Journal of the Meteorological Society of Japan. Ser. II
Online ISSN : 2186-9057
Print ISSN : 0026-1165
ISSN-L : 0026-1165
Volume 82 , Issue 1
Showing 1-15 articles out of 15 articles from the selected issue
Articles
  • Xiaogu ZHENG, Masato SUGI, Carsten S FREDERIKSEN
    2004 Volume 82 Issue 1 Pages 1-18
    Published: 2004
    Released: April 15, 2004
    JOURNALS FREE ACCESS
    An analysis of variance approach, for systematically studying and evaluating the interannual variability and predictability of seasonal mean fields, is demonstrated using an ensemble of six 50-year simulations of the 500 hPa geopotential height field from the Meteorological Research Institute-Japan Meteorological Agency (MRI-JMA) global atmosphere model forced by observed sea surface temperatures (SSTs). The model performance is analysed, for the seasons June-July-August (JJA) and December-January-February (DJF), and compared with NCEP reanalysis.
    The magnitude and geographical distribution of the unpredictable weather noise variability (interannual variability of seasonal mean series arising from intraseasonal variability) are simulated well by the model. The spatial distribution of the potentially predictable variability (the interannual variability of seasonal means from which sampling error due to weather noise variability is removed) is simulated fairly well for DJF, but relatively poorly for JJA.
    Despite this, however, several extratropical wintertime patterns, identified as the EOFs of the seasonal mean fields, are well simulated by the model. These include the two patterns forced by the El Niño-Southern Oscillation (ENSO): the Tropical Northern Hemisphere (for DJF), and the Tropical Southern Hemisphere (for JJA) patterns. In addition, the three patterns forced by the tropical Indian Ocean: Western Pacific (for DJF), Meridional Wavetrain (for JJA), and Southern Indian Ocean (for JJA) patterns, are also well simulated.
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  • Qoosaku MOTEKI, Hiroshi UYEDA, Takeshi MAESAKA, Taro SHINODA, Masanori ...
    2004 Volume 82 Issue 1 Pages 19-44
    Published: 2004
    Released: April 15, 2004
    JOURNALS FREE ACCESS
    This paper is the first in a two-part series in which the multiscale structures and development of oceanic precipitation systems observed in the Baiu frontal region during a field experiment of X-BAIU-99 are investigated. The meso-β-scale structure, and development of two merged rainbands on 27 June 1999, were observed by dual Doppler radars over the eastern part of the East China Sea. A southern rainband called LINE1 formed in a southwesterly wind field associated with a weak convergence line in a layer of 1-2 km. A northern rainband called LINE2 formed along the Baiu front ahead of cold northwesterly winds. LINE2 moved southeastward and merged into the quasi-stationary LINE1. As the merging occurred, LINE1 developed rapidly resulting from an intensification of low-level convergence associated with the cold northwesterly winds in LINE2. The two merged rainbands were reproduced well by a 5 km-resolution non-hydrostatic model, and the thermodynamic and moisture structures of the circumstances of the rainbands before the merging were analyzed in detail. The weak convergence line of LINE1 in the southwesterly wind field had a large water vapor gradient in a layer of 0.5-1.5 km. This line with the large water vapor gradient distinct from the Baiu front is named a “water vapor front” in this study. The present meso-β-scale analyses showed that two distinct fronts without any land effects existed in the Baiu frontal region: the “water vapor front” (LINE1) and the Baiu front (LINE2). The rapid intensification of the rainfall in LINE1 was induced by a combination of a strong convergence in the Baiu front, and a large water vapor supply from the south in the “water vapor front.”
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  • Qoosaku MOTEKI, Hiroshi UYEDA, Takeshi MAESAKA, Taro SHINODA, Masanori ...
