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Large-and-Sparse-particle Clouds (LSC), characterized by large particle size (radius > 50 μm) and small number concentration (

The chlorophyll-a (Chla) concentration product of the Himawari-8 geostationary meteorological satellite is used to show the temporal variation of Chla owing to the passage of typhoons, namely, tropical cyclones in the western North Pacific Ocean. The daily Chla variation shows that Chla usually increases along the paths of typhoons, whereas the same observations are almost impossible when using the data of polar-orbiting satellites as shown in previous studies. This is because the temporal resolution of Himawari-8 is ten times more than that of polar-orbiting satellites, and the daily Chla distribution contains a few disturbances attributed to clouds after compositing cloud-free data. Chla usually increases on the day of typhoon arrival, but mostly, the ratio of Chla increased by a typhoon to the background Chla, R Chla HIMA , is less than 2. Only a few typhoons considerably increased Chla. As a whole, R Chla HIMA is proportional to the maximum 10-min sustained wind speed up to 85 knots (44 m s−1), namely, 0.01 mg m−3 knot−1 (0.019 mg s m−4). However, there is no clear dependence between Chla and the wind speed in seas with higher Chla, such as the South China Sea. The result that typhoons are usually cultivating the ocean is important for studies of primary ocean productivity and carbon flux between the atmosphere and ocean.

A meteorological balloon-borne cloud sensor called the cloud particle sensor (CPS) has been developed. The CPS is equipped with a diode laser at ∼ 790 nm and two photodetectors, with a polarization plate in front of one of the detectors, to count the number of particles per second and to obtain the cloud-phase information (i.e. liquid, ice, or mixed). The lower detection limit for particle size was evaluated in laboratory experiments as ∼ 2 µm diameter for water droplets. For the current model the output voltage often saturates for water droplets with diameter equal to or greater than ∼ 80 µm. The upper limit of the directly measured particle number concentration is ∼ 2 cm−3 (2 × 103 L−1), which is determined by the volume of the detection area of the instrument. In a cloud layer with a number concentration higher than this value, particle signal overlap and multiple scattering of light occur within the detection area, resulting in a counting loss, though a partial correction may be possible using the particle signal width data. The CPS is currently interfaced with either a Meisei RS-06G radiosonde or a Meisei RS-11G radiosonde that measures vertical profiles of temperature, relative humidity, height, pressure, and horizontal winds. Twenty-five test flights have been made between 2012 and 2015 at midlatitude and tropical sites. In this paper, results from four flights are discussed in detail. A simultaneous flight of two CPSs with different instrumental configurations confirmed the robustness of the technique. At a midlatitude site, a profile containing, from low to high altitude, water clouds, mixed-phase clouds, and ice clouds was successfully obtained. In the tropics, vertically thick cloud layers in the middle to upper troposphere and vertically thin cirrus layers in the upper troposphere were successfully detected in two separate flights. The data quality is much better at night, dusk, and dawn than during the daytime because strong sunlight affects the measurements of scattered light.

A unique type of cloud in the tropical lower stratosphere, which we call “stratospheric cirrus”, is described in this study. Stratospheric cirrus clouds are generally detached from overshooting deep convection and are much smaller than subvisual cirrus often observed near the tropical tropopause. We analyzed two cases of stratospheric cirrus in the tropical and subtropical lower stratosphere captured by the space-borne lidar, Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). Both cases occurred 2–3 hours after the most active phase of the nearby convective cloud clusters. Case 1 has a double-layer structure above the cold point height (CPH); the CPH and two cloud top heights are, respectively, 17.8, 18.9, and 19.9 km. Case 2 has a single cloud layer where CPH and the cloud top height are, respectively, 16.5 and 18.7 km. The mode radius and ice water content of the stratospheric cirrus clouds are estimated to be 4–10 μm and 0.2–0.8 mg/m 3 based on the radar-lidar method and consideration of the cloud particle terminal velocity. Comparisons with previous numerical model simulation studies suggest that the double-layer stratospheric cirrus clouds are likely from an overshooting plume, pushed up into the stratosphere in an overshoot when warm stratospheric air is inhomogeneously mixed with cold overshooting air. The single-layer stratospheric cirrus cloud is associated with some non-negligible wind shear, so it could be a jumping cirrus cloud, although we cannot rule out the possibility that it came from an overshooting plume because of the similarity in cloud characteristics and morphology between the two cases. Guided by the case studies, an automatic algorithm was developed to select stratospheric cirrus clouds for global survey and statistical analysis. A total of four years of CALIPSO and space-borne cloud radar (CloudSat) data were analyzed. Statistical analysis suggests that stratospheric cirrus clouds occur on the order of 3.0 × 10 3 times a year between 30 °S and 30 °N. Many of the stratospheric cirrus clouds are found in the pre-monsoon season in the South and Southeast Asia, where convection is deep and intense.

