly with short period variations of the polar motion excitation functions. The correlation coefficients vary in time and latitude and reach maximum values in the northern latitudes from 50°N to 60°N. In the cross-spectra between the polar motion excitation functions and pressure terms of the zonal EAAM excitation functions there are peaks of common prograde oscillations with the periods around 20, 30, 40–50, 60 and 80–150 days and of common retrograde oscillations around 20, 30, 40 and 50–70 days.Paper presented at the IERS Workshop in Paris, March 1994     

海洋和大气对Chandler摆动激发的贡献

用1985～1995年期间海洋角动量变化序列和大气角动量变化序列,分析它们对Chandler摆动的激发能量以及它们与天文观测激发的相干性. 结果表明，在Chandler摆动频带内，海洋角动量变化提供的激发能量大约占观测激发的64髎，其中洋底压力变化起主导作用；NCEP/NCAR(美国国家环境预测中心/国家大气研究中心)和JMA(日本气象厅)大气角动量变化提供的激发能量分别为观测激发的23髎和214髎. 海洋激发与观测激发的相干系数约为0.52，接近99髎置信度下限(0.54)，海洋激发的相位滞后观测激发约19°；NCEP/NCAR和JMA的大气激发与观测激发的相干系数分别为0.32和0.37，大气激发的相位超前观测激发分别约47°和19°. 用更短期间(9年、6年)的海洋和大气角动量序列与更长期间(16、39年)的大气角动量序列作分析表明，在Chandler摆动频带内，无论是它们的激发能量，还是它们与观测激发之间的相干系数都呈现很大的变化，而且这些变化具有某种程度的随机性.     

The Contrasting Features of Winter Circulation During Surplus and Deficient Precipitation Over Western Himalayas

Contrasting features associated with surplus and deficient precipitation years are studied to examine atmospheric circulation characteristics during the winter season viz., December, January February and March (DJFM) to assess the wintertime synoptic weather system affecting the western Himalayas. Large-scale balances of kinetic energy, vorticity, angular momentum, heat and moisture fields are analyzed. Winter circulations are studied over the domain 15°S–45°S and 30°E–120°E. This domain is considered particularly to illustrate the distribution of precipitation due to wintertime eastward moving synoptic weather systems called western disturbances. Surplus and deficient years of seasonal (DJFM) precipitation are identified using±20% departure from mean from uninitialized daily reanalysis data of fourty (1958–1997) years of the National Center for Environmental Prediction (NCEP), USA. The years 1965–1969, 1973 and 1991 are found to be surplus years and years 1962, 1963, 1971, 1977 and 1985 are found to be deficient years. Composites of these two categories are made. Comparative study is made using Students t-test of significance. Examining the aspects associated with energetics during the two extreme categories of winter seasonal precipitation years, higher heat flux convergence in excess years in the area of study of precipitation takes place. Diabatic heating shows cooling. Higher flux of convergence of kinetic energy and higher dissipation of kinetic energy are observed during surplus years.     

27.3-day and 13.6-day atmospheric tide

An analysis of time variations in the earth's length of day (LOD) for 25 years (1973-1998) versus at- mospheric circulation changes and lunar phase is presented. It is found that, on the average, there is a 27.3-day and 13.6-day period oscillation in global zonal wind speed, atmospheric geopotential height, and LOD following alternating changes in lunar phase. Every 5-9 days (6.8 days on average), the fields of global atmospheric zonal wind and geopotential height and LOD undergo a sudden change in rela- tion to a change in lunar declination. The observed atmospheric oscillation with this time period may be viewed as a type of atmospheric tide. Ten atmospheric tidal cases have been analyzed by comparing changes in LOD, global zonal wind speed and atmospheric geopotential height versus change in lunar declination. Taken together these cases reveal prominent 27.3-day and 13.6-day tides. The lunar forcing on the earth's atmosphere is great and obvious changes occur in global fields of zonal wind speed and atmospheric geopotential height over the equatorial and low latitude areas. The driving force for the 27.3-day and 13.6-day atmospheric tides is the periodic change in lunar forcing during the moon's revolution around the earth. When the moon is located on the celestial equator the lunar declination equals zero and the lunar tidal forcing on the atmosphere reaches its maximum, at this time the global zonal wind speed increases and the earth's rotation rate decreases and LOD increases. Conversely, when the moon reaches its most northern or southern positions the lunar declination is maximized, lunar tidal forcing decreases, global zonal wind speed decreases, earth's rotation rate increases and LOD decreases. 27.3-day and 13.6-day period atmospheric tides deserve deeper study. Lunar tidal forcing should be considered in models of atmospheric circulation and in short and medium range weather forecasting.     