    2004 Volume 82 Issue 1 Pages 45-65
    Published: 2004
    Released: April 15, 2004
    JOURNALS FREE ACCESS
    In this paper, the synoptic- and meso-α scales structure of two oceanic rainbands, and build-up processes of the frontal convergence, are investigated with the use of a regional spectral model (RSM) and a nonhydrostatic model (NHM). Over the eastern part of the East China Sea on 27 June 1999 during the X-BAIU-99, we observed that a northern rainband (LINE2) merged into a southern rainband (LINE1), and LINE1 developed rapidly. Before their merging, LINE1 and LINE2 developed along the “water vapor front” and the Baiu front, respectively. The “water vapor front,” found by the meso-β-scale analyses of Part I of this series, is a weak convergence line with a large moisture gradient in a southerly wind field. In the RSM-simulated field, the “water vapor front” extended from the eastern coast of China with a length of about 1000 km. The NHM simulation revealed that the “water vapor front” is a convergence line with oceanic southwesterly and continental westerly flows. The convergence line formed a meso-α-scale rainband (LINE1) in the southerly wind field over the ocean without any land effects. Because an abundant moisture supply with the oceanic airflow was blocked at the “water vapor front” by the continental airflow, the rainfall intensity was quite weak along the western part of the Baiu front. The lowlevel convergence of the eastern part of the “water vapor front” was quite weak, the oceanic air had partially advected into the eastern part of the Baiu front, and LINE2 developed strongly. In a synoptic-scale cold air mass to the north of the Baiu front, a meso-α-scale cold pool formed in a stratiform precipitation region. The cold pool expanded to the south, and pushed rapidly southward the Baiu front, about 50 km in 2 hours. It was confirmed that the cold pool was created by an evaporation cooling of raindrops from a sensitivity experiment. The experiment revealed that the cold pool continuously accelerated northerly winds, and intensified the low-level convergence along the Baiu front. In the areas of the southern side of the Baiu front, and the “water vapor front,” southerly winds were greatly accelerated over 5 m s-1 in 4 hours by the pressure gradient force enhanced near the convective rainfalls of LINE1 and LINE2. The frontal convergence along both fronts were greatly enhanced by the acceleration of the southerly winds.
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  • Hiroyuki KUSAKA, Fujio KIMURA
    2004 Volume 82 Issue 1 Pages 67-80
    Published: 2004
    Released: April 15, 2004
    JOURNALS FREE ACCESS
    We incorporated a single-layer urban canopy model into a simple two-dimensional atmospheric model in order to describe the fundamental impact of the urban canopy model on an idealized urban heat island simulation. We found that the heat island circulation developed less strongly than when using the atmospheric model with the standard slab urban model. Additionally, the coupling with urban canopy model (i) delays the phase of surface air temperature, (ii) reduces the diurnal range of the temperature, and (iii) produces a nocturnal heat island, which results from the difference in atmospheric stability between city and its surroundings. The features from the atmospheric model coupled with the canopy model agree well with those from observation, although the atmospheric model with the slab model does not. The simulated nocturnal heat island is caused by the larger heat storage of the canopy model which releases sensible heat after sunset.
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  • Shuichiro KATAGIRI, Teruyuki NAKAJIMA
    2004 Volume 82 Issue 1 Pages 81-99
    Published: 2004
    Released: April 15, 2004
    JOURNALS FREE ACCESS
    An algorithm is developed to retrieve the effective particle radius, cloud optical thickness, and cloud top temperature of cirrus clouds on a global scale using two infrared window channels and a nearinfrared channel of the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) on board NOAA-9 and NOAA-11. In the algorithm, overlapped cloud cases are taken into account. Data from the satellites are reconstructed to segmented data that contain a hundred satellite pixels in each 0.5° × 0.5° latitude and longitude grid. The algorithm is applied to fourmonth segmented AVHRR Global Area Coverage data from 1986 through 1994. The resulted cloud parameters are compared with airborne measurements and the products of International Satellite Cloud Climatology Project (ISCCP). These comparisons show that the effective radius obtained by this algorithm is smaller than that by airborne measurements, and that the cirrus cloud top temperature is about 5∼20 K lower than that of ISCCP. The global distribution, and the time series of these parameters, are shown and discussed.