Variation in stratospheric water vapor is controlled mainly by the dehydration process in the tropical tropopause layer (TTL) over the western Pacific; however, this process is poorly understood. To address this shortcoming, in this study the match method is applied to quantify the dehydration process in the TTL over the western Pacific. The match pairs are sought from the Soundings of Ozone and Water in the Equatorial Region (SOWER) campaign network observations using isentropic trajectories. For the pairs identified, extensive screening procedures are performed to verify the representativeness of the air parcel and the validity of the isentropic treatment, and to check for possible water injection by deep convection, consistency between the sonde data and analysis field, and conservation of the ozone content. Among the pairs that passed the screening test, we found some cases corresponding to the first quantitative value of dehydration associated with horizontal advection in the TTL. The statistical features of dehydration for the air parcels advected in the lower TTL are derived from the match pairs. Match analysis indicates that ice nucleation starts before the relative humidity with respect to ice (RHice) reaches 207 ± 81% (1σ) and that the air mass is dehydrated until RHice reaches 83 ± 30% (1σ). The efficiency of dehydration is estimated as the relaxation time required for the relative humidity of the supersaturated air parcel to approach the saturation state. This is empirically estimated from the match pairs as the quantity that reproduces the second water vapor observation, given the first observed water vapor amount and the history of the saturation mixing ratio of the match air mass exposed during the advection. The relaxation time is found to range from 2 to 3 h, which is consistent with previous studies.

An optical particle counter (OPC) is used in conjunction with lidar measurements to examine the characteristics of the particle size distribution in cirrus cloud in the tropical tropopause layer (TTL) over Thailand where the TTL is defined as the height at which temperature is lower than −75°C in this paper. Of 11 OPC launches, cirrus cloud was detected at 10–15 km high on 7 occasions, cirrus was detected in the TTL in 6 cases, and simultaneous OPC and lidar measurements were made on two occasions. Comparison of lidar and OPC measurements reveal that the cloud heights of cirrus in the TTL varies by several hundred meters over distances of tens kilometers; hence the height is not always horizontally uniform. The mode radii of particles constituting the clouds are estimated by lidar and OPC measurements to be less than approximately 10 μm. The regression lines of the particle size distribution with and without cirrus cloud exhibit similar features at equivalent radii of

In this study, the authors focused on the seasonal variations of precipitation properties over the western Pacific, particularly those associated with the wind direction of the monsoon. An observational project over Peleliu Island in the Republic of Palau was carried out, and data on precipitation, equivalent cloud amount, and precipitable water were collected from 28 June 2001 to 30 April 2002. First, the monsoon season over Palau was defined as a period with 850-hPa zonal-wind sounding data with sustained winds exceeding 5 m s−1. The westerly wind regime continued until 25 November 2001, and the next westerly wind regime began on 18 May 2002. The equivalent cloud amount increased during the period when the westerly wind intensified. The precipitation had a diurnal variation in the active phase of the westerly wind regime, increasing from nighttime to early morning and decreasing in the afternoon. The diurnal variation was weak in the inactive phase and had a lesser afternoon maximum. Precipitation intensity was high and its duration was short during the westerly wind regime. The precipitable water decreased during the easterly wind regime when a dry period appeared, and precipitation was also suppressed during those days. However, there was little difference between the precipitation amounts of the westerly and easterly wind regimes. The equivalent cloud amount did not decrease as the zonal-wind direction changed to easterlies during the easterly wind regime. The authors noticed no diurnal variation of precipitation during the easterly wind regime. These differences in the precipitation properties during westerlies and easterlies may be related to the seasonal variation of humidity in the environment.