Assessment of the Global and Regional Land Hydrosphere and Its Impact on the Balance of the Geophysical Excitation Function of Polar Motion

The impact of continental hydrological loading from land water, snow and ice on polar motion excitation, calculated as hydrological angular momentum (HAM), is difficult to estimate, and not as much is known about it as about atmospheric angular momentum (AAM) and oceanic angular momentum (OAM). In this paper, regional hydrological excitations to polar motion are investigated using monthly terrestrial water storage data derived from the Gravity Recovery and Climate Experiment (GRACE) mission and from the five models of land hydrology. The results show that the areas where the variance shows large variability are similar for the different models of land hydrology and for the GRACE data. Areas which have a small amplitude on the maps make an important contribution to the global hydrological excitation function of polar motion. The comparison of geodetic residuals and global hydrological excitation functions of polar motion shows that none of the hydrological excitation has enough energy to significantly improve the agreement between the observed geodetic excitation and geophysical ones.     

Low-latitude total ozone measurements in the Brazilian sector

Regular measurements of the atmospheric ozone in the Brazilian sector were started at Cachoeira Paulista (22.7°S, 45.0°W), and Natal (5.8°S, 35.2°W) in May 1974 and November 1978, respectively. The results of the total ozone measurements carried out at these two stations up to 1981 are presented in this communication and compared with other low-and mid-latitude stations. Although Natal is an equatorial station, it presents a prominent annual variation, and the average total ozone content is high compared to satellite measurements. During 1977–78, abnormally low values of total ozone were observed at Cachoeira Paulista. Some preliminary results about the QBO 9quasi-biennial oscillation) during 1974–81 are also presented.     

Short Period Variations In Earth Rotation As Seen By VLBI

An overview of the abilities of Very Long Baseline Interferometry (VLBI) to measure the variable Earth rotation and of the international VLBI collaboration is given. The paper concentrates on the short-period, i.e. subseasonal variations of Earth rotation which can be seen in VLBI measurements of length of day (lod) and polar motion between 1981 and 1999. The wavelet transform allows the time localisation of an irregular quasi-harmonic signal within a given data set. The wavelet analysis of lod series yields in the high-frequency range periods of 28 days, 14 days down to 6.86 days caused by the lunisolar tides and irregular quasi-periodic variations between 40 and 130 days. These are mainly associated with global zonal wind changes which can be seen when looking on the wavelet cross-scalogram between the lod series and the atmospheric angular momentum (AAM) time series. In polar motion variable periods between two and five months and even down to 7–10 days can be made visible by the wavelet scalograms.Today it is possible by VLBI to determine polar motion and UT1-UTC with a temporal resolution of as short as 3–7 minutes. The results of parallel VLBI sessions which took place since 1998 using two independent VLBI networks were analyzed in the subdiurnal period range and compared by computing the wavelet cross-scalograms, the covariance spectrum and the normed coherency. Periods between 5 and 7 hours can be seen in many of the UT1-UTC data sets besides the well-known diurnal and semi-diurnal periods. The wavelet analyses reveal interesting patterns in the subdiurnal range in polar motion, too.     