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  • Hideo SHIOGAMA, Toru TERAO, Hideji KIDA
    2004 Volume 82 Issue 1 Pages 101-113
    Published: 2004
    Released: April 15, 2004
    JOURNALS FREE ACCESS
    The role of high-frequency eddy forcing in the Southern Hemisphere Annular Mode (SAM) is diagnosed with the use of the 21-yr (1979-1999) NCEP/NCAR daily reanalysis dataset. The SAM is described as a meridional vacillation of the polar jet. The present study focuses on a zonally localized sector, 30°W-20°E, where both the polar jet and high-frequency eddies are dominant.
    In the maintenance of the extreme phases of the SAM, two positive feedback processes play important roles. The storm tracks move with the polar jet between the extreme positions of the polar jet. The displacement of the storm tracks sustains their anomalous positions. Together with this process, the alternation of the horizontal eddy structure also plays a role in the maintenance of the extreme phases. The southeast-northwest tilt of eddy is emphasized when the polar jet resides at higher latitudes, as has been mentioned in earlier studies. The southeast-northwest oriented eddies transport momentum to higher latitudes, keeping the jet in the higher latitudes.
    To both the poleward and equatorward jet transitions, momentum flux anomalies due to highfrequency eddies contribute. Characteristics of the eddies associated with these momentum flux anomalies are examined. For the poleward transitional phase, flux anomalies are induced by both increased eddy kinetic energy and an emphasized southeast-northwest tilt of the eddy. For the equatorward transitional phase, changes in the horizontal eddy structure are found to be more important.
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  • Jae-Gwang WON, Soon-Chang YOON, Sang-Woo KIM, Ann JEFFERSON, Ellsworth ...
    2004 Volume 82 Issue 1 Pages 115-130
    Published: 2004
    Released: April 15, 2004
    JOURNALS FREE ACCESS
    In this study the aerosol direct radiative forcing (ADRF) of Asian dust is evaluated by model simulation at Gosan, Jeju using the data from a sun/sky radiometer, a Micro-Pulse Lidar (MPL), and column radiometer measurements of solar downwelling irradiance in April, 2001. We suggest a method of determining aerosol parameters for the radiative transfer model from the Aerosol Robotic Network (AERONET) data set. Since the AERONET measurements provide the refractive indices at only four wavelengths, and the aerosol parameters can be calculated at these wavelengths with a Mie code, we use a linear regression method for extending these measurements to the full wavelength spectrum of the radiative transfer model.
    The aerosol forcing by the Asian dust aerosols is estimated and compared to the aerosol forcing of non-dust aerosols. On the Asian dust event day, April 13, the daily average ADRF was estimated as -58.1 W/m² at the surface and -25.7 W/m² at the top of the atmosphere (TOA). On April 15, a nondust day slightly influenced by anthropogenic aerosols, the ADRF was -29.0 W/m² at the surface and -11.6 W/m² at the TOA. Although the Asian dust aerosols show larger forcing, its forcing efficiency (forcing per unit optical thickness) is smaller than that of non-dust aerosols; ²41.0 W/m²/τ670 at the TOA and -94.9 W/m²/τ670 at the surface on the dust day for dust aerosols, as opposed to -50.0 W/m²/τ670 at the TOA and -129.3 W/m²/τ670 at the surface on the non-dust day for non-dust aerosols. We believe that this is due to the larger single scattering albedo of dust aerosols, which causes smaller absorption, and the larger asymmetry factor which causes more forward scattering or less reflection, compared to anthropogenic aerosols.
    The model results were validated with the surface irradiance measurement data and the comparison showed a good agreement. The radiative transfer calculation underestimates the solar irradiance of 2∼3% on average. The aerosol profiles measured by lidar are used to estimate the influence of the vertical distribution of Asian dust aerosols on the ADRF. Using the vertical aerosol profiles, we found an instantaneous short wave radiative heating larger than 2 K/day. We believe the enhanced heating rate by the aerosol layers contributes to the increase in static stability within the dust layer. This fact is verified by the temperature profile measured by the sonde, and may explain the longevity and consequently long-range transport of Asian dust.