[1] Synergetic spaceborne observations of overshooting air, defined as cloud intrusion through the level of neutral buoyancy above deep convection, are analyzed using various thresholds introduced in previous studies to detect overshooting. The brightness temperature of the overshooting air measured by the Moderate Resolution Imaging Spectroradiometer (MODIS) is generally 2 K higher than that retrieved by the radiative transfer model, in which the size distribution of ice cloud particles is estimated from Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and CloudSat data and the vertical temperature profile of cloud is assumed to follow that of the European Centre for Medium Range Weather Forecast (ECMWF). The lapse rate of overshooting whose cloud top is higher than the level of the cold-point temperature (CPT) is lower than that of an adiabatic expansion. These observations can be rationalized as being due to the overshooting air being locally warmed by a mixture of warmer stratospheric air. Analysis of CALIOP and CloudSat data by using a radar-lidar algorithm shows that the mode of averaged ice water content of the overshoot above the CPT height is 6.3–10 mg/m3. Therefore, if 5% or more of ice particles in the overshoot are sublimated and mixed into the lower stratosphere, the lower stratospheric air will be hydrated. The difference between the brightness temperatures of 6.7 and 11 μm channels observed with MODIS demonstrates that the overshoot enhances stratospheric water vapor. These results indicate that the warm stratospheric air moves downward at and around the overshoot and mixes with the overshooting air and that the overshooting hydrates the lower stratosphere.

We investigated water vapor variations in the tropical lower stratosphere on seasonal, quasi-biennial oscillation (QBO), and decadal time scales using balloon-borne cryogenic frost point hygrometer data taken between 1993 and 2009 during various campaigns including the Central Equatorial Pacific Experiment (March 1993), campaigns once or twice annually during the Soundings of Ozone and Water in the Equatorial Region (SOWER) project in the eastern Pacific (1998-2003) and in the western Pacific and Southeast Asia (2001-2009), and the Ticosonde campaigns and regular sounding at Costa Rica (2005-2009). Quasi-regular sounding data taken at Costa Rica clearly show the tape recorder signal. The observed ascent rates agree well with the ones from the Halogen Occultation Experiment (HALOE) satellite sensor. Average profiles from the recent five SOWER campaigns in the equatorial western, Pacific in northern winter and from the three Ticosonde campaigns at Costa Rica (10degN) in northern summer clearly show two effects of the QBO. One is the vertical displacement of water vapor profiles associated with the QBO meridional circulation anomalies, and the other is the concentration variations associated with the QBO tropopause temperature variations. Time series of cryogenic frost point hygrometer data averaged in a lower stratospheric layer together with HALOE and Aura Microwave Limb Sounder data show the existence of decadal variations: The mixing ratios were higher and increasing in the 1990s, lower in the early 2000s, and probably slightly higher again or recovering after 2004. Thus linear trend analysis is not appropriate to investigate the behavior of the tropical lower stratospheric water vapor.