Climate Change in the Urals,Russia, Inferred from Borehole Temperature Data

Borehole temperatures in the central and south Urals were analysed for the past ground surface temperature (GST) signal. 31 highquality temperature logs were selected for this purpose and inverted with algorithms based on the generalised least squares theory. The signal to noise ratio was improved by averaging the results of individual borehole inversions. No distinct regional trends were found in the studied region except for some indications of more pronounced warming in the south. The mean GST history (GSTH) was characterised by cooling down to –0.6 °C in the 18th century and subsequent warming to 0.5 °C above the longterm mean at the beginning of this century, and to 1 – 1.5 °C by 1980. The stability of the mean GSTH was tested in dependence on the number of holes used for the averaging. It showed that any subset of 15 holes yielded a GSTH similar to that obtained from the whole set. A surface air temperature (SAT) time series comprising the period 1832 – 1989 was combined from 17 meteorological records. Its least squares warming rate of 1.1 °C per 100 years is somewhat higher than that of the GST (0.7 – 0.8°C/100 years) in the same period.     

Ice sheets and the CO2 problem

In this review, the carbon dioxide problem is discussed, with special reference to the possible effects of a global warming on the ice sheets of Greenland and Antarctica. Instead of detailed projections of future climate and the consequences, the basic mechanisms are explained and illustrated with results described in the literature.It is concluded that a doubling of the atmospheric CO₂ content (most likely to occur somewhere in the second half of the next century) will result in a globally-averaged warming of 2–4°C, and an intensification of the hydrological cycle. In the polar regions, this warming will be a few degrees larger and as a consequence the Greenland Ice Sheet will decrease in size. Antarctica, on the other hand, is expected to grow because of the increased snowfall. The instability of the West Antarctic Ice Sheet is also discussed and, although no conclusive prediction to its long-term response can be made, it is argued that on a short time scale (less than about 100 y) nothing dramatically wil happen to this part of Antarctica.     

Numerical modelling of the thermospheric and ionospheric effects of magnetospheric processes in the cusp region

The thermospheric and ionospheric effects of the precipitating electron flux and field-aligned-current variations in the cusp have been modelled by the use of a new version of the global numerical model of the Earths upper atmosphere developed for studies of polar phenomena. The responses of the electron concentration, ion, electron and neutral temperature, thermospheric wind velocity and electric-field potential to the variations of the precipitating 0.23-keV electron flux intensity and field-aligned current density in the cusp have been calculated by solving the corresponding continuity, momentum and heat balance equations. Features of the atmospheric gravity wave generation and propagation from the cusp region after the electron precipitation and field-aligned current-density increases have been found for the cases of the motionless and moving cusp region. The magnitudes of the disturbances are noticeably larger in the case of the moving region of the precipitation. The thermospheric disturbances are generated mainly by the thermospheric heating due to the soft electron precipitation and propagate to lower latitudes as large-scale atmospheric gravity waves with the mean horizontal velocity of about 690 ms^–1. They reveal appreciable magnitudes at significant distances from the cusp region. The meridional-wind-velocity disturbance at 65° geomagnetic latitude is of the same order (100 ms^–1) as the background wind due to the solar heating, but is oppositely directed. The ionospheric disturbances have appreciable magnitudes at the geomagnetic latitudes 70°–85°. The electron-concentration and -temperature disturbances are caused mainly by the ionization and heating processes due to the precipitation, whereas the ion-temperature disturbances are influence strongly by Joule heating of the ion gas due to the electric-field disturbances in the cusp. The latter strongly influence the zonal- and meridional-wind disturbances as well via the effects of ion drag in the cusp region. The results obtained are of interest because of the location of the     