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  • Kun YANG, Toshio KOIKE, Hirohiko ISHIKAWA, Yaoming MA
    2004 Volume 82 Issue 1 Pages 131-153
    Published: 2004
    Released: April 15, 2004
    JOURNALS FREE ACCESS
    In the GAME/Tibet project, the Anduo site is a typical plateau prairie area that is covered by short and sparse vegetation. From May to September 1998, we measured all the surface energy fluxes at this site to quantitatively describe the surface energy budget, but it was still questionable because of low energy closure ratios in most days of the rainy season. To clarify the surface energy budget at this site, this study proposes a single-source energy partition model, to simplify the processes of heat and water vapor transfer from the surface. The model does not distinguish the contribution of turbulent fluxes from the vegetation, and the one from the ground, and thus has fewer parameters to be calibrated comparing to a dual-source model. The main model parameters are: the soil surface evaporation resistance, the parameter kB-1 (the logarithm of the ratio of the aerodynamic roughness length to the thermal roughness length), and the surface emissivity. Their values are calibrated by minimizing the discrepancy between measured and model-predicted values of soil temperatures.
    This tuned single-source model is then validated by the agreement between the measured and simulated net radiation flux, surface soil heat flux, sensible heat flux, and latent heat flux on the days with high energy closure ratios. This model also reproduces these measured fluxes, except latent heat flux on the days with low closure ratios. The simulated latent heat flux is much higher than the measured one. We further show that the measured latent heat flux is untrustable due to an instrumental limitation, while the model provides a reasonable surrogate. Therefore, the single-source concept is applicable to the heat and water vapor transfer on the Tibetan plateau sparse-vegetation surface, and would contribute to a further research on the land-atmosphere interactions over the plateau.
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  • Riyu LU
    2004 Volume 82 Issue 1 Pages 155-165
    Published: 2004
    Released: April 15, 2004
    JOURNALS FREE ACCESS
    The East Asian summer monsoon is characterized by strong interactions among its components in the meridional direction. The atmospheric convection over the Philippine Sea (PSAC), the western North Pacific subtropical high (WNPSH) and the East Asian westerly jet stream (EAJ) are all closely related to the summer rainfall in East Asia. In this study, we examined the relationship on the interannual timescale among these factors, by using the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Re-analysis data and satellite-observed outgoing long-wave radiation (OLR) data for the 20-year period from 1979 to 1998.
    It is found that the PSAC-EAJ relation is weak in June, but strong in July and August. Similar difference exists in the relationship between the PSAC and convective activity along the East Asian summer rainy belt. Corresponding to enhanced PSAC, the EAJ is weakened in July and strengthened in August, and tends to exhibit a slight poleward displacement in both months. All these variations in the EAJ intensity and meridional displacement, on the other hand, correspond to suppressed convection along the East Asian summer rainy belt. Finally, the monthly difference in the PSAC-EAJ relation is interpreted by the role of vertical shear of zonal wind. The easterly shear in July and August over the Philippine Sea excites external modes, which are necessary for the tropical-extratropical teleconnection mechanism according to previous numerical studies, but the neutral shear in June is inefficient in exciting external modes.
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  • Daisuke NOHARA, H.L TANAKA
    2004 Volume 82 Issue 1 Pages 167-178
    Published: 2004
    Released: April 15, 2004
    JOURNALS FREE ACCESS
    In this study a new type of ensemble forecast assimilation technique is developed in order to improve the forecast skill in the nonlinear dynamical system. The forecast assimilation is an analysis technique in which a true value contained in each ensemble forecast is accumulated into a single assimilated forecast such as a data assimilation. For the experiments, we used a Lorenz model, and a Kalman filter is applied for the forecast assimilation.
