Temperature difference between coast and inland and its relationship with wind field

In r ecent year s, Cat egor y A tended t o appear mor e frequentl y. In t his

categor y, hi gh temper ature anomal y was confir med in a wide ar ea, and i n t he afternoon, t he temper ature di fference was si gnificant in the southern Kant o region, including areas such as the coast of Tokyo Bay, and in the norther n Kanto regi on, i ncludi ng areas such as Kumagaya . To examine the increasi ng trend of hi gh temperatures i n t he inland of the Kanto Pl ain and its relationship with the wind fiel d, sunny li ght -wi nd days wer e di vi ded on t he basis of t he te mper at ure diff erence bet ween coast and inl and, and relati ve frequency of wi nd pattern categories and charact eristics of wi nd field and temp eratur e distri buti on were examined. In additi on to the char acteristics of the t emperat ure distri bution, based on t he difference in winds t hat we have previousl y covered herein, charact eristics of wind fiel d based on t he difference in temper at ure distribution were also deter min ed. The temperatur e difference bet ween coast and i nland (T_{K - T}) was defi ned by the di fference between the dail y maxi mum temperatur e i n the inland area of Kumagaya and the dail y maxi mum temper ature in the coastal area of Tokyo. Thus t here was an even number of days for convenience, and data were di vided int o t hree

T_{K - T} gr oups: 2.5 °C or hi gher, betw een 1.5 °C and 2.5 °C, and bel ow 1.5 °C.

Table 6 shows t he number of sunny li ght -wind days for each gr oup of temperatur e differ ence (T_{K − T}), and the relati ve freque ncy for each wi nd pattern categor y. When T_{K − T} was below 1.5 °C, t he relati ve fr equencies of Categories C, D, and E were hi gh; t he se days account ed f or 83% of th ese 3 categori es. When T_{K - T} was between 1.5 °C and 2.5 °C , the rel ati ve frequencies of Categories B and C were hi gh, and t he rel ati ve f requency of

Categor y E was low. When T_{K − T} was 2.5 °C or hi gher, t he relati ve frequenci es of Categories A and B were extremel y hi gh at 42% and 37% , respecti vel y. The categor y of wind patt ern that appear ed most freque ntl y di ffered accordi ng t o whet her T_{K − T} was large or small . Thus, it was presumed that the magnitude of TK − T and the categor y of wind patt ern wer e closel y relat ed.

Table 7 shows the number of sunny li ght -w ind days f or each 11 -year peri od, and the r elati ve fr equency of each gr oup of temperat ure diff erence . The proportion of days w hen T_{K − T} was bel ow 1.5 °C was 39% during the peri od 1979–1989 , and it was 25% duri ng the peri od 2001 –2011, showi ng a decadal trend t o decrease . On the ot her hand, the proportion of the days when T_{K − T} was between 1.5 °C and 2.5 °C and when it was 2.5 °C or more, were 34% and 27% during t he peri od 1979 –1989, and 41% and 34% during the period 2001–2011, respecti vel y, showing a decada l trend t o incr ease . Moreover, the number of days when the dail y maxi mum temper ature at Kumagaya was 35 °C or hi gher (extr emel y hot days) on sunny li ght -wind days was 31 out of 115 days when TK − T was below 1.5 °C (approxi matel y 27%), 79 out of 142 days when T_{K − T} was between 1.5 °C and 2.5 °C (approxi matel y 56%), and 85 out of 112 days when T_{K − T} was 2.5 °C or hi gher (approxi mat el y 76%). Thus, extremel y hot days were li kel y t o appear when T_{K − T} was large. The pr oporti on of days with l arge T_{K − T} among sunny li ght -wi nd days tended to increase, which was li kel y t o be a r esponse to the incr easing temperatures i n the inl and area of the Kant o Plai n.

The distri buti on of wind and the amount of convergence/ di vergence

averaged for each hour when T_{K − T} was 2.5 °C or hi gher are sho wn in Fi g. 38.