Atmosphere and Earth's rotation

The theoretical aspects of the transfer of angular momentum between atmosphere and Earth are treated with particular emphasis on analytical solutions. This is made possible by the consequent usage of spherical harmonics of low degree and by the development of large-scale atmospheric dynamics in terms of orthogonal wave modes as solutions of Laplace's tidal equations.An outline of the theory of atmospheric ultralong planetary waves is given leading to analytical expressions for the meridional and height structure of such waves. The properties of the atmospheric boundary layer, where the exchange of atmospheric angular momentum with the solid Earth takes place, are briefly reviewed. The characteristic coupling time is the Ekman spin-down time of about one week.The axial component of the atmospheric angular momentum (AAM), consisting of a pressure loading component and a zonal wind component, can be described by only two spherical functions of latitude : the zonal harmonicP ₂ ⁰ (), responsible for pressure loading, and the spherical functionP ₁ ¹ () simulating supperrotation of the zonal wind. All other wind and pressure components merely redistributeAAM internally such that their contributions toAAM disappear if averaged over the globe. It is shown that both spherical harmonics belong to the meridional structure functions of the gravest symmetric Rossby-Haurwitz wave (0, –1)^*. This wave describes retrograde rotation of the atmosphere within the tropics (the tropical easterlies), while the gravest symmetric external wave mode (0, –2) is responsible for the westerlies at midlatitudes. Applying appropriate lower boundary conditions and assuming that secular angular momentum exchange between solid Earth and atmosphere disappears, the sum of both waves leads to an analytical solution of the zonal mean flow which roughly simulates the observed zonal wind structure as a function of latitude and height. This formalism is used as a basis for a quantitative discussion of the seasonal variations of theAAM within the troposphere and middle atmosphere.Atmospheric excitation of polar motion is due to pressure loading configurations, which contain the antisymmetric functionP ₂ ¹ () exp(i) of zonal wavenumberm=1, while the winds must have a superrotation component in a coordinate system with the polar axis within the equator. The Rossby-Haurwitz wave (1, –3)^* can simulate well the atmospheric excitation of the observed polar motion of all periods from the Chandler wobble down to normal modes with periods of about 10 days. Its superrotation component disappears so that only pressure loading contributes to polar motion.The solar gravitational semidiurnal tidal force acting on the thermally driven atmospheric solar semidiurnal tidal wave can accelerate the rotation rat of the Earth by about 0.2 ms per century. It is speculated that the viscous-like friction of the geomagnetic field at the boundary between magnetosphere and solar wind may be responsible for the westward drift of the dipole component of the internal geomagnetic field. Electromagnetic or mechanical coupling between outer core and mantle may then contribute to a decrease of the Earth's rotation rate.     

Simulated changes due to global warming in the variability of precipitation, and their interpretation using a gamma-distributed stochastic model

The interannual variability of monthly mean January and July precipitation and its possible change due to global warming are assessed using a five-member ensemble of climate for the period 1871–2100, simulated by the CSIRO Mark 2 global coupled atmosphere–ocean model. In the 1961–1990 climate, for much of the middle to high latitudes the standard deviation of precipitation for both months is roughly proportional to the mean, with the coefficient of variation (C) typically 0.3–0.5. The variability there is shown to be largely consistent with that from a first-order Markov chain model of the daily rainfall occurrence, with the distribution of wet-day amounts approximated by a gamma distribution. Global distributions of Mark 2-based parameters of this stochastic model, commonly used in weather generators, are presented. In low latitudes, however, the variability from the coupled model is typically double that anticipated by the stochastic model, as quantified by an ‘overdispersion ratio’. C often exceeds one at subtropical locations, where rain is less frequent, but sometimes relatively heavy.The standard deviation of monthly mean precipitation S generally increases as the global model warms, with the global mean S in 2071–2100 in January (July) being 9.0% (11.5%) larger than in 1961–1990. Decreases in some subtropical locations occur, particularly where mean precipitation decreases. The global pattern of overdispersion is largely unchanged, however, and the changes in S can be related to those in the stochastic model parameters. Much of the increase in S is associated with increases in the scale parameter of the gamma distribution of wet-day amounts. Changes in C, which is unaffected by this parameter, are generally small. Increases in C in several subtropical bands and over northern midlatitude land in July are related to a decreased frequency of precipitation, and (to a lesser degree) changes in the gamma shape parameter. Some potential applications of the results to downscaling are discussed, and illustrated using observed rainfall from southeast Australia.     