    The experiments are started by calculating 101 members of the ensemble forecast in which the initial error with Gaussian distribution is superimposed around the truth, and one of the members is arbitrarily selected as a control forecast. The experiments of the forecast assimilation are repeated 5000 times for different sectors of the solution trajectory to obtain the statistical significance of the results. The distribution of the ensemble members is stretched by a linear error growth at the beginning of the forecast. After that, the nonlinear effect becomes dominant to distort the distribution. The forecast assimilation is then started when the errors of the ensemble forecasts have grown to a certain threshold. It is demonstrated that the forecast skill of the assimilated forecast is always superior to the control forecast. In the range of the small root mean square error (RMSE) of the ensemble forecast, the skill of the assimilated forecast is inferior to the ordinary ensemble mean. However, for the sufficiently large RMSE before the saturation, it is shown that the skill of the assimilated forecast is superior to the ensemble mean. The result suggests that the forecast assimilation is one of the viable approaches to the medium or extended range forecast.
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  • Hiroyuki YAMADA, Hiroshi UYEDA, Katsuhiro KIKUCHI, Masayuki MAKI, Koyu ...
    2004 Volume 82 Issue 1 Pages 179-206
    Published: 2004
    Released: April 15, 2004
    JOURNALS FREE ACCESS
    Various processes of development in a convective cell were investigated in order to clarify the factors causing differences in the structure of snow clouds. Convective cells in snow clouds were observed by two Doppler radars over Ishikari Bay, Hokkaido, Japan, during winter monsoon surges. Seven cells that allowed us to examine structural changes were selected for the investigation. From the time series of maximum reflectivity and vertical mass flux in each cell, the analyzed cells were classified into two groups: “rapid change” and “slow change.” The former was further divided into two types according to the strength of vertical wind shear in the environment: rapid change in weak shear (Rw), and rapid change in strong shear (Rs). The structure of the Rw-type changed greatly, due to the formation and the descent of a high-reflectivity core (> 30 dBZ), and the subsequent dissipation of the updraft. Since the updraft hardly tilted and collapsed when the core descended in the updraft, loading by graupel particles was suggested to be effective to terminate the updraft. The structure of the Rs-type changed greatly due to the short lifetime of the updraft that was tilted toward the downshear side due to the strong vertical shear. In contrast, the cell of slow-change group (S-type) maintained its structure because of a persistent updraft. Since the updraft, which was tilted hardly, was sustained even when a core (≤30 dBZ) descended in the updraft region, the loading effect was thought to be small due to the small amount of graupel particles. From a comparison of the three types, it was found that the different features of the cell’s structure were caused by two factors: the tilt of the updraft, and the effect of loading by graupel particles. Based on these results, we discussed the maintenance process of a snow cloud composed of convective cells. The fact that convective cells in the past observational studies can also be classified in the same way as cells analyzed in the present study, was also discussed. The relationship between the growth of graupel particles, and the temperature in the environment, was also discussed.
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  • Sento NAKAI, Kenji NAKAMURA, Haruya MINDA, Hiromu SEKO
    2004 Volume 82 Issue 1 Pages 207-227
    Published: 2004
    Released: April 15, 2004
    JOURNALS FREE ACCESS
    The Tropical Rainfall Measuring Mission (TRMM) satellite and a dropsonde-equipped aircraft made simultaneous observations of a cloud cluster (CC) over the East China Sea. Hourly GMS equivalent blackbody temperature (TBB) showed that the CC was in the dissipating stage. The structure of the CC was analyzed using TRMM, dropsonde and rawinsonde data. The cloud top of the CC was an anvil composed of a dense area and a thin area. The precipitation within the cloud area of the CC (defined by TBB < -30°C) was stratiform, and corresponded to the dense anvil area of the CC. The thin anvil area extended to the outside of an apparent CC cloud area. The CC had a multi-layer structure, and shallow convection developed below the thin anvil in the convectively unstable lower troposphere with low-level convergence. The echo top of the shallow convection was less than 4 km (630 hPa). The shallow convection generated an outflow from its upper part. The outflow blew into the area of negative pressure anomaly below the dense anvil at levels of 650 hPa and 750 hPa. Meanwhile, a southeasterly dry wind blew into the stratiform precipitation area of the CC at levels between 700 hPa and 850 hPa. The dry inflow was cooled by evaporation within the precipitation of the CC, resulting in the formation of the negative potential temperature anomaly. Evaporation cooling occurred in the stratiform precipitation region; however, the negative potential temperature anomaly did not reach the surface. It is inferred that the evaporation cooling was not important to the initiation of the shallow convection, although it affected the structure of the CC.