The distribution f or when T_{K − T} was below 1.5 °C i s shown in Fig. 3 9. When

T_{K − T} was 2.5 °C or hi gher, the di urnal vari ation i n the wind syst em was quite

si milar to that of Categories A ( Fi g. 19) and B (Fi g. 20) . Southerl y wind was generall y domi nant , and wi nd systems wit h a weak east wind component were obser ved . Compar ed with t he mean of sunny li ght -wi nd days ( Fi g. 7), the ti me when the sea breeze started and the penetration of t he sea breeze front were bot h earl y. Moreover, wind speed was gener all y l ow for t he wind from south to sout hwest compared wit h Category A. In the after noon, southeast wind was confir med in the Kashi ma -nada coast . Thus, t h ese winds were somewhat si mil ar to Categor y B. On the other hand, when T_{K − T} was below 1.5 °C, t he diurnal var iation i n the wind syst em was quite si mil ar t o Categor y D (Fi g. 22) . In the Sagami Bay coast, south wind bl ew, and in the Kashi ma -nada coast , east wind blew, a t ypical sea breeze was predominant.

However, compared with t he mean of sunny li ght -wi nd days, t he east wi nd component was somewhat l arge. The ti me when t he sea breeze st arted and the penetrati on of the sea breeze fr ont were bot h late.

Next , t he t emperat ure anomal y fr om sunny li ght -wind days aver aged for each hour, and its dist ribution when T_{K − T} was 2.5 °C or hi gher is shown i n Fi g.

40. The distribution when T_{K − T} was below 1.5 °C is shown in Fig. 41. When T_{K - T} was 2.5 °C or hi gher, fr om 09:00 (Fi g. 40a) to 11:00 (Fi g. 40b), hi gh temperatur e anomal y was obser ved on the prefect ural bor der bet ween Tokyo and Sait ama, and inl and area s such as Kumagaya . These ar eas were weak

wind areas on the inl and side of the sea br eeze front, and where land breeze from nort h was obser ved when T_{K − T} was bel ow 1.5 °C ( Fi g. 39a). Therefore, a temperatur e rise in the morni ng in t his area mi ght be related t o t he low wi nd speed because of t he lack of land breeze from north . In t he af ternoon, the center of t his hi gh temper ature anomal y gr aduall y moved nort hward, and hi gh temperatur e anomal y around Tokyo and souther n Saitama Prefecture disappeared corr esponding t o the penetrat ion of sea breeze fr ont and the transition to t he ESB. Moreover on the K ashi ma -nada coast , fr om around 11:00 to afternoon, hi gh temperatur e anomal y corr espondi ng to a weak penetrati on of east erl y sea br eeze wit h l ow temperat ure was observed.

On the other hand, when T_{K − T} was below 1.5 °C, low temper atur e anomal y was obser ved in the mor ning over a wi de area i n the Kashi ma -nada coast , around the Tokyo Me tropolitan ar ea, and i nland areas. At 13: 00 (Fi g. 41c) , the low temperature anomal y disappeared ar ound the Tokyo Metr opolitan area wher e sout herl y wi nd began t o bl ow. In the Sagami Bay coast , in response to south wind bei ng weaker than the aver age, hi gh te mperature anomal y appear ed. From 15:00 ( Fi g. 41d) to 17: 00 (Fi g. 41e), l ow temperatur e anomal y conti nued t o be obser ved in t he Kashi ma -nada coast and the prefect ural border of Tokyo and Saitama toward inland. I ts locat ion however did not change si gnifi cantl y relati ve t o the area where east wind blew.

Based on the magnit ude of the temperat ure diff erence T_{K − T} bet ween coast and inland, the strengt h of the east wind component changed; the di urnal wind variation also changed. These differ ences li kel y corresponded to the

differences in t he cat egor y of t he win d pat tern that appeared on the basis of the magnitude of T_{K − T}. When T_{K − T} was large, the relati ve fr equency of Categor y A was hi gh, and hi gh temper atures appeared disti nctl y i n t he inland area. Mean while, the diurnal variati on in the wi nd system was close to Categor y B, and the r elati ve frequency of Categor y B was si mil arl y hi gh, as in Cat egor y A. The di fficult y of low temper ature east wi nd enteri ng the area, the lack of land breeze in t he mor ning, a nd the weak wind mi ght all have been possi ble reasons for the t emperat ure rise. Such characteristics of t he wi nd system wer e obser ved in Categor y B as well. In recent years, the relati ve frequency of Categor y B has been decr easi ng, but t hat f or bot h Categories A and B t oget her has been i ncreasing (Table 2). Thus, it i s thought t hat t he increase in hi gh temperatur es in the i nland area of the Kant o Plai n and changes i n t he wind system fiel d ar e rel ated to each ot her.