A preliminary dynamic view of the circulation of Jupiter's atmosphere

Summary The problem of the gross nature of the Jovian atmospheric circulation is examined from the viewpoint of the following previous findings of the writer and others. 1) The equatorial acceleration cannot be accounted for by axisymmetric motions. 2) The departures from symmetry in a rotating system having an equatorial acceleration must impart angular momentum selectively to those particles moving toward the jet maximum and abstract it from those moving away. 3) These selective (pressure) torques and associated sorting processes arise spontaneously in the presence of a vertical convection mode involving motions not independent of longitude, if the cell sizes and other conditions are right.Since there is evidence that Jovian dark spots have statistical maxima of occurrence along the tropical shear lines flanking the equator, these are assumed to be vertical convective systems forming, in effect,convective vortex sheets which generate the high angular momentum of the equatorial zone. Various additional concepts are discussed, and many comparisons with conditions in the sun and in the earth's atmosphere are made.     

Spectral characteristics of the meridional transport of angular momentum in the mid-troposhere of the Southern Hemisphere

Summary The wavenumber-frequency spectra of the meridional flux of angular momentum at 20°, 30°, 40°, 50°, 60° and 70°S, at 500 mb, show a definite domain of wave interactions between the zonal and meridional components of the velocity at various latitudes. In middle latitudes, the spectral band of the meridional flux of angular momentum is oriented from a region of low wavenumbers and low frequencies to a region of high wavenumbers and negative frequencies assigned for waves moving from west to east. In low latitudes, however, the spectral domain is confined to a narrow band centered near the zero frquency.In contrast to the meridional flux of angular momentum in the Northern Hemisphere in which the intensity in winter is about twice that in Summer, in the Southern Hemisphere the meridional flux shows same intensity for all seasons.In the Southern Hemisphere, most of the meridional flux of angular momentum is directed toward the south pole and is accomplished by the eastward moving waves. In the Northern Hemisphere, however, most of the meridional flux is directed toward the north pole and is contributed by the stationary waves.The National Center for Atmospheric Research, Boulder, Colorado 80302, (USA).     

On the excitation of short-term variations in the length of the day and polar motion

Variations in the distribution of mass within the atmosphere, and changes in the pattern of winds produce fluctuations in all three components of the angular momentum of the atmosphere on time-scales upwards of a few days. It, has been shown that variations in theaxial component of atmospheric angular momentum during the Special Observing Periods in the recent First GARP Global Experiment (FGGE, where GARP is the Global Atmospheric Research Programme) are well correlated with short-term changes in the length of the day. They are consistent with the total angular momentum of the atmosphere and solid Earth being conserved on short timescales (allowing for lunar and solar effects), without requiring significant angular momentum transfer between the Earth's liquid core and solid mantle on timescales of weeks or months. It has also been shown that fluctuations, in the equatorial components of atmospheric angular momentum make a major contribution to the observed wobble of the instantaneous pole of the Earth's rotation with respect to the Earth's crust. A necessary step in the investigation was a re-examination of the underlying theory of non-rigid body rotational dynamics and angular momentum exchange between the atmosphere and solid Earth. Since only viscous or topographic coupling between the atmosphere and solid Earth can transfer angular momentum, no atmospheric flow that everywhere satisfied inviscid equations (including, but not solely, geostrophic flow) could affect the rotation of a spherical solid Earth. New effective angular momentum functions were introduced in order to exploit the available data and allow for rotational and surface loading deformation of the Earth. A theoretical basis has now been established for future routine determinations of atmopheric, angular momentum fluctuations for the purpose of meteorological and geophysical research, including the assessment of the extent to which movements in the solid Earth associated with very large earthquakes contribute to the excitation of the Chandlerian wobble.     