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  • Yoshimitsu OGURA, Ryoji KUMABE, Masayuki YAMAMOTO
    2004 Volume 82 Issue 1 Pages 229-240
    Published: 2004
    Released: April 15, 2004
    JOURNALS FREE ACCESS
    The purpose of this article is to report the result of our effort to uncover the nature, and possible cause(s), of the high wind that was responsible for some human and property damage in the morning of 2 March 2003 in Yaita city, Totigi prefecture. Our approach is through the analysis of observed data and all data used are conventional. It is found that the damage-causing high wind was a foehn-like downslope wind, which occurred when a bomb-class midlatitude cyclone passed over the Kanto area, and Yaita city was situated on the lee side of the mountain range in the strong northwesterly flow in the back side of the cyclone. The unique feature of the present high wind event is that it was followed by another foehn-like episode, in that surface temperature was higher and dewpoint temperature was lower than in the preceding foehn, while the wind was less violent. It is concluded, through the analysis of the precipitation field, that the first foehn was wet (thermodynamic), whereas the second foehn was dry (dynamic). Further, in our quest to understand why the surface air was warmer and dryer in the second foehn, it is found that, by the time of the commencement of the second foehn, the region of the unusually strong mid-level descending motion, representing the dry intrusion, had approached the Kanto area and this helped bring down the air possessing high potential temperature and low mixing ratio into the downslope wind in the second foehn. Finally, it is pointed out that a well-defined low-level jet was present in the northwesterly flow behind the cyclone center and the strong wind associated with the low level jet was instrumental in the present foehn event. Thus, presented here are documentations showing the sequence of events associated with successive foehn formations, that occurred in a quite limited local area but was intimately linked with the evolution and structure of a synoptic-scale midlatitude cyclone.
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Nots and Correspondence
  • Shinjiro KANAE, Taikan OKI, Akira KASHIDA
    2004 Volume 82 Issue 1 Pages 241-247
    Published: 2004
    Released: April 15, 2004
    JOURNALS FREE ACCESS
    Intensification of heavy precipitation foreseen in climate change studies has become a public concern, but it has not yet been examined well with observed data, particularly with data at short temporal scale like hourly data. On hourly heavy precipitation at Tokyo, previous studies investigated the data only from the 1970's due to the availability of digital data. In this research, we digitalized hourly precipitation since 1890 recorded at the Tokyo observatory in order to investigate historical changes in hourly heavy precipitation at Tokyo. The recent decade, the 1990's, was indeed a period with considerably strong and frequent hourly heavy precipitation, but another period with strong/frequent hourly heavy precipitation was found around the 1940's. Hourly heavy precipitation around the 1940's was even stronger/more frequent than in the 1990's. Thereby, it cannot be said that recent hourly heavy precipitation has become unprecedentedly strong or frequent. In addition, the numbers of hourly heavy precipitation events by tropical cyclone and by Baiu front were counted respectively, resulting in that the composition of the causes of hourly heavy precipitation events in the 1940's appears to be different from that in the 1990's.
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  • Hirotada KANEHISA
    2004 Volume 82 Issue 1 Pages 249-254
    Published: 2004
    Released: April 15, 2004
    JOURNALS FREE ACCESS
    In a stationary rotating system, such a quantity is constructed, that is related to the absolute vorticity component in the direction of ∇θ×u. Here, θ is the potential temperature, and u is the wind velocity. In a nondissipative and adiabatic case, this quantity is materially conserved along the streamline. By the conservation property, if the pressure increases (decreases) along the streamline, then the circulation on the {∇θ, u} plane decreases (increases) there. This quantity is the derivative of the Bernoulli function B in the direction of ∇θ. In a dissipative case, wherein the Bernoulli function is decreased along the streamline, the gradient of the Bernoulli function is generated. As a result, this quantity is increased or decreased by the dissipation, just in the same way as the potential vorticity generation due to dissipation.
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