[1] We show characteristics of a tropical deep convection observed in an experiment employing the A-train constellation, the spaceborne imager Moderate Resolution Imaging Spectroradiometer (MODIS), the sounder Atmospheric Infrared Sounder (AIRS)-advanced microwave sounding unit (AMSU), the cloud radar CloudSat, and the lidar Cloud-Aerosol Lidar with Orthogonal Polarisation (CALIOP). CloudSat and CALIOP measured a vertical cross section of a deep convection at 1.1 km from its center, where the center is defined as the local minimum of the brightness temperature TB (11 μm) measured by using MODIS. This deep convection should be overshooting since its cloud top height measured by using CALIOP was 840 m higher than that of 380 K potential temperature as estimated by using AIRS-AMSU data. The cloud morphology observed by using CALIOP indicates that deep convections raised the isentropic surface in the tropical tropopause layer and that there were downdrafts around the deep convection. The averaged mode radius of ice particles and ice water content (IWC) in the deep convection above 380 K are estimated as 23.0 ± 4.9 μm and 7.2 ± 8.0 mg/m3, respectively, by the use of CloudSat and CALIOP data. The volume of the deep convection above a height of 380 K and the averaged IWC, of which the particle size is less than 20 μm, are estimated and the deep convection has the potential to hydrate the stratosphere with about 1 × 102 t of water vapor. We also show deep convections above a height of 380 K are not rare phenomena over the tropical land and warm water pool.

[1] Here we present extensive observations of stratospheric and upper tropospheric water vapor using the balloon-borne Cryogenic Frost point Hygrometer (CFH) in support of the Aura Microwave Limb Sounder (MLS) satellite instrument. Coincident measurements were used for the validation of MLS version 1.5 and for a limited validation of MLS version 2.2 water vapor. The sensitivity of MLS is on average 30% lower than that of CFH, which is fully compensated by a constant offset at stratospheric levels but only partially compensated at tropospheric levels, leading to an upper tropospheric dry bias. The sensitivity of MLS observations may be adjusted using the correlation parameters provided here. For version 1.5 stratospheric observations at pressures of 68 hPa and smaller MLS retrievals and CFH in situ observations agree on average to within 2.3% ± 11.8%. At 100 hPa the agreement is to within 6.4% ± 22% and at upper tropospheric pressures to within 23% ± 37%. In the tropical stratosphere during the boreal winter the agreement is not as good. The “tape recorder” amplitude in MLS observations depends on the vertical profile of water vapor mixing ratio and shows a significant interannual variation. The agreement between stratospheric observations by MLS version 2.2 and CFH is comparable to the agreement using MLS version 1.5. The variability in the difference between observations by MLS version 2.2 and CFH at tropospheric levels is significantly reduced, but a tropospheric dry bias and a reduced sensitivity remain in this version. In the validation data set a dry bias at 177.8 hPa of −24.1% ± 16.0% is statistically significant.

Cloud profiling radar can measure global distribution of cloud. Not only the information of the height of cloud tops and bases but also the information of particle shapes and water content (including whether ice or water) are expected. Multiparameter function of radar can be used for such purpose and the precise calibration of radar is necessary. The possibility for usage of sea surface return as an external calibration target is proposed because is stable under known condition of sea state. In addition, results of airborne measurements will be shown.

[1] An aerosol layer was found 1–2 km around the tropical cold point tropopause by observations using ground-based lidar and balloon-borne optical particle counters (OPC) over Biak, Indonesia, in January 2011. The layer was observed throughout the survey period from 6 to 13 January. The backscattering coefficient of the layer was about 5 times larger than that of the background aerosols. The lidar-observed depolarization ratio of the layer was very low, and the wavelength dependence of the backscattering coefficients of the layer was similar to that of stratospheric aerosols. A layer of the particles at the size of the accumulation mode was also observed by an OPC at ambient temperature, but the particles were volatile at 200°C. These properties indicate that the aerosol layer was composed of liquid phase aqueous sulfuric acid solution particles and probably originated from a volcanic eruption. It was observed by lidar that a thin cirrus cloud layer appeared within this aerosol layer. Backward trajectory analysis and satellite-observed equivalent blackbody temperature indicate that the cirrus cloud layer probably formed in situ. The estimated upper limit of the number concentration of cloud particles was 105 m−3. The number concentration of the volatile aerosol particles (∼3 × 106 m−3) was 30 times larger than this upper limit. This upper limit, however, is comparable to the aerosol particle concentration observed by the OPC at 200°C. These results are consistent with the cirrus cloud formation with solid sulfate particles in tropical upper troposphere suggested by previous studies.