Long-period planetary waves in the mesosphere and lower thermosphere above Davis, Antarctica

The accumulation of MF radar wind and hydroxyl temperature measurements at Davis from 1997 to 2005 has enabled the compilation of a climatology of long-period (period >1 day) wave activity. A time domain filtering technique that makes allowance for the differing sampling characteristics of the measurements is described and wave amplitudes are presented for 1.7–4, 4–8 and 8–16 day period bands. Product averages of the time series yield horizontal heat and momentum fluxes for the height of the hydroxyl layer (approximately 86 km). The climatology is then discussed in terms of current knowledge of planetary wave characteristics and forcing. Heat and momentum fluxes during the year of the southern hemisphere stratospheric warming (2002) are also presented.     

Application of general circulation models to the study of stratospheric ozone

Summary Observations of the ozone distribution indicate that modifications are required to the photochemical theory. These modifications involve ozone destruction by hydrogen and nitrogen products and ozone transport (both vertical and horizontal) due to atmospheric motions in the stratosphere. If the photochemical terms in the ozone continuity equation are omitted, changes due to atmospheric transport alone can be evaluated.Numerical computations were made of the three-dimensional wind structure as derived from the 12-layer (0–36 km) General Circulation Model developed by NCAR. The results showed that ozone is transported from the equatorial stratosphere poleward and downward in both hemispheres. The horizontal transport is primarily by the Hadley Cell in the tropics and by large-scale eddies in mid and high latitudes. The dominant mechanism for ozone transport are found to be similar to those derived for the horizontal heat and momentum transport found in other general circulation studies.     

Response of equatorial ionosphere to episodes of asymmetric ring current activity

We present the characteristics of the response of equatorial ionospheric zonal electric field and F-region plasma density to the asymmetric ring current intensifications that occurred in succession on 16 December 1991, corresponding to the STEP/EITS-2 campaign period. The study is based on high-time-resolution (1-min) data of asymmetic ring current indices, ASY(H/D) and F-region vertical plasma drift, Vz measurements at Kodaikanal (10.25°N; 77.5°E; dip 4°), India and quarter-hourly ionosonde data of For-taleza (4°S; 322°E; dip -9°), Brazil. It is shown that short-lived disturbances in F-layer vertical plasma drift, Vz and height (hF/hpF2) indicative of westward and eastward electric fields prevail simultaneously in the dusk (18–21 LT) and predawn (02–05 LT) sectors, respectively, in association with the decay phase of asymmetic ring current events. Electric fields of opposite polarity do also seem to manifest at these local times, particularly in the early-morning sector in conjunction with the intensification of the asymmetric ring current. At a given location, electric field disturbances associated with individual asymmetric ring current events are thus bipolar in nature, with fields of opposite polarity during the growth and decay phases. The nature and polarity structure of the observed electric field disturbances are in agreement with the theoretical/model predictions of prompt penetration of high-latitude electric fields to the equatorial region.On sabbatical leave from Indian Institute of Astrophysics, Bangalore, India     

Upper atmosphere tidal oscillations due to latent heat release in the tropical troposphere

Latent heat release associated with tropical deep convective activity is investigated as a source for migrating (sun-synchronous) diurnal and semidiurnal tidal oscillations in the 80–150-km height region. Satellite-based cloud brightness temperature measurements made between 1988 and 1994 and averaged into 3–h bins are used to determine the annual- and longitude-average local-time distribution of rainfall rate, and hence latent heating, between ±40° latitude. Regional average rainfall rates are shown to be in good agreement with climatological values derived from surface rain gauge data. A global linearized wave model is used to estimate the corresponding atmospheric perturbations in the mesosphere/lower thermosphere (80–150 km) resulting from upward-propagating tidal components excited by the latent heating. The annual-average migrating diurnal and semidiurnal components achieve velocity and temperature amplitudes of order 10–20 m s^–1 and 5–10 K, respectively, which represent substantial contributions to the dynamics of the region. The latent heat forcing also shifts the phase (local solar time of maximum) of the semidiurnal surface pressure oscillation from 0912 to 0936 h, much closer to the observed value of 0944